B 459168
FARADAY'S
EXPERIMENTAL
RESEARCHES
IN
ELECTRICITY
VOL. III.
PHYSICS LIB.
Q C
503
#219
839

ARTES
[1817
SCIENTIA
LIBRARY
VERITAS
OF THE
UNIVERSITY OF MICHIGAN
PLURIOUS UNUN
TCEBOR
SI-QUARIS-PENINSULAM-AMŒNAM
CIRCUMSPICE
THE GIFT OF
Mrs. G. W₁ Patterson
Physics Lib.
Gemp M. Patterson Jr.
Ann Arbor.
Dai. 1892.
QC
503
.F219
1839



EXPERIMENTAL RESEARCHES
IN
ELECTRICITY.
VOL. III.
EXPERIMENTAL RESEARCHES
IN
ELECTRICITY.
BY
MICHAEL FARADAY, D.C.L., F.R.S.
FULLERIAN PROFESSOR OF CHEMISTRY IN THE ROYAL INSTITUTION.
FOREIGN ASSOCIATE OF THE ACAD. SCIENCES, PARIS, ORD. BORUSS. POUR LE MÉRITE
EQ., MEMB. ROYAL AND IMPERIAL ACADD. OF SCIENCES, PETERSBURGH,
FLORENCE, COPENHAGEN, BERLIN, GOTTINGEN, MODENA,
STOCKHOLM, MUNICH, BRUXELLES, VIENNA,
BOLOGNA, ETC. ETC.
Reprinted from the PHILOSOPHICAL TRANSACTIONS of 1846-1852.
With other Electrical Papers
from the PROCEEDINGS of the ROYAL INSTITUTION and PHILOSOPHICAL MAGAZINE.
VOL. III.
LONDON:
BERNARD QUARITCH, 15 PICCADILLY.
1855.
[Facsimile reprint.]
PRINTED BY TAYLOR AND FRANCIS,
RED LION COURT, FLEET STREET.

ALERE
FLAMMAM.
Physiis hib
JIMEN
GIFT
MRS. G. W. PATTERSON
12-2-1931
PREFACE.
FOR reasons stated in the First Volume of these Experi-
mental Researches, I have been induced to gather the
remaining Series together, and to add to them certain
other papers devoted to Electrical and Magnetic
Research.
To the prefatory remarks containing these reasons,
I would recall the recollection of those who may honour
these Researches with any further attention. I have
printed the papers in this Volume, as before, with little
or no alteration, except that I have placed the fair and
just date of each at the top of the pages.
As regards magnecrystallic action, which commences
at Paragraph 2454, the reader will see the gradual
change and enlargement of view respecting its nature
in the course of long investigations at the following
places, 2550. 2562. 2576. 2584. &c., 2591. 2639. 2797.
2818. 2836. &c. I would refer readers to the paper by
Tyndall and Knoblauch in the Philosophical Magazine,
1850, vol. xxxvii. p. 1, for a very philosophical acccount
of the physical cause of the magnecrystallic action*, and
to the paper by Professor W. Thomson on the theory
* Marchand and Scheerer say that bismuth is expanded by pressure and
has its structure changed. Gmelin's Handbook, iv. p. 428.
vi
PREFACE.
of magnetic induction in crystalline and non-crystal-
line substances in the Philosophical Magazine, 1851,
vol. i. p. 177, as being in all parts in perfect accordance
with the various experimental results which I have at
different times obtained.
With respect to Paragraphs 2967. 3242, and the in-
tentions there expressed of experimenting with oxygen
at low temperatures, I have endeavoured to carry these
intentions out; but the extreme difficulty of working on
such attenuated matter as gases at low temperatures,
without the production of air-currents able to influence
the very delicate torsion-balance and apparatus required to
measure the result, is so great as to have prevented me
as yet from obtaining any results worthy of confidence.
I owe many thanks to the Royal Society and to
the Proprietors of the Philosophical Magazine, for the
great kindness I have received in the loan of plates, &c.,
and in other facilities granted to me for the printing of
the volume.
As the Index belongs both to the Experimental
Researches and to the other papers, its references are of
necessity made in two ways; those to the Researches
are, as before, to the numbers of the paragraphs, and are
easily recognized by the greatness of the numbers: the
other references are to the pages, and being always pre-
ceded by p. or pp. are known by that mark.
MICHAEL FARADAY.
January, 1855.
CONTENTS.
Series XIX. § 26. On the magnetization of light and the illu-
mination of magnetic lines of force
1. Action of magnets on light
Par.
2146
2146
2. Action of electric currents on light.. 2189
3. General considerations
2221
•
Series XX.
§ 27. On new magnetic actions, and on the mag-
netic condition of all matter
2243
•
2245
| | |
¶ 1. Apparatus required
¶ 2. Action of magnets on heavy glass.... 2253
¶ 3. Action of magnets on other substances
acting magnetically on light.... 2275
T 4. Action of magnets on metals generally 2287
Revulsive phænomena
2309
Series XXI. § 27. (Continued.)
5. Action of magnets on the magnetic
metals and their compounds......
2343
¶ 6. Action of magnets on air and gases.. 2400
¶ 7. General considerations
2417
Series XXII. § 28. On the crystalline polarity of bismuth (and
other bodies), and on its relation to the
magnetic form of force
•
¶ 1. Crystalline polarity of bismuth.
¶ 2. Crystalline polarity of antimony
¶ 3. Crystalline polarity of arsenic
2454
2457
2508
2532
¶ 4. Crystalline condition of various bodies 2535
5. Nature of the magnecrystallic force, and
general observations ..
2550
¶ 6. On the position of a crystal of sulphate
of iron in the magnetic field........ 2615
Series XXIII. § 29. On the polar or other condition of dia-
magnetic bodies
Series XXIV. § 30. On the possible relation of gravity to elec-
2640
2702
tricity ....
Series XXV. § 31. On the magnetic and diamagnetic condition
of bodies....
2718
¶ 1. Non-expansion of gaseous bodies by
magnetic force ....
2718
2. Differential magnetic action
2757
¶ 3. Magnetic characters of oxygen, nitro-
gen, and space
2770
viii
CONTENTS.
Series XXVI. § 32. Magnetic conducting power
¶ 1. Magnetic conduction
¶ 2. Conduction polarity
¶ 3. Magnecrystallic conduction
§ 33. Atmospheric magnetism..
1. General principles
Series XXVII. § 33. 2. Experimental inquiry into the laws
of atmospheric magnetic action, and
Par.
2797
2797
2818
2836
2847
2847
their application to particular cases 2969
Royal Institution Proceedings (Report)
p. 323
Series XXVIII. § 34. On lines of magnetic force; their definite
character; and their distribution within
a magnet and through space
Series XXIX. § 35. On the employment of the induced mag-
neto-electric current as a test and mea-
3070
sure of magnetic forces.
•
¶ 1. Galvanometer
•
2. Revolving rectangles and rings ...
§ 36. On the amount and general disposition of
§ 37. Delineation of lines of magnetic force by
iron filings...
On the lines of magnetic force (R. I.)
•
On the physical character of the lines of magnetic force
On the physical lines of magnetic force (R. I.)
3177
3178
3192
the forces of a magnet when associated
with other magnets
3215
3234
•
•
p.
402
3243
Page
.. 438
On the magnetic relations and characters of the metals
Thoughts on ray-vibrations
•
444
447
On the magnetic affection of light (repeated reflections)
On the distinctions between the ferro-magnetic and diamagnetic
conditions of matter ...
453
457
On the diamagnetic conditions of flame and gases
On the use of gutta percha in electrical insulation
467
494
•
Observations on the magnetic force-law of distance (R. I.) . . .
On electric induction-associated cases of current and static
effects (R. I.)
497
508
On subterraneous electro-telegraph wires
521
On magnetic hypotheses (R. I.) .
524
On some points of magnetic philosophy
528
The same and on the nature of force (R. I.).
566
•
Further observations on associated cases of current and static
effects
575
EXPERIMENTAL RESEARCHES
IN
ELECTRICITY.
NINETEENTH SERIES.
Tii.
§ 26. On the magnetization of light and the illumination of mag-
netic lines of force². ¶i. Action of magnets on light.
Action of electric currents on light. ¶iii. General considera-
tions.
Received November 6,-Read November 20, 1845.
¶i. Action of magnets on light.
2146. I HAVE long held an opinion, almost amounting to
conviction, in common I believe with many other lovers of
natural knowledge, that the various forms under which the forces
of matter are made manifest have one common origin; or, in other
words, are so directly related and mutually dependent, that they
are convertible, as it were, one into another, and possess equi-
1 Philosophical Transactions, 1846, p. 1.
2 The title of this paper has, I understand, lead many to a misapprehension
of its contents, and I therefore take the liberty of appending this explanatory
note. Neither accepting nor rejecting the hypothesis of an æther, or the cor-
puscular, or any other view that may be entertained of the nature of light;
and, as far as I can see, nothing being really known of a ray of light more
than of a line of magnetic or electric force, or even of a line of gravitating
force, except as it and they are manifest in and by substances; I believe that,
in the experiments I describe in the paper, light has been magnetically
affected, i. e. that that which is magnetic in the forces of matter has been
affected, and in turn has affected that which is truly magnetic in the force of
light: by the term magnetic I include here either of the peculiar exertions of
the power of a magnet, whether it be that which is manifest in the magnetic
or the diamagnetic class of bodies. The phrase "illumination of the lines of
VOL. III.
B
2
[SERIES XIX.
Action of magnets on light.
•
valents of power in their action'. In modern times the proofs
of their convertibility have been accumulated to a very consider-
able extent, and a commencement made of the determination of
their equivalent forces.
2147. This strong persuasion extended to the powers of light,
and led, on a former occasion, to many exertions, having for
their object the discovery of the direct relation of light and
electricity, and their mutual action in bodies subject jointly to
their power2; but the results were negative and were after-
wards confirmed, in that respect, by Wartmann 3.
2148. These ineffectual exertions, and many others which
were never published, could not remove my strong persuasion
derived from philosophical considerations; and, therefore, I
recently resumed the inquiry by experiment in a most strict and
searching manner, and have at last succeeded in magnetizing and
· electrifying a ray of light, and in illuminating a magnetic line of
force. These results, without entering into the detail of many
unproductive experiments, I will describe as briefly and clearly
as I can.
2149. But before I proceed to them, I will define the mean-
ing I connect with certain terms which I shall have occasion to
use-thus by line of magnetic force, or magnetic line of force,
or magnetic curve, I mean that exercise of magnetic force which
is exerted in the lines usually called magnetic curves, and which
equally exist as passing from or to magnetic poles, or forming
concentric circles round an electric current. By line of electric
force, I mean the force exerted in the lines joining two bodies,
acting on each other according to the principles of static electric
induction (1161, &c.), which may also be either in curved or
magnetic force" has been understood to imply that I had rendered them
luminous. This was not within my thought. I intended to express that the
line of magnetic force was illuminated as the earth is illuminated by the sun,
or the spider's web illuminated by the astronomer's lamp. Employing a ray
of light, we can tell, by the eye, the direction of the magnetic lines through a
body; and by the alteration of the ray and its optical effect on the eye, can
see the course of the lines just as we can see the course of a thread of glass,
or any other transparent substance, rendered visible by the light: and this is
what I meant by illumination, as the paper fully explains.-December 15,
1845. M. F.
¹ Experimental Researches, 57, 366, 376, 877, 961, 2071.
Philosophical Transactions, 1834. Experimental Researches, 951-955.
³ Archives de l'Electricité, ii. pp. 596–600.
Nov. 1845.]
Rotation of a ray by magnetism.
3
straight lines. By diamagnetic, I mean a body through which
lines of magnetic force are passing, and which does not by their
action assume the usual magnetic state of iron or loadstone.
2150. A ray of light issuing from an Argand lamp, was
polarized in a horizontal plane by reflexion from a surface of
glass, and the polarized ray passed through a Nichol's eye-piece
revolving on a horizontal axis, so as to be easily examined by
the latter. Between the polarizing mirror and the eye-piece,
two powerful electro-magnetic poles were arranged, being either
the poles of a horse-shoe magnet, or the contrary poles of two
cylinder magnets; they were separated from each other about
2 inches in the direction of the line of the ray, and so placed,
that, if on the same side of the polarized ray, it might pass near
them; or if on contrary sides, it might go between them, its
direction being always parallel, or nearly so, to the magnetic
lines of force (2149.). After that, any transparent substance
placed between the two poles, would have passing through it,
both the polarized ray and the magnetic lines of force at the
same time and in the same direction.
2151. Sixteen years ago I published certain experiments
made upon optical glass, and described the formation and
general characters of one variety of heavy glass, which, from its
materials, was called silicated borate of lead. It was this glass
which first gave me the discovery of the relation between light
and magnetism, and it has power to illustrate it in a degree
beyond that of any other body; for the sake of perspicuity I
will first describe the phænomena as presented by this substance.
2152. A piece of this glass, about 2 inches square and 0·5
of an inch thick, having flat and polished edges, was placed as
a diamagnetic (2149.) between the poles (not as yet magnetized
by the electric current), so that the polarized ray should pass
through its length; the glass acted as air, water, or any other
indifferent substance would do; and if the eye-piece were pre-
¹ Philosophical Transactions, 1830, p. 1. I cannot resist the occasion
which is thus offered to me of mentioning the name of Mr. Anderson, who
came to me as an assistant in the glass experiments, and has remained ever
since in the Laboratory of the Royal Institution. He has assisted me in all
the researches into which I have entered since that time, and to his care,
steadiness, exactitude, and faithfulness in the performance of all that has been
committed to his charge, I am much indebted.-M. F.
B 2
4
[SERIES XIX.
Action of magnets on light.
viously turned into such a position that the polarized ray was
extinguished, or rather the image produced by it rendered in-
visible, then the introduction of this glass made no alteration in
that respect. In this state of circumstances the force of the
electro-magnet was developed, by sending an electric current
through its coils, and immediately the image of the lamp-flame
became visible, and continued so as long as the arrangement
continued magnetic. On stopping the electric current, and so
causing the magnetic force to cease, the light instantly disap-
peared; these phænomena could be renewed at pleasure, at any
instant of time, and upon any occasion, showing a perfect
dependence of cause and effect.
2153. The voltaic current which I used upon this occasion,
was that of five pair of Grove's construction, and the electro-
magnets were of such power that the poles would singly sustain
a weight of from twenty-eight to fifty-six, or more, pounds. A
person looking for the phænomenon for the first time would not
be able to see it with a weak magnet.
2154. The character of the force thus impressed upon the
diamagnetic is that of rotation; for when the image of the lamp-
flame has thus been rendered visible, revolution of the eye-piece
to the right or left, more or less, will cause its extinction; and
the further motion of the eye-piece to the one side or other of
this position will produce the reappearance of the light, and
that with complementary tints, according as this further motion
is to the right- or left-hand.
2155. When the pole nearest to the observer was a marked
pole, i. e. the same as the north end of a magnetic needle, and
the further pole was unmarked, the rotation of the ray was
right-handed; for the eye-piece had to be turned to the right-hand,
or clock fashion, to overtake the ray and restore the image to its
first condition. When the poles were reversed, which was in-
stantly done by changing the direction of the electric current,
the rotation was changed also and became left-handed, the altera-
tion being to an equal degree in extent as before. The direction
was always the same for the same line of magnetic force (2149.).
2156. When the diamagnetic was placed in the numerous
other positions, which can easily be conceived, about the mag-
netic poles, results were obtained more or less marked in extent,
and very definite in character, but of which the phænomena
Nov. 1845.]
OT
Rotation of a ray by magnetism.
just described may be considered as the chief example: they
will be referred to, as far as is necessary, hereafter.
2157. The same phænomena were produced in the silicated
borate of lead (2151.) by the action of a good ordinary steel
horse-shoe magnet, no electric current being now used. The
results were feeble, but still sufficient to show the perfect iden-
tity of action between electro-magnets and common magnets in
this their power over light.
2158. Two magnetic poles were employed end-ways, i. e. the
cores of the electro-magnets were hollow iron cylinders, and the
ray of polarized light passed along their axes and through the
diamagnetic placed between them: the effect was the same.
2159. One magnetic pole only was used, that being one end
of a powerful cylinder electro-magnet. When the heavy glass
was beyond the magnet, being close to it but between the mag-
net and the polarizing reflector, the rotation was in one direc-
tion, dependent on the nature of the pole; when the diamag-
netic was on the near side, being close to it but between it
and the eye, the rotation for the same pole was in the contrary
direction to what it was before; and when the magnetic pole
was changed, both these directions were changed with it. When
the heavy glass was placed in a corresponding position to the
pole, but above or below it, so that the magnetic curves were no
longer passing through the glass parallel to the ray of polarized
light, but rather perpendicular to it, then no effect was pro-
duced. These particularities may be understood by reference to
fig. 1, where a and b represent the
first positions of the diamagnetic, and
c and d the latter positions, the course
of the ray being marked by the dot-
ted line. If also the glass were placed
directly at the end of the magnet,
then no effect was produced on a ray
passing in the direction heredescribed,
though it is evident, from what has
been already said (2155.), that a ray passing parallel to the
magnetic lines through the glass so placed, would have been
affected by it.
2160. Magnetic lines, then, in passing through silicated
borate of lead, and a great number of other substances (2173.),

6
Action of magnets on light. [SERIES XIX.
J
cause these bodies to act upon a polarized ray of light when the
lines are parallel to the ray, or in proportion as they are parallel
to it if they are perpendicular to the ray, they have no action
upon it. They give the diamagnetic the power of rotating the
ray; and the law of this action on light is, that if a magnetic
line of force be going from a north pole, or coming from a south
pole, along the path of a polarized ray coming to the observer,
it will rotate that ray to the right-hand; or, that if such a line
of force be coming from a north pole, or going from a south
pole, it will rotate such a ray to the left-hand.
N
2161. If a cork or a cylinder of glass, representing the dia-
magnetic, be marked at its ends with the letters
N and S, to represent the poles of a magnet,
the line joining these letters may be considered
as a magnetic line of force; and further, if a
line be traced round the cylinder with arrow
heads on it to represent direction, as in the
figure, such a simple model, held up before the
eye, will express the whole of the law, and give
and consequence of direction resulting from it. If a watch be
considered as the diamagnetic, the north pole of a magnet being
imagined against the face, and a south pole against the back,
then the motion of the hand will indicate the direction of rota-
tion which a ray of light undergoes by magnetization.

every position
2162. I will now proceed to the different circumstances which
affect, limit, and define the extent and nature of this new power
of action on light.
2163. In the first place, the rotation appears to be in propor-
tion to the extent of the diamagnetic through which the ray and
the magnetic lines pass. I preserved the strength of the mag-
net and the interval between its poles constant, and then inter-
posed different pieces of the same heavy glass (2151.) between
the poles. The greater the extent of the diamagnetic in the
line of the ray, whether in one, two, or three pieces, the greater
was the rotation of the ray; and, as far as I could judge by these
first experiments, the amount of rotation was exactly propor-
tionate to the extent of diamagnetic through which the ray
passed.
No addition or diminution of the heavy glass on the
side of the course of the ray made any difference in the effect of
that part through which the ray passed.
Nov. 1845.]
7
Rotation of a ray by magnetism.
2164. The power of rotating the ray of light increased with
the intensity of the magnetic lines of force. This general effect
is very easily ascertained by the use of electro-magnets; and
within such range of power as I have employed, it appears to
be directly proportionate to the intensity of the magnetic force.
2165. Other bodies, besides the heavy glass, possess the
same power of becoming, under the influence of magnetic force,
active on light (2173.). When these bodies possess a rotative
power of their own, as is the case with oil of turpentine, sugar,
tartaric acid, tartrates, &c., the effect of the magnetic force is to
add to, or subtract from, their specific force, according as the
natural rotation and that induced by the magnetism is right- or
left-handed (2231.).
2166. I could not perceive that this power was affected by
any degree of motion which I was able to communicate to the
diamagnetic, whilst jointly subject to the action of the mag-
netism and the light.
2167. The interposition of copper, lead, tin, silver, and other
ordinary non-magnetic bodies in the course of the magnetic
curves, either between the pole and the diamagnetic, or in other
positions, produced no effect either in kind or degree upon the
phænomena.
2168. Iron frequently affected the results in a very consider-
able degree; but it always appeared to be, either by altering the
direction of the magnetic lines, or disposing within itself of their
force. Thus when the two contrary poles were on one side
of the polarized ray (2150.), and the heavy glass in its best
position between them and in the ray (2152.), the bringing of a
large piece of iron near to the glass on the other side of the ray,
caused the power of the diamagnetic to fall. This was because
certain lines of magnetic force, which at first passed through the
glass parallel to the ray, now crossed the glass and the ray; the
iron giving two contrary poles opposite the poles of the magnet,
and thus determining a new course for a certain portion of the
magnetic power, and that across the polarized ray.
2169. Or, if the iron, instead of being applied on the opposite
side of the glass, were applied on the same side with the mag-
net, either near it or in contact with it, then, again, the power
of the diamagnetic fell, simply because the power of the magnet
was diverted from it into a new direction. These effects depend
8
Action of magnets on light. [SERIES XIX.
much of course on the intensity and power of the magnet, and
on the size and softness of the iron.
2170. The electro-helices (2190.) without the iron cores were
very feeble in power, and indeed hardly sensible in their effect.
With the iron cores they were powerful, though no more elec-
tricity was then passing through the coils than before (1071.).
This shows, in a very simple manner, that the phænomena ex-
hibited by light under these circumstances, is directly connected
with the magnetic form of force supplied by the arrangement.
Another effect which occurred illustrated the same point. When
the contact at the voltaic battery is made, and the current sent
round the electro-magnet, the image produced by the rotation
of the polarized ray does not rise up to its full lustre imme-
diately, but increases for a couple of seconds, gradually acquiring
its greatest intensity; on breaking the contact, it sinks instantly
and disappears apparently at once. The gradual rise in bright-
ness is due to the time which the iron core of the magnet re-
quires to evolve all that magnetic power which the electric cur-
rent can develope in it; and as the magnetism rises in intensity,
so does its effect on the light increase in power; hence the pro-
gressive condition of the rotation.
2171. I cannot as yet find that the heavy glass (2151.), when
in this state, i. e. with magnetic lines of force passing through
it, exhibits any increased degree, or has any specific magneto-
inductive action of the recognized kind. I have placed it in
large quantities, and in different positions, between magnets and
magnetic needles, having at the time very delicate means of ap-
preciating any difference between it and air, but could find none.
2172. Using water, alcohol, mercury, and other fluids con-
tained in very large delicate thermometer-shaped vessels, I could
not discover that any difference in volume occurred when the
magnetic curves passed through them.
2173. It is time that I should pass to a consideration of this.
power of magnetism over light as exercised, not only in the sili-
cated borate of lead (2151.), but in many other substances; and
here we perceive, in the first place, that if all transparent bodies
possess the power of exhibiting the action, they have it in very
different degrees, and that up to this time there are some that
have not shown it at all.
Nov. 1845.]
9
Rotation of a ray by magnetism.
2174. Next, we may observe, that bodies that are exceedingly
different to each other in chemical, physical, and mechanical
properties, develope this effect; for solids and liquids, acids,
alkalies, oils, water, alcohol, æther, all possess the power.
2175. And lastly, we may observe, that in all of them, though
the degree of action may differ, still it is always the same in
kind, being a rotative power over the ray of light; and further,
the direction of the rotation is, in every case, independent of the
nature or state of the substance, and dependent upon the direc-
tion of the magnetic line of force, according to the law before
laid down (2160.).
2176. Amongst the substances in which this power of action
is found, I have already distinguished the silico-borate of lead
(2151.) as eminently fitted for the purpose of exhibiting the phæ-
nomena. I regret that it should be the best, since it is not
likely to be in the possession of many, and few will be induced
to take the trouble of preparing it. If made, it should be well
annealed, for otherwise the pieces will have considerable power
of depolarizing light, and then the particular phænomena under
consideration are much less strikingly observed. The borate of
lead, however, is a substance much more fusible, softening at
the heat of boiling oil, and therefore far more easily prepared in
the form of glass plates and annealed; and it possesses as much
magneto-rotative power over light as the silico-borate itself.
Flint-glass exhibits the property, but in a less degree than the
substances above. Crown-glass shows it, but in a still smaller
degree.
2177. Whilst employing crystalline bodies as diamagnetics, I
generally gave them that position in which they did not affect
the polarized ray, and then induced the magnetic curves through
them. As a class, they seemed to resist the assumption of the
rotating state. Rock-salt and fluor-spar gave evidence of the
power in a slight degree; and I think that a crystal of alum
did the same, but its ray length in the transparent part was so
small that I could not ascertain the fact decisively. Two spe-
cimens of transparent fluor, lent me by Mr. Tennant, gave the
effect.
2178. Rock-crystal, 4 inches across, gave no indications of
action on the ray, neither did smaller crystals, nor cubes about
three-fourths of an inch in the side, which were so cut as to
10
[SERIES XIX.
Action of magnets on light.
have two of their faces perpendicular to the axis of the crystal
(1692, 1693.), though they were examined in every direction.
2179. Iceland spar exhibited no signs of effect, either in the
form of rhomboids, or of cubes like those just described (1695.).
2180. Sulphate of baryta, sulphate of lime, and carbonate of
soda, were also without action on the light.
2181. A piece of fine clear ice gave me no effect. I cannot
however say there is none, for the effect of water in the same
mass would be very small, and the irregularity of the flattened
surface from the fusion of the ice and flow of water, made the
observation very difficult.
2182. With some degree of curiosity and hope, I put gold-
leaf into the magnetic lines, but could perceive no effect. Con-
sidering the extremely small dimensions of the length of the
path of the polarized ray in it, any positive result was hardly to
be expected.
2183. In experiments with liquids, a very good method of
observing the effect, is to enclose them in bottles from 1 to 3
or 4 inches in diameter, placing these in succession between the
magnetic poles (2150.), and bringing the analysing eye-piece so
near to the bottle, that, by adjustment of the latter, its cylindri-
cal form may cause a diffuse but useful image of the lamp-flame
to be seen through it: the light of this image is easily distin-
guished from that which passes by irregular refraction through
the striæ and deformations of the glass, and the phænomena
being looked for in this light are easily seen.
2184. Water, alcohol, and æther, all show the effect; water
most, alcohol less, and æther the least. All the fixed oils which
I have tried, including almond, castor, olive, poppy, linseed,
sperm, elaine from hog's lard, and distilled resin oil, produce it.
The essential oils of turpentine, bitter almonds, spike lavender,
lavender, jessamine, cloves, and laurel, produce it. Also naph-
tha of various kinds, melted spermaceti, fused sulphur, chloride
of sulphur, chloride of arsenic, and every other liquid substance
which I had at hand and could submit in sufficient bulk to ex-
periment.
2185. Of aqueous solutions I tried 150 or more, including the
soluble acids, alkalies and salts, with sugar, gum, &c., the list of
which would be too long to give here, since the great conclusion
was, that the exceeding diversity of substance caused no ex-
Nov. 1845.]
11
Rotation of a ray by magnetism.
ception to the general result, for all the bodies showed the pro-
perty. It is indeed more than probable, that in all these cases
the water and not the other substance present was the ruling
matter. The same general result was obtained with alcoholic
solutions.
2186. Proceeding from liquids to air and gaseous bodies, I
have here to state that, as yet, I have not been able to detect
the exercise of this power in any one of the substances in this
class. I have tried the experiment with bottles 4 inches in dia-
meter, and the following gases: oxygen, nitrogen, hydrogen,
nitrous oxide, olefiant gas, sulphurous acid, muriatic acid, car-
bonic acid, carbonic oxide, ammonia, sulphuretted hydrogen,
and bromine vapour, at ordinary temperatures; but they all
gave negative results. With air, the trial has been carried, by
another form of apparatus, to a much higher degree, but still
ineffectually (2212.).
2187. Before dismissing the consideration of the substances
which exhibited this power, and in reference to those in which
it was superinduced upon bodies possessing, naturally, rotative
force (2165. 2231.), I may record, that the following are the
substances submitted to experiment; castor oil, resin oil, oil of
spike lavender, of laurel, Canada balsam, alcoholic solution of
camphor, alcoholic solution of camphor and corrosive sublimate,
aqueous solutions of sugar, tartaric acid, tartrate of soda, tar-
trate of potassa and antimony, tartaric and boracic acid, and
sulphate of nickel, which rotated to the right-hand; copaiba
balsam, which rotated the ray to the left-hand; and two speci-
mens of camphine or oil of turpentine, in one of which the ro-
tation was to the right-hand, and in the other to the left.
all these cases, as already said (2165.), the superinduced mag-
netic rotation was according to the general law (2160.), and with-
out reference to the previous power of the body.
.
2188. Camphor being melted in a tube about an inch in dia-
meter, exhibited high natural rotative force, but I could not
discover that the magnetic curves induced additional force in it.
It may be, however, that the shortness of the ray length and
the quantity of coloured light left, even when the eye-piece was
adjusted to the most favourable position for darkening the
image produced by the naturally rotated ray, rendered the
small magneto-power of the camphor insensible.
12
Action of electric currents on light. [SERIES XIX.
Tii. Action of electric currents on light.
2189. From a consideration of the nature and position of the
lines of magnetic and electric force, and the relation of a mag-
net to a current of electricity, it appeared almost certain that an
electric current would give the same result of action on light as
a magnet; and, in the helix, would supply a form of apparatus
in which great lengths of diamagnetics, and especially of such
bodies as appeared to be but little affected between the poles of
the magnet, might be submitted to examination and their effect
exalted: this expectation was, by experiment, realized.
0·4
2190. Helices of copper wire were employed, three of which
I will refer to. The first, or long helix, was 0.4 of an inch in-
ternal diameter; the wire was 0.03 of an inch in diameter, and
having gone round the axis from one end of the helix to the
other, then returned in the same manner, forming a coil 65
inches long, double in its whole extent, and containing 1240 feet
of wire.
2191. The second, or medium helix, is 19 inches long, 1.87
inch internal diameter, and 3 inches external diameter. The
wire is 0-2 of an inch in diameter, and 80 feet in length, being
disposed in the coil as two concentric spirals. The electric cur-
rent, in passing through it, is not divided, but traverses the
whole length of the wire.
2192. The third, or Woolwich helix, was made under my in-
struction for the use of Lieut.-Colonel Sabine's establishment
at Woolwich. It is 26.5 inches long, 2.5 inches internal dia-
meter, and 4.75 inches external diameter. The wire is 0.17 of
an inch in diameter, and 501 feet in length. It is disposed in the
coil in four concentric spirals connected end to end, so that the
whole of the electric current employed passes through all the wire.
2193. The long helix (2190.) acted very feebly on a mag-
netic needle placed at a little distance from it; the medium helix
(2191.) acted more powerfully, and the Woolwich helix (2192.)
very strongly; the same battery of ten pairs of Grove's plate
being employed in all cases.
2194. Solid bodies were easily subjected to the action of these
electro-helices, being for that purpose merely cut into the form
of bars or prisms with flat and polished ends, and then intro-
Nov. 1845.]
13
Rotation of a ray by electricity.
duced as cores into the helices. For the purpose of submitting
liquid bodies to the same action, tubes of glass were provided,
furnished at the ends with caps; the cylindrical part of the cap
was brass, and had a tubular aperture for the introduction of
the liquids, but the end was a flat glass plate. When the tube
was intended to contain aqueous fluids, the plates were attached
to the caps, and the caps to the tube by Canada balsam; when
the tube had to contain alcohol, æther or essential oils, a thick
mixture of powdered gum with a little water was employed as
the cement.
2195. The general effect produced by this form of apparatus
may be stated as follows:-The tube within the long helix
(2190.) was filled with distilled water and placed in the line of
the polarized ray, so that by examination through the eye-piece
(2150.), the image of the lamp-flame produced by the ray could
be seen through it. Then the eye-piece was turned until the
image of the flame disappeared, and, afterwards, the current of
ten pairs of plates sent through the helix; instantly the image
of the flame reappeared, and continued as long as the electric
current was passing through the helix; on stopping the current
the image disappeared. The light did not rise up gradually,
as in the case of electro-magnets (2170.), but instantly. These
results could be produced at pleasure. In this experiment we
may, I think, justly say that a ray of light is electrified and the
electric forces illuminated.
2196. The phænomena may be made more striking, by the
adjustment of a lens of long focus between the tube and the
polarizing mirror, or one of short focus between the tube and
the eye; and where the helix, or the battery, or the substance
experimented with, is feeble in power, such means offer assist-
ance in working out the effects: but after a little experience,
they are easily dispensed with, and are only useful as accessories
in doubtful cases.
2197. In cases where the effect is feeble, it is more easily
perceived if the Nichol eye-piece be adjusted, not to the perfect
extinction of the ray, but a little short of or beyond that position;
so that the image of the flame may be but just visible. Then,
on the exertion of the power of the electric current, the light is
either increased in intensity, or else diminished, or extinguished,
or even re-illuminated on the other side of the dark condition ;
14
Action of electric currents on light. [SERIES XIX.
and this change is more easily perceived than if the eye began
to observe from a state of utter darkness. Such a mode of ob-
serving also assists in demonstrating the rotatory character of
the action on light; for, if the light be made visible beforehand
by the motion of the eye-piece in one direction, and the power
of the current be to increase that light, an instant only suffices,
after stopping the current, to move the eye-piece in the other
direction until the light is apparent as at first, and then the
power of the current will be to diminish it; the tints of the lights
being affected also at the same time.
2198. When the current was sent round the helix in one di-
rection, the rotation induced upon the ray of light was one way ;
and when the current was changed to the contrary direction, the
rotation was the other way. In order to express the direction,
I will assume, as is usually done, that the current passes from
the zinc through the acid to the platinum in the same cell (663.
667. 1627.): if such a current pass under the ray towards the
right, upwards on its right side, and over the ray towards the
left, it will give left-handed rotation to it; or, if the current pass
over the ray to the right, down on the right side, and under it
towards the left, it will induce it to rotate to the right-hand.
2199. The Law, therefore, by which an electric current acts
on a ray of light is easily expressed. When an electric current
passes round a ray of polarized light in a plane perpendicular to
the ray, it causes the ray to revolve on its axis, as long as it is
under the influence of the current, in the same direction as that
in which the current is passing.
2200. The simplicity of this law, and its identity with that
given before, as expressing the action of magnetism on light
(2160.), is very beautiful. A model is not wanted to assist the
memory; but if that already described (2161.) be looked at, the
line round it will express at the same time the direction both of
the current and the rotation. It will indeed do much more;
for if the cylinder be considered as a piece of iron, and not a
piece of glass or other diamagnetic, placed between the two poles
N and S, then the line round it will represent the direction of the
currents, which, according to Ampère's theory, are moving
round its particles; or if it be considered as a core of iron (in
place of a core of water), having an electric current running
round it in the direction of the line, it will also represent such
a
Nov. 1845.]
15
Rotation of a ray by electricity.
magnet as would be formed if it were placed between the poles
whose marks are affixed to its ends.
2201. I will now notice certain points respecting the degree
of this action under different circumstances. By using a tube
of water (2194.) as long as the helix, but placing it so that more
or less of the tube projected at either end of the helix, I was
able, in some degree, to ascertain the effect of length of the dia-
magnetic, the force of the helix and current remaining the same.
The greater the column of water subjected to the action of the
helix, the greater was the rotation of the polarized ray; and the
amount of rotation seemed to be directly proportionate to the
length of fluid round which the electric current passed.
2202. A short tube of water, or a piece of heavy glass, being
placed in the axis of the Woolwich helix (2192.), seemed to pro-
duce equal effect on the ray of light, whether it were in the middle
of the helix or at either end; provided it was always within the
helix and in the line of the axis. From this it would appear
that every part of the helix has the same effect; and, that by
using long helices, substances may be submitted to this kind of
examination which could not be placed in sufficient length
between the poles of magnets (2150.).
2203. A tube of water as long as the Woolwich helix (2192.),
but only 0.4 of an inch in diameter, was placed in the helix
parallel to the axis, but sometimes in the axis and sometimes
near the side. No apparent difference was produced in these
different situations; and I am inclined to believe (without being
quite sure) that the action on the ray is the same, wherever the
tube is placed, within the helix, in relation to the axis. The
same result was obtained when a larger tube of water was looked
through, whether the ray passed through the axis of the helix
and tube, or near the side.
2204. If bodies be introduced into the helix possessing, natu-
rally, rotating force, then the rotating power given by the electric
current is superinduced upon them, exactly as in the cases al-
ready described of magnetic action (2165. 2187.).
2205. A helix, 20 inches long and 0.3 of an inch in diameter,
was made of uncovered copper wire, 0·05 of an inch in dia-
meter, in close spirals. This was placed in a large tube of
water, so that the fluid, both in the inside and at the outside of
the helix, could be examined by the polarized ray. When the
16
Action of electric currents on light. [SERIES XIX.
current was sent through the helix, the water within it received
rotating power; but no trace of such an action on the light was
seen on the outside of the helix, even in the line most close to
the uncovered wire.
2206. The water was enclosed in brass and copper tubes, but
this alteration caused not the slightest change in the effect.
2207. The water in the brass tube was put into an iron tube,
much longer than either the Woolwich helix or the brass tube,
and quite one eighth of an inch thick in the side; yet when
placed in the Woolwich helix (2192.), the water rotated the ray
of light apparently as well as before.
2208. An iron bar, 1 inch square and longer than the helix,
was put into the helix, and the small water tube (2203.) upon it.
The water exerted as much action on the light as before.
2209. Three iron tubes, each 27 inches long and one-eighth
of an inch in thickness in the side, were selected of such dia-
meters as to pass easily one into the other, and the whole
into the Woolwich helix (2192.). The smaller one was sup-
plied with glass ends and filled with water; and being placed
in the axis of the Woolwich helix, had a certain amount of ro-
tating power over the polarized ray. The second tube was then
placed over this, so that there was now a thickness of iron equal
to two-eighths of an inch between the water and the helix; the
water had more power of rotation than before. On placing the
third tube of iron over the two former, the power of the water
fell, but was still very considerable. These results are compli-
cated, being dependent on the new condition which the character
of iron gives to its action on the forces. Up to a certain
amount, by increasing the development of magnetic forces, the
helix and core, as a whole, produce increased action on the
water; but on the addition of more iron and the disposal of the
forces through it, their action is removed in part from the water
and the rotation is lessened.
2210. Pieces of heavy glass (2151.), placed in iron tubes in
the helices, produced similar effects.
2211. The bodies which were submitted to the action of an
electric current in a helix, in the manner already described,
were as follows: Heavy glass (2151. 2176.), water, solution of
sulphate of soda, solution of tartaric acid, alcohol, æther, and oil
of turpentine; all of which were affected, and acted on light
Nov. 1845.]
17
Rotation of light by electric force.
exactly in the manner described in relation to magnetic action
(2173.).
2212. I submitted air to the influence of these helices care-
fully and anxiously, but could not discover any trace of action
on the polarized ray of light. I put the long helix (2190.) into
the other two (2191. 2192.), and combined them all into one
consistent series, so as to accumulate power, but could not ob-
serve any effect of them on light passing through air.
2213. In the use of helices, it is necessary to be aware of one
effect, which might otherwise cause confusion and trouble. At
first, the wire of the long helix (2190.) was wound directly upon
the thin glass tube which served to contain the fluid. When
the electric current passed through the helix it raised the tem-
perature of the metal, and that gradually raised the temperature
of the glass and the film of water in contact with it, and so the
cylinder of water, warmer at its surface than its axis, acted as a
lens, gathering and sending rays of light to the eye, and con-
tinuing to act for a time after the current was stopped. By
separating the tube of water from the helix, and by other pre-
cautions, this source of confusion is easily avoided.
2214. Another point of which the experimenter should be
aware, is the difficulty, and almost impossibility, of obtain-
ing a piece of glass which, especially after it is cut, does not de-
polarize light. When it does depolarize, difference of position
makes an immense difference in the appearance. By always
referring to the parts that do not depolarize, as the black cross,
for instance, and by bringing the eye as near as may be to the
glass, this difficulty is more or less overcome.
2215. For the sake of supplying a general indication of the
amount of this induced rotating force in two or three bodies,
and without any pretence of offering correct numbers, I will
give, generally, the results of a few attempts to measure the force,
and compare it with the natural power of a specimen of oil of
turpentine. A very powerful electro-magnet was employed,
with a constant distance between its poles of 24 inches. In this
space was placed different substances; the amount of rotation
of the eye-piece observed several times and the average taken,
as expressing the rotation for the ray length of substance used.
VOL. 111.
C
18
Rotation of light by magnetic force. [SERIES XIX.
But as the substances were of different dimensions, the ray
lengths were, by calculation, corrected to one standard length,
upon the assumption that the power was proportionate to this
length (2163.). The oil of turpentine was of course observed in
its natural state, i. e. without magnetic action. Making water
1, the numbers were as follows :—
11.8
Oil of turpentine
Heavy glass (2151.)
6.0
•
Flint-glass
2.8
Rock-salt
2.2
Water
1.0
Alcohol.
Æther
lesss than water.
less than alcohol.
2216. In relation to the action of magnetic and electric forces.
on light, I consider, that to know the conditions under which
there is no apparent action, is to add to our knowledge of their
mutual relations; and will, therefore, very briefly state how I have
lately combined these forces, obtaining no apparent result (955.).
;
2217. Heavy glass, flint-glass, rock crystal, Iceland spar, oil
of turpentine, and air, had a polarized ray passed through them
and, at the same time, lines of electro-static tension (2149.)
were, by means of coatings, the Leyden jar, and the electric
machine, directed across the bodies, parallel to the polarized ray,
and perpendicular to it, both in and across the plane of polariza-
tion; but without any visible effect. The tension of a rapidly
recurring, induced secondary current, was also directed upon
the same bodies and upon water (as an electrolyte), but with the
same negative result.
2218. A polarized ray, powerful magnetic lines of force, and
the electric lines of force (2149.) just described, were combined
in various directions in their action on heavy glass (2151. 2176.),
but with no other result than that due to the mutual action of
the magnetic lines of light, already described in this paper.
2219. A polarized ray and electric currents were combined in
every possible way in electrolytes (951-954). The substances
used were distilled water, solution of sugar, dilute sulphuric
acid, solution of sulphate of soda, using platinum electrodes; and
solution of sulphate of copper, using copper electrodes: the
current was sent along the ray, and perpendicular to it in two
Nov. 1815.]
19
Relation of light to magnetism.
directions at right angles with each other; the ray was made to
rotate, by altering the position of the polarizing mirror, that the
plane of polarization might be varied; the current was used as
a continuous current, as a rapidly intermitting current, and as
a rapidly alternating double current of induction; but in no case
was any trace of action perceived.
2220. Lastly, a ray of polarized light, electric currents, and
magnetic lines of force, were directed in every possible way
through dilute sulphuric acid and solution of sulphate of soda,
but still with negative results, except in those positions where
the phænomena already described were produced. In one
arrangement, the current passed in the direction of radii from a
central to a circumferential electrode, the contrary magnetic
poles being placed above and below; and the arrangements were
so good, that when the electric current was passing, the fluid
rapidly rotated; but a polarized ray sent horizontally across this
arrangement was not at all affected. Also, when the ray was
sent vertically through it, and the eye-piece moved to corre-
spond to the rotation impressed upon the ray in this position
by the magnetic curves alone, the superinduction of the passage
of the electric current made not the least difference in the effect
upon the ray.
Tiii. General considerations.
2221. Thus is established, I think for the first time¹, a true,
direct relation and dependence between light and the magnetic
and electric forces; and thus a great addition made to the facts
¹ I say, for the first time, because I do not think that the experiments of
Morrichini on the production of magnetism by the rays at the violet end of
the spectrum prove any such relation. When in Rome with Sir H. Davy in
the month of May 1814, I spent several hours at the house of Morrichini,
working with his apparatus and under his directions, but could not succeed
in magnetising a needle. I have no confidence in the effect as a direct result
of the action of the sun's rays; but think, that when it has occurred it has
been secondary, incidental, and perhaps even accidental; a result that might
well happen with a needle that was preserved during the whole experiment in
a north and south position.
January 2, 1846.-I should not have written "for the first time" as above,
if I had remembered Mr. Christie's experiments and papers on the Influence of
the Solar Rays on Magnets, communicated in the Philosophical Transactions
for 1826, p. 219, and 1828, p. 379.—M. F.
c 2
20
Relation of light to magnetism. [SERIES XIX.
and considerations which tend to prove that all natural forces
are tied together, and have one common origin (2146.). It is
no doubt, difficult in the present state of our knowledge to ex-
press our expectation in exact terms; and, though I have said
that another of the powers of nature is, in these experiments,
directly related to the rest, I ought, perhaps, rather to say that
another form of the great power is distinctly and directly related
to the other forms; or, that the great power manifested by par-
ticular phænomena in particular forms, is here further identified
and recognized, by the direct relation of its form of light to its
forms of electricity and magnetism.
2222. The relation existing between polarized light and mag-
netism and electricity, is even more interesting than if it had
been shown to exist with common light only. It cannot but
extend to common light; and, as it belongs to light made, in a
certain respect, more precise in its character and properties by
polarization, it collates and connects it with these powers, in
the duality of character which they possess, and yields an
opening, which before was wanting to us, for the appliance of
these powers to the investigation of the nature of this and other
radiant agencies.
2223. Referring to the conventional distinction before made
(2149.), it may be again stated, that it is the magnetic lines of
force only which are effectual on the rays of light, and they only
(in appearance) when parallel to the ray of light, or as they tend
to parallelism with it. As, in reference to matter not magnetic
after the manner of iron, the phænomena of electric induction
and electrolyzation show a vast superiority in the energy with
which electric forces can act as compared to magnetic forces, so
here, in another direction and in the peculiar and correspondent
effects which belong to magnetic forces, they are shown, in turn,
to possess great superiority, and to have their full equivalent of
action on the same kind of matter.
2224. The magnetic forces do not act on the ray of light
directly and without the intervention of matter, but through
the mediation of the substance in which they and the ray have
a simultaneous existence; the substances and the forces giving
to and receiving from each other the power of acting on the
light. This is shown by the non-action of a vacuum, of air or
gases; and it is also further shown by the special degree in
Nov. 1845.]
21
Relation of light to magnetism.
which different matters possess the property. That magnetic
force acts upon the ray of light always with the same character
of manner and in the same direction, independent of the differ-
ent varieties of substance, or their states of solid or liquid, or
their specific rotative force (2232.), shows that the magnetic
force and the light have a direct relation: but that substances
are necessary, and that these act in different degrees, shows that
the magnetism and the light act on each other through the in-
tervention of the matter.
2225. Recognizing or perceiving matter only by its powers,
and knowing nothing of any imaginary nucleus, abstract from
the idea of these powers, the phænomena described in this paper
much strengthen my inclination to trust in the views I have on
a former occasion advanced in reference to its nature¹.
2226. It cannot be doubted that the magnetic forces act upon
and affect the internal constitution of the diamagnetic, just as
freely in the dark as when a ray of light is passing through it;
though the phænomena produced by light seem, as yet, to pre-
sent the only means of observing this constitution and the change.
Further, any such change as this must belong to opake bodies,
such as wood, stone, and metal; for as diamagnetics, there is no
distinction between them and those which are transparent.
The degree of transparency can at the utmost, in this respect,
only make a distinction between the individuals of a class.
2227. If the magnetic forces had made these bodies magnets,
we could, by light, have examined a transparent magnet; and
that would have been a great help to our investigation of the
forces of matter. But it does not make them magnets (2171.),
and therefore the molecular condition of these bodies, when in
the state described, must be specifically distinct from that of
magnetized iron, or other such matter, and must be a new mag-
netic condition; and as the condition is a state of tension (mani-
fested by its instantaneous return to the normal state when the
magnetic induction is removed), so the force which the matter
in this state possesses and its mode of action, must be to us a
new magnetic force or mode of action of matter.
2228. For it is impossible, I think, to observe and see the
action of magnetic forces, rising in intensity, upon a piece of heavy
glass or a tube of water, without also perceiving that the latter
¹ Vol. ii. p. 284, or Philosophical Magazine, 1844, vol. xxiv. p. 136.
22
[SERIES XIX.
Rotation of light by magnetism.
acquire properties which are not only new to the substance, but
are also in subjection to very definite and precise laws (2160.
2199.), and are equivalent in proportion to the magnetic forces
producing them.
2229. Perhaps this state is a state of electric tension tending
to a current; as in magnets, according to Ampère's theory, the
state is a state of current. When a core of iron is put into a
helix, everything leads us to believe that currents of electricity
are produced within it, which rotate or move in a plane perpen-
dicular to the axis of the helix. If a diamagnetic be placed in
the same position, it acquires power to make light rotate in the
same plane. The state it has received is a state of tension, but
it has not passed on into currents, though the acting force and
every other circumstance and condition are the same as those
which do produce currents in iron, nickel, cobalt, and such
other matters as are fitted to receive them. Hence the idea that
there exists in diamagnetics, under such circumstances, a ten-
dency to currents, is consistent with all the phænomena as yet
described, and is further strengthened by the fact, that, leaving
the loadstone or the electric current, which by inductive action
is rendering a piece of iron, nickel, or cobalt magnetic, perfectly
unchanged, a mere change of temperature will take from these
bodies their extra power, and make them pass into the common
class of diamagnetics.
2230. The present is, I believe, the first time that the mole-
cular condition of a body, required to produce the circular po-
larization of light, has been artificially given; and it is therefore
very interesting to consider this known state and condition of the
body, comparing it with the relatively unknown state of those
which possess the power naturally: especially as some of the lat-
ter rotate to the right-hand and others to the left; and as in the
cases of quartz and oil of turpentine, the same body chemically
speaking, being in the latter instance a liquid with particles free
to move, presents different specimens, some rotating one way
and some the other.
2231. At first one would be inclined to conclude that the
natural state and the state conferred by magnetic and electric
forces must be the same, since the effect is the same; but on
Nov. 1845.] Natural and magnetic rotation compared.
23
:
further consideration it seems very difficult to come to such a
conclusion. Oil of turpentine will rotate a ray of light, the
power depending upon its particles and not upon the arrange-
ment of the mass. Whichever way a ray of polarized light
passes through this fluid, it is rotated in the same manner;
and rays passing in every possible direction through it simulta-
neously are all rotated with equal force and according to one
common law of direction; i. e. either all right-handed or else all
to the left. Not so with the rotation superinduced on the same
oil of turpentine by the magnetic or electric forces it exists
only in one direction, i. e. in a plane perpendicular to the mag-
netic line; and being limited to this plane, it can be changed in
direction by a reversal of the direction of the inducing force.
The direction of the rotation produced by the natural state is
connected invariably with the direction of the ray of light; but
the power to produce it appears to be possessed in every direc-
tion and at all times by the particles of the fluid: the direction
of the rotation produced by the induced condition is connected
invariably with the direction of the magnetic line or the electric
current, and the condition is possessed by the particles of mat-
ter, but strictly limited by the line or the current, changing and
disappearing with it.
Fig. 3.
d
2232. Let m, in fig. 3, represent a glass cell filled with oil of
turpentine, possessing naturally the power of producing right-
hand rotation, and a b a polarized ray of light. If the ray pro-
ceed from a to b, and the eye be placed at b, the rotation will
be right-handed, or according to the
direction expressed by the arrow heads
on the circle c; if the ray proceed
from b to a, and the eye be placed at a,
the rotation will still be right-handed to
the observer, i. e. according to the
direction indicated on the circle d. Let
now an electric current pass round the
oil of turpentine in the direction indi-
cated on the circle c, or magnetic poles
be placed so as to produce the same
effect (2155.); the particles will ac-
quire a further rotative force (which no

m
motion amongst themselves will disturb), and a ray coming from
24
Natural and magnetic rotation compared. [SERIES XIX.
a to b will be seen by an eye placed at b to rotate to the right-
hand more than before, or in the direction on the circle c; but
pass a ray from b to a, and observe with the eye at a, and
the phænomenon is no longer the same as before; for instead of
the new rotation being according to the direction indicated on
the circle d, it will be in the contrary direction, or to the obser-
ver's left-hand (2199.). In fact the induced rotation will be
added to the natural rotation as respects a ray passing from a to
b, but it will be subtracted from the natural rotation as regards
the ray passing from 6 to a.
b
Hence the particles of this fluid
which rotate by virtue of their natural force, and those which
rotate by virtue of the induced force, cannot be in the same
condition.
2233. As respects the power of the oil of turpentine to rotate
a ray in whatever direction it is passing through the liquid, it
may well be, that though all the particles possess the power of
rotating the light, only those whose planes of rotation are more
or less perpendicular to the ray affect it; and that it is the result-
ant of sum of forces in any one direction which is active in pro-
ducing rotation. But even then a striking difference remains,
because the resultant in the same plane is not absolute in direc-
tion, but relative to the course of the ray, being in the one case
as the circle c, and in the other as the circle d, fig. 3; whereas
the resultant of the magnetic or electric induction is absolute,
and not changing with the course of the ray, being always either
as expressed by c or else as indicated by d.
2234. All these differences, however, will doubtless disap-
pear or come into harmony as these investigations are extended;
and their very existence opens so many paths, by which we
may pursue our inquiries, more and more deeply, into the
powers and constitution of matter.
2235. Bodies having rotating power of themselves, do not
seem by that to have a greater or a less tendency to assume a
further degree of the same force under the influence of magnetic
or electric power.
2236. Were it not for these and other differences, we might
see an analogy between those bodies, which possess at all times
the rotating power, as a specimen of quartz which rotates only
in one plane, and also those to which the power is given by the
induction of other forces, as a prism of heavy glass in a helix,
Nov. 1845.]
25
Magnetic rotation of light.
on the one hand; and, on the other, a natural magnet and a helix
through which the current is passing. The natural condition
of the magnet and quartz, and the constrained condition of the
helix and heavy glass, form the link of the analogy in one direc-
tion; whilst the supposition of currents existing in the magnet
and helix, and only a tendency or tension to currents existing
in the quartz and heavy glass, supplies the link in the transverse
direction.
2237. As to those bodies which seem as yet to give no indi-
cation of the power over light, and therefore none of the assump-
tion of the new magnetic conditions, these may be divided into
two classes, the one including air, gases and vapours, and the
other rock crystal, Iceland spar, and certain other crystalline
bodies. As regards the latter class, I shall give, in the next
series of these researches, proofs drawn from phænomena of an
entirely different hind, that they do acquire the new magnetic
condition; and these being so disposed of for the moment, I am
inclined to believe that even air and gases have the power to
assume the peculiar state, and even to affect light, but in a de-
gree so small that as yet it has not been made sensible. Still
the gaseous state is such a remarkable condition of matter, that
we ought not too hastily to assume that the substances which,
in the solid and liquid state, possess properties even general in
character, always carry these into their gaseous condition.
2238. Rock-salt, fluor-spar, and, I think, alum, affect the ray
of light; the other crystals experimented with did not; these
are equiaxed and singly refracting, the others are unequiaxed
and doubly refracting. Perhaps these instances, with that of
the rotation of quartz, may even now indicate a relation between
magnetism, electricity, and the crystallizing forces of matter.
2239. All bodies are affected by helices as by magnets, and
according to laws which show that the causes of the action are
identical as well as the effects. This result supplies another
fine proof in favour of the identity of helices and magnets, ac-
cording to the views of Ampère.
2240. The theory of static induction which I formerly ventured
to set forth (1161, &c.), and which depends upon the action of
the contiguous particles of the dielectric intervening between the
inductric and the inducteous bodies, lead me to expect that the
same kind of dependence upon the intervening particles would
26
[SERIES XIX.
Magnetic rotation of light.
be found to exist in magnetic action; and I published certain
experiments and considerations on this point seven years ago
(1709-1736). I could not then discover any peculiar con-
dition of the intervening substance or diamagnetic; but now
that I have been able to make out such a state, which is not
only a state of tension (2227.), but dependent entirely upon the
magnetic lines which pass through the substance, I am more
than ever encouraged to believe that the view then advanced is
correct.
2241. Although the magnetic and electric forces appear to
exert no power on the ordinary or on the depolarized ray of
light, we can hardly doubt but that they have some special influ-
ence, which probably will soon be made apparent by experiment.
Neither can it be supposed otherwise than that the same kind
of action should take place on the other forms of radiant agents
as heat and chemical force.
2242. This mode of magnetic and electric action, and the
phænomena presented by it, will, I hope, greatly assist hereafter
in the investigation of the nature of transparent bodies, of light,
of magnets, and their action one on another or on magnetic
substances. I am at this time engaged in investigating the new
magnetic condition, and shall shortly send a further account of
it to the Royal Society. What the possible effect of the force
may be in the earth as a whole or in magnets, or in relation to
the sun, and what may be the best means of causing light to
evolve electricity and magnetism, are thoughts continually press-
ing upon the mind; but it will be better to occupy both time
and thought, aided by experiment, in the investigation and de-
velopment of real truth, than to use them in the invention of
suppositions which may or may not be founded on, or consistent
with, fact.
Royal Institution,
Oct. 29, 1845.
27
TWENTIETH SERIES¹.
§ 27. On new magnetic actions, and on the magnetic condition of
all matter. ¶i. Apparatus required. ¶ii. Action of mag-
nets on heavy glass. ¶ iii. Action of magnets on other sub-
stances acting magnetically on light. iv. Action of magnets
on the metals generally.
¶
Received December 6,—Read December 18, 1845.
2243. THE contents of the last series of these Researches were,
I think, sufficient to justify the statement, that a new magnetic
¹ Philosophical Transactions, 1846, p. 21.
2
My friend Mr. Wheatstone has this day called my attention to a paper by
M. Becquerel, "On the magnetic actions excited in all bodies by the influence
of very energetic magnets," read to the Academy of Sciences on the 27th of
September 1827, and published in the Annales de Chimie, xxxvi. p. 337. It
relates to the action of the magnet on a magnetic needle, on soft iron, on the
deutoxide and tritoxide of iron, on the tritoxide alone, and on a needle of wood.
The author observed, and quotes Coulomb as having also observed, that a
needle of wood under certain conditions, pointed across the magnetic curves ;
and he also states the striking fact that he had found a needle of wood place
itself parallel to the wires of a galvanometer. These effects, however, he refers
to a degree of magnetism less than that of the tritoxide of iron, but the same
in character, for the bodies take the same position. The polarity of steel and
iron is stated to be in the direction of the length of the substance, but that of
tritoxide of iron, wood and gum-lac, most frequently in the direction of the
width, and always when one magnetic pole is employed. "This difference of
effect, which establishes a line of demarcation between these two species of
phænomena, is due to this, that the magnetism being very feeble in the trit-
oxide of iron, wood, &c., we may neglect the reaction of the body on itself, and
therefore the direct action of the bar ought to overrule it.”
As the paper does not refer the phænomena of wood and gum-lac to an ele-
mentary repulsive action, nor show that they are common to an immense class
of bodies, nor distinguish this class, which I have called diamagnetic, from the
magnetic class; and, as it makes all magnetic action of one kind, whereas I
show that there are two kinds of such action, as distinct from each other as
positive and negative electric action are in their way, so I do not think I need
alter a word or the date of that which I have written; but am most glad here
to acknowledge M. Becquerel's important facts and labours in reference to this
subject.-M. F. Dec. 5, 1845.
28
[SERIES XX.
On new magnetic actions.
condition (i. e. one new to our knowledge) had been impressed
on matter by subjecting it to the action of magnetic and electric
forces (2227.); which new condition was made manifest by the
powers of action which the matter had acquired over light. The
phænomena now to be described are altogether different in their
nature; and they prove, not only a magnetic condition of the
substances referred to unknown to us before, but also of many
others, including a vast number of opake and metallic bodies,
and perhaps all except the magnetic metals and their com-
pounds and they also, through that condition, present us with
the means of undertaking the correlation of magnetic phæno-
mena, and perhaps the construction of a theory of general mag-
netic action founded on simple fundamental principles.
2244. The whole matter is so new, and the phænomena so
varied and general, that I must, with every desire to be brief,
describe much which at last will be found to concentrate under
simple principles of action. Still, in the present state of our
knowledge, such is the only method by which I can make these
principles and their results sufficiently manifest.
¶i. Apparatus required.
2245. The effects to be described require magnetic apparatus
of great power, and under perfect command. Both these points
are obtained by the use of electro-magnets, which can be raised
to a degree of force far beyond that of natural or steel magnets;
and further, can be suddenly altogether deprived of power, or
made energetic to the highest degree, without the slightest
alteration of the arrangement, or of any other circumstance
belonging to an experiment.
2246. One of the electro-magnets which I use is that already
described under the term Woolwich helix (2192.). The soft
iron core belonging to it is 28 inches in length and 2.5 inches
in diameter. When thrown into action by ten pair of Grove's
plates, either end will sustain one or two half- hundred weights
hanging to it. The magnet can be placed either in the vertical
or the horizontal position. The iron core is a cylinder with flat
ends, but I have had a cone of iron made, 2 inches in diameter
at the base and 1 inch in height, and this placed at the end of
the core, forms a conical termination to it, when required.
DEC. 1845.]
29
Apparatus employed.
2247. Another magnet which I have had made has the horse-
shoe form. The bar of iron is 46 inches in length and 3.75
inches in diameter, and is so bent that the extremities forming
the poles are 6 inches from each other; 522 feet of copper wire
0.17 of an inch in diameter, and covered with tape, are wound
round the two straight parts of the bar, forming two coils on
these parts, each 16 inches in length, and composed of three
layers of wire: the poles are, of course, 6 inches apart, the
ends are planed true, and against these move two short bars of soft
iron, 7 inches long and 2 by 1 inch thick, which can be ad-
justed by screws, and held at any distance less than 6 inches
from each other. The ends of these bars form the opposite poles
of contrary name; the magnetic field between them can be
made of greater or smaller extent, and the intensity of the lines
of magnetic force be proportionately varied.
2248. For the suspension of substances between and near the
poles of these magnets, I occasionally used a glass jar, with a
plate and sliding wire at the top. Six or eight lengths of cocoon
silk being equally stretched, were made into one thread and at-
tached, at the upper end, to the sliding rod, and at the lower
end to a stirrup of paper, in which anything to be experimented
on could be sustained.
2249. Another very useful mode of suspension was to attach
one end of a fine thread, 6 feet long, to an adjustible arm near
the ceiling of the room, and terminating at the lower end by a
little ring of copper wire; any substance to be suspended could
be held in a simple cradle of fine copper wire having 8 or 10
inches of the wire prolonged upward; this being bent into a
hook at the superior extremity, gave the means of attachment to
the ring. The height of the suspended substance could be varied
at pleasure, by bending any part of the wire at the instant into
the hook form. A glass cylinder placed between the magnetic
poles was quite sufficient to keep the suspended substance free
from any motion, due to the agitation of the air.
2250. It is necessary, before entering upon an experimental
investigation with such an apparatus, to be aware of the effect
of any magnetism which the bodies used may possess; the
power of the apparatus to make manifest such magnetism is so
great, that it is difficult on that account to find writing-paper fit
for the stirrup above mentioned. Before therefore any experi-
30
[SERIES XX.
On new magnetic actions.
ments are instituted, it must be ascertained that the suspending
apparatus employed does not point, i. e. does not take up a posi-
tion parallel to the lines joining the magnetic poles, by virtue of
the magnetic force. When copper suspensions are employed, a
peculiar effect is produced (2309.), but when understood, as it
will be hereafter, it does not interfere with the results of experi-
ment. The wire should be fine, not magnetic as iron, and the
form of the suspending cradle should not be elongated horizon-
tally, but be round or square as to its general dimensions, in
that direction.
2251. The substances to be experimented with should be care-
fully examined, and rejected if not found free from magnetism.
Their state is easily ascertained; for, if magnetic, they will either
be attracted to the one or the other pole of the great magnet, or
else point between them. No examination by smaller magnets,
or by a magnetic needle, is sufficient for this purpose.
2252. I shall have such fre-
quent occasion to refer to two
chief directions of position across
the magnetic field, that to avoid
periphrasis, I will here ask leave
to use a term or two, condition-
ally. One of these directions is
e
that from pole to pole, or along the line of magnetic force; I
will call it the axial direction: the other is the direction perpen-
dicular to this, and across the line of magnetic force; and for
the time, and as respects the spaces between the poles, I will call
it the equatorial direction. Other terms that I may use, I hope
will explain themselves.
Tii. Action of magnets on heavy glass.
2253. The bar of silicated borate of lead, or heavy glass al-
ready described as the substance in which magnetic forces were
first made effectually to bear on a ray of light (2152.), and
which is 2 inches long, and about 0·5 of an inch wide and thick,
was suspended centrally between the magnetic poles (2247.), and
left until the effect of torsion was over. The magnet was then
thrown into action by making contact at the voltaic battery:
immediately the bar moved, turning round its point of suspen-
DEC. 1845.] Action of magnets on heavy glass.
31
sion, into a position across the magnetic curve or line of force,
and after a few vibrations took up its place of rest there. On
being displaced by hand from this position, it returned to it,
and this occurred many times in succession.
2254. Either end of the bar indifferently went to either side
of the axial line. The determining circumstance was simply in-
clination of the bar one way or the other to the axial line, at the
beginning of the experiment. If a particular or marked end of
the bar were on one side of the magnetic, or axial line, when
the magnet was rendered active that end went further outwards,
until the bar had taken up the equatorial position.
2255. Neither did any change in the magnetism of the poles,
by change in the direction of the electric current, cause any dif
ference in this respect. The bar went by the shortest course to
the equatorial position.
2256. The power which urged the bar into this position was
so thoroughly under command, that if the bar were swinging it
could easily be hastened in its course into this position, or ar-
rested as it was passing from it, by seasonable contacts at the
voltaic battery.
2257. There are two positions of equilibrium for the bar; one
stable, the other unstable. When in the direction of the axis
or magnetic line of force, the completion of the electric com-
munication causes no change of place; but if it be the least
oblique to this position, then the obliquity increases until the
bar arrives at the equatorial position; or if the bar be originally
in the equatorial position, then the magnetism causes no further
changes, but retains it there (2298. 2299. 2384.).
2258. Here then we have a magnetic bar which points east
and west, in relation to north and south poles, i. e. points per-
pendicularly to the lines of magnetic force.
2259. If the bar be adjusted so that its point of suspension,
being in the axial line, is not equidistant from the poles, but
near to one of them, then the magnetism again makes the bar
take up a position perpendicular to the magnetic lines of force;
either end of the bar being on the one side of the axial line, or
the other, at pleasure. But at the same time there is another
effect, for at the moment of completing the electric contact, the
centre of gravity of the bar recedes from the pole and remains
repelled from it as long as the magnet is retained excited. On
32
Action of magnets on heavy glass. [SERIES XX.
allowing the magnetism to pass away, the bar returns to the
place due to it by its gravity.
2260. Precisely the same effect takes place at the other pole
of the magnet. Either of them is able to repel the bar, what-
ever its position may be, and at the same time the bar is made
to assume a position, at right angles, to the line of magnetic force.
2261. If the bar be equidistant from the two poles, and in the
axial line, then no repulsive effect is or can be observed.
2262. But preserving the point of suspension in the equatorial
line, i. e. equidistant from the two poles, and removing it a little
on one side or the other of the axial line (2252.), then another
effect is brought forth. The bar points as before across the
magnetic line of force, but at the same time it recedes from the
axial line, increasing its distance from it, and this new position
is retained as long as the magnetism continues, and is quitted
with its cessation.
2263. Instead of two magnetic poles, a single pole may be
used, and that either in a vertical or a horizontal position. The
effects are in perfect accordance with those described above; for
the bar, when near the pole, is repelled from it in the direction
of the line of magnetic force, and at the same time it moves into
a position perpendicular to the direction of the magnetic lines
passing through it. When the magnet is vertical (2246.) and
the bar by its side, this action makes the bar a tangent to the
curve of its surface.
2264. To produce these effects, of pointing across the mag-
netic curves, the form of the heavy glass must be long; a cube,
or a fragment approaching roundness in form, will not point,
but a long piece will. Two or three rounded pieces or cubes,
placed side by side in a paper tray, so as to form an oblong ac-
cumulation, will also point.
2265. Portions, however, of any form, are repelled: so if two
pieces be hung up at once in the axial line, one near each pole,
they are repelled by their respective poles, and approach, seeming
to attract each other. Or if two pieces be hung up in the equa-
torial line, one on each side of the axis, then they both recede
from the axis, seeming to repel each other.
2266. From the little that has been said, it is evident that the
bar presents in its motion a complicated result of the force exerted
by the magnetic power over the heavy glass, and that, when
DEC. 1845.]
33
Action of magnets on heavy glass.
cubes or spheres are employed, a much simpler indication of the
effect may be obtained. Accordingly, when a cube was thus
used with the two poles, the effect was repulsion or recession
from either pole, and also recession from the magnetic axis on
either side.
2267. So, the indicating particle would move, either along the
magnetic curves, or across them; and it would do this either in
one direction or the other; the only constant point being, that
its tendency was to move from stronger to weaker places of
magnetic force.
2268. This appeared much more simply in the case of a
single magnetic pole, for then the tendency of the indicating cube
or sphere was to move outwards, in the direction of the mag-
netic lines of force. The appearance was remarkably like a case
of weak electric repulsion.
2269. The cause of the pointing of the bar, or any oblong ar-
rangement of the heavy glass, is now evident. It is merely a
result of the tendency of the particles to move outwards, or into
the positions of weakest magnetic action. The joint exertion of
the action of all the particles brings the mass into the position,
which, by experiment, is found to belong to it.
2270. When one or two magnetic poles are active at once,
the courses described by particles of heavy glass free to move,
form a set of lines or curves, which I may have occasion here-
after to refer to; and as I have called air, glass, water, &c. dia-
magnetic (2149.), so I will distinguish these lines by the term
diamagnetic curves, both in relation to, and contradistinction
from, the lines called magnetic curves.
2271. When the bar of heavy glass is immersed in water,
alcohol, or æther, contained in a vessel between the poles, all
the preceding effects occur; the bar points and the cube recedes
exactly in the same manner as in air.
2272. The effects equally occur in vessels of wood, stone, earth,
copper, lead, silver, or any of those substances which belong to
the diamagnetic class (2149.).
•
2273. I have obtained the same equatorial direction and
motions of the heavy glass bar as those just described, but in a
very feeble degree, by the use of a good common steel horse-shoe
magnet (2517.). I have not obtained them by the use of the
helices (2191, 2192.) without the iron cores.
VOL. III.
D
34
[SERIES XX.
Action of magnets on
2274. Here therefore we have magnetic repulsion without po-
larity, i. e. without reference to a particular pole of the magnet,
for either pole will repel the substance, and both poles will repel
it at once (2262.). The heavy glass, though subject to magnetic
action, cannot be considered as magnetic, in the usual accepta-
tion of that term, or as iron, nickel, cobalt, and their com-
pounds. It presents to us, under these circumstances, a mag-
netic property new to our knowledge; and though the phæno-
mena are very different in their nature and character to those
presented by the action of the heavy glass on light (2152.), still
they appear to be dependent on, or connected with, the same
condition of the glass as made it then effective, and there-
fore, with those phænomena, prove the reality of this new con-
dition.
¶iii. Action of magnets on other substances acting magnetically
on light.
2275. We may now pass from heavy glass to the examination
of the other substances, which, when under the power of mag-
netic or electric forces, are able to effect and rotate a polarized
ray (2173.), and may also easily extend the investigation to
bodies which, from their irregularity of form, imperfect trans-
parency, or actual opacity, could not be examined by a polarized
ray, for here we have no difficulty in the application of the test
to all such substances.
2276. The property of being thus repelled and affected by
magnetic poles, was soon found not to be peculiar to heavy
glass. Borate of lead, flint-glass, and crown glass set in the
same manner equatorially, and were repelled when near to the
poles, though not to the same degree as the heavy glass.
2277. Amongst substances which could not be subjected to
the examination by light, phosphorus in the form of a cylinder
presented the phænomena very well; I think as powerfully as
heavy glass, if not more so. A cylinder of sulphur, and a long
piece of thick India rubber, neither being magnetic after the or-
dinary fashion, were well directed and repelled.
2278. Crystalline bodies were equally obedient, whether taken
from the single or double refracting class (2237.). Prisms of
quartz, calcareous spar, nitre and sulphate of soda, all pointed
well, and were repelled.
DEC. 1845.]
35
diamagnetic bodies generally.
2279. I then proceeded to subject a great number of bodies,
taken from every class, to the magnetic forces, and will, to illus-
trate the variety in the nature of the substances, give a com-
paratively short list of crystalline, amorphous, liquid and organic
bodies below. When the bodies were fluids, I enclosed them
in thin glass tubes. Flint-glass points equatorially, but if the
tube be of very thin glass, this effect is found to be small when
the tube is experimented with alone; afterwards, when it is filled
with liquid and examined, the effect is such that there is no fear
of mistaking that due to

the glass for that of the
fluid. The tubes must
not be closed with cork,
sealing-wax, or any ordi-
nary substance taken at
random, for these are generally magnetic (2285.). I have usually
so shaped them in the making, and drawn them off at the neck,
as to leave the aperture on one side, so that when filled with
liquid they require no closing.
2280. Rock crystal.
Sulphate of lime.
Sulphate of baryta.
Sulphate of soda.
Sulphate of potassa.
Sulphate of magnesia.
Alum.
Muriate of ammonia.
Chloride of lead.
Chloride of sodium.
Nitrate of potassa.
Nitrate of lead.
Carbonate of soda.
Iceland spar.
Acetate of lead.
Tartrate of potash and
antimony.
Tartrate of potash and
soda.
Tartaric acid.
Citric acid.
Water.
Alcohol.
Æther.
Nitric acid.
Sulphuric acid.
Muriatic acid.
Solutions of various alka-
line and earthy salts.
Glass.
Litharge.
White arsenic.
Iodine.
Phosphorus.
Sulphur.
Resin.
Spermaceti.
Caffeine.
Cinchonia.
Margaric acid.
Wax from shell-lac.
Sealing-wax.
D 2
36
[SERIES XX.
Action of magnets on
Olive oil.
Mutton, dried.
Oil of turpentine.
Beef, fresh.
Jet.
Beef, dried.
Caoutchouc.
Blood, fresh.
Sugar.
Blood, dried.
Starch.
Leather.
Gum-arabic.
Apple.
Bread.
Wood.
Ivory.
2281. It is curious to see such a list as this of bodies present-
ing on a sudden this remarkable property, and it is strange to
find a piece of wood, or beef, or apple, obedient to or repelled
by a magnet. If a man could be suspended, with sufficient
delicacy, after the manner of Dufay, and placed in the magnetic
field, he would point equatorially; for all the substances of which
he is formed, including the blood, possess this property.
2282. The setting equatorially depends upon the form of the
body, and the diversity of form presented by the different sub-
stances in the list was very great; still the general result, that
elongation in one direction was sufficient to make them take up
an equatorial position, was established. It was not difficult to
perceive that comparatively large masses would point as readily
as small ones, because in larger masses more lines of magnetic
force would bear in their action on the body, and this was proved
to be the case. Neither was it long before it evidently appeared
that the form of a plate or a ring was quite as good as that of a
cylinder or a prism; and in practice it was found that plates
and flat rings of wood, spermaceti, sulphur, &c., if suspended in
the right direction, took up the equatorial position very well.
If a plate or ring of heavy glass could be floated in water, so as
to be free to move in every direction, and were in that condition
subject to magnetic forces diminishing in intensity, it would im-
mediately set itself equatorially, and if its centre coincided with
the axis of magnetic power, would remain there; but if its
centre were out of this line, it would then, perhaps, gradually
pass off from this axis in the plane of the equator, and go out
from between the poles.
2283. I do not find that division of the substance has any
distinct influence on the effects. A piece of Iceland spar was
observed, as to the degree of force with which it set equatorially;
DEC. 1845.]
37
diamagnetic bodies generally.
it was then broken into six or eight fragments, put into a glass
tube and tried again; as well as I could ascertian, the effect was
the same.
By a second operation, the calcareous spar was re-
duced into coarse particles; afterwards to a coarse powder, and
ultimately to a fine powder: being examined as to the equa-
torial set each time, I could perceive no difference in the effect,
until the very last, when I thought there might be a slight
diminution of the tendency; but if so, it was almost insensible.
I made the same experiment on silica with the same result, of
no diminution of power. In reference to this point I may observe,
that starch and other bodies in fine powder exhibited the effect
very well.
2284. It would require very nice experiments and great care
to ascertain the specific degree of this power of magnetic action
possessed by different bodies, and I have made very little pro-
gress in that part of the subject. Heavy glass stands above
flint-glass, and the latter above plate-glass. Water is beneath
all these, and I think alcohol is below water, and æther below
alcohol. The borate of lead is I think as high as heavy glass,
if not above it, and phosphorus is probably at the head of all
the substances just named. I verified the equatorial set of
phosphorus between the poles of a common magnet (2273.).
2285. I was much impressed by the fact that blood was not
magnetic (2280.), nor any of the specimens tried of red muscular
fibre of beef or mutton. This was the more striking, because,
as will be seen hereafter, iron is always and in almost all states
magnetic. But in respect to this point it may be observed,
that the ordinary magnetic property of matter and this new pro-
perty are in their effects opposed to each other; and that when
this property is strong it may overcome a very slight degree of
ordinary magnetic force, just as also a certain amount of the
magnetic property may oppose and effectually hide the presence
of this force (2422.). It is this circumstance which makes it so
necessary to be careful in examining the magnetic condition of
the bodies in the first instance (2250.). The following list of
a few substances which were found slightly magnetic, will
illustrate this point:-Paper, sealing-wax, china ink, Berlin
porcelain, silkworm-gut, asbestos, fluor-spar, red lead, vermi-
lion, peroxide of lead, sulphate of zinc, tourmaline, plumbago,
shell-lac, charcoal. In some of these cases the magnetism was
38
[SERIES XX.
Action of magnets on
generally diffused through the body, in other cases it was limited
to a particular part.
2286. Having arrived at this point, I may observe, that we
can now have no difficulty in admitting that the phænomena
abundantly establish the existence of a magnetic property in
matter, new to our knowledge. Not the least interesting of the
consequences that flow from it, is the manner in which it dis-
poses of the assertion which has sometimes been made, that
all bodies are magnetic. Those who hold this view, mean that
all bodies are magnetic as iron is, and say that they point be-
tween the poles. The new facts give not a mere negative to
this statement, but something beyond, namely, an affirmative as
to the existence of forces in all ordinary bodies, directly the op-
posite of those existing in magnetic bodies, for whereas those
practically produce attraction, these produce repulsion; those
set a body in the axial direction, but these make it take up an
equatorial position: and the facts, with regard to bodies gene-
rally, are exactly the reverse of those which the view quoted in-
dicates.
¶ iv. Action of magnets on metals generally.
2287. The metals, as a class, stand amongst bodies having a
high and distinct interest in relation both to magnetic and elec-
tric forces, and might at first well be expected to present some
peculiar phænomena, in relation to the striking property found
to be possessed in common by so large a number of substances,
so varied in their general characters. As yet no distinction
associated with conduction or non-conduction, transparent or
opake, solid or liquid, crystalline or amorphous, whole or broken,
has presented itself; whether the metals, distinct as they are as
a class, would fall into the great generalization, or whether at last
a separation would occur, was to me a point of the highest in-
terest.
2288. That the metals, iron, nickel and cobalt, would stand
in a distinct class, appeared almost undoubted; and it will be, I
think, for the advantage of the inquiry, that I should consider
them in a section apart by themselves. Further, if any other
metals appeared to be magnetic, as these are, it would be right
and expedient to include them in the same class.
2289. My first point, therefore, was to examine the metals
DEC. 1845.]
39
diamagnetic metals generally.
for any indication of ordinary magnetism. Such an examina-
tion cannot be carried on by magnets anything short in power
of those to be used in the further investigation; and in proof of
this point I found many specimens of the metals, which ap-
peared to be perfectly free from magnetism when in the presence
of a magnetic needle, or a strong horse-shoe magnet (2157.),
that yet gave abundant indications when suspended near to one
or both poles of the magnets described (2246.).
2290. My test of magnetism was this. If a bar of the metal
to be examined, about 2 inches long, was suspended (2249.) in
the magnetic field, and being at first oblique to the axial line
was upon the supervention of the magnetic forces drawn into
the axial position instead of being driven into the equatorial
line, or remaining in some oblique direction, then I considered
it magnetic. Or, if being near one magnetic pole, it was at-
tracted by the pole, instead of being repelled, then I concluded
it was magnetic. It is evident that the test is not strict, because,
as before pointed out (2285.), a body may have a slight degree
of magnetic force, and yet the power of the new property be so
great as to neutralize or surpass it. In the first case, it might
seem neither to have the one property nor the other; in the
second case, it might appear free from magnetism, and
ing the special property in a small degree.
possess-
2291. I obtained the following metals, so that when examined
as above, they did not appear to be magnetic; and in fact, if
magnetic, were so to an amount so small as not to destroy the
results of the other force, or to stop the progress of the inquiry.
Antimony.
Bismuth.
Cadmium.
Copper.
Gold.
Lead.
Mercury.
Silver.
Tin.
Zinc.
2292. The following metals were, and are as yet to me, mag-
netic, and therefore companions of iron, nickel and cobalt :-
Platinum.
Palladium.
Titanium.
2293. Whether all these metals are magnetic, in consequence
of the presence of a little iron, nickel, or cobalt in them, or
whether any of them are really so of themselves, I do not under-
take to decide at present; nor do I mean to say that the metals
40
[SERIES XX.
Action of magnets on metals.
of the former list are free. I have been much struck by the
apparent freedom from iron of almost all the specimens of zinc,
copper, antimony and bismuth, which I have examined; and it
appears to me very likely that some metals, as arsenic, &c., may
have much power in quelling and suppressing the magnetic
properties of any portion of iron in them, whilst other metals,
as silver or platinum, may have little or no power in this respect.
2294. Resuming the consideration of the influence exerted by
the magnetic force over those metals which are not magnetic
after the manner of iron (2291.), I may state that there are two
sets of effects produced which require to be carefully distin-
guished. One of these depends upon induced magneto-electric
currents, and shall be resumed hereafter (2309.). The other in-
cludes effects of the same nature as those produced with heavy
glass and many other bodies (2276.).
-
2295. All the non-magnetic metals are subject to the mag-
netic power, and produce the same general effects as the large
class of bodies already described. The force which they then
manifest, they possess in different degrees. Antimony and bis-
muth show it well, and bismuth appears to be especially fitted
for the purpose. It excels heavy glass, or borate of lead, and
perhaps phosphorus; and a small bar or cylinder of it about 2
inches long, and from 0·25 to 0·5 of an inch in width, is as well
fitted to show the various peculiar phænomena as anything I
have yet submitted to examination.
2296. To speak accurately, the bismuth bar which I employed
was 2 inches long, 0.33 of an inch wide, and 0.2 of an inch
thick. When this bar was suspended in the magnetic field, be-
tween the two poles, and subject to the magnetic force, it pointed
freely in the equatorial direction, as the heavy glass did (2253.),
and if disturbed from that position, returned freely to it. This
latter point, though perfectly in accordance with the former
phænomena, is in such striking contrast with the phænomena
presented by copper and some other of the metals (2309.), as to
require particular notice here.
2297. The comparative sensibility of bismuth causes several
movements to take place under various circumstances, which
being complicated in their nature, require careful analysis and
explanation. The chief of these, with their causes, I will pro-
ceed to point out.
DEC. 1845.]
41
Bismuth, as a diamagnetic body.
2298. If the cylinder electro-magnet (2246.) be placed ver-
tically so as to present one pole upwards, that pole will exist in
the upper end of an iron cylinder, having a flat horizontal face
2 inches in diameter. A small indicating sphere (2266.) of
bismuth, hung over the centre of this face and close to it, does
not move by the magnetism. If the ball be carried outwards,
half-way, for instance, between the centre and the edge, the
magnetism makes it move inwards, or towards the axis (pro-
longed) of the iron cylinder. If carried still further outwards,
it still moves inwards under the influence of the magnetism, and
such continues to be the case until it is placed just over the
edge of the terminal face of the core, where it has no motion at
all (here by another arrangement of the experiment, it is known
to tend in what is at present an upward direction from the core).
If carried a little further outwards, the magnetism then makes
the bismuth ball tend to go outwards or be repelled, and such
continues to be the direction of the force in any further position,
or down the side of the end of the core.
2299. In fact, the circular edge formed by the intersection of
the end of the core with its sides, is virtually the apex of the
magnetic pole, to a body placed like the bismuth ball close to it,
and it is because the lines of magnetic force issuing from it
diverge as it were, and weaken rapidly in all directions from it,
that the ball also tends to pass in all directions either inwards
or upwards, or outwards from it, and thus produces the motions
described. These same effects do not in fact all occur when the
ball, being taken to a greater distance from the iron, is placed
in magnetic curves, having generally a simpler direction. In
order to remove the effect of the edge, an iron cone was placed
on the top of the core, converting the flat end into a cone, and
then the indicating ball was urged to move upwards, only when
over the apex of the cone, and upwards and outwards, as it was
more or less on one side of it, being always repelled from the
pole in that direction, which transferred it most rapidly from
strong to weaker points of magnetic force.
2300. To return to the vertical flat pole: when a horizontal
bar of bismuth was suspended concentrically and close to the
pole, it could take up a position in any direction relative to the
axis of the pole, having at the same time a tendency to move
upwards or be repelled from it. If its point of suspension was
42
[SERIES XX.
Bismuth, as a diamagnetic metal.
a little excentric, the bar gradually turned, until it was parallel
to a line joining its point of suspension with the prolonged
axis of the pole, and the centre of gravity moved inwards.
When its point of suspension was just outside the edge of the
flat circular terminating face, and the bar formed a certain angle
with a radial line joining the axis of the core and the point of
suspension, then the movements of the bar were uncertain and
wavering. If the angle with the radial line were less than that
above, the bar would move into parallelism with the radius and
go inwards: if the angle were greater, the bar would move until
perpendicular to the radial line and go outwards. If the centre
of the bar were still further out than in the last case, or down
by the side of the core, the bar would always place itself per-
pendicular to the radius and go outwards. All these compli-
cations of motion are easily resolved into their simple ele-
mentary origin, if reference be had to the character of the cir-
cular angle bounding the end of the core; to the direction of
the magnetic lines of force issuing from it and the other parts of
the pole; to the position of the different parts of the bar in these
lines; and the ruling principle that each particle tends to go by
the nearest course from strong to weaker points of magnetic force.
2301. The bismuth points well, and is well repelled (2296.)
when immersed in water, alcohol, æther, oil, mercury, &c., and
also when enclosed within vessels of earth, glass, copper, lead &c.
(2272.), or when screens of 0·75 or 1 inch in thickness of bis-
muth, copper, or lead intervene. Even when a bismuth cube
(2266.) was placed in an iron vessel 2 inches in diameter and
0.17 of an inch in thickness, it was well and freely repelled by
the magnetic pole.
2302. Whether the bismuth be in one piece or in very fine
powder, appears to make no difference in the character or in the
degree of its magnetic property (2283.).
2303. I made many experiments with masses and bars of
bismuth suspended, or otherwise circumstanced, to ascertain
whether two pieces had any mutual action on each other, either
of attraction or repulsion, whilst jointly under the influence of
the magnetic forces, but I could not find any indication of such
mutual action: they appeared to be perfectly indifferent one to
another, each tending only to go from stronger to weaker points
of magnetic power.
DEC. 1845.]
43
Diamagnetic metals generally.
2304. Bismuth, in very fine powder, was sprinkled upon paper,
laid over the horizontal circular termination of the vertical pole
(2246.). If the paper were tapped, the magnet not being excited,
nothing particular occurred; but if the magnetic power were on,
then the powder retreated in both directions, inwards and out-
wards, from a circular line just over the edge of the core,
leaving the circle clear, and at the same time showing the ten-
dency of the particles of bismuth in all directions from that line
(2299.).
2305. When the pole was terminated by a cone (2246.) and
the magnet not in action, paper with bismuth powder sprinkled
over it being drawn over the point of the cone, gave no parti-
cular result; but when the magnetism was on, such an opera-
tion cleared the powder from every point which came over the
cone, so that a mark was traced or written out in clear lines
running through the powder, and showing every place where
the pole had passed.
2306. The bar of bismuth and a bar of antimony was found
to set equatorially between the poles of the ordinary horse-shoe
magnet.
2307. The following list may serve to give an idea of the ap-
parent order of some metals, as regards their power of producing
these new effects, but I cannot be sure that they are perfectly
free from the magnetic metals. In addition to that, there are
certain other effects produced by the action of magnetism on
metals (2309.) which greatly interfere with the results due to
the present property.
Bismuth.
Antimony.
Zinc.
Tin.
Cadmium.
Mercury.
Silver.
Copper.
2308. I have a vague impression that the repulsion of bismuth
by a magnet has been observed and published several years ago.
If so, it will appear that what must then have been considered
as a peculiar and isolated effect, was the consequence of a gene-
ral property, which is now shown to belong to all matter¹.
¹ M. de la Rive has this day referred me to the Bibliothèque Universelle for
1829, tome xl. p. 82, where it will be found that the experiment spoken of
above is due to M. la Baillif of Paris. M. la Baillif showed sixteen years ago that
44
[SERIES XX.
Revulsive action of magnets
2309. I now turn to the consideration of some peculiar pha-
nomena which are presented by copper and several of the metals
when they are subjected to the action of magnetic forces, and
which so tend to mask effects of the kind already described, that
if not known to the inquirer they would lead to much confusion
and doubt. These I will first describe as to their appearances,
and then proceed to consider their origin.
2310. If instead of a bar of bismuth (2296.) a bar of copper of
the same size be suspended between the poles (2247.), and
magnetic power be developed whilst the bar is in a position
oblique to the axial and equatorial lines, the experimenter will
perceive the bar to be affected, but this will not be manifest by
any tendency of the bar to go to the equatorial line; on the
contrary, it will advance towards the axial position as if it were
magnetic. It will not, however, continue its course until in that
position, but, unlike any effect produced by magnetism, will
stop short, and making no vibration beyond or about a given
point, will remain there coming at once to a dead rest and
this it will do even though the bar by the effect of torsion or
momentum was previously moving with a force that would have
caused it to make several gyrations. This effect is in striking
contrast with that which occurs when antimony, bismuth, heavy
glass, or other such bodies are employed, and it is equally re-
moved from an ordinary magnetic effect.
2311. The position which the bar has taken up it retains with
a considerable degree of tenacity, provided the magnetic force
be continued. If pushed out of it, it does not return into it,
but takes up its new position in the same manner, and holds it
with the same stiffness; a push, however, which would make
the bar spin round several times if no magnetism were present,
will now not move it through more than 20° or 30°. This is
not the case with bismuth or heavy glass; they vibrate freely in
the magnetic field, and always return to the equatorial position.
both bismuth and antimony repelled the magnetic needle. It is astonishing
that such an experiment has remained so long without further results. I re-
Joice that I am able to insert this reference before the present series of these
Researches goes to press. Those who read my papers will see here, as on many
other occasions, the results of a memory which becomes continually weaker;
I only hope that they will be excused, and that omissions and errors of that
nature will be considered as involuntary.-M. F. Dec. 30, 1845.
DEC. 1845.] on copper and good conductors.
45
2312. The position taken up by the bar may be any position.
The bar is moved a little at the instant of superinducing the
magnetism, but allowing and providing for that, it may be finally
fixed in any position required. Even when swinging with con-
siderable power by torsion or momentum, it may be caught and
retained in any place the experimenter wishes.
2313. There are two positions in which the bar may be placed
at the begining of the experiment, from which the magnetism
does not move it, the equatorial and the axial positions. When
the bar is nearly midway between these, it is usually most
strongly affected by the first action of the magnet, but the posi-
tion of most effect varies with the form and dimensions of the
magnetic poles and of the bar.
2314. If the centre of suspension of the bar be in the axial
line, but near to one of the poles, these movements occur well,
and are clear and distinct in their direction: if it be in the equa-
torial line, but on one side of the axial line, they are modified,
but in a manner which will easily be understood hereafter.
2315. Having thus stated the effect of the supervention of
the magnetic force, let us now remark what occurs at the mo-
ment of its cessation; for during its continuance there is no
change. If, then, after the magnetism has been sustained for
two or three seconds, the electric current be stopped, there is
instantly a strong action on the bar, which has the appearance
of a revulsion (for the bar returns upon the course which it took
for a moment when the electric contact was made), but with
such force, that whereas the advance might be perhaps 15° or
20°, the revulsion will cause the bar occasionally to move
through two or three revolutions.
2316. Heavy glass or bismuth presents no such phænomena
as this.
2317. If, whilst the bar is revolving from revulsion the elec-
tric current at the magnet be renewed, the bar instantly stops
with the former appearances and results (2310.), and then upon
removing the magnetic force is affected again, and, of course,
now in a contrary direction to the former revulsion.
2318. When the bar is caught by the magnetic force in the
axial or equatorial position, there is no revulsion. When in-
clined to these positions, there is; and the places most powerful
in this respect appear to be those most favourable to the first
46
[SERIES XX.
Sluggish action of copper, &c.
brief advance (2313.). If the bar be in a position at which
strong revulsion would occur, and whilst the magnetism is con-
tinued to be moved by hand into the equatorial or axial position,
then on taking off the magnetic force there is no revulsion.
2319. If the continuance of the electric current and conse-
quently of the magnetism be for a moment only, the revulsion
is very little, and the shorter the continuance of the magnetic
force the less is the revulsion. If the magnetic force be con-
tinued for two or three seconds and then interrupted and instantly
renewed, the bar is loosened and caught again by the power
before it sensibly changes its place; and now it may be observed
that it does not advance on the renewal of the force as it would
have done had it been acted on by a first contact in that place
(2310.) ; i. e. if the bar be in a certain place inclined to the axial
position, the first supervention of the magnetic power causes it to
advance towards the axial position; but the bar being in the same
place and the magnetic power suspended and instantly renewed,
the second supervention of force does not move the bar as the
first did.
2320. When the copper bar is immersed in water, alchol, or
even mercury, the same effects take place as in the air, but the
movements are, of course, not to the same extent.
2321. When plates of copper or bismuth, an inch in thickness,
intervene between the poles and the copper bar, the same results
occur.
2322. If one magnetic pole only be employed the effects
occur near it as well as before, provided that pole have a face
large in proportion to the bar, as the end of the iron core
(2246.): but if the pole be pointed by the use of the conical ter-
mination, or if the bar be opposite the edge of the end of the
core, then they become greatly enfeebled or disappear altogether;
and only the general fact of repulsion remains (2295.).
2323. The peculiar effects which have just been described are
perhaps more strikingly shown if the bar of copper be suspended
perpendicularly, and then hung opposite and near to the large
face of a single magnetic pole, or the pole being placed verti-
cally, as described (2246. 2263.), anywhere near to its side. The
bar, it will be remembered, is 2 inches in length by 0.33 of an
inch in width, and 0.2 of an inch in thickness, and as it now
will revolve on an axis parallel to its length, the two smaller di-
DEC. 1845.]
47
in the magnetic field.
mensions are those which are free to move into new positions.
In this case the establishment of the magnetic force causes the
bar to turn a little in accordance with the effects before described,
and the removal of the magnetic force causes a revulsion, which
sends the bar spinning round on its axis several times. But at
any moment the bar can again be caught and held in a position
as before. The tendency on making contact at the battery is to
place the longest moving dimension, i. e. the width of the bar,
parallel to the line joining the centre of action of the magnet
and the bar.
2324. The bar, as before (2311.), is extremely sluggish and
as if immersed in a dense fluid, as respects rotatiou on its own
axis; but this sluggishness does not affect the bar as a whole,
for any pendulum vibration it has, continues unaffected. It is
very curious to see the bar, jointly vibrating from its point of
suspension (2249.) and rotating on its axis, when first affected
by the magnetic force, for instantly the latter motion ceases, but
the former goes on with undiminished power.
2325. The same effect of sluggishness occurs with a cube or
a globe of copper as with the bar, but the phænomena of the
first turn and the revulsion cease (2310. 2315.).
2326. The bars of bismuth and heavy glass present no ap-
pearance of this kind. The peculiar phænomena produced by
copper are as distinct from the actions of these substances as
they are from ordinary magnetic actions.
2327. Endeavouring to explain the cause of these effects, it
appears to me that they depend upon the excellent conducting
power of copper for electric currents, the gradual acquisition
and loss of magnetic power by the iron core of the electro-mag-
net, and the production of those induced currents of magneto-
electricity which I described in the First Series of these Experi-
mental Researches (55. 109.).
2328. The obstruction to motion on its own axis, when the
bar is subjected to the magnetic forces, belongs equally to the
form of a sphere or a cube. It belongs to these bodies, how-
ever, only when their axes of rotation are perpendicular or oblique
to the lines of magnetic force, and not when they are parallel to
it; for the horizontal bar, or the vertical bar, or the cube or
sphere, rotate with perfect facility when they are suspended
above the vertical pole (2246.), the rotation and vibration being
48
[SERIES XX.
Sluggish action of copper, &c.
then equally free, and the same as the corresponding movements
of bismuth or heavy glass. The obstruction is at a maximum
when the axis of rotation is perpendicular to the lines of mag-
netic force, and when the bar or cube, &c. is near to the
magnet.
2329. Without going much into the particular circumstances,
I may say that the effect is fully explained by the electric cur-
rents induced in the copper mass. By reference to the Second
Series of these Researches (160.)¹, it will be seen that when a
globe, subject to the action of lines of magnetic force, is revolving
on an axis perpendicular to these lines, an electric current runs
round it in a plane parallel to the axis of rotation and to the
magnetic lines, producing consequently a magnetic axis in the
globe, at right angles to the magnetic curves of the inpucing
magnet. The magnetic poles of this axis therefore are in that
direction which, in conjunction with the chief magnetic pole,
tends to draw the globe back against the direction in which it is
revolving. Thus, if a piece of copper be revolving before a north
magnetic pole, so that the parts nearest the pole move towards
the right-hand, then the right-hand side of that copper will have
a south magnetic state, and the left-hand side a north magnetic
state; and these states will tend to counteract the motion of the
copper towards the right-hand : or if it revolve in the contrary
direction, then the right-hand side will have a south magnetic
state, and the left-hand side a north magnetic state. Which-
ever way, therefore, the copper tends to revolve on its own axis
the instant it moves, a power is evolved in such a direction as
tends to stop its motion and bring it to rest. Being at rest
in reference to this direction of motion, then there is no re-
sidual or other effect which tends to disturb it, and it remains
still.
2330. If the whole mass be moving parallel to itself, and be
small in comparison with the face of the magnetic pole opposite
to which it is placed, then, though it pass through the magnetic
lines of force, and consequently have a tendency to the forma-
tion of magneto-electric currents within it, yet as all parts move
with equal velocity and in the same direction through similar
magnetic lines of force, the tendency to the formation of a cur-
rent is the same in every part, and there is no actual production
1 Philosophical Transactions, 1832, p. 168.
DEC. 1845.]
49
in the magnetic field.
of current, and consequently nothing occurs which can in any
way interfere with its freedom of motion. Hence the reason
that though the rotation of the bar or cube (2324. 2328.) upon
its own axis is stopped, its vibration as a pendulum is not
affected.
2331. That neither the one nor the other motion is affected
when the bar or cube is over the vertical pole (2328.), is simply
because in both cases (with the given dimensions of the pole
and the moving metal) the lines of particles through which
the induced currents tend to move are parallel throughout the
whole mass; and therefore, as there is no part by which the
return of the current can be carried on, no current can be
formed.
2332. Before proceeding to the explanation of the other phe-
nomena, it will be necessary to point out the fact generally un-
derstood and acknowledged, I believe, that time is required for
the development of magnetism in an iron core by a current
of electricity; and also for its fall back again when the current
is stopped. One effect of the gradual rise in power was referred
to in the last series of these Researches (2170.). This time is
probably longer with iron not well annealed than with very good
and perfectly annealed iron. The last portions of magnetism
which a given current can develope in a certain core of iron, are
also apparently acquired more slowly than the first portions;
and these portions (or the condition of iron to which they are
due) also appear to be lost more slowly than the other portions
of the power. If electric contact be made for an instant only,
the magnetism developed by the current disappears as instantly
on the breaking of the current, as it appeared on its formation;
but if contact be continued for three or four seconds, breaking
the contact is by no means accompanied by a disappearance of
the magnetism with equal rapidity.
2333. In order to trace the peculiar effect of the copper, and
its cause, let us consider the condition of the horizontal bar
(2310. 2313.) when in the equatorial position, between the two
magnetic poles, or before a single pole; the point of suspension
being in a line with the axis of the pole and its exciting wire
helix. On sending an electric current through the helix, both
it and the magnet it produces will conduce to the formation of
currents in the copper bar in the contrary direction. This is
·
VOL. III.
E
50
[SERIES XX.
Copper and good conductors
shown from my former researches (26.), and may be proved, by
placing a small or large wire helix-shaped (if it be desired) in
the form of the bar, and carrying away the currents produced in
it, by wires to a galvanometer at a distance. Such currents,
being produced in the copper, only continue whilst the magnet-
ism of the core is rising, and then cease (18. 39.), but whilst they
continue, they give a virtual magnetic polarity to that face of
the copper bar which is opposite to a certain pole, the polarity
being the same in kind as the pole it faces. Thus on the side
of the bar facing the north pole of the magnet, a north polarity
will be developed; and on that side facing the south pole, a
south polarity will be generated.
2334. It is easy to see that if the copper during this time
were opposite only one pole, or being between two poles, were
nearer to one than the other, this effect would cause its repul-
sion. Still, it cannot account for the whole amount of the re-
pulsion observed alike with copper as with bismuth (2295.), be-
cause the currents are of but momentary duration, and the re-
pulsion due to them would cease with them. They do, however,
cause a brief repulsive effort, to which is chiefly due the first
part of the peculiar effect.
2335. For if the copper bar, instead of being parallel to the
face of the magnetic pole, and therefore at right angles to the
resultant of magnetic force, be inclined, forming, for instance,
an angle of 45° with the face, then the induced currents will
move generally in a plane corresponding more or less to that
angle, nearly as they do in the examining helix (2333.), if it be
inclined in the same manner. This throws the polar axis of the
bar of copper on one side, so that the north polarity is not di-
rectly opposed to the north pole of the inducing magnets, and
hence the action both of this and the other magnetic pole upon
the two polarities of the copper will be to send it further round,
or to place it edgeways to the poles, or with its breadth. parallel
to the magnetic resultant passing through it (2323.): the bar
therefore receives an impulse, and the angle of it nearest to the
magnet appears to be pulled up towards the magnet. This ac-
tion of course stops the instant the magnetism of the helix core
ceases to rise, and then the motion due to this cause ceases, and
the copper is simply subject to the action before described
(2295.). At the same time that this twist or small portion of a
DEC. 1845.]
51
in the magnetic field.
turn round the point of suspension occurs, the centre of gravity
of the whole mass is repelled, and thus I believe all the actions
up to this condition of things is accounted for.
2336. Then comes the revulsion which occurs upon the cessa-
tion of the electric current, and the falling of the magnetism in
the core. According to the law of magneto-electric induction,
the disappearance of the magnetic force will induce brief currents
in the copper bar (28.), but in the contrary direction to those
induced in the first instance; and therefore the virtual magnetic
pole belonging to the copper for the moment, which is nearest
the north end of the electro-magnet, will be a south pole; and
that which is furthest from the same pole of the magnet will be
a north pole. Hence will arise an exertion of force on the bar
tending to turn it round its centre of suspension in the contrary
direction to that which occurred before, and hence the apparent
revulsion; for the angle nearest the magnetic pole will recede
from it, the broad face (2323.) or length (2315.) of the bar will
come round and face towards the magnet, and an action the re-
verse in every respect of the first action will take place, except
that whereas the motion was then only a few degrees, now it
may extend to two or three revolutions.
2337. The cause of this difference is very obvious. In the
first instance, the bar of copper was moving under influences
powerfully tending to retard and stop it (2329.); in the second
case these influences are gone, and the bar revolves freely with
a force proportionate to the power exerted by the magnet upon
the currents induced by its own action.
2338. Even when the copper is of such form as not to give
the oblique resultant of magnetic action from the currents in-
duced in it, when, for instance, it is a cube or a sphere, still the
effect of the action described above is evident (2325.). When a
plate of copper about three-fourths of an inch in thickness, and
weighing two pounds, was sustained upon some loose blocks of
wood and placed about 0·1 of an inch from the face of the mag-
netic pole, it was repelled and held off a certain distance upon
the making and continuing of electric contact at the battery;
and when the battery current was stopped, it returned towards
the pole; but the return was much more powerful than that
due to gravity alone (as was ascertained by an experiment), the
plate being at that moment actually attracted, as well as tending
E 2
52
Peculiar action on good conductors [SERIES XX
by gravitation towards the magnet, so that it gave a strong tap
against it.
2339. Such is, I believe, the explanation of the peculiar phæ-
nomena presented by copper in the magnetic field; and the
reason why they appear with this metal and not with bismuth
or heavy glass, is almost certainly to be found in its high electro-
conducting power, which permits the formation of currents in it
by inductive forces, that cannot produce the same in a corre-
sponding degree in bismuth, and of course not at all in heavy
glass.
2340. Any ordinary magnetism due to metals by virtue of
their inherent power, or the presence of small portions of the
magnetic metals in them, must oppose the development of the
results I have been describing; and hence metals not of abso-
lute purity cannot be compared with each other in this respect.
I have, nevertheless, observed the same phænomena in other
metals; and as far as regards the sluggishnesss of rotatory mo-
tion, traced it even into bismuth. The following are the metals
which have presented the phænomena in a greater or smaller
degree :-
Copper.
Silver.
Gold.
Zinc.
Mercury.
Platinum.
Palladium.
Lead.
Cadmium.
Tin.
Antimony.
Bismuth.
2341. The accordance of these phænomena with the beautiful
discovery of Arago¹, with the results of the experiments of Her-
schel and Babbage2, and with my own former inquiries (81.),
is very evident. Whether the effect obtained by Ampère, with
his copper cylinder and helix, was of this nature, I cannot judge,
inasmuch as the circumstances of the experiment and the energy
of the apparatus are not sufficiently stated; but it probably may
have been.
1 Annales de Chimie, xxvii. 363; xxviii. 325; xxxii. 213. I am very glad
to refer here to the Comptes Rendus of June 9, 1845, where it appears that it
was M. Arago who first obtained his peculiar results by the use of electro- as
well as common magnets.
2
Philosophical Transactions, 1825, p. 467.
4 Bibliothèque Universelle, xxi. p. 48.
³ Ibid. 1832, p. 146.
DEC. 1845.]
53
in the magnetic field.
2342. As, because of other duties, three or four weeks may
elapse before I shall be able to complete the verification of cer-
tain experiments and conclusions, I submit at once these results
to the attention of the Royal Society, and will shortly embody
the account of the action of magnets on magnetic metals, their
action on gases and vapours, and the general considerations in
another series of these Researches.
Royal Institution,
Nov. 27, 1845.
54
TWENTY-FIRST SERIES'.
§ 27. On new magnetic actions, and on the magnetic condition of
all matter-continued. Tv. Action of magnets on the mag-
netic metals and their compounds. vi. Action of magnets
on air and gases. ¶ vii. General considerations.
Received December 24, 1845,-Read January 8, 1846.
¶v. Action of magnets on the magnetic metals and their compounds.
2343. THE magnetic characters of iron, uickel, and cobalt, are
well known; and also the fact that at certain temperatures they
lose their usual property and become, to ordinary test and
observation, non-magnetic; then entering into the list of dia-
magnetic bodies and acting in like manner with them. Closer
investigation, however, has shown me that they are still very
different to other bodies, and that though inactive when hot, on
common magnets or to common tests, they are not so abso-
lutely, but retain a certain amount of magnetic power what-
ever their temperature; and also that this power is the same in
character with that which they ordinarily possess.
2344. A piece of iron wire, about 1 inch long and 0·05 of an
inch in diameter, being thoroughly cleaned, was suspended at
the middle by a fine platinum wire connected with the suspend-
ing thread (2249.) so as to swing between the poles of the
electro-magnet. The heat of a spirit lamp was applied to it, and
it soon acquired a temperature which rendered it quite insensible
to the presence of a good ordinary magnet, however closely it
was approached to the heated iron. The temperature of the
iron was then raised considerably higher by adjustment of the
flame, and the electro-magnet thrown into action. Immediately
the hot iron became magnetic and pointed between the poles.
The power was feeble, and in this respect the state of the iron
¹ Philosophical Transactions, 1846, p. 41.
DEC. 1845.]
55
Action on iron and nickel.
was in striking contrast with that which it had when cold; but
in character the force was precisely the same.
2345. The iron was then allowed to fall in temperature slowly,
so that its assumption of the higher magnetic condition might
be observed. The intensity of the force did not appear to in-
crease until the temperature arrived near a certain point, and
then as the heat continued to diminish, the iron rapidly, but not
instantaneously, acquired its high magnetic power; at which
time it could not be kept from the magnet, but flew to it, bending
the suspending wire and trembling as it were with magnetic
energy as it adhered by one end to the core.
2346. A small bar of nickel was submitted to an experimental
examination in the same manner. This metal, as I have shown',
loses its magnetism as respects ordinary tests at a heat below
that of boiling oil, and hence it is very well fitted to show
whether the magnetic metals can have their power entirely re-
moved by heat or not; and also whether the disappearance of
the whole or greater portion of their power is sudden or gradual.
The smallness of the mass to be experimented on assisted much
in the determination of the latter point. Upon being heated the
nickel soon became indifferent to ordinary magnets; but however
high the temperature, still it is pointed to and was attracted by the
electro-magnet. The power was very feeble, but certain. It
was scarcely enough to sustain the weight of the nickel by the
magnetic action alone; but was abundantly evident when the
metal was supported as described (2344.).
2347. On carefully lowering the temperature of the nickel,
it was again found that the transition from one degree of magnetic
force to the other was progressive and not instantaneous. With
iron it is difficult to preserve all the parts, either in heating or
cooling, so nearly at the same temperature as to be sure that it
is not the union of hotter and colder portions which gives the
appearance of an intermediate degree of magnetism; but with
nickel that is not so difficult, for the progression is more gra-
dual, so that when in cooling the power began to increase, the
cooling might be continued some time before the full degree of
power came on; at any time in that period the temperature
might be slightly raised, and though the power would then
1
¹ Philosophical Magazine, 1836, vol viii. p. 179, or Experimental Researches,
vol. ii. p. 219.
56
Action of magnets on the [SERIES XXI.
diminish a little, it could yet be retained at a degree stronger
than the weakest. In fact it was easy to keep the nickel at
many of the intermediate degrees of power, and thus to remove
all doubt of the progressive assumption of the full degree of
force.
2348. I have expressed an opinion, founded on the different
temperatures at which the magnetic metals appeared to lose
their peculiar power', that all the metals would probably have the
same character of magnetism if their temperature could be lowered
sufficiently. The facts just described appear to me entirely
against such an opinion. The metals which are magnetic re-
tain a portion of their power after the great change has been ef-
fected, or in what might be called their diamagnetic state; but
the other metals, such as bismuth, tin, &c., present no trace of
this power, and therefore are not in the condition of the heated
iron, nickel, or cobalt; for in fact whilst these point axially and
are attracted, the others point equatorially and are repelled. I
therefore hope to be allowed to withdraw the view I then put
forth.
2349. I next proceeded to examine the peroxides of iron, and
in accordance with the observations of M. Becquerel2 and others.
found them all, both natural and artificial, possessed of magnetic
power at common temperatures. I heated them in tubes but
found them still magnetic, suffering no diminution of the force
by such temperature as I could apply to them.
2350. Different specimens of the oxide of nickel were found
to present the same phænomena. They were magnetic both
when hot and cold; and that heat should cause no change in
this respect is the more striking, because the hot oxide had a
temperature given to it far higher than that necessary to produce
the great magnetic change in the metal itself (2346.).
2351. The oxide of cobalt also was magnetic, and equally mag-
netic, whether hot or cold. Glass coloured blue by cobalt is
magnetic in consequence of the presence of the oxide of that
metal, and is so whether hot or cold. In all these cases the de-
gree of power retained was very small compared to that of the
pure metal.
1
¹ Philosophical Magazine, 1836, vol. viii. p. 177; ibid. 1839, vol. xiv. p. 161,
or Experimental Researches, vol. ii. pp. 217, 225.
2 Annales de Chimie, 1827, vol. xxxvi. p. 337. Comptes Rendus, 1845,
vol. xx. p. 1708.
DEC. 1845.]
57
compounds of magnetic metals.
2352. Proceeding to the salts of iron, I found them magnetic.
Clean crystals of the proto-sulphate of iron were attracted and
pointed axially very well; so also did the dry salt. As I pro-
ceeded I found that every salt and compound containing iron in
the basic part was magnetic. To enumerate the different sub-
stances subjected to trial would be tedious; the following are
selected as illustrations of the variety in kind :—
Protochloride.
Perchloride.
Iodide
Protosulphate.
Persulphate.
Protophosphate.
Perphosphate.
Nitrate.
Carbonate.
Prussian Blue.
2353. Amongst native compounds-
Bog iron ore.
Hæmatite.
Chromate of iron.
Yellow sulphuret of iron.
Arsenical pyrites.
Copper pyrites, and many
others were magnetic.
2354. Green bottle-glass is comparatively very magnetic from
the iron it contains, and cannot be used as tubes to hold other
substances. Crown glass is magnetic from the same cause.
Flint glass is not magnetic, but points equatorially.
2355. Crystals of the yellow ferro-prussiate of potassa were
not magnetic, but were repelled and set equatorially; and such
was the case also with red ferro-prussiate.
2356. According to my hopes, even the solutions of the fer-
ruginous salts, whether in water or alcohol, were magnetic. A
tube filled with a clear solution of proto- or persulphate of iron,
or proto- or perchloride, or tincture of muriate of iron, was at-
tracted by the poles, and pointed very well between them in the
axial direction.
2357. These solutions supply a very important means of ad-
vancing magnetical investigation, for they present us with the
power of making a magnet, which is at the same time liquid,
transparent, and within certain limits, adjustible to any degree
of strength. Hence the power of examining a magnet optically.
Hence also, the capability of placing magnetic portions of mat-
ter one within another, and so observing dynamic and other
phænomena within magnetic media. In fact, not only may these
substances be placed as magnets in the magnetic field, but the
58
[SERIES XXI.
Action of magnets on
field generally may be filled with them, and then other bodies
and other magnets examined as to their joint or separate actions
in it (2361. &c.).
2358. In reference to the salts of nickel and cobalt, pure cry-
stals of the sulphate of nickel were found to be well magnetic,
and also pure crystals of sulphate of cobalt. Solutions of the
sulphate of nickel, the chloride of nickel, and the chloride of co-
balt, were also magnetic. That I might be perfectly safe in these
conclusions I applied to Mr. Askin of Birmingham, whose power
of separating nickel and cobalt from each other and other metals
is well known, as also the scale upon which he carries on these
operations; and he favoured me with a solution of chloride of
nickel and another of chloride of cobalt perfectly pure, both of
which proved to be well magnetic between the poles of my
magnet.
2359. Heat applied to any of these magnetic solutions did
not diminish or affect their power.
2360. These results with the salts of the magnetic metals con-
join with those before quoted, as tending to show that the non-
magnetic metals could not by any change of temperature be
rendered magnetic (2398.), but as a class are distinct from iron,
nickel, and cobalt; for none of the compounds of the non-mag-
netic metals show, as yet, any indication of ordinary magnetic
force, whereas in respect of these three substances all their
compounds possess it.
2361. In illustration of the power which the iron and other
similar solutions give in the investigation of magnetic phæno-
mena (2357.), as well as in reference to the general conclusions
to be drawn from all the facts described in this paper, I will
proceed to describe certain anticipated results which were ob-
tained by the employment of these solutions in the magnetic
field.
2362. A clear solution of the proto-sulphate of iron was pre-
pared, in which one ounce of the liquid contained seventy-four
grains of the hydrated crystals; a second solution was prepared
containing one volume of the former and three volumes of water;
a third solution was made of one volume of the stronger solu-
tion and fifteen volumes of water. These solutions I will distin-
guish as Nos. 1, 2, and 3; the proportions of crystals of sul-
phate of iron in them were respectively as 16, 4, and 1 per. cent.
DEC. 1845.]
59
solutions of sulphate of iron.
nearly. These numbers may, therefore, be taken as represent-
ing (generally only (2423.)) the strength of the magnetic part
of the liquids.
2363. Tubes like that before described (2279.) were prepared
and filled respectively with these solutions and then hermetically
sealed, as little air as possible being left in them. Glasses of
the solutions were also prepared, large enough to allow the
tubes to move freely in them, and yet of such size and shape as
would permit of their being placed between the magnetic poles.
In this manner the action of the magnetic forces upon the matter
in the tubes could be examined and observed, both when the tubes
were in diamagnetic media, as air, water, alcohol, &c., and also
in magnetic media, either stronger or weaker in magnetic force,
than the substances in the tubes.
2364. When these tubes were suspended in air between the
poles, they all pointed axially or magnetically, as was to be ex-
pected; and with forces apparently proportionate to the strengths
of the solutions. When they were immersed in alcohol or water
they also pointed in the same direction; the strongest solution
very well, and also the second, but the weakest solution was
feeble in its action, though very distinct in its character (2422.).
2365. When the tubes, immersed in the different ferruginous
solutions, were acted upon, the results were very interesting.
The tube No. 1 (the strongest magnetically), when in solution
No. 1, had no tendency, under the influence of the magnetic
power, to any particular position, bnt remained wherever it was
placed. Being placed in solution No. 2, it pointed well axially,
and in solution No. 3 it took the same direction, but with still
more power.
2366. The tube No. 2, when in the solution No. 1, pointed
equatorially, i. e. as heavy glass, bismuth, or a diamagnetic body
generally, in air. In solution No. 2 it was indifferent, not point-
ing either way; and in solution No. 3 it pointed axially, or as a
magnetic body. The tube No. 3, containing the weakest solu-
tion, pointed equatorially in solutions No. 1 and 2, and not at all
in solution No. 3.
2367. Several other ferruginous solutions varying in strength
were prepared, and, as a general and constant result, it was
found that any tube pointed axially if the solution in it was
60
[SERIES XXI.
Action of magnets on
stronger than the surrounding solution, and equatorially if the
tube solution was the weaker of the two.
2368. The tubes were now suspended vertically, so that being
in the different solutions they could be brought near to one of
the magnetic poles, and employed in place of the indicating
cube or sphere of bismuth, or heavy glass (2266.). The con-
stant result was, that when the tube contained a stronger solu-
tion than that which surrounded it, it was attracted to the pole,
but when its solution was the weaker of the two it was repelled.
The latter phænomena were as to appearance in every respect
the same as those presented in the repulsion of heavy glass,
bismuth, or any other diamagnetic body in air.
2369. Having described these phænomena, I will defer their
further consideration until I arrive at the last division of this
paper, and proceed to certain results more especially belonging
to the present part of these Researches.
2370. As the magnetic metals, iron, nickel and cobalt pre-
sent in their compounds substances also distinguished by the
possession of magnetic properties (2360.), so it appeared very
probable that other metals, of whose magnetic character doubts
were entertained, because of the possible presence of iron in the
specimens experimented with, might in this way have their
magnetic character tested; for it seemed likely, from analogy,
that every metal well magnetic per se, would be magnetic in its
compounds; and, judging from the character of the great class
of diamagnetic bodies (2275.), that no magnetic compounds
would be obtained of a metal not magnetic of itself. Accord-
ingly I proceeded to apply this kind of test to the combinations
of many of the metals, and obtained the following results:-
2371. Titanium.-Wollaston has described the magnetic effects
of crystals of titanium, expressing at the same time a belief that
they are due to iron¹. I took a specimen of the oxide of tita-
nium, which I believe to be perfectly free from iron, and in-
closing it in a tube (2279.), subjected it to the action of the
electro-magnet (2246. 2247.). It proved to be freely magnetic.
Another specimen obtained from Mr. Johnson, and believed by
him to be perfectly free from iron, was also magnetic. Hence
I conclude that titanium is truly a magnetic metal.
1 Philosophical Transactions, 1823, p. 400.
DEC. 1845.]
61
metals and their compounds.
2372. Manganese.-Berthier, as far as I am aware, first an-
nounced that this metal was magnetic at very low tempera-
tures'. On submitting specimens of the various oxides, which
were considered as pure, to the magnetic force, they were all
found to be magnetic, especially the protoxide. So were the
following compounds of manganese in the pure, dry, or crystal-
lized state:-chloride, sulphate, ammonio-sulphate, phosphate,
carbonate, borate; and also the chloride, nitrate, sulphate, and
ammonio-sulphate when in solution. A specimen of the am-
monio-sulphate was rendered alkaline by the addition of a little
carbonate of ammonia boiled and then carefully crystallized
thrice: after that the crystals and solution of the purified salt
were perfectly and well magnetic. Ihave no doubt, therefore, that
manganese is a magnetic metal, as Berthier said. If any opinion
may be drawn concerning the magnetic force of the metal from
the degree of magnetism of the compounds, I should expect
that manganese possesses considerable power of this kind when
at a sufficiently low temperature 2.
2373. Cerium.-I am not aware that cerium has as yet been
classed with the magnetic metals. Having made experiments
with the hydrated protoxide, the carbonate, and the chloride of
this metal, and also with the double sulphate of the oxide and
potassa prepared with great care, I found them all magnetic;
and those that are soluble are magnetic in the state of solution.
Hence, as the compounds are undoubtedly magnetic, there is
every reason to believe that cerium also is a magnetic metal
(2370.).
2374. Chromium.-The magnetic phænomena of chromium
compounds are very interesting. Portions of the chromate
and the bichromate of potassa were purified by three careful
crystallizations each; part of the bichromate was heated in a
platinum crucible, until the second equivalent of chromic acid
was converted into the crystallized oxide, and this being washed
out and dried was found to be well magnetic. So were all the
other specimens of oxide of chromium which were examined.
A specimen of Warrington's chromic acid was found to be
very feebly magnetic.
¹ Traité des Essais par la Voie Sêche, tome i. p. 532. Philosophical Ma-
gazine, 1845, vol. xxvii. p. 2.
2 Philosophical Magazine, 1845, vol. xxvii. p. 2.
62
[SERIES XXI.
Action of magnets on
2375. Chromate of lead, when subjected to the magnet, pointed
equatorially and was repelled. Such was the case also with
crystals of the chromate of potassa. Crystals of the bichromate,
however, did not act thus; for if in any way affected they were
in the least degree magnetic, showing the influence of the in-
creased proportion of chromic acid. Solutions of either salt
pointed well equatorially and were repelled; thus showing the
diamagnetic influence of the water present (2422.).
2376. As just stated, a solution of the bichromate contained
in a tube, pointed equatorially and was repelled; but if the same
solution had a little alcohol added to it, and also some pure mu-
riatic or sulphuric acid, and were then heated for a few minutes
to reduce the chromic acid to the state of oxide or chloride, then,
on being returned to the tube and subjected to the magnet, it
was found strongly magnetic.
2377. I think it has before been said that chromium is a mag-
netic metal; as these results have been obtained with its pure
compounds, there is no longer any doubt on my mind that such
is the case.
2378. Lead.—The compounds of lead point equatorially and
are repelled. The substances tried were the chloride, iodide
sulphuret, nitrate, sulphate, phosphate, carbonate, protoxide
fused, and the acetate. A portion of very carefully crystallized
nitrate being dissolved was precipitated by pure zinc, and the
lead obtained washed with dilute nitric acid, to remove subsalts.
Such lead was free from magnetism, and therefore the metal
ranks in the diamagnetic class, both directly and by its com-
pounds. Lead usually appears to be magnetic, and it is not
very easy to obtain the metal in the pure diamagnetic state.
2379. Platinum.—I have, as yet, found no wrought specimens
of this metal free from magnetism, not even those prepared by
Dr. Wollaston himself, and left with the Royal Society. Speci-
mens of the purest platinum obtained from Mr. Johnson were
also found to be slightly magnetic.
2380. Clean platinum foil and cuttings were dissolved in pure
nitro-muriatic acid, and the solution evaporated to dryness. Both
the solution and the dry chloride pointed equatorially and were
repelled by the magnet. A part of the chloride, being dissolved
and rendered acid, was precipitated by an acid solution of muri-
ate of ammonia, and the ammonia-chloride of platinum washed
DEC. 1845.]
63
metals and their compounds.
:
and dried it also, at the magnet, pointed equatorially and was
repelled. A portion of this ammonio-chloride, decomposed in
a flint-glass tube by heat, gave spongy platinum, which being
pressed together into a cake, pointing axially and was attracted
at the side of the magnetic pole, being magnetic.
2381. At present I believe that platinum is as a metal mag-
netic, though very slightly so; and that in the compounds, the
change of state and the presence of other substances having the
diamagnetic character, are sufficient to cover this property and
make the whole compound diamagnetic (2422.).
2382. Palladium.—All the palladium in the possession of the
Royal Society, prepared by Dr. Wollaston, amounting to ten
ingots and rolled plates, is magnetic. Specimens of the metal
from Mr. Johnson, considered as pure, were also slightly mag-
netic. The chloride, the ammonio-bichloride, and the cyanuret
of palladium, pointed equatorially and were repelled by the mag-
net. The same cyanuret, reduced by heat either in open plati-
num vessels or in close glass tubes, gave palladium possessing a
feeble degree of magnetic property. Some of Wollaston's palla-
dium was dissolved in pure nitromuriatic acid, and the solution
slowly acted upon by pure zinc, free from iron, and not mag-
netic. Five successive portions of the precipitated metal were
collected, and all were magnetic. Ammonio-bichloride of palla-
dium was prepared from the same solution by pure acid muriate
of ammonia, and digested in nitromuriatic acid. The salt itself
was repelled, being diamagnetic; but when reduced by heat in
glass tubes, or in Berlin capsules, the palladium obtained was
magnetic. From the result of all the experiments, I believe the
metal to be feebly but truly magnetic.
2383. Arsenic. This metal required very particular examina-
tion, and even when carefully sublimed twice or thrice in suc-
cession, presented appearances which sometimes made me class
it with the magnetic, and at other times with the diamagnetic
bodies. On the whole, I incline to believe that it belongs to the
latter series of substances, being only in a very small degree re-
moved from the zero or medium point. Pure white arsenic
points freely in an equatorial direction, and is repelled by a mag-
netic pole.
2384. In reference to the pointing of short bars between mag-
64
[SERIES XXI.
Action of magnets on
netic poles exposing large flat faces, I ought to observe, that
such bars will sometimes point axially and seem to be magnetic
when they do not belong to that class, and are repelled by a
single polc. The cause of this effect has been already given
(2298. 2299.), and is obviated by the use of poles having wedge-
shaped or conical terminations.
2385. Osmium.—Osmic acid from Mr. Johnson, in fine trans-
parent crystals, was clearly diamagnetic, being repelled. Speci-
mens of the metal and of the protoxide were both slightly mag-
netic. The protoxide had been obtained by the action of alcohol
on a solution of osmic acid which had twice been distilled with
water, and the metal was believed to be perfectly free from other
substances. Probably, therefore, osmium belongs to the mag-
netic class.
2386. Iridium.-Mr. Johnson supplied me with several pre-
parations of iridium. The oxide, chloride, and ammonio-chlo-
ride were magnetic; and so was a sample of the metal. One
specimen of the metal, which seemed to be very pure, was
scarcely at all magnetic; and on the whole, I incline to believe
that iridium does not stand in the magnetic class.
2387. Rhodium.-A well-fused specimen of this metal, pre-
pared by Dr. Wollaston, was magnetic; but crystals of the chlo-
ride and the sodio-chloride of rhodium prepared by the same
philosopher, and others also from Mr. Johnson, were not mag-
netic, but pointed well equatorially. I conclude, therefore, that
the metal is probably not magnetic, or if magnetic, is but little
removed from the zero point.
2388. Uranium.-Peroxide of this metal was obtained not
magnetic; protoxide very slightly magnetic: I have set the
metal for the present in the diamagnetic class.
2389. Tungsten.-The oxide of this metal, and also the acid,
were submitted to examination, and found to point well equa-
torially. The acid was distinctly repelled by a single magnetic
pole; the oxide appeared nearly neutral. Hence I have, for the
present, considered tungsten as a diamagnetic metal.
2390. Silver is not magnetic (2291.), nor its compounds.
2391. Antimony is not magnetic (2291.), nor its com-
pounds.
2392. Bismuth is not magnetic (2291.), nor its compounds.
DEC. 1845.]
65
Metals and their compounds.
Having tried many of the compounds of each of these three
metals, I thought it well to record the accordance existing be-
tween them and their metallic bases (2370.).
2393. Sodium.-A fine large globule, equal to half a cubic
inch in size, was well repelled, and is therefore diamagnetic.
2394. Magnesium.-None of the compounds or salts of this
base are magnetic.
2395.
Calcium.
Strontium.
Barium.
Sodium.
Potassium.
Ammonia.
None of the compounds or salts of these substances are magnetic.
2396. From the characters, therefore, of the compounds, as
well as from direct evidence in respect of some of the metals, it
would appear that, besides iron, nickel, and cobalt, the following
are also magnetic; namely, titanium, manganese, cerium, chro-
mium, palladium, platinum. It is, however, very probable that
there may be metals possessing distinct magnetic power, yet in
so slight a degree, as, like platinum and palladium, not to exhibit
in their compounds any sensible trace of it. Such may be the
case with tungsten, uranium, rhodium, &c.
2397. I have heated several of the diamagnetic metals, even
up to their fusing points, but have not been able to observe any
change, either in the character or degree of their magnetic rela-
tions.
2398. Perhaps the cooling of some of the metals, whose com-
pounds, like those of iron, nickel and cobalt, are magnetic,
might develope in them a much higher degree of force, than
any which they have as yet been known to possess. Manganese,
chromium, cerium, titanium, are metals of much interest in this
point of view. Osmium, iridium, rhodium, and uranium, ought
to be subjected with them to the same trial.
2399. The following is an attempt to arrange some of the
metals in order, as respects their relation to magnetic force.
The 0° or medium point is supposed to be the condition of a
metal or substance indifferent to the magnetic force as respects
attraction or repulsion in air or space. The further substances
are placed from this point, the more distinctive are they as re-
gards their attraction or repulsion by the magnet. Nevertheless
this order may, very probably, be found inaccurate by more
careful observation.
VOL. III.
F
66
Action of magnets
[SERIES XXI.
Diamagnetic.
Bismuth.
Antimony.
Zinc.
Tin.
Cadmium.
Sodium.
Magnetic.
Iron
Mercury.
Nickel.
Cobalt.
Manganese.
Lead.
Silver.
Copper.
Chromium.
Gold.
Cerium.
Arsenic.
Titanium.
Uranium.
Palladium.
Rhodium.
Platinum.
Iridium.
Osmium.
Tungsten.
0°
¶ vi. Action of magnets on air and gases.
2400. It was impossible to advance, in an experimental in-
vestigation of the kind now described, without having the mind
impressed with various theoretical views, of the mode of action
of the bodies producing the phænomena. In the passing con-
sideration of these views, the apparently middle condition which
air held between magnetic and diamagnetic substances was of
the utmost interest, and led to many experiments upon its pro-
bable influence, which I will now proceed briefly to describe.
2401. A thin flint-glass tube, in which common air was her-
metically enclosed, was placed between the magnetic poles
(2249.) surrounded by air, and the effect of the magnetic force
observed upon it. There was a very feeble tendency of the tube
to an equatorial position, due to the substance of the tube in
which the air was enclosed.
2402. The air was then withdrawn from around the tube
more or less, and at last up to the highest amount which a good
air-pump would effect; but whatever the degree of rarefaction,
the tube of air still seemed to be affected exactly in the same
manner as if surrounded by air of its own density.
2403. I then surrounded the air-tube with hydrogen and car-
DEC. 1845.]
67
on air and gases.
bonic acid in succession; but in both these, and in each of them
at different degrees of rarefaction, the tube of air remained as
indifferent as before.
2404. Hence there appears to be no sensible distinction be-
tween dense or rare air; or, as far as these experiments go, be-
tween one gas or vapour and another.
2405. As it did not seem at all unlikely that the equatorial and
axial set of bodies, or their repulsions and attractions, might
depend upon converse actions of the media by which they were
surrounded (2361.), so I proceeded to examine what would occur
with diamagnetic substances, when the air or gas which sur-
rounded them was changed in its density or nature, or what
would happen to air itself when surrounded by these substances.
2406. The air-tube (2401.) was suspended horizontally in
water (being retained below the surface by a cube of bismuth
attached to it, just beneath the point of suspension, which there-
fore could have no power of giving it direction); it was then
subjected to the magnetic forces, and immediately pointed well in
an axial direction, or as a magnet would have done. Being
brought near to one pole, it moved, on the supervention of the
magnetic force, appearing as if attracted after a manner of a
magnetic body; and this continued as long as the magnetic
force was sustained in action.
2407. The air-tube was in like manner subjected to the action
of the magnetic force, when surrounded by alcohol, and also by
oil of turpentine, with precisely the same results as in water.
In all these cases the action of air in the fluids was precisely the
same as the action of a magnetic body in air. The air-tube
was subjected to the action of the magnet even when under the
surface of mercury, and here also it pointed axially.
2408. In order to extend the experimental relations of air and
gases, I proceeded to place substances of the diamagnetic class
in them. Thus the bar of heavy glass (2253.) was suspended
in a jar of air, and then the air about it more or less rarefied,
but as before, in the case of the air-tube (2402.), alterations
of this kind produced no effect. Whether the bar were in air
at the ordinary pressure, or as rare as the pump could render it,
it still pointed equatorially, and apparently always with the
same degree of force.
2409. The bar of bismuth (2296.) was suspended in the jar
F2
68
[SERIES XXI.
Action of magnets on gases.
and the same alteration in the density of the air made as before;
but this caused no difference in the action of the bismuth,
either in kind or degree. Carbonic acid and hydrogen gases
were then introduced in succession into the jar, and these also
were employed in different degrees of rarefaction, but the re-
sults were the same; no change took place in the action on the
bismuth,
2410. A bismuth cube was suspended in air and gases at or-
dinary pressure, and also rarefied as much as could be, and
under these circumstances it was brought near the magnetic pole
and its repulsion observed; its action was in all these cases pre-
cisely the same as in the atmosphere.
2411. The perpendicular copper bar (2323.) was suspended
near the magnetic pole in vacuo, but its set, sluggish move-
ments and revulsion were just the same as before in air (2324).
2412. The following preparations in tubes (2401.), namely, a
vacuum, air, hydrogen, carbonic acid gas, sulphurous acid gas,
and vapour of æther, were surrounded by water, and then sub-
jected to the magnetic force; they all pointed axially, and, as
far as I could perceive, with equal force. Being placed in alco-
hol, the same effect occurred.
2413. The same preparations being surrounded by air, or by
carbonic acid gas, all set equatorially.
2414. The axial position of the tubes in the liquid (2412.)
depends, doubtless, upon the relation of the contents of the
tube to the surrounding medium; for as far as the matter of the
tube is concerned, it alone would have tended to give the equa-
torial position. In the following succeeding experiments (2413.),
where the tubes of gases were in surrounding gases, the equa-
torial position is due to this effect of the glass of the tube; and
that it should produce its constant feeble effect, undisturbed by
all the variations of the gases and vapours, is a proof how like
and how indifferent these are one to the other.
2415. I suspended a tube of liquid sulphurous acid in gaseous
sulphurous acid; when under the magnetic influence, the liquid
pointed well equatorially. I surrounded liquid nitrous acid by
gaseous nitrous acid; the liquid pointed well equatorially. I
placed liquid æther in the vapour of æther; the former pointed
equatorially. Upon suspending the tube of vapour of æther in
liquid æther, the vapour pointed axially.
DEC. 1845.]
69
Law of diamagnetic action.
2416. In every kind of trial, therefore, and in every form of
experiment, the gases and vapours still occupy a medium posi-
tion between the magnetic and the diamagnetic classes. Fur-
ther, whatever the chemical or other properties of the substances,
however different in their specific gravity, or however varied in
their own degree of rarefaction, they all become alike in their
magnetic relation, and apparently equivalent to a perfect vacuum.
Bodies which are very marked as diamagnetic substances, im-
mediately lose all traces of this character when they become
vaporous (2415.). It would be exceedingly interesting to know
whether a body from the magnetic class, as chloride of iron,
would undergo the same change.
¶ vii. General considerations.
2417. Such are the facts which, in addition to those presented
by the phænomena of light, establish a magnetic action or con-
dition of matter new to our knowledge. Under this action, an
elongated portion of such matter usually (2253. 2384.) places
itself at right angles to the lines of magnetic force; this result
may be resolved into the simpler one of repulsion of the matter
by either magnetic pole. The set of the elongated portion, or
the repulsion of the whole mass, continues as long as the mag-
netic force is sustained, and ceases with its cessation.
2418. By the exertion of this new condition of force, the
body moved may pass either along the magnetic lines or across
them; and it may move along or across them in either or any
direction. So that two portions of matter, simultaneously sub-
ject to this power, may be made to approach each other as if
they were mutually attracted, or recede as if mutually repelled.
All the phænomena resolve themselves into this, that a portion
of such matter, when under magnetic action, tends to move
from stronger to weaker places or points of force. When the
substance is surrounded by lines of magnetic force of equal
power on all sides, it does not tend to move, and is then in
marked contradistinction with a linear current of electricity
under the same circumstances.
2419. This condition and effect is new, not only as it respects
the exertion of power by a magnet over bodies previously sup-
posed to be indifferent to its influence, but is new as a magnetic
action, presenting us with a second mode in which the magnetic
70
[SERIES XXI.
Generality of magnetic action.
These two modes are in the
power can exert its influence.
same general antithetical relation to each other as positive and
negative in electricity, or as northness and southness in polarity,
or as the lines of electric and magnetic force in magneto-elec-
tricity; and the diamagnetic phænomena are the more import-
ant, because they extend largely, and in a new direction, that
character of duality which the magnetic force already, in a cer-
tain degree, was known to possess.
2420. All matter appears to be subject to the magnetic force
as universally as it is to the gravitating, the electric and the
chemical or cohesive forces; for that which is not affected by it
in the manner of ordinary magnetic action, is affected in the man-
ner I have now described; the matter possessing for the time the
solid or fluid state. Hence substances appear to arrange them-
selves into two great divisions; the magnetic, and that which I
have called the diamagnetic classes; and between these classes
the contrast is so great and direct, though varying in degree,
that where a substance from the one class will be attracted, a
body from the other will be repelled; and where a bar of the one
will assume a certain position, a bar of the other will acquire a
position at right angles to it.
2421. As yet I have not found a single solid or fluid body,
not being a mixture, that is perfectly neutral in relation to the
two lists; i. e. that is neither attracted nor repelled in air. It
would probably be important to the consideration of magnetic
action, to know if there were any natural simple substance pos-
sessing this condition in the solid or fluid state. Of compound
or mixed bodies there may be many; and as it may be im-
portant to the advancement of experimental investigation, I will
describe the principles on which such a substance was prepared
when required for use as a circumambient medium.
2422. It is manifest that the properties of magnetic and dia-
magnetic bodies are in opposition as respects their dynamic
effects; and, therefore, that by a due mixture of bodies from
each class, a substance having any intermediate degree of the
property of either may be obtained. Protosulphate of iron
belongs to the magnetic, and water to the diamagnetic class ;
and using these substances, I found it easy to make a solution
which was neither attracted nor repelled, nor pointed when in
air. Such a solution pointed axially when surrounded by water.
DEC. 1845.]
71
Generality of magnetic action.
If made somewhat weaker in respect of the iron, it would point
axially in water but equatorially in air; and it could be made to
pass more and more into the magnetic or the diamagnetic class
by the addition of more sulphate of iron or more water.
2423. Thus a fluid medium was obtained, which, practically,
as far as I could perceive, had every magnetic character and
effect of a gas, and even of a vacuum; and as we possess both
magnetic and diamagnetic glass (2354.), it is evidently possible
to prepare a solid substance possessing the same neutral mag-
netic character.
2424. The endeavour to form a general list of substances in
the present imperfect state of our knowledge would be very
premature: the one below is given therefore only for the pur-
pose of conveying an idea of the singular association under
which bodies come in relation to magnetic force, and for the pur-
pose of general reference hereafter:-
Iron.
Nickel.
Cobalt.
Manganese.
Palladium.
Crown-glass.
Platinum.
Osmium.
0° Air and vacuum.
Arsenic.
Æther.
Alcohol.
Gold.
Water.
Mercury.
Flint-glass.
Tin.
Heavy-glass.
Antimony.
Phosphorus.
Bismuth.
2425. It is very interesting to observe that metals are the
substances which stand at the extremities of the list, being of
all bodies those which are most powerfully opposed to each
72 Paramagnetic and diamagnetic action compared. [SERIESXXI.
other in their magnetic condition. It is also a very remarkable
circumstance, that these differences and departures from the
medium condition, are in the metals at the two extremes, iron
and bismuth, associated with a small conducting power for elec-
tricity. At the same time the contrast between these metals, as
to their fibrous and granular state, their malleable and brittle cha-
racter, will press upon the mind whilst contemplating the possi-
ble condition of their molecules when subjected to magnetic force.
2426. In reference to the metals, as well as to the diamagnetics
not of that class (2286.), it is satisfactory to have such an
answer to the opinion that all bodies are magnetic as iron, as
does not consist in a mere negation of that which is affirmed,
but in proofs that they are in a different and opposed state, and
are able to counteract a very considerable degree of magnetic
force (2448.).
2427. As already stated, the magnetic force is so strikingly
distinct in its action upon bodies of the magnetic and the dia-
magnetic class, that when it causes the attraction of the one it
produces the repulsion of the other; and this we cannot help re-
ferring, in some way, to an action upon the molecules or the mass
of the substances acted upon, by which they are thrown into
different conditions and affected accordingly. In that point of
view it is very striking to compare the results with those which
are presented to us by a polarized ray, especially as then a re-
markable difference comes into view; for if transparent bodies
be taken from the two classes, as for instance, heavy glass or
water from the diamagnetic, and a piece of green glass or a
solution of green vitriol from the magnetic class, then a given
line of magnetic force will cause the repulsion of one and the
attraction of the other; but this same line of force, which thus
affects the particles so differently, affects the polarized ray when
passing through them precisely in the same manner in both
cases; for the two bodies cause its rotation in the same direction
(2160. 2199. 2224.).
2428. This consideration becomes even more important when
we connect it with the diamagnetic and the optical properties of
bodies which rotate a polarized ray. Thus the iron solution
and a piece of quartz, having the power to rotate a ray, point
by the influence of the same line of magnetic force, the one
axially and the other equatorially; but the rotation which is
DEC. 1845.]
73
Nature of the diamagnetic condition.
impressed on a ray of light by these two bodies, as far as they
are under the influence of the same magnetic force, is the same
for both. Further, this rotation is quite independent of, and
quite unlike that of the quartz in a most important point; for
the quartz by itself can only rotate the ray in one direction, but
under the influence of the magnetic force it can rotate it both to
the right and left, according to the course of the ray (2231.
2232.). Or, if two pieces of quartz (or two tubes of oil of tur-
pentine) be taken which can rotate the ray different ways, the
further rotative force manifested by them when under the
dominion of the magnetism is always the same way; and the
direction of that way may be made either to the right or left in
either crystal or quartz. All this time the contrast between the
quartz as a diamagnetic, and the solution of iron as a magnetic
body remains undisturbed. Certain considerations regarding
the character of a ray, arising from these contrasts, press strongly
on my mind, which, when I have had time to submit them to
further experiment, I hope to present to the Society.
2429. Theoretically, an explanation of the movements of the
diamagnetic bodies, and all the dynamic phænomena consequent
upon the actions of magnets on them, might be offered in the
supposition that magnetic induction caused in them a contrary
state to that which it produced in magnetic matter; i. e. that if
a particle of each kind of matter were placed in the magnetic
field both would become magnetic, and each would have its axis
parallel to the resultant of magnetic force passing through it; but
the particle of magnetic matter would have its north and south
poles opposite, or facing towards the contrary poles of the in-
ducing magnet, whereas with the diamagnetic particles the
reverse would be the case; and hence would result approxima-
tion in the one substance, recession in the other.
2430. Upon Ampère's theory, this view would be equivalent
to the supposition, that as currents are induced in iron and
magnetics parallel to those existing in the inducing magnet or
battery wire; so in bismuth, heavy glass and diamagnetic bodies,
the currents induced are in the contrary direction. This would
make the currents in diamagnetics the same in direction as those
which are induced in diamagnetic conductors at the commence-
ment of the inducing current; and those in magnetic bodies the
same as those produced at the cessation of the same inducing
74
[SERIES XXI.
Action of magnets on
current. No difficulty would occur as respects non-conducting
magnetic and diamagnetic substances, because the hypothetical
currents are supposed to exist not in the mass, but round the
particles of the matter.
2431. As far as experiment yet bears upon such a notion, we
may observe, that the known inductive effects upon masses of
magnetic and diamagnetic metals are the same. If a straight
rod of iron be carried across magnetic lines of force, or if it, or
a helix of iron rods or wire, be held near a magnet, as the power
in it rises electric currents are induced, which move through the
bars or helix in certain determinate directions (38. 114., &c.).
If a bar or a helix of bismuth be employed under the same cir-
cumstances the currents are again induced, and precisely in the
same direction as in the iron, so that here no difference occurs
in the direction of the induced current, and not very much in
its force, nothing like so much indeed as between the current
induced in either of these metals and a metal taken from near
the neutral point (2399.). Still there is this difference remain-
ing between the conditions of the experiment and the hypo-
thetical case; that in the former the induction is manifested by
currents in the masses, whilst in the latter, i. e. in the special
magnetic and diamagnetic effects, the currents, if they exist, are
probably about the particles of the matter.
2432. The magnetic relation of aëriform bodies is exceedingly
remarkable. That oxygen or nitrogen gas should stand in a
position intermediate between the magnetic and diamagnetic
classes; that it should occupy the place which no solid or liquid
element can take; that it should show no change in its relations
by rarefaction to any possible degree, or even when the space it
occupies passes into a vacuum; that it should be the same mag-
netically with any other gas or vapour; that it should not take
its place at one end but in the very middle of the great series of
bodies; and that all gases or vapours should be alike, from the
rarest state of hydrogen to the densest state of carbonic acid,
sulphurous acid, or æther vapour, are points so striking, as to
persuade one at once that air must have a great and perhaps an
active part to play in the physical and terrestrial arrangement of
magnetic forces.
2433. At one time I looked to air and gases as the bodies
DEC. 1845.]
75
gaseous bodies.
which, allowing attenuation of their substance without addition,
would permit of the observation of corresponding variations in
their magnetic properties; but now all such power by rarefac-
tion appears to be taken away; and though it is easy to prepare
a liquid medium which shall act with other bodies as air does
(2422.), still it is not truly in the same relation to them; neither
does it allow of dilution, for to add water or any such substance
is to add to the diamagnetic power of the liquid; and if it were
possible to convert it into vapour and so dilute it by heat, it
would pass into the class of gases and be magnetically undistin-
guishable from the rest.
2434. It is also very remarkable to observe the apparent dis-
appearance of magnetic condition and effect when bodies assume
the vaporous or gaseous state, comparing it at the same time
with the similar relation to light; for as yet no gas or vapour
has been made to show any magnetic influence over the po-
larized ray, even by the use of powers far more than enough
to manifest such action freely in liquid and solid bodies.
2435. Whether the negative results obtained by the use of
gases and vapours depend upon the smaller quantity of matter
in a given volume, or whether they are direct consequences of
the altered physical condition of the substance, is a point of very
great importance to the theory of magnetism. I have imagined,
in elucidation of the subject, an experiment with one of M.
Cagniard de la Tour's æther tubes, but expect to find great
difficulty in carrying it into execution, chiefly on account of the
strength, and therefore the mass of the tube necessary to resist
the expansion of the imprisoned heated æther.
2436. The remarkable condition of air and its relation to
bodies taken from the magnetic and the diamagnetic classes,
causes it to point equatorially in the former and axially in the
latter. Or, if the experiment presents its results under the form
of attraction and repulsion, the air moves as if repelled in a mag-
netic medium and attracted in a medium from the diamagnetic
class. Hence it seems as if the air were magnetic when com-
pared with diamagnetic bodies, and of the latter class when
compared to magnetic bodies.
2437. This result I have considered as explained by the as-
sumption that bismuth and its congeners are absolutely repelled
by the magnetic poles, and would, if there were nothing else
76
Action of magnets on air and gases. [SERIES XXI.
concerned in the phænomenon than the magnet and the bismuth,
be equally repelled. So also with the iron and its similars, the
attraction has been assumed as a direct result of the mutual ac-
tion of them and the magnets; further, these actions have been
admitted as sufficient to account for the pointing of the air both
axially and equatorially, as also for its apparent attraction and
repulsion; the effect in these cases being considered as due to
the travelling of the air to those positions which the magnetic
or diamagnetic bodies tended to leave.
2438. The effects with air are, however, in these results pre-
cisely the same as those which were obtained with the solutions
of iron of various strength (2365.), where all the bodies belonged
to the magnetic class, and where the effect was evidently due to
the greater or smaller degree of magnetic power possessed by
the solutions. A weak solution in a stronger pointed equa-
torially and was repelled like a diamagnetic, not because it did
not tend by attraction to an axial position, but because it tended
to that position with less force than the matter around it; so the
question will enter the mind, whether the diamagnetics, when in
air, are repelled and tend to the equatorial position for any other
reason, than that the air is more magnetic than they are, and
tends to occupy the axial space. It is easy to perceive that if all
bodies were magnetic in different degrees, forming one great
series from end to end, with air in the middle of the series, the
effects would take place as they do actually occur. Any body
from the middle part of the series would point equatorially in
the bodies above it and axially in those beneath it; for the
matter which, like bismuth, goes from a strong to a weak point
of action, may do so only because that substance, which is al-
ready at the place of weak action, tends to come to the place
where the action is strong; just as in electrical induction the
bodies best fitted to carry on the force are drawn into the
shortest line of action. And so air in water, or even under
mercury, is, or appears to be, drawn towards the magnetic pole.
.
2439. But if this were the true view, and air had such power
amongst other bodies as to stand in the midst of them, then one
would be led to expect that rarefaction of the air would affect
its place, rendering it, perhaps, more diamagnetic, or at all
events altering its situation in the list. If such were the case,
bodies that set equatorially in it in one state of density, would,
DEC. 1845.] General nature of diamagnetic action.
77
as it varied, change their position, and at last set axially: but
this they do not do; and whether the rarefied air be compared
with the magnetic or the diamagnetic class, or even with dense
air, it keeps it place.
2440. Such a view also would make mere space magnetic, and
precisely to the same degree as air and gases. Now though it
may very well be, that space, air and gases, have the same
general relation to magnetic force, it seems to me a great addi-
tional assumption to suppose that they are all absolutely mag-
netic, and in the midst of a series of bodies, rather than to sup-
pose that they are in a normal or zero state. For the present,
therefore, I incline to the former view, and consequently to the
opinion that diamagnetics have a specific action antithetically
distinct from ordinary magnetic action, and have thus presented
us with a magnetic property new to our knowledge.
2441. The amount of this power in diamagnetic substances
seems to be very small, when estimated by its dynamic effect,
but the motion which it can generate is perhaps not the most
striking measure of its force; and it is probable that when its
nature is more intimately known to us, other effects produced by
it and other indicators and measures of its powers, than those
so imperfectly made known in this paper, will come to our
knowledge; and perhaps even new classes of phænomena will
serve to make it manifest and indicate its operation. It is
very striking to observe the feeble condition of a helix when
alone, and the astonishing force which, in giving and re-
ceiving, it manifests by association with a piece of soft iron.
So also here we may hope for some analogous development of
this element of power, so new as yet to our experience. It can-
not for a moment be supposed, that, being given to natural
bodies, it is either superfluous or insufficient, or unnecessary.
It doubtless has its appointed office, and that one which relates
to the whole mass of the globe; and it is probably because of
its relation to the whole earth, that its amount is necessarily so
small (so to speak) in the portions of matter which we handle
and subject to experiment. And small as it is, how vastly
greater is this force, even in dynamic results, than the mighty
power of gravitation, for instance, which binds the whole uni-
verse together, when manifested by masses of matter of equal
magnitude!
78 Action of matter in diamagnetic phænomena. [SERIES XXI.
2442. With a full conviction that the uses of this
power in
nature will be developed hereafter, and that they will prove, as
all other natural results of force do, not merely important but
essential, I will venture a few hasty observations.
2443. Matter cannot thus be affected by the magnetic forces
without being itself concerned in the phænomenon, and exert-
ing in turn a due amount of influence upon the magnetic force.
It requires mere observation to be satisfied that when a magnet
is acting upon a piece of soft iron, the iron itself, by the condi-
tion which its particles assume, carries on the force to distant
points, giving it direction and concentration in a manner most
striking. So also here the condition which the particles of in-
tervening diamagnetics acquire, may be the very condition which
carries on and causes the transfer of force through them. In
former papers (1161. &c.)¹ I proposed a theory of electrical in-
duction founded on the action of contiguous particles with which
I am now even more content than at the time of its proposition:
and I then ventured to suggest that probably the lateral action
of electrical currents which is equivalent to electro-dynamic or
magnetic action, was also conveyed onwards in a similar manner
(1663. 1710. 1729. 1735.). At that time I could discover no
peculiar condition of the intervening or diamagnetic matter; but
now that we are able to distinguish such an action, so like in its
nature in bodies so unlike in theirs, and by that so like in cha-
racter to the manner in which the magnetic force pervades all
kinds of bodies, being at the same time as universal in its pre-
sence as it is in its action; now that diamagnetics are shown not
to be indifferent bodies, I feel still more confidence in repeating
the same suggestion, and asking whether it may not be by the
action of the contiguous or next succeeding particles that the
magnetic force is carried onwards, and whether the peculiar
condition acquired by diamagnetics when subject to magnetic
action, is not that condition by which such propagation of the
force is affected?
2444. Whichever view we take of solid and liquid substances,
whether as forming two lists, or one great magnetic class (2424.
2437.), it will not, as far as I can perceive, affect the question.
They are all subject to the influence of the magnetic lines of
1 ¹ Philosophical Transactions, 1838, Part I.
DEC. 1845.]
79
Magnetic action of matter.
force passing through them, and the virtual difference in pro-
perty and character between any two substances taken from
different places in the list (2424.) will be the same; for it is
the differential relation of the two which governs their mutual
effects.
2445. It is that group which includes air, gases, vapours, and
even a vacuum which presents any difficulty to the mind; but
here there is such a wonderful change in the physical constitu-
tion of the bodies, and such high powers in some respects are
retained by them, whilst others seem to vanish, that we might
almost expect some peculiar condition to be assumed in regard
to a power so universal as the magnetic force. Electric induc-
tion being an action through distance, is varied enough amongst
solid and liquid bodies; but, when it comes to be exerted in air
or gases, where it most manifestly exists, it is alike in amount
in all (1292.); neither does it vary in degree in air however rare
or dense it may be (1284.). Now magnetic action may be con-
sidered as a mere function of electric force, and if it should be
found to correspond with the latter in this particular relation
to air, gases, &c., it would not excite in my mind any surprise.
2446. In reference to the manner in which it is possible for
electric force, either static or dynamic, to be transferred from
particle to particle when they are at a distance from each other,
or across a vacuum, I have nothing to add to what I have said
before (1614. &c.). The supposition that such can take place,
can present nothing startling to the mind of those who have en-
deavoured to comprehend the radiation and the conduction of
heat under one principle of action.
2447. When we consider the magnetic condition of the earth
as a whole, without a reference to its possible relation to the sun,
and reflect upon the enormous amount of diamagnetic matters
which, to our knowledge, forms its crust; and when we remem-
ber that magnetic curves of a certain amount of force and uni-
versal in their presence, are passing through these matters and
keeping them constantly in that state of tension, and therefore
of action, which I hope successfully to have developed, we cannot
doubt but that some great purpose of utility to the system, and
us its inhabitants, is thereby fulfilled, which now we shall have
the pleasure of searching out.
2448. Of the substances which compose the crust of the earth,
80
[SERIES XXI.
Terrestrial diamagnetic action.
by far the greater portion belongs to the diamagnetic class; and
though ferruginous and other magnetic matters, being more
energetic in their action, are consequently more striking in their
phænomena, we should be hasty in assuming that therefore they
overrule entirely the effect of the former bodies. As regards
the ocean, lakes, rivers, and the atmosphere, they will exert
their peculiar effect almost uninfluenced by any magnetic mat-
ter in them; and as respects the rocks and mountains, their dia-
magnetic influence is perhaps greater than might be anticipated.
I mentioned that by adjusting water and a salt of iron together,
I obtained a solution inactive in air (2422.); that is, by a due
association of the forces of a body from each class, water and a
salt of iron, the magnetic force of the latter was entirely coun-
teracted by the diamagnetic force of the former, and the mix-
ture was neither attracted nor repelled. To produce this effect,
it required that more than 486 grains of crystallized protosul-
phate of iron should be added to 10 cubic inches of water (for
these proportions gave a solution which still set equatorially), a
quantity so large, that I was greatly astonished on observing the
power of the water to overcome it. It is not therefore at all
unlikely that many of the masses which form the crust of this
our globe may have an excess of diamagnetic power and act
accordingly.
2449. Though the general disposition of the magnetic curves
which permeate and surround our globe resemble those of a very
short magnet, and therefore give lines of force rapidly diverging
in their general form, yet the magnitude of the system prevents
us from observing any diminution of their power within small
limits; so that probably any attempt on the surface of the earth
to observe the tendency of matter to pass from stronger to
weaker places of action would fail. Theoretically, however, and
at first sight, I think a pound of bismuth or of water, estimated
at the equator, where the magnetic needle does not dip, ought to
weigh less when taken into latitudes where the dip is consider-
able; whilst a pound of iron, nickel or cobalt, ought, under the
same change of circumstances, to weigh more. If such should
really prove to be the case, then a ball of iron and another of
bismuth, attached to the ends of a delicate balance beam, should
cause that beam to take different inclinations on different parts
of the surface of the earth; and it does not seem quite impossible
DEC. 1845.]
81
Terrestrial diamagnetic action.
that an instrument to measure one of the conditions of terres-
trial magnetic force might be constructed on such a principle.
2450. If one might speculate upon the effect of the whole
system of curves upon very large masses, and these masses were
in plates or rings, then they would, according to analogy with
the magnetic field, place themselves equatorially. If Saturn
were a magnet as the earth is, and his ring composed of dia-
magnetic substances, the tendency of the magnetic forces would
be to place it in the position which it actually has.
2451. It is a curious sight to see a piece of wood, or of beef,
or an apple, or a bottle of water repelled by a magnet, or taking
the leaf of a tree and hanging it up between the poles, to observe
it take an equatorial position. Whether any similar effects oc-
cur in nature among the myriads of forms which, upon all parts
of its surface, are surrounded by air, and are subjected to the action
of lines of magnetic force, is a question which can only be an-
swered by future observation.
.
2452. Of the interior of the earth we know nothing, but there
are many reasons for believing that it is of a high temperature. On
this supposition I have recently remarked, that at a certain di-
stance from the surface downwards, magnetic substances must be
entirely destitute, either of the power of retaining magnetism, or
becoming magnetic by induction from currents in the crust or
otherwise¹. This is evidently an error; that the iron, &c. can
retain no magnetic condition of itself, is very probably true, but
that the magnetic metals and all their compounds retain a
certain power of becoming magnetic by induction, whatever
their temperature, has now been proved (2344. &c.). The
deep magnetic contents of the earth, therefore, though they pro-
bably do not constitute of themselves a central magnet, are just
in the condition to act as a very weak iron core to the currents
around them, or other inducing actions, and very likely are
highly important in this respect. What the effect of the dia-
magnetic part may be under the influence of such inductive
forces, we are not prepared to state; but as far as I have been
able to observe, such bodies have not their power diminished by
heat (2397.).
2453. If the sun have anything to be with the magnetism of
the globe, then it is probable that part of its effect is due to the
' Philosophical Magazine, 1845, vol. xxvii. p. 3.
VOL. III.
G
>
82
[SERIES XXI.
Terrestrial magnetic action.
action of the light that comes to us from it; and in that expec-
tation the air seems most strikingly placed round our sphere,
investing it with a transparent diamagnetic, which therefore,
is permeable to his rays, and at the same time moving with
great velocity across them. Such conditions seem to suggest
the possibility of magnetism being there generated; but I shall
do better to refrain from giving expression to these vague
thoughts (though they will press in upon the mind), and first
submitting them to rigid investigation by experiment, if they
prove worthy, then present them hereafter to the Royal Society.
Royal Institution,
Dec. 22, 1845.
Feb. 2, 1846.-I add the following notes and references to
these Researches.
Brugmans first observed the repulsion of bismuth by a magnet in 1778. An-
toni Brugmans Magnetismus seu de affinitatibus magneticis observationes magne-
tica. Lugd. Batav. 1778, § 41.
M. le Baillif on the Repulsion of a Magnet by Bismuth and Antimony,
Bulletin Universel, 1827, vol. vii. p. 371; vol. viii. pp. 87, 91, 94.
Saigey on the Magnetism of certain natural combinations of Iron, and on
the mutual repulsions of Bodies in general. Ibid. 1828, vol. ix. pp. 89, 167,
239.
Seebeck on the Magnetic Polarity of different Metals, Alloys and Oxides.
Ibid. 1828, vol. ix. p. 175.
83
TWENTY-SECOND SERIES'.
§ 28. On the Crystalline polarity of bismuth (and other bodies),
and on its relation to the magnetic form of force. ¶i. Cry-
stalline polarity of bismuth. ii. Crystalline polarity of an-
¶ii.
timony. ¶ iii. Crystalline polarity of arsenic.
Received October 4,—Read December 7, 1848.
2454. MANY results obtained by subjecting bismuth to the
action of the magnet have at various times embarrassed me, and
I have either been contented with an imperfect explanation, or
have left them for a future examination: that examination I
have now taken up, and it has led to the discovery of the follow-
ing results. I cannot, however, better enter upon the subject
than by a brief description of the anomalies which occurred,
and which may be obtained at pleasure.
2455. If a small open glass tube have a bulb formed in its
middle part and some clean good bismuth be placed in the bulb
and melted by a spirit-lamp, it is easy afterward, by turning
the metal into the tubular part of the arrangement, to cast it
into long cylinders: these are very clean, and when broken are
seen to be crystallized, usually giving cleavage planes, which
run across the metal. I prepare them from 0.05 to 0·1 of an
inch in diameter, and, if the glass be thin, usually break both it
and the bismuth together, and then keep the little cylinders in
their vitreous cases.
2456. Taking some of these cylinders at random and suspend-
ing them horizontally between the poles of the electro-magnet
(2247.), they presented the following phænomena. The first
pointed axially; the second, equatorially; the third, equatorial
in one position, and obliquely equatorial if turned round on its
axis 50° or 60°; the fourth, equatorially and axially under the
same treatment; and all of them, if suspended perpendicularly,
pointed well, vibrating about a final fixed position which
¹ Philosophical Transactions, 1849, p. 1. The Bakerian Lecture.
G 2
84
[SERIES XXII.
Crystalline polarity of bismuth.
seemed to have no reference to the form of the cylinders. In
all these cases the bismuth was strongly diamagnetic (2295. &c.),
being repelled by a single magnetic pole, or passing off on either
side from the axial line between two poles. A similar piece of
finely grained or granular bismuth was, under the same circum-
stances and at the same time, affected in a perfectly regular
manner, taking up the equatorial position (2253.), as a body
simply diamagnetic ought to do. The cause of these variations
was finally traced to the regularly crystalline condition of the
metallic cylinders.
¶i. Crystalline polarity of bismuth.
2457. Some bismuth was crystallized in the usual manner by
melting it in a clean iron ladle, allowing it partly to congeal, and
then pouring away the internal fluid portion. Pieces so obtained
were then broken up by copper hammers and tools, and groups
of the crystals separated, each group or piece consisting only of
those crystals which were symmetrically arranged, and therefore
likely to act in one direction. If any part of the fragments had
been in contact with the iron ladle, it was cleared away by rub-
bing on sandstone and sand-paper. Pieces weighing from 18
grains to 100 grains were thus easily obtained.
That
2458. The electro-magnet employed in the first instance was
that already described (2247.), having moveable terminations
which supplied either conical, round, or flatfaced poles.
the suspension of the bismuth might be readily effected and un-
objectionable as to magnetic influence, the following arrangement
was generally adopted. A single fibre of cocoon silk, from 12
to 24 inches in length, was attached to a fit support above, and
made fast below to the end of a piece of fine, straight, well-cleaned
copper wire, about 2 inches in length; the lower end of this wire
was twisted up into a little head, and then furnished with a pellet
of cement, made by melting together a portion of pure white
wax, with about one-fourth its weight of Canada balsam. The
cement was soft enough to adhere by pressure to any dry sub-
stance, and sufficiently hard to sustain weights up to 300 grains,
When prepared, the suspender was subjected by
itself to the action of the magnet, to ascertain that it was free
from any tendency to point, or be affected; without which pre-
or even more.
Ост. 1848.]
85
Crystalline polarity of bismuth.
caution no confidence could be reposed in the results of the ex-
periments.
2459. A piece of selected bismuth (2457.), weighing 25 grains,
was hung up between the poles of the magnet, and moved with
great freedom. The constituent cubes were associated in the
usual manner, being attached to each other chiefly in the line
joining two opposite solid angles; and this line was in thegreatest
length of the piece. The instant that the magnetic force was on,
the bismuth vibrated strongly about a given line, in which, at
last, it settled; and if moved out of that position, it returned,
when at liberty, into it; pointing with considerable force, and
having its greatest length axial.
2460. Another piece was then selected, having a flatter form,
which when subjected to the magnetic power, pointed with the
same facility and force, but its greatest length was equatorial :
still the line according to which the cubes tended to associate
diametrically, was, as before, in the axial direction. Other pieces
were then taken of different forms, or shaped into various forms
by rubbing them down on stone, but they all pointed well; and
took up a final position, which had no reference to the shape,
but was manifestly dependent on the crystalline condition of the
substance.
2461. In all these cases the bismuth was diamagnetic, and
strongly repelled by either magnetic pole, or from the axial line.
It was affected only whilst the magnetic force was present. It
set in a given constant position perfectly determinate; and, if
moved, always returned to it, unless the extent of motion was
above 90°, and then the piece moved further round and took up
a new position diametrically opposed to the former, which it then
retained with equal force, and in the same manner. This phe-
nomenon is general in all the results I have to refer to, and I
will express it by the word diametral:-diametral set or position.
2462. The effect occurs with a single magnetic pole, and it is
then striking to observe a long piece of a substance, so diamag-
netic as bismuth, repelled, and yet at the same moment set
round with force, axially or end on, as a piece of magnetic sub-
stance would do.
2463. Whether the magnetic poles employed (2458.) are
pointed, round, or flatfaced, still the effect on the bismuth is the
same: nevertheless, the form of the poles has an important in-
86
Magnecrystallic polarity of bismuth. [SERIES XXII.
fluence of a subordinate kind; and some forms are much more
fitted for these investigations than others. When pointed poles
are employed, the lines of magnetic force (2149.) rapidly diverge,
and the force itself diminishes in intensity to the middle distance
from each pole. But when flat-faced poles are used, though the
lines of power are curved and vary in intensity at and towards
the edges of the flat faces, yet there is a space at the middle of
the magnetic field where they may be considered as parallel to
the magnetic axes, and of equal force throughout. If the flat
faces of the poles be square or circular, and their distance apart
about one-third of their diameter, this space of uniform power is
of considerable extent. In my experience the central or axial
portion of the magnetic field is sensibly weaker than the circum-
jacent parts; but, then, there is a small screw-hole in the middle
of each pole face, for the attachment of other forms of termi-
nation.
2464. Now the law of action of bismuth, as a diamagnetic
body, is, that it tends to go from stronger to weaker places of
magnetic force (2267. 2418.); but as a magnecrystallic body it
is subject to no effect of the kind; and is as powerfully affected
by lines of equal force as by any other. So a piece of amor-
phous bismuth, suspended in a magnetic field of uniform power,
seems to have lost its diamagnetic force altogether, and tends to
acquire no motion but what is due to torsion of the suspending
fibre, or currents of air: but a piece of regularly crystallized
bismuth is, in the same situation, very powerfully affected by
virtue of its magnecrystallic condition.
2465. Hence the great value of a magnetic field of uniform
force; and, if, hereafter, in the extension of these investigations
to bodies having only a small degree of crystalline power, a per-
fectly uniform field should be required, it could easily be given
by making the form of the pole face somewhat convex, and
rounded at the edges more or less. The required shape could
be ascertained by calculation, or perhaps better in practice, by
the use of a little test cylinder of bismuth in the granular or
amorphous state, or of phosphorus.
2466. In addition to these observations, it may be remarked,
that small crystals, or masses of crystals, and such as approach
in their general shape to that of a cube or a sphere, are better
than large or elongated pieces; inasmuch, as if there be irregu-
OCT. 1848.] Magnecrystallic polarity of bismuth.
87
larities in the force of a magnetic field, such pieces are less likely
to be affected by them.
2467. When the crystal of bismuth is in a magnetic field of
equal strength, it is equally affected whether it be in the middle
of the field or close up to one or the other magnetic pole; i. e.
the number of vibrations in equal times appears to be equal.
Much care, however, is required in estimating it by such means,
because, from the occurrence of two positions of unstable equili-
brium in the equatorial direction, the vibrations in large arcs are
much slower than those in small arcs; and it is difficult in dif-
ferent cases to adjust them to the same extent of vibration.
2468. Whether the bismuth be in a field of intense magnetic
force or one of feeble powers; whether the magnetic poles are
close up to the piece, or are opened out until they are five or six
inches or even a foot asunder; whether the bismuth be in the
line of maximum force, or raised above, or lowered beneath it;
whether the electric current be strong or weak, and the mag-
netic force, therefore, more or less in that respect; if the bismuth
be affected at all it is always affected in the same manner.
2469. The results are, altogether, very different from those
produced by diamagnetic action (2418.). They are equally di-
stinct from those discovered and described by Plücker, in his
beautiful researches into the relation of the optic axis to mag-
netic action for there the force is equatorial, whereas here it is
axial. So they appear to present to us a new force, or a new
form of force, in the molecules of matter, which, for convenience
sake, I will conventionally designate by a new word, as the mag-
necrystallic force.
2470. The direction of this force is, in relation to the mag-
netic field, axial and not equatorial: this is proved by several
considerations. Thus, when a piece of regularly crystallized bis-
muth was suspended in the magnetic field, it pointed; keeping it
in this position, the point of suspension was removed 90° in the
equatorial plane (2252.), so that when again freely suspended,
the line through the crystal, which was before horizontal in the
equatorial plane, was now vertical; the piece again pointed, and
generally with more force than before. The line passing through
the crystal, coincident with the magnetic axis, may now be taken
as a line of force; and if the process of a quarter revolution in
the equatorial plane be repeated, however often, the crystal still
88
[SERIES XXII.
Magnecrystallic polarity of bismuth.
continues to point with the assumed line of force in the mag-
netic axis, and with a maximum degree of power. But now, if the
point of suspension be removed 90° in the plane of the axis, i. e.
to the end of the assumed line of force, so that when the crystal
is again freely suspended this line is vertical; then, the crystal
presents its peculiar effect at a minimum, being almost or en-
tirely devoid of pointing power, and exhibits in relation to the
magnet, only the ordinary diamagnetic force (2418.).
2471. Now if the power had been equatorial and polar, its
maximum effect would not have been produced by a change of
the point of suspension through 90° in the equatorial plane, but
by the same change in the axial plane, and any similar change
after that in the axial plane, would not have disturbed the
maximum force; whereas a single change of 90° in the equa-
torial plane, would have brought the line of force vertical (as in
Plücker's case of Iceland spar), and reduced the results to a
minimum or zero.
2472. The directing force, therefore, and the set of the
crystal are in the axial direction. This force is, doubtless, resi-
dent in the particles of the crystal. It is such, that the crystal
can set with equal readiness and permanence in two diametral
positions; and that between these there are two positions of
equatorial equilibrium which are, of course, unstable in their
nature. Either end of the mass or of its molecules, is, to all
intents and purposes, both in these phænomena, and in the ordi-
nary results of crystalization, like the other end; and in many ·
cases, therefore, the words axial and axiality would seem more
expressive than the words polar and polarity. In presenting
the ideas to my own mind, I have found the meaning belonging
to the former word the more useful.
2473. On placing the metal in other positions, and therefore
in a constrained condition, no alteration of the state or power
of the bismuth, either in force or direction, is produced by the
power of the magnet, however strong its enforcement or long
its continuance.
2474. It is difficult readily to describe the position of this
force in relation to the crystal, though most easy to ascertain it
experimentally. The form of the bismuth crystals is said to be
that of a cube, and of its primitive particle a regular octohedron.
To me the crystals do not seem to be cubes, but either rhomboids
Ocr. 1848.] Form and cleavage of bismuth crystals.
89
or rhombic prisms, approaching very nearly to cubes. My
measurements were very imperfect and the crystals not regular;
but as an average of several observations, the planes were in-
clined to each other at angles of 9110 and 8810; and the bound-
ary lines of a plane at 8740 and 9240. Whatever be the true
form, it is manifest, upon inspection, that the aggregating force
tends to produce crystals having more or less of the rhomboidal
shape and rhombic planes; and that these crystals run together
in symmetric groups, generally in the direction of their longest
diameters. Now the line of magnecrystallic force almost always
coincides with this direction where the latter is apparent.
2475. The cleavage of bismuth crystals removes the solid
angles and replaces them by planes; so that there are four
directions producing the octohedron. These cleavages are not
(in my experience) made with equal facility, nor do they pro-
duce planes equally bright and perfect. Two, and more fre-
quently one, of these planes is more perfect than the others;
and this, the most perfect plane, is that which is produced at
the most acute solid angle (2474.); and is generally easily
recognized. When a bismuth crystal presents many planes of
cleavage and is suspended in the magnetic field, one of these
planes faces towards one of the magnetic poles, and its corre-
sponding plane, if it be there, towards the other; so that the line
of magnecrystallic force is perpendicular to this plane: and this
plane corresponds to the one which I have already described as
being, generally, the most perfect, and replacing the acute
angle of the crystal.
2476. A single crystal of bismuth was selected and cut out
from the mass by copper tools, and the places where it had
adhered were rubbed down on sand-paper, so as to give the
fragment a cube-like form with six planes; four of these planes
were natural. One of the solid angles, expected to be that
terminating or in the direction of the line of magnecrystallic
force, was removed, so as to expose a small cleavage plane, which
was bright and perfect, as also was expected. When suspended
in the magnetic field with this plane vertical, the crystal in-
stantly pointed with considerable force, and with the plane to-
wards either one or the other magnetic pole; so that the magne-
crystallic axis appeared now to be horizontal and acting with its
greatest power. When this axial line was made vertical, and
90
Law of magnecrystallic action. [SERIES XXII.
the plane therefore horizontal, the position being carefully ad-
justed, the crystal did not point at all. Being now suspended
in succession at all the angles and faces of the cube, it always
pointed with more or less force; but always so that a line
drawn perpendicularly through the indicating cleavage plane
(representing therefore the line of force) was in the same vertical
plane as that including the magnetic axis; and, finally, when
the bright cleavage plane was horizontal and the line of
directive force therefore vertical, inclining it a little in a given
direction would make any given part of the crystal point to the
magnetic poles.
2477. A group of bismuth crystals, the apex of which was
terminated by a single small cleavage facet, was found to give
the same results.
2478. Occasionally groups of crystals (2457.) occurred which
did not seem capable of being placed in some one position in
which they lost all directive power, but seemed to retain a mini-
mum degree of force. It is very unlikely, however, that all the
groups should be perfectly symmetric in the arrangement of
their parts. It is more surprising that they should be so
distinct in their action as they are. In reference to bismuth,
and many other bodies, it is probable that magnetic force will
give a more important indication in relation to the essential and
real crystalline structure of the mass than its form can do.
2479. I have already stated that the magnecrystallic force
does not manifest itself by attraction or repulsion, or, at least,
does not cause approach or recession, but gives position only.
The law of action appears to be, that, the line or axis
of MAGNECRYSTALLIC force (being the resultant of the action
of all the molecules), tends to place itself parallel, or as a
tangent, to the magnetic curve or line of magnetic force, passing
through the place where the crystal is situated.
2480. I now broke up masses of bismuth which had been
melted and solidified in the ordinary way, and, selecting those
fragments which appeared to be most regularly crystallized, sub-
mitted them to experiment. It was almost impossible to take a
small piece which did not obey the magnet and point more or
OCT. 1818.]
91
Action of bismuth plates.
less readily. By selecting the thin plates with perfect cleavage
planes, I readily obtained specimens which corresponded in all
respects with the crystals; but thicker plates or angular pieces
often proved complicated in the results, though apparently
simple and regular as to form. Occasionally, the cleavage
planc, which I have beforehand taken for that perpendicular to
the line of force (2475.), has proved not to be the plane sup-
posed; but, after observing experimentally the direction of the
magnecrystallic power, I have always either found, or else ob-
tained by cleavage, a plane corresponding to it, possessing the
appearance and character before described (2175.). Bismuth
plates from the one-twentieth to the one-tenth of an inch in
thickness, and bounded by parallel and similar planes, when
broken up, often proved, upon ocular examination, to be com-
pounded and irregular.
2481. When a well-selected plate of bismuth (mine arc about
0.3 of an inch in length and breadth, and 0·05, more or less, in
thickness) is hung up by the edge in the magnetic field, it vi-
brates and points, presenting its faces to the magnetic poles,
and setting diametrally (2461.). By whatever part of the edge
it is suspended, the same results follow. But if it be suspended
horizontally, the cleavage planes of the fragment and of the mag-
netic axis being parallel to the plane of motion of the plate,
then it is perfectly indifferent; for then the line of magnecrys-
tallic force is perpendicular to the line of magnetic force in every
position that it can take.
2482. But if the plate be inclined only a very small quantity
from this position, it points, and that with more force as the
planes become more nearly vertical (2475.); and the phænomena
before described with a crystal (2476.), can here be obtained.
with a fragment from a mass, and any part of the edge of the
plate made to point axially, by elevating or depressing it above
or below the horizontal planc.
2483. If a number of thesc crystalline plates be selected at the
magnet, they may afterwards be built up together, with a little
good cement (2458.), into a mass which has perfectly regular
magnecrystallic action; and in that respect resembles the crys-
tals before spoken of (2459. 2468. 2176.). In this manner,
also, the diamagnetic effect of the bismuth may be neutralized;
for it is easy to build up a prism whose breadth and thickness
92
Magnecrystallic action of bismuth. [SERIES XXII.
are equal, and this being hung with the length vertical, points
well and without any interference of diamagnetic action.
2484. By placing three equal plates at right angles to each
other, a system is obtained, which has lost all power of pointing
under the influence of the magnet, the force being, in every
direction, neutralized. This represents the case of finely crys-
tallized or amorphous bismuth. The same result (having the
same nature) may be obtained by taking a selected uniform mass
of crystals (2157.), melting it in a glass tube and resolidifying
it unless the crystallization is large and distinct, which rarely
happens, the picce obtained is apparently without magnecrys-
tallic force. A like result is also obtained by breaking up the
crystal and putting the small fragments or powder into a tube,
and submitting the whole to the force of the magnet.
:
2485. These experiments on bismuth are not difficult of repe-
tition; for, except those which require the sudden production
or cessation of the magnetic force, the whole may be repeated
with an ordinary horse-shoe magnet. A magnet with which I
have wrought considerably, consists of seven bars placed side by
side, and being fixed in a box with the poles upwards, presents
two magnet cheeks, an inch and a quarter apart, between which
is the magnetic field, having the lines of force in a horizontal
direction. The poles of the magnet should be covered, each
with paper, to prevent communication of particles of iron or
rust. The best place for the piece of bismuth is, of course,
between the poles; not level, however, with their tops, but from
0.4 to 1.0 inch lower down (2463.), that the effect of flat-faced
poles may be obtained. If it be desired to strengthen the lines
of magnetic force, this may be done by introducing a piece of
iron between the poles of the magnet, and so, by virtually
causing them to approach, lessen the width of the magnetic field
between them.
2486. The magnet I used would sustain 30 lbs. at the
keeper; but employing small pieces of bismuth, I have easily
obtained the effects with magnets weighing themselves not more
than 7 ounces, and able to sustain only 22 ounces; so that the
experiments are within the reach of every one.
OCT. 1848.]
93
Disturbing influence of iron.
2487. Whilst the crystal of bismuth is in the magnetic field,
it is affected very distinctly, and even strongly, by the near ap-
proximation of soft iron or magnets, and after the following
manner. Let fig. 1 represent in
Fig. 1.
plan the position of the two chief
magnetic poles, and of a piece.
of crystallized bismuth between
them, which, by its magnecrys-
tallic condition, points axially.
Then, if a piece of soft iron be
applied against the cheek of the
pole, as at e, and also near to the bismuth, as at a, it will affect the
latter and cause its approach to the iron. If the iron be ap-
plied in a similar manner at f, g, or h, it will have a like result
in causing motion of the bismuth; and the parts marked b, c,
and d, will in turn approach it, seeming to be attracted. If
the soft iron do not touch the magnetic pole, but be held
between it and the bismuth so as to represent generally the
same positions, the same effects, but in a weaker degree, are
produced.
2488. Though these motions seem to indicate an effect of
attraction, I do not believe them to be due to any such cause,
but simply to the influence of the law of action (2479.) before
expressed. The previously uniform condition of the magnetic
field is destroyed by the presence of the iron; lines of magnetic
force, of greater intensity than the others, proceed from the
angle a of the iron in the position represented, or from the cor-
responding angles in the other positions (the shape of the pole
now approximating more or less to the conical or pointed form),
and therefore the crystal of bismuth moves round on the axis of
suspension, that it may place the line of magnecrystallic force
parallel or as a tangent to the resultant of the magnetic forces
which pass through its mass.


Fig. 2.
2489. When in place of the group of crystals a crystalline
plate of bismuth (2481.) is em-
ployed, the appearances pro-
duced under similar circum-
stances, are those of repulsion;


for if fig. 2 be allowed to re-
present this state of things, the
piece of iron applied at e causes
the plate to recede from it at
ひ
​94
Disturbing influence of iron and magnets. [SERIES XXII.
a, or if applied at f, g, or h, it causes recession of the bismuth
from it at the points b, c, and d. Now though these effects
look like repulsion, they are, as I conclude, nothing more
than the consequences of the endeavour which the bismuth
makes under the law before expressed (2479.), to place the mag-
necrystallic line of force parallel to, or as a tangent to the
resultant of magnetic force passing through the bismuth.
Fig. 3.
2490. A piece of iron wire about 1½ inch long, and 0·1 or 0·2
of an inch thick, being held in the equatorial plane to the edge
of the plate (fig. 3), did not
alter its position; but if the
end e were inclined to either
pole, the plate began to move,
and moved most when the
iron touched the pole as in the
figure. When it approached
or touched the N pole, the in-
clination of the crystal plate of
bismuth was as indicated by

the dotted figure.
€
When it touched the S, the inclination was
the contrary way. If the end e were kept in contact with the
N pole, and the other end of the soft iron rod placed in the
position m, the bismuth was not affected; but if then this sub-
sidiary pole were moved the one way or the other towards the
edge of the plate, the latter turned as the pole moved, always
tending to keep its face towards it, and evidently by the
tendency of the magnecrystallic axis to place itself parallel
to the resultant of magnetic force passing through the
bismuth. The same results were obtained with the crystal
(2487.) under similar circumstances, and corresponding results
were obtained when the soft iron rod was applied between the
S cheek of the magnet and the bismuth. The like effects were
also obtained with plates of arsenic and antimony.
2491. When a magnet is used instead of soft iron, corre-
sponding effects are produced; only it must be remembered, that
if the chief magnet be very powerful, it may often neutralize,
and even change, the magnetism of the small approximated
magnet; and this can happen with the latter (as to external in-
fluence), whilst in the magnetic field, even though when with-
drawn it may appear to remain unaltered.
2492. Thus, when the plate of bismuth was suspended be-
OCT. 1848.]
95
On the magnetic field of force.
tween the cheeks of the horse-shoe magnet (2485.), fig. 2, and
the north pole of a small magnet (the blade of a pocket-knife)
was placed at a or b, it caused recession of the part of the bis-
muth near it, and precisely for the same reasons as those that
existed when the soft iron was there. When the extra pole was
placed at c or d, the action was more feeble than in the former
case, and consisted in an approximation of that part of the bis-
muth to the pole. As this position of the subordinate pole
would terminate and neutralize certain of the lines of magnetic
force proceeding from the south pole of the horse-shoe magnet,
so the resultant of the lines of force passing through the
bismuth would be changed in direction, being rendered oblique
to their former course, and precisely in the manner represented
by the motion of the bismuth, in its tendency to place its line
of force parallel with them in their new position.
2493. An approximated south pole caused motions in the
contrary direction.
2494. When the subordinate pole was applied to the edge of
the plate, the little magnet being in the equatorial position (fig.
3), then instead of being neutral, as the iron was, it caused the
plate to move in a tangential direction, either to the right or the
left, according as it was either a south or a north pole, just in-
deed as the iron did when, by inclining it, the approximated end
became a pole (2490.). This effect was shown in a still more
striking degree by using the crystal of bismuth (2487.), because,
from its form and position the magnetic curves most affected by
the extra pole were more included in the bismuth than when the
plate was used.
2495. Innumerable variations of these motions may be caused,
and appearances of attraction or repulsion, or tangential action
be obtained at pleasure by the use of crystals having the mag-
necrystallic axis corresponding with their length, or plates where
it accords with their thickness; and either permanent or tempo-
rary subsidiary magnetic poles. By making the moveable pole
travel slowly round the bismuth from the neutral point m to the
other neutral point n, fig. 3, a summary of the whole can be ob-
tained, and it is found that they all resolve themselves into
the general law before expressed (2479.); the magnecrystallic
axis and the resultant of magnetic force passing through the
bismuth, tending to become parallel.
2496. Hence a small crystal or plate of bismuth (or arsenic
96
[SERIES XXII.
Crystals of bismuth in various media.
(2532.)) may become a very useful and important indicator of
the direction of the lines of force in a magnetic field, for at the
same time that it takes up a position showing their course, it
does not by its own action tend sensibly to disturb them.
2497. Many of these motions are similar to, and have relation
with, those described by Plücker, Reich, and others, as ob-
tained by the action of iron and magnets on bismuth, in its simple
diamagnetic condition. These results are by them and others con-
sidered as indicating that the bismuth, as I had originally sup-
posed (2429. &c.), has really, in its diamagnetic state, a magnetic
condition the reverse of that of iron. I am not acquainted with
all of them, or with the reasoning thereon (being in the German
language); but such as I am aware of, and having reobtained,
seem to me to be simple results of the law I formerly laid down
(2267. 2418.), namely, that diamagnetic bodies tend to proceed
from stronger to weaker places of magnetic force; and give no
additional or other proof of the assumed reverse polarity of bis-
muth than the former cases of action which I had given, coming
under that law.
2498. Supposing that the intervening or surrounding matter
might, in some manner, affect the magnecrystallic action of bis-
muth and other bodies, I fixed the magnetic poles at a given
distance (about two inches) asunder, suspended a crystal of bis-
muth in the middle of the magnetic field, and observed its vibra-
tions and set. Then, without any other change, I introduced
screens of bismuth, being blocks about two inches square and
0·75 of an inch in thickness, between the poles and the crystal,
but I could not perceive that any change in the phænomena was
produced by their presence.
2499. The bismuth crystal (2459.) was suspended in water
between the magnetic poles of the horse-shoe magnet. It set
well in accordance with the general law (2479.), and it took five
revolutions of the torsion index at the upper end of the sus-
pending silk filament to displace it, and cause it to turn into the
diametral position. This is, as well as I could observe the
results, the same amount of torsion force required to effect its
displacement when the crystal was placed in the same position,
but surrounded with air only.
2500. The same bismuth was then suspended in a saturated
OCT. 1848.] Bismuth crystallized in the magnetic field.
97
solution of protosulphate of iron (adapted as a magnetic medium),
it set as before with apparently no change of any kind; and
when the torsion force was put on, it still required five turns of
the index, as before, to cause the displacement of the crystal,
and its passage into the diametrical position.
2501. Whether therefore crystals of bismuth be immersed in
air, or water, or solution of sulphate of iron, or placed between
thick masses of bismuth, if they be subject to the same magnetic
force, the magnecrystallic force exerted by them is the same both
in nature, direction and amount.
2502. It seemed possible and probable that magnetic force
might affect the crystallization of bismuth, if not of other bodies.
For, as the force affects the mass of a crystal by that power
which its particles possess, and which they give to the crystal
as a whole by their polar (or axial (2472.)) and symmetric con-
dition; and, as the final position of the crystalline mass in the
magnetic field may be considered as that of the least constraint,
so it was likely enough that, if the bismuth in a fluid state were
placed under the influence of the magnetism, the individual
particles would tend to assume one and the same axial condition,
and the crystalline arrangement and direction of the mass
upon its solidification, be in some degree determined and under
government.
2503. Some bismuth, therefore, was fused in a glass tube and
held in a fixed position in the strong magnetic field until it had
become solid; then, being removed from the glass, it was sus-
pended so that it might assume the same position under the in-
fluence of the magnet; but no signs of magnecrystallic force
were evident. It was not expected that the whole would become
regularly crystallized, but that a difference between one direc-
tion and another might appear. Nothing of the kind however
occurred, whatever the direction in which the piece was sus-
pended; and when it was broken open, the crystallization
within was found to be small, confused, and in all directions.
Perhaps if longer time were allowed, and a permanent magnet
used, a better result might be obtained. I had built many
hopes upon the process, in reference to the crystalline condition
.
VOL. III.
H
98
[SERIES XXII.
Magnecrystallic action.
of gold, silver, platina, and the metals generally, and also in
respect of other bodies.
2504. I cannot find that crystals of bismuth acquire any
power, either temporary or permanent, which they can bring
away from the magnetic field. I held crystals in different posi-
tions in the field of intense action of a powerful electro-magnet,
having conical terminations very near to each other; and, after
some time, removed them and applied them instantly to a very
delicate astatic magnetic needle; but I could not perceive that
they had the least extra effect upon it, because of such treatment.
2505. As a crystal of bismuth is subject to, and obeys the
influence of, the lines of magnetic force (2479.), so it follows
that it ought to obey even the earth's action, and point, though
with a very feeble degree of power. I have suspended a good
crystal by a long filament of cocoon silk, and sheltered it as well
as I could from currents of air by concentric glass tubes, and I
think have observed indications of a set or pointing. The cry-
stal was so hung that the magnecrystallic axis made the same
angle with the horizontal plane (about 70°) as the magnetic dip,
and the indication was, that the axis and the dip tended to coin-
cide: but the experiments require careful repetition.
2506. A more important point, as to the nature of the polar
or axial forces of bismuth, is to know whether two crystals, or
uniformly crystallized masses of bismuth, can mutually affect
each other; and if so, what the nature of these affections are?
what is the relation of the equatorial and terminal parts? and
what the direction of the forces? I have made many experi-
ments, in relation to this subject, both in and out of the mag-
netic field, but obtained only negative results. I employed how-
ever small masses of bismuth, and it is my purpose to repeat
and extend them at a more convenient season with larger masses,
built up, if necessary, in the manner already described (2483.).
2507. I need hardly say that a crystal of bismuth ought to
point in a helix or ring of wire carrying an electric current, and
so that its magnecrystallic axis should be parallel to the axis of
the ring or helix. This I find experimentally to be the case.
OCT. 1848.]
99
Crystalline polarity of antimony.
¶ ii. Crystalline Polarity of Antimony.
2508. Antimony is a magnecrystallic body. Some crystalline
masses, procured in the manner before described (2457.), were
broken up with copper tools, and some excellent groups of cry-
stals were obtained, weighing from ten to twenty grains each, in
which all the constituent crystals appeared to be uniformly
placed. The individual crystals were very good on the whole,
and much more frequently complete and full at the faces than
those of bismuth. They were very bright, having a steel-gray or
silvery appearance, and to the eye appeared more surely as cubes
than bismuth, though here and there distinctly rhomboidal faces
presented themselves. Planes of cleavage can be made to re-
place the solid angles; and, as with bismuth, there is one plane
generally brighter and more perfect than the others.
2509. In the first place, it was ascertained that all these cry-
stals were diamagnetic and strongly so.
2510. In the next it was ascertained, as with bismuth, that
all of them exhibited the magnecrystallic phænomena with con-
siderable power, showing the existence of a line of force (2470.) :
which, when placed vertically, left the crystal free to move in
any direction (2476.); but when placed horizontally, caused the
crystal to point, and in so doing took up its own position parallel
to the resultant of magnetic force passing through the crystal
(2479.). This line proceeded, as in bismuth, from one of the
solid angles to the opposite one, and was perpendicular to the
bright cleavage plane just spoken of (2508.).
2511. So, generally, the action of the magnet upon these
crystals was the same as upon the crystals of bismuth; but there
are some points of variation which require to be more distinctly
stated and distinguished.
2512. In the first place, when the magnecrystallic axis was
horizontal, and a certain crystal used, upon the evolution of the
magnetic force, the crystal went up to its position slowly, and
pointed, as with a dead set. If the crystal were moved from
this position on either side, it returned to it at once: there was
no vibration. Other crystals did the same imperfectly; and
others again made one or perhaps two vibrations, but all ap-
peared as if they were moving in a thick fluid, and were, in that
respect, utterly unlike bismuth, in the freedom and mobility
with which it vibrated (2459.).
H 2
100
[SERIES XXII.
Magnecrystallic action.
2513. In the next place, when the crystals were so suspended
as to have the magnecrystallic axis vertical, there was no point-
ing nor any other signs of magnecrystallic force; but other ap-
pearances presented themselves. For, if the crystalline mass
was revolving when the magnetic force was excited, it suddenly
stoppar, and was caught in a position which might, as was found
by experience, be any position; but if the greatest length was
out of the axial or equatorial position, the arrest was followed by
a revulsive motion on the discontinuance of the electric current
(2315.). This revulsive motion was never great, but was most
when the length of the mass formed about an angle of 45° with
the axis of the magnetic field.
2514. On further examination it appeared that this arresting
and revulsive effect was precisely the same in kind as that ob-
served on a former occasion with copper and other metals
(2309.), and due to the same cause, namely, the production of
circular electric currents in the metal under the inductive force
of the magnet. Now, the reason appeared why, in the former
case, the crystals of antimony did not oscillate (2512.); and
why, also, they went up to their position of rest with a dead set;
for the currents produced by the motion are just those which
tend to stop the motion (2329.)¹; and though the magnecry-
stallic force was sufficient to make the crystal move and point,
yet the very motion so produced generated the current which
reacted upon the tendency to motion, and so caused the mass to
advance towards its position of rest as if it moved in a thick fluid.
2515. Having this additional knowledge respecting the arrest
and revulsion of the antimony, (effects dependent upon its
superior conducting power, in this compact crystalline state, as
compared with bismuth,) one has no difficulty in identifying the
magnecrystallic force of this metal with that of the former, and
establishing the correspondence of the results in all essential
characters and particulars. In most of the pieces of crystals of
1
Any one who wishes to form a sufficient idea of the arresting powers of
these induced currents, should take a lump of solid copper, approaching to the
cubical or globular form, weighing from a quarter to half a pound; should
suspend it by a long thread, give it a rapid rotation, and then introduce it,
spinning, into the magnetic field of the electro-magnet; he will find its motion
to be instantly stopped; and if he further tries to spin it, whilst in the field,
will find it impossible to do so.

OCT. 1848.] Revulsive action of antimony crystals.
antimony the force seemed less than in bismuth, but the fact
may not really be so, for the inductive current action just
described tends to hide the magnecrystallic phænomena.
2516. Different pieces of antimony also seem to differ from
each other in their setting force, and also in their tendency to
exhibit revulsive effects; but these differences are either only
apparent, or may easily be explained. The arresting and revul-
sive action depends much upon the continuity of the mass, so
that one large piece shows it much better than several small
pieces, and these again better than a powdered substance Even
the revulsive action of copper may be entirely destroyed by re-
ducing the single lump to filings. It is easy to perceive, there-
fore, that of two groups of antimony crystals, each symmetrically
disposed within itself, the one may have larger crystals well
connected together, as regards the induction of currents through
the whole mass, and the other smaller crystals less favourably
united. These would present very different appearances, as re-
gards the arrest of motion and succeeding revulsive action;
and further, on that very account, would differ in their readiness
to present the magnecrystallic phænomena, though they might
possess precisely equal degrees of that force.
2517. On proceeding to experiment with plates of antimony,
further illustrations of the effects resulting from the causes just
described were obtained, with abundant accompanying evidence
of the existence of the magnecrystallic condition in the metal.
The plates were selected from broken masses, as with bismuth
(2480.). Some were soon found which acted simply, instantly,
and well; their large surfaces were bright cleavage planes.
When suspended by any part of the edge, these planes faced
towards the magnetic poles; and the plate oscillated on each
side of its final position, gradually acquiring its state of rest.
2518. When these plates were suspended with their planes
horizontal, they had no power of pointing in the magnetic field.
When they were inclined, the points which were most depressed
below and raised above the horizontal plane, were those which
took up their places nearest the magnetic poles (2482.).
2519. When several plates were arranged together into a con-
sistent bundle (2483.), the diamagnetic effect was removed, and
the magnecrystallic oscillation and pointing became very ready
a characteristic.

Magnecrystallic action.
[SERIES XXII.
2520. Thus it is evident that, in all these cases, there was a
line of magnecrystallic force perpendicular to the planes of the
plates, and perfectly consistent in its position and action with
the force before found in the solid crystals of antimony.
2521. But another plate of antimony was now selected, which
had every appearance of being able to present all the pha-
nomena of the former plates; and yet, when hung up by its
edge, it showed no signs of magnecrystallic results; for it first
advanced a little (2310.), then was arrested and kept in its
place, and if standing between the axial and equatorial positions,
was revulsed when the battery current was interrupted, exhibit-
ing effects equal to those of copper (2315.). Many other plates
were tried with precisely the same result.
2522. When this plate (2521.) was placed in the field of in-
tense power between two conical magnetic poles, it exhibited
the same phænomena; but notwithstanding the arresting action,
it moved slowly until it stood in the equatorial position; a
result which was probably due to the exertion of both magne-
crystallic and diamagnetic force. When the plate was suspended
with its planes horizontal, the arresting and revulsive actions
were gone; for the induced currents which before caused them
could not now exist in the necessary vertical plane; further, it
had no setting power, which showed that there was no axis of
magnecrystallic force in the length or breadth of the plates.
2523. Other plates were then found able to produce mixed
effects, and those in different degrees. Thus, some, like the first,
vibrated freely, pointed well, and presented no indication of the
arrest and revulsive phænomena. Others vibrated sluggishly,
set well, and showed a tendency to be arrested. Others pointed
well, going up to their place with a dead set, but moving as if
in a fluid; or, if the magnetic force were taken off before the
piece had settled, it was revulsed feebly: and others were caught
at once, did not set (within the time of my observation), and
were strongly revulsed.
2524. Finally, a careful investigation, carried on by means
both of the horse-shoe (2485.) and the great electro-magnet
(2247.), made the cause of these differences in the effects ap-
parent.
2525. It may be observed, in the first place, that sometimes a
plate of antimony being selected (2517.), having planes very
OCT. 1848.] Currents induced in crystals of antimony.
103
bright and perfect in their appearance, and, therefore, giving
reason to think that it may point well in the magnetic field,
when submitted to the horse-shoe magnet does not do so; but
points obliquely, feebly, and perhaps in two undiametral posi-
tions. This is, I have no doubt, because the crystallization is
complicated and confused. Such a plate, if it be sufficiently
broad and long (i. e. not less than a quarter or one-third of an
inch), when submitted to the electro-magnet, will show the
arresting (2310.) and revulsive (2315.) action well.
2526. In the next place, we have to remember that, for the
development of the induced currents which cause the arresting
and revulsive action, the plate must have certain sufficient
dimensions in a vertical plane (2329.). The currents occur in
the mass and not round the separate particles (2329.), and the
resultant of the magnetic lines of force passing through the sub-
stance, is the axis round which these curreuts are produced.
Hence the reason why the effect does not occur with plates sus-
pended in the horizontal position, which yet produce it well in
the vertical position; a result which a disc half an inch in
diameter of thin foil or plate, being copper, silver, gold, tin, or
almost any malleable metal, will show; though the best con-
ductors are the fittest for the purpose. Now this condition is
of no consequence in respect of magnecrystallic action, and a
narrow plate has as much force as a broad one, having the same
mass. The first plate that I happened to select (2517.) was well
crystallized, thick and narrow; hence it was favourable for
magnecrystallic action, unfavourable to the arresting and revul-
sive action, and showed no signs, comparatively, of the latter.
2527. When a broad and well-crystallized plate is obtained,
then both sets of effects appear: thus, if the plate is revolving
when the magnetic force is brought into action, it quickens its
velocity for an instant, then is stopped; and if the magnetic
force is at once taken off, it is revulsed, exactly as a piece of
copper would be (2315.). But if the magnetic force be continued,
it will then be perceived that the stop is only apparent; for the
plate moves, though with a greatly reduced velocity, and con-
tinues to move until it has taken up its magnecrystallic position.
It moves as if in a thick fluid. Hence the magnecrystallic force
is there and produces its full effect; and the reason why the
appearances have changed is, that the very motion which the
104
[SERIES XXII.
Magnecrystallic action.
force tends to give, and does give to the mass, causes those
magneto-electro currents (2329.) which by their mutual action
with the magnet tends to stop the motion; and therefore its
slowness and the final dead set (2512. 2523.).
2528. A magnet which is weaker (as the horse-shoe instru-
ment described (2485.)) produces the currents by induction in
a much weaker degree, and yet manifests the magnecrystallic
power well; hence it is more favourable, under certain circum-
stances, for such investigations; as it helps to distinguish the
one effect from the other.
2529. It will readily be seen that plates, whether of the same
metal or of different metals, cannot, even roughly, be com-
pared with each other as to magnecrystallic force by their vibra-
tions; for under the influence of these induced currents, plates
of the same magnecrystallic force oscillate in very different
manners. I took a plate, and by cement (2458.) attached selected
paper to its faces, and then observed how it acted in the mag-
netic field; it set slowly, and it showed the arresting and revul-
sive effects (2521.) I then pressed it in a mortar, so as to
break it up into many parts, which still kept their place; and
now it set more freely and quickly, and showed very little of the
revulsive action.
2530. Though the indication by vibration is thus uncertain,
the torsion force still remains to us, I believe, a very accurate
indication of the strength of the set (2500.), and, therefore, of
the degree of the magnecrystallic force; and though the sus-
pending silk fibre may give way a little, a glass thread, accord-
ing to Ritchie's suggestion, would answer perfectly.
2531. Antimony must be a good conductor of electricity in
the direction of the plates of the crystals, or it would not give,
so freely, these indications of revulsive action. The groups of
crystals of antimony (2508.) showed the effect in such a degree,
as to make me think that the constituent cubes possessed the
power nearly equally in all directions. A piece of finely cry-
stallized or granular antimony does not, however, show it in the
same proportion; from which it would seem as if an effect equi-
valent in some degree to that of division occurs, either at the
meeting of two incongruous crystals, or between the contiguous
plates of the crystals, and affects the conducting power in these
directions.
OCT. 1848.]
105
Crystalline polarity of arsenic.
ness.
¶ iii. Crystalline Polarity of Arsenic.
2532. A mass of the metal arsenic exhibiting crystalline
structure (2480.), was broken up, and several plates selected
from the fragments, having good cleavage plane surfaces, about
0.3 of an inch in length, 0·1 inch in width, and 0.03 in thick-
These, when suspended opposite one conical pole, proved
to be perfectly diamagnetic; and when before it or between two
poles strongly magnecrystallic. I have a pair of flat-faced poles
with screw-holes in the centre of the faces, and these so much
weaken the intensity of the lines of magnetic force about the
middle of the field, when the faces are within half an inch of
each other, that a cylinder of granular bismuth 0-3 in length
sets axially, or from pole to pole (2384). But with the plates
of arsenic between the same poles there was no tendency of this
kind; so much was the magnecrystallic force predominant over
the diamagnetic force of the substance.
2533. When the plates of arsenic were suspended with their
planes horizontal, then they did not point at all between the
flat-faced poles. Any inclination of the planes of the horizontal
line produced pointing, with more or less force as the planes
approached more or less to the vertical position, exactly in the
manner already described in relation to bismuth and antimony
(2482. 2518.).
2534. Thus, arsenic with bismuth and antimony are found to
possess the magnecrystallic force or condition.
Royal Institution,
September 23, 1848.
M
106
TWENTY-SECOND SERIES (continued)¹.
§ 28. On the crystalline polarity of bismuth and other bodies,
and on its relation to the magnetic and electric form of force
(continued). iv. Crystalline condition of various bodies,
¶ v. Nature of the magnecrystallic force, and general obser-
vations.
Received October 31,-Read December 7, 1848.
¶iv. Crystalline condition of various bodies.
2535. ZINC.-Plates of zinc broken out of crystallized masses
gave irregular indications, and, being magnetic from the impu-
rity in them, the effects might be due entirely to that circum-
stance. Pure zinc was thrown down electro-chemically on
platina from solutions of the chloride and the sulphate. The
former occurred in ramifying dendritic associations of small cry-
stal; the latter in a compact close form. Both were free from
magnetic action and freely diamagnetic, but neither showed any
trace of the magnecrystallic action.
2536. Titanium².-Some good crystals of titanium obtained
from the bottom of an iron furnace, were cleansed by the alter-
nate action of acids and fluxes until as clear from iron as I could
procure them. They were bright, well-formed and magnetic
(2371.), and contained iron, I think, diffused through their whole
mass, for nitromuriatic acid, by long boiling, continually re-
moved titanium and iron from them. These crystals had a cer-
tain magnetic property which I am inclined to refer to their
crystalline condition. When between the poles of the electro-
magnet, they set; and when the electric current was discon-
tinued, they still set between the poles of the enfeebled magnet
as they did before. If left to itself, a crystal always took the
same position, showing that it was constantly rendered magnetic
Philosophical Transactions, 1849, p. 19.
1
2 For these and many other crystals I am indebted to the kindness of Sir
Henry T. De la Beche and Mr. Tennant.
OCT. 1848.] Magnecrystallic action-copper-tin.
107
in the same direction. But if a crystal was placed and kept in
another position between the magnetic poles whilst the electric
current was on, and afterwards the current suspended, and then
the crystal set free, it pointed between the poles of the enfeebled
magnet in this new direction; showing that the magnetism was
in a different direction in the body of the crystal to that which
it had before. If now the magnet were reinvigorated by the
electric current, the crystal instantly spun round and took a
magnetic state in the first or original direction. The crystals
could in fact become magnetized in any direction, but there was
one direction in which they could be magnetized with a facility
and force greater than in any other. From the appearances I
am inclined to refer this to the crystalline condition, but it may
be due to an irregular diffusion of iron in the masses of titanium.
The crystals were too small for me to make out the point clearly.
2537. Copper.-I selected some good crystals of native cop-
per, and, having carefully separated them from the mass, ex-
amined them in respect of their magnecrystallic force. At the
horse-shoe magnet (2486.) they gave no signs of such power,
whatever the direction in which they were suspended, but stood
in any position; and any degree of torsion, however small, ap-
plied at the upper extremity of the suspending filament, was
obeyed at once, and to the full extent, by the crystal beneath.
When subjected to the electro-magnet, the phænomena of arrest
and revulsion were produced (2513. 2310.), as was to be ex-
pected. If after the arrest the magnetic force were continued,
there was no slow advance of the crystal up to a distinct point-
ing position (2512.); it stood perfectly still in any position. So
there is no evidence of magnecrystallic action in this case.
.
2538. Tin.-I selected from block and grain tin some pieces
which appeared, by their external forms and the surface pro-
duced under the action of acids, to have a regular crystalline
structure internally; and, cutting off portions, carefully sub-
mitted them to the power of the magnets, but there was no ap-
pearance of any magnecrystallic phænomena. Indications of the
arresting and revulsive actions were presented, and also of dia-
magnetic force, but nothing else. I also examined some crystals
of tin obtained by electro-chemical deposition. They were pure
and diamagnetic; they were arrested and revulsed, but they
showed no signs of magnecrystallic action.
108
Magnecrystallic action. [SERIES XXII.
2539. Lead.-Lead was crystallized by fusion, partial solidifi-
cation, and pouring off (2457.), and some very fair crystals,
having the general form of octohedra, were obtained. Observed
at the magnets, these were arrested and revulsed feebly, but pre-
sented no magnecrystallic phænomena. Some fine crystalline
plates of lead obtained electro-chemically from the decomposi-
tion of the acetate by zinc, were submitted to the magnet: they
were pure, diamagnetic, and were arrested and revulsed, but
presented no appearance of magnecrystallic action.
2540. Gold. Three fine large crystals of gold were examined.
They were diamagnetic, and easily arrested (2310. 2340.); the
revulsion did not take place, because of their octohedral or orbi-
cular form. They presented no magnecrystallic indications.
2541. Tellurium.-Two fractured pieces of this substance,
presenting large and parallel planes of cleavage, were examined :
both pointed, and the greatest length was across the axial line
between flat-faced poles (2463.). I think the effects were in part,
if not altogether, due to the magnecrystallic state of the substance;
but I do not think the evidence was quite conclusive.
2542. Iridium and Osmium alloy.-The native grains of iri-
dium and osmium are often flat, presenting two planes looking
like crystal planes, which are parallel to each other even when
the grains are thick. Some of the largest and most crystalline
were selected, and, after ignition with flux and digestion in
nitromuriatic acid, were examined at the magnet. Some were
more magnetic than others, being attracted; others were very
little magnetic: the latter were selected and examined more care-
fully. These all pointed with great readiness and force, com-
paratively speaking; for they were not above one-fifteenth of an
inch long, and yet they set freely when the magnetic poles were
3 or 4 inches apart. The faces of the crystalline particles
were always towards the poles, and their length consequently
not in but across the axial line; and this was true whether the
distance between the poles was small or great, or whether flat-
faced or conical poles were used. I believe they were magne-
crystallic.
2543. Fusible metal. - Crystals of fusible metal (2457.)
pointed, but the crystals, which were apparently quadrangular
plates or prisms, were not good, and the evidence not clear and
distinct,
Ост. 1848.]
109
Wires, &c.—Sulphate of iron.
2544. Wires.-I thought it possible that thin wires, which by
the action of acids exhibited fibrous arrangements, might have
their particles in a state approaching to the crystalline condition,
and therefore submitted bundles of platinum, copper, and tin
wire to the action of the magnet; but no indications of magne-
crystallic action appeared.
2545. I submitted several metallic compounds to the power of
the magnet, applied so as to develope any indication of the
magnecrystallic phænomena. Galena, native cinnabar, oxide of
tin, sulphuret of tin, native red oxide of copper, Brookite or
oxide of titanium, iron pyrites, and also diamond, fluor spar,
rock-salt and boracite, being all well crystallized and diamagnetic,
presented no evidence of the magnecrystallic force. Native and
well-crystallized sulphuret of copper, sulphuret of zinc, cobalt
glance and leucites were magnetic. Arsenical iron, specular iron,
and magnetic oxide of iron were still more so. I could not in
any of them distinguish any magnetic results due to crystalli-
zation.
2546. On examining magnetic salts, several of them presented
very striking magnecrystallic phænomena. Thus, with sulphate
of iron, the first crystal which I employed was suspended with
the magnecrystallic axis vertical, and it presented no particular
appearances; only the longest horizontal direction went into
the magnetic axis pointing feebly. But on turning the piece
90° (2470.), instantly it pointed with much force, and the greatest
length went equatorially. The crystal was compounded of
superposed flat crystals or plates, and the magnecrystallic axis.
went directly across these; it was easy therefore, after one or
two experiments, to tell beforehand how the crystal should be
suspended, and how it would point. Whether the crystals were
long, or oblique, or irregular, still the magnecrystallic force pre-
dominated and determined the position of the crystal, and this
happened whether pointed or flat poles were used, and whether
they were near together or far asunder. The magnecrystallic
axis is perpendicular, or nearly so, to two of the sides of the
rhomboidal prism. I have some small prismatic crystals of
which the length is nearly three times the width of the prism ;
but when both the length and the magnecrystallic axis are
horizontal, no power of the magnet, or shape, or position of the
poles, will cause the length to take the axial direction, for that is
110
[SERIES XXII.
Magnecrystallic action.
constantly retained by the magnecrystallic axis, so greatly does
it predominate in power over the mere magnetic force of the
crystal. Yet this latter is so great as at times to pull the suspend-
ing fibre asunder when the crystal is above the poles (2615.).
2547. Sulphate of nickel.-When a crystal of sulphate of
nickel was suspended in the magnetic field, its length set
axially. This might be due, either to mere magnetic force, or
partly to magnecrystallic force. Therefore I cut a cube out of
the crystal, two faces of which were perpendicular to the length
of the original prism. This cube pointed well in the magnetic
field, and the line coincident with the axis of the prism was that
which pointed axially, and represented the magnecrystallic axis.
Even when the cube was reduced in this direction and con-
verted into a square plate whose thickness coincided with the
magnecrystallic axis, it pointed as well as before, though the
shortest dimensions of the piece were now axial.
2548. The persulphate of ammonia and iron, and the sulphate
of manganese, did not give any indication of magnecrystallic
phænomena; the sulphate of ammonia and manganese I think
did, but the crystals were not good. The sulphate of potassa
and nickel is magnecrystallic. All three salts were magnetic.
2549. Thus it seems that other bodies besides bismuth, anti-
mony and arsenic, present magnecrystallic effects. Amongst
these are the alloy of iridium and osmium, probably tellurium
and titanium, and certainly the sulphates of iron and nickel.
Before leaving this part of the subject, I may remark that this
property has probably led me into error at times on a former
occasion (2290.). A mistake with arsenic (2383.) might very
easily arise from this cause.
¶v. On the nature of the magnecrystallic force, and general
observations ¹.
1
2550. The magnecrystallic force appears to be very clearly
distinguished from either the magnetic or diamagnetic forces, in
that it causes neither approach nor recession; consisting not in
attraction or repulsion, but in its giving a certain determinate
position to the mass under its influence, so that a given line in
relation to the mass is brought by it into a given relation with
the direction of the external magnetic power.
See onwards, 2836, &c.
OCT. 1848.] Nature of the magnecrystallic force.
111
2551. I thought it right very carefully to examine and prove
the conclusion, that there was no connexion of the force with
either attractive or repulsive influences. For this purpose I
constructed a torsion-balance, with a bifilar suspension of
cocoon silk, consisting of two bundles of seven filaments each,
4 inches long and one-twelfth of an inch apart; and sus-
pended a crystal of bismuth (2457.) from one end of the lever,
so that it might be fixed and retained in any position. This
balance was protected by a glass case, outside of which the
conical terminal of one pole of the great electro-magnet (2247.)
was adjusted, so as to be horizontal, at right angles to the
lever of the torsion-balance, and in such a position that the
bismuth crystal was in the prolongation of the axis of the pole,
and about half an inch from its extremity when all was at rest.
The other pole, 4 inches off, was left large so that the lines
of magnetic force should diverge, as it were, and rapidly dimi-
nish in strength from the end of the conical pole. The object
was to observe the degree of repulsion exerted by the magnet on
the bismuth, as a diamagnetic body, either by the distance to
which it was repelled, or by the torsion required to bring it
back to its first position; and to do this with the bismuth,
having its magnecrystallic axis at one time axial or parallel
to the lines of magnetic force, at another equatorial, observing
whether any difference was produced.
2552. The crystal was therefore placed with its magnecry-
stallic axis first parallel to the lines of magnetic force, and then
turned four times in succession 90° in a horizontal plane, so as
to observe it under all positions of the magnecrystallic axis; but
in no case could any difference in the amount of the repulsion
be observed. In other experiments the axis was placed oblique,
but still with the same result. If there be therefore
ence it must be exceedingly small¹.
any differ-
2553. A corresponding experiment was made, hanging the
crystal as a pendulum by a bifilar suspension of cocoon silk
30 feet in length, with the same result.
2554. Another very striking series of proofs that the effect is
not due to attraction or repulsion, was obtained in the following
manner. A skein of fifteen filaments of cocoon silk, about 14
inches long, was made fast above, and then a weight of an
¹ See now 2839, &c.
112
[SERIES XXII.
Magnecrystallic action.
ounce or more hung to the lower end; the middle of this skein
was about the middle of the magnetic field of the electro-magnet,
and the square weight below rested against the side of a block
of wood, so as to give a steady, silken vertical axis, without
swing or revolution. A small strip of card, about half an inch
long, and the tenth of an inch broad, was fastened across the
middle of this axis by cement; and then a small prismatic
crystal of sulphate of iron about 0·3 of an inch long, and 0·1 in
thickness, was attached to the card, so that the length, and also
the magnecrystallic axis, were in the horizontal plane; all the
length was on one side of the silken axis, so that as the crystal
swung round, the length was radius to the circle described, and
the magnecrystallic axis parallel to the tangent.
2555. This crystal took a position of rest due to the torsion
force of the suspending skein of silk; and the position could be
made any one that was desired, by turning the weight below.
The torsion force was such, that, when the crystal was made to
vibrate on its silken axis, forty complete (or to and fro) vibrations
were performed in a minute.
2556. When the crystal was made to
stand between the flat-faced poles (2463.)
obliquely, as in fig. 4, the moment the mag-
net was excited it moved, tending to stand
with its length equatorial or its magnecry-
stallic axis parallel to the lines of magnetic
Fig. 4.
force. When the N pole was removed, and the experiment re-
peated, the same effect took place, but not as strongly as before;
and when, finally, the pole S was brought as near to the crystal
as it could be, without touching it, the same result occurred, and
with more strength than in the last case.
2557. In the two latter experiments, therefore, the crystal of
sulphate of iron, though a magnetic body and strongly attracted
by such a magnet as that used, actually receded from the pole
of the magnet under the influence of the magnecrystallic con-
dition.
2558. If the pole S be removed and that marked N be retained
for action on the crystal, then the latter approaches the pole,
urged by both the magnetic and magnecrystallic forces; but if
the crystal be revolved 90° to the left, or 180° to the right, round
the silken axis, so as to come into the contrary or opposite posi-
tion, then this pole repels or rather causes the removal to a
OCT. 1848.] Magnecrystallic force-peculiarities.
Ост.
113
distance of the crystals, just as the former did. The experiment
requires care, and I find that conical poles are not good; but
with attention I could obtain the results with the utmost readiness.
2559. The sulphate of iron was then replaced by a crystalline
plate (2480.) of bismuth, placed as before on one side of the silk
suspender, and with its magnecrystallic axis horizontal. Making
the position the same as that which the crystal had in relation
to the N pole in the former experiment (2556.), so that to place
its axis parallel to the lines of magnetic force it must approach
this magnetic pole, and then throwing the magnet into an active
state, the bismuth moved accordingly, and did approach the
pole, against its diamagnetic tendency, but under the influence
of the magnecrystallic force. The effect was small but distinct.
2560. Anticipating, for a short time, the result of the reasoning
to be given further on (2607.), I will describe a corresponding
effect obtained with the red ferro-prussiate of potassa. A crystal
of this salt had its acute linear angles ground away, so as to
convert it into a plate with faces parallel to the plane of the optic
axis, and was then made to replace the plate of bismuth. Being
in the position before represented (2556.), and the magnet ren-
dered active, it moved, placing the plane of the optic axis equa-
torially, as Plücker describes. When the pole N was removed
and S brought up to the crystal, the same motion occurred, the
crystal retreating from the pole; and when S pole was removed
and N brought towards the crystal, it moved as before, the
whole body now approaching towards the pole. On inclining
the crystal the other way, i. e. making its place on the other side
of the equatorial line, the S pole caused it to approach and the
N pole to recede. So that the same pole seemed able either to
attract or repel the same side of the crystal; and either pole
could be made to show this apparent attractive and repulsive
force.
2561. Hence a proof that neither attraction nor repulsion
causes the set, or governs the final position of the body, or of
any of the bodies whose movements are due to the same cause
(2607.).
2562. This force then is distinct in its character and effects
from the magnetic and diamagnetic forms of force. On the
other hand, it has a most manifest relation to the crystalline
structure of the bismuth and other bodies; and therefore to the
VOL. III.
I
114
[SERIES XXII.
Magnecrystallic force ;
molecules, and to the power by which these molecules are able to
build up the crystalline masses. It appears to me impossible to
conceive of the results in any other way than by a mutual re-
action of the magnetic force, and the force of the particles of the
crystal on each other: and this leads the mind to another con-
clusion, namely, that as far as they can act on each other they
partake of a like nature; and brings, I think, fresh help for the
solution of that great problem in the philosophy of molecular
forces, which assumes that they all have one common origin
(2146.).
2563. Whether we consider a crystal or a particle of bismuth,
its polarity has a very extraordinary character, as compared
with the polarity of a particle in the ordinary magnetic state, or
when compared with any other of the dual conditions of phy-
sical force; for the opposite poles have like characters; as is
shown first of all by the diametral pointing of the masses
(2461.), and also by the physical characters and relations of
crystals generally. As the molecules lie in the mass of a cry-
stal, therefore, they can in no way represent, or be represented
by, the condition of a parcel of iron filings between the poles of
a magnet, or the particles of iron in the keeper when in its
place; for these have poles of different names and quality ad-
hering together, and so giving a sort of structure; whereas, in
the crystal, the molecules have poles of like nature towards each
other, for, so to say, all the poles are alike.
2564. As made manifest by the phænomena, the magnecry-
stallic force is a force acting at a distance; for the crystal is
moved by the magnet at a distance (2556. 2574.), and the
crystal also can move the magnet at a distace. To produce
the latter result, I converted a steel bodkin, about 3 inches
long, into a magnet; and then suspended it perpendicularly by
a single cocoon filament 4 inches long, from a small horizon-
tal rod, which again was suspended by its centre and another
length of cocoon filament, from a fixed point of support. In
this manner the bodkin was free to move on its own axis, and
could also describe a circle about 1 inch in diameter; and the
latter motion was not hindered by any tendency of the needle to
point under the earth's influence, because it could take any
position in the circle and yet remain parallel to itself.
2565. A support perfectly free from magnetic action was con-
OCT. 1848.]
115
its nature and peculiarities.
structed of glass rod and copper wire, which passing through
the bottom of the stand, and being in the prolongation of the
upper axis of motion, was concentric with the circle which the
little magnet could describe; its height was such that it could
sustain a crystal or any other substance level with the pole at
the lower end of the needle, and in the centre of the small circle
in which the latter could revolve around it. By moving the
lower end of the support, the upper end also could be made to
approach to or recede from the magnet. The whole was
covered with a glass shade, and when left to become of uniform
temperature, and at rest, the needle magnet was found to take
up a constant position under the torsion force of the suspending
filaments. Further, any rotation of the glass and copper wire
support did not produce a final change in the position of the
magnet; for though the motion of the air would carry the
magnet away, it returned, ultimately, to the same spot. When
removed from this spot, the torsion force of the silk suspension
made the system oscillate; the time of a half oscillation, or a
passage in one direction, was about three minutes, and of a
whole oscillation therefore six minutes.
.
2566. When a crystal bismuth was fixed on the support with
the magnecrystallic axis in a horizontal direction, it could be
placed near the lower pole of the magnet in any position, and
being then left for two or three hours, or until by repeated ex-
amination the magnetic pole was found to be stationary, the
place of the latter could be examined, and the degree and
direction in which it was affected by the bismuth ascertained.
Extreme precaution was required in these observations, and all
steel or iron things, as spectacles, knives, keys, &c., had to be dis-
missed from the observer before he entered the place of experi-
ment; and glass candlesticks were used. The effect produced was
but small, but the result was, that if the direction of the magne-
crystallic axis made an angle of 10°, 20°, or 30° with the
line from the magnetic pole to the middle of the bismuth
crystal, then the pole followed it, tending to bring the two lines
into parallelism; and this it did whichever end of the magne-
crystallic axis was towards the pole, or whichever side it was in-
clined to. By moving the bismuth at successive times, the
deviation of the magnetic pole could be carried up to 60°.
I 2
116
[SERIES XXII.
Magnecrystallic force ;
2567. The crystal of bismuth therefore is able to react upon
and affect the magnet at a distance.
2568. But though it thus take up the character of a force
acting at a distance, still it is due to that power of the particles
which makes them cohere in regular order, and gives the mass
its crystalline aggregation; which we call at other times the
attraction of aggregation, and so often speak of as acting at
insensible distances.
2569. For the further explication of the nature of this force,
I proceeded to examine the effect of heat on crystals of bismuth
when in the magnetic field. The crystals were suspended
either by platina or fine copper wire, and heated, sometimes by
a small spirit-lamp flame applied directly, sometimes in an oil-
bath placed between the magnetic poles; and though the up-
ward currents of air and fluid were strong in these cases, they
were far too weak to overcome the set caused by magnecrystallic
action, and helped rather to show when that action was weakened
or ceased.
2570. When the temperature was gradually raised in the air
the bismuth crystal continued to point, until of a sudden it be-
came indifferent in that respect, and turned in any direction
under the influence of the rising currents of air. Instantly
removing the lamp flame the bismuth revolved slowly and regu-
larly, as if there were no tendency to take up one position more
than another, or no remains of magnecrystallic action; but in a
few seconds, as the temperature fell, it resumed its power of
pointing; and, apparently, in an instant and with full force, and
the pointing was precisely in the same direction as at first. On
examining the crystal carefully, its external shape and its
cleavage showed that, as a crystal, it was unchanged; but the
appearance of a minute globule of bismuth, which had exuded
upon the surface in one place, showed that the temperature had
been close upon the point of fusion.
2571. The same result occurred in the oil-bath, except that
as removing the lamp from the oil-bath did not immediately
stop the addition of heat to the bismuth, so more of the latter
was melted; and about one-fourth of the metal appeared as
a drop hanging at the lower part. Still the whole mass lost its
power at the high temperature, and the power was regained in
OCT. 1848.]
117
effect of heat-position.
the same direction, but in a less degree on cooling. The dimi-
nished force was accounted for on breaking up the crystal;
for the parts which had been liquefied were now crystallized
irregularly, and therefore, though active at the beginning of the
experiment, were neutral at the end.
2572. As heat has this effect, the expectation entertained
(2502.) of crystallizing bismuth regularly in the magnetic field
is of course unfounded; for the metal must acquire the solid
state, and be lowered through several degrees probably, before
it can exhibit the magnecrystallic phænomena. If heat has the
same effect on all bodies prior to their liquefaction, then, of
course, such a process can be applied to none of them.
2573. A crystallized piece of antimony was subjected to the
same experiment, and it also lost its magnecrystallic power
below a dull red heat, and just as it was softening so as to take
the impression of the copper loop in which it was hung. On
being cooled it did not resume its former state, but then became
ordinarily magnetic and pointed. This I conclude arose from
iron affected by the flame and heat of the spirit-lamp; for, as
the heat was high enough to burn off part of the antimony and
make it rise in fumes of oxide of antimony, so this might set a
certain portion of iron free which the carbon and hydrogen of
the flame would leave in a very magnetic state (2608.).
Fig. 5.
2574. In further elucidation of the mutual action of the bis-
muth and the magnet, the bismuth was suspended, as already
described (2551.), on the bifilar balance, but so turned, that its
magnecrystallic axis, being horizontal, was not parallel or per-
pendicular to the arm of the lever, but
a little inclined, as in the figure (5.),
where 1 represents the crystal of
bismuth attached to the balance arm b,
the axis of which is so placed that the
crystal can swing through the various
positions 1, 2, 3, 4; S is the pole of
the magnet separated only by the glass
of the shade. It is manifest, that in

S
סא
position 1 the magnecrystallic axes and the lines of magnetic
force are parallel to each other; whereas in the positions 2, 3, 4,
they are oblique. When the apparatus was so arranged that
the crystal of bismuth rested at 1, the superinduction of the full
118
[SERIES XXII.
Magnecrystallic force;
magnetic force sent it towards 4; a result of diamagnetic action.
When however the bismuth had its place of rest at 2, the
development of the magnetic force did not make it pass to-
wards 3, in accordance with the former result, but towards 1,
which is usually attained and often passed, going a little towards
4. In this case the magnecrystallic and the diamagnetic forces
were opposed to each other, and the former gained the advan-
tage up to position 1.
2575. But though the crystal of bismuth in these cases moves
across the lines of force in the magnetic field, it cannot be ex-
pected to do so in a field where the lines are parallel and of
equal force, as between flat-faced poles; the crystal being re-
strained so as to move only parallel to itself; for under such
circumstances the forces are equal in both directions and on
both sides of the mass, and the only tendency the crystal has,
in relation to its magnecrystallic condition, is to turn round a
vertical axis until it is in its natural position in the magnetic
field.
2576. A most important question next arises in relation to
the magnecrystallic force, namely, whether it is an original force
inherent in the crystal of bismuth, &c., or whether it is induced
under the magnetic and electric influences. When a piece of
soft iron is held in the vicinity of a magnet it acquires new
powers and properties; some persons assume this to depend
upon the development by induction of a new force in the iron
and its particles, like in nature to that in the inducing magnet:
by others it is considered that the force originally existed in the
particles of the iron, and that the inductive action consisted only
in the arrangement of all the elementary forces in one general
direction. Applying this to the crystal of bismuth, we cannot
make use of the latter supposition in the same manner; for all
the particles are arranged beforehand, and it is that very
arrangement of them and their forces which gives the bismuth
its power. If the particles of a substance be in the heteroge-
neous condition possessed by those of the iron in its unmagnetic
state, then the magnetic force may develope the magnetic, and
also the diamagnetic condition, which probably is a condition of
induction; but it does not appear at once, that it can develope
a state of the kind now under consideration.
OCT. 1848.]
119
condition of the particles.
2577. That the particles hold their own to a great extent in
all the results is manifest, by the consideration that they have
an inherent power or force, the crystalline force, which is so
unchangeable that no treatment to which they can be subjected
can alter it; that it is this very force which, placing the particles
in a regular position in the mass, enables them to act jointly on
the magnet or the electric current, and affect or be affected by
them; and that if the particles are not so arranged, but are in
all directions in the mass, then the sum of their forces externally
is nothing, and no inductive exertion of the magnet or current
can develope the slightest trace of the phænomena.
.
2578. And that particles even before crystallization can act in
some degree at a distance, by virtue of their crystallizing force,
is, I think, shown by the following fact. A jar containing
about a quart of solution of sulphate of soda, of such strength as
to crystallize when cold by the touch of a crystal of the salt or
an extraneous body, was left, accidentally, for a week or more
unattended to and undisturbed. The solution remained fluid;
but on the jar being touched, crystallization took place through-
out the whole mass at once, producing clear, distinct, trans-
parent plates, which were an inch or more in length, up to
half an inch in breadth; and very thin, perhaps about the one-
fiftieth or one-sixtieth of an inch. These were all horizontal,
and of course parallel to each other; and I think, if I remember
rightly, had their length in the same direction; and they were
alike in character, and, apparently, in quantity in every part of
the jar. They almost held the fluid in its place when the jar
was tilted; and when the liquid was poured off presented a
beautiful and uniform assemblage of crystals. The result per-
suaded me, at the time, that though the influence of a particle
in solution and about to crystallize, must be immediately and
essentially upon its neighbours, yet that it could exert an in-
fluence beyond these, without which influence, the whole mass of
solution could hardly have been brought into such a uniform
crystallizing state. Whether the horizontality of the plates can
have any relation to the almost vertical lines of magnetic force,
which from the earth's magnetism was pervading the solution
during the whole time of its rest, is more than I will venture to
say.
120
[SERIES XXII.
Magnecrystallic force ;
I
2579. The following are considerations which bear upon this
great question (2576.) of an original or an induced state.
2580. In the first place, the bismuth carries off no power or
particular state from the magnetic field, able to make it affect a
magnet (2504.); so that if the condition acquired by the crystal
be an induced condition, it is probably a transient one, and con-
tinues only whilst under induction. The fact, therefore, though
negative in its evidence, agrees, as far as it tells, with that sup-
position.
.
2581. In the next place, if the effect were wholly due, as far
as the crystal is concerned, to an original power inherent in the
mass, we might expect to find the earth's magnetism, or any
weak magnet, affecting the crystal. It is true that a weak mag-
netic force ought to induce any given condition in a crystal of
bismuth just as well as a stronger, only proportionally. But if
the given condition were inherent in the crystal, and did not
change in its amount by the degree of magnetic force to which
it was subjected, then a weak magnetic force ought to act more
decidedly on the bismuth than it would do if the condition were
induced in the bismuth, and only in proportion to its own
force. Whatever the value of the argument, I was induced
to repeat the experiment of the earth's influence (2505.) very
carefully, and by sheltering the suspended crystals in small
flasks or jars contained within the larger covering jar, and
making the experiment in an underground place of uniform and
constant temperature, I was able to exclude every effect of
currents of air, so that the crystals obeyed the slightest degree
of torsion given to the suspending fibre by the index above.
Under these circumstances I could obtain no indications of
pointing by the earth's action, either with crystals of bismuth
or of sulphate of iron. Perhaps at the equator, where the lines
of force are horizontal, they might be rendered sensible.
2582. In the third place, assuming that there is an original
force in the crystals and their molecules, it might be expected
that they would show some direct influence upon each other,
independent of the magnetic force, and if so the best possible
argument would be thus obtained that the force which is ren-
dered manifest in the magnetic field was inherent in them. But
on placing a large crystal with its magnecrystallic axis horizontal
Ост. 1848.]
121
induced or inherent.
under a smaller and suspended one, or side by side with it, I
could procure no signs of mutual action; even when the ap-
proximated parts of the crystals were ground or dissolved away,
so as to let the two masses come as near as possible to each
other, having large surfaces at the smallest possible distance.
Extreme care is required in such experiments (2581.), or else
many results are produced which seem to show a mutual affec-
tion of the bodies.
2583. Neither could I find any trace of mutual action between
crystals of bismuth, or of sulphate of iron, when they were both
in the magnetic field, the one being freely suspended and the
other brought in various positions near to it.
2584. From the absence therefore or extreme weakness of any
power in the crystals to affect each other, and also from the
action of heat which can take away the power of the crystal
before it has lost its mere crystalline condition (2570.), I am
induced to believe that the force manifested in the crystal when
in the magnetic field, which appears by external actions, and
causes the motion of the mass, is chiefly and almost entirely
induced, in a manner, subject indeed to the crystalline force, and
finally additive to it; but at the same time exalting the force
and the effects to a degree which they could not have approached
without the induction.
2585. In that case the word magnetocrystallic ought pro-
bably to be applied to this force, as it is generated or deve-
loped under the influence of the magnet. The word magnecry-
stallic I used purposely to indicate that which I believed be-
longed to the crystal itself, and I shall still speak of the magne-
crystallic axis, &c. in that sense.
2586. This force appears to me to be very strange and striking
in its character. It is not polar, for there is no attraction or re-
pulsion. Then what is the nature of the mechanical force which
turns the crystal round (2460.), or makes it affect a magnet
(2564.)? It is not like a turning helix of wire acted on by the
lines of magnetic force; for there, there is a current of electricity
required, and the ring has polarity all the time and is powerfully
attracted or repelled'.
Perhaps these points may find their explication hereafter in the action of
contiguous particles (1663. 1710. 1729. 1735. 2443.).
122
[SERIES XXII.
Magnecrystallic force;
2587. If we suppose for a moment that the axial position is
that in which the crystal is unaffected, and that it is in the
oblique position that the magnecrystallic axial direction is
affected and rendered polar, giving two tensions pulling the
crystal round, then there ought to be attractions at these times,
and an obliquely presented crystal ought to be attracted by a
single pole, or the nearest of two poles; but no action of this
kind appears.
2588. Or we might suppose that the crystal is a little more
apt for magnetic induction, or a little less apt for diamagnetic
induction, in the direction of the magnecrystallic axis than in
other directions. But, if so, it should surely show polar at-
tractions in the case of the magnetic bodies, as sulphate of iron
(2557. 2583.); and in the case of diamagnetic bodies, as bismuth,
a difference in the degree of repulsion when presented with the
magnecrystallic axis parallel and perpendicular to the lines of
magnetic force (2552.); which it does not do.
2589. I do not remember heretofore such a case of force as
the present one, where a body is brought into position only,
without attraction or repulsion.
2590. If the power be induced, it must be like, generally, to
its inducing predominants; and these are, at present, the mag-
netic and electric forces. If induced, subject to the crystal-
line force (2577.), it must show an intimate relation between it
and them. How hopeful we may be, therefore, that the results
will help to throw open the doors which may lead us to a full
knowledge of these powers (2146.), and the combined manner in
which they dwell in the particles of matter, and exert their in-
fluence in producing the wonderful phænomena which they
present!
2591. I cannot resist throwing forth another view of these
phænomena which may possibly be the true one. The lines of
magnetic force may perhaps be assumed as in some degree re-
sembling the rays of light, heat, &c.; and may find difficulty in
passing through bodies, and so be affected by them, as light is
affected. They may, for instance, when a crystalline body is
interposed, pass more freely, or with less disturbance, through it
in the direction of the magnecrystallic axis than in other direc-
tions. In that case, the position which the crystal takes in the
magnetic field with its magnecrystallic axis parallel to the lines
Ост. 1848.]
123
suppositions as to its nature.
of magnetic force, may be the position of no, or of least resist-
ance; and therefore the position of rest and stable equilibrium.
All the diametral effects would agree with this view. Then, just
as the optic axis is to a ray of polarized light, namely, the direc-
tion in which it is not affected, so would the magnecrystallic
axis be to the lines of magnetic force. If such were the case,
then, also, as the phænomena are developed in crystalline bodies,
we might hope for the discovery of a series of effects dependent
upon retardation and influence in direction, parallel to the beau-
tiful phænomena presented by light with similar bodies. In
making this supposition, I do not forget the points of inertia
and momentum; but such an idea as I can form of inertia does
not exclude the above view as altogether irrational. I remember
too, that, when a magnetic pole and a wire carrying an electric
current are fastened together, so that one cannot turn without the
other, if the one be made axis the other will revolve round and
carry the first with it; and also, that if a magnet be floated in
mercury and a current sent down it, the magnet will revolve by
the powers which are within its mass. With my imperfect
mathematical knowledge, there seems as much difficulty in these
motions as in the one I am supposing, and therefore I venture to
put forth the idea¹. The hope of a polarized bundle of magnetic
forces is enough of itself to make one work earnestly with such
an object, though only in imagination, before us; and I may well
say that no man, if he take industry, impartiality and caution
with him in his investigations of science, ever works experi-
mentally in vain.
.
2592. I have already referred, in the former paper (2469.), to
Plücker's beautiful discovery and results in reference to the
repulsion of the optic axis 2 of certain crystals by the magnet, and
have distinguished them from my own obtained with bismuth,
antimony and arsenic, which are not cases of either repulsion or
attraction; believing then, with Plücker, that the force there
manifested is an optic axis force, exerted in the equatorial direc-
tion; and therefore existing in a direction at right angles to that
which produces the magnecrystallic phænomena.
¹ See note (2639.).
2 On the Repulsion of the Optic Axes of Crystals by the Poles of a Magnet,
Poggendorff's Annalen, vol. lxxii., October 1847, or Taylor's Scientific
Memoirs, vol. v. p. 353.
124
[SERIES XXII.
Magnecrystallic force;
2593. But the relations of both to crystalline structure, and
therefore to the force which confers that condition, are most
evident. Other considerations as to position, set, and turning, also
show that the two forces, so to say, have a very different relation
to each other to that which exists between them and the mag-
netic or diamagnetic force. As, therefore, this strong likeness
on the one hand, and distinct separation on the other is clearly
indicated, I will endeavour to compare the two sets of effects,
with the view of ascertaining whether the force exerted in pro-
ducing them is not identical.
2594. I had the advantage of verifying Plücker's results
under his own personal tuition in respect of tourmaline, staurolite,
red ferro-prussiate of potassa, and Iceland spar. Since then, and
in reference to the present inquiry, I have carefully examined
calcareous spar, as being that one of the bodies which was at the
same time free from magnetic action, and so simple in its cry-
stalline relations as to possess but one optic axis.
2595. When a small rhomboid, about 0.3 of an inch in its greatest
dimension, is suspended, with its optic axis horizontal, between
the pointed poles (2458.) of the electro-magnet, approximated
as closely as they can be to allow free motion, the rhomboid sets
in the equatorial direction, and the optic axis coincides with the
magnetic axis; but, if the poles be separated to the distance of
half, or three-quarters of an inch, the rhomboid turned through
90°, and set with the optic axis in the equatorial direction, and
the greatest length axial. In the first instance the diamagnetic
force overcame the optic axis force; in the second the optic axis
force was the stronger of the two.
2596. To remove the diamagnetic effect I used flat poles
(2463.), and then the little rhomboid always set in, or vibrated
about, that position in which its optic axis was equatorial.
2597. I also took three cubes of calcareous spar (1695.), in
which the optic axes were perpendicular to two of the faces, of
the respective dimensions of 0.3, 0.5, and 0.8 of an inch in the
side, and placed these in succession in the magnetic field, be-
tween either flat or pointed poles. In all cases, the optic axis,
if horizontal, passed into the equatorial position; or, if vertical,
left the cubes indifferent as to direction. It was easy by the
method of two positions (2470.) to find the line of force, which,
being vertical, left the mass unaffected by the magnet; or being
Ост. 1848.]
125
its nature considered.
horizontal, went into the equatorial position; and then exami-
ning the cube by polarized light, it was found that this line coin-
cided with the optic axis.
2598. Even the horse-shoe magnet (2485.) is sufficiently
strong to produce these effects.
2599. I tried two similar cubes of rock-crystal (1692.), but
could perceive no traces of any phænomena having either mag-
neoptic, or magnecrystallic, or any other relation to the crystal-
line structure of the masses.
2600. But though it is thus very certain that there is a line
in a crystal of calcareous spar coinciding with the optic axis,
which line seems to represent the resultant of the forces which
make the crystal take up a given position in the magnetic field;
and, though it is equally certain that this line takes up its posi-
tion in the equatorial direction; yet, considered as a line of force,
i. e. as representing the direction of the force which places the
crystal in that position, it seems to me to have something anoma-
lous in its character. For, that a directing and determining line
of force should have, as its full effect, the result of going into a
plane (the equatorial), in which it can take up any one of an
infinite number of positions indifferently, leaves an imperfect
idea on my mind; and a thought, that there is some other effect
or residual phænomena to be recognized and accounted for.
2601. On further consideration, it appears that a simple com-
bination of the magnecrystalline condition, as it exists in bis-
muth, will supply us with a perfect representation of the state
of calcareous spar; for, by placing two equal pieces of bismuth
with their magnecrystallic axes perpendicular to each other
(2484.), we have a system of forces which seems to possess, as
a resultant, a line setting in the equatorial direction. When
that line is vertical, the system is, as regards position, indifferent;
but when horizontal, the system so stands, that the line is in
the equatorial plane. Still, the real force is not in the equatorial
direction, but axial; and the system is moved by what may be
considered a plane of axial force (resultant from the union of
the two axes at right angles to each other), rather by a line
of equatorial force.
2602. Doubtless, the rhomboid or cube (2597.) of calcareous
spar is not a compound crystal, like the system of bismuth
crystals just referred to (2601.); but its molecules may possess
126
[SERIES XXII.
Magnecrystallic force;
a compound disposition of their forces, and may have two or
more axes of power, which at the same time that they cause the
crystalline structure, may exert such force in relation to the
magnet, as to give results in the same manner, and of the same
kind, as those of the double crystal of bismuth (2601.). Indeed,
that there should be but one axis of crystalline force, either in
the particle of Iceland spar, or in those of bismuth, does not
seem to me to be any way consistent with the cleavage of the
substances in three or more directions.
2603. The optic axis in a piece of calcareous spar, is simply
the line in which, if a polarized, or ordinary ray of light moves,
it is the least affected. It may be a line which, as a resultant of
the molecular forces, is that of the least intensity; and, cer-
tainly, as regards ordinary and mechanical means of observing
cohesion, a piece of calcareous spar is sensibly, and much harder
on the faces and parts which are parallel to the optic axis, than
on those perpendicular to it. An ordinary file or a piece of
sandstone shows this. So that the plane equatorial to the optic
axis, as it represents directions in which the force causing cry-
stallization is greater in degree than in the direction of the optic
axis, may also be that in which the resultant of its magnecry-
stallic force is exerted.
2604. I am bound to state, as in some degree in contrast with
such considerations, that, with bismuth, antimony and arsenic,
the cleavage is very facile perpendicular to the magnecrystallic
axis (2475. 2510. 2532.). But we must remember that the
cleavage (and therefore the cohesive) force is not the only thing
to be considered, for in calcareous spar it does not coincide with
either the axial or the equatorial direction of the substance in
the magnetic field: we must endeavour to look beyond this to
the polar (or axial) condition of the particles of the masses, for
the full understanding and true relation of all these points.
2605. I am bound, also, to admit that, if we considered calca-
reous spar as giving the simple system of force, we may, by the
juxtaposition of two crystals with their optic axes at right angles
to each other, produce a compound mass, which will truly
represent the bismuth in the direction of the force; i. e. it will,
in the magnetic field, point with apparently one line of force
only, and that in the axial direction, whilst it may be really
moved by a system of forces lying in the equatorial plane. I
OCT. 1848.]
127
its nature considered.
will not at present pretend to say that this is not the state of
things; but I think, however, that the metals, bismuth, anti-
mony and arsenic, present us with the simplest as they do the
strongest cases of magnecrystallic force; and whether that be
so or not, I am still of opinion that the phænomena discovered
by Plücker and those of which I have given an account in
these two papers, have one common origin and cause.
2606. I went through all the experiments and reasoning with
Plücker's crystals (as the carbonate of lime, tourmaline, and
red ferro-prussiate of potassa), in reference to the question of
original or induced power (2576.), as before, and came to the
same conclusion as in the former case (2584.).
2607. I could not find that crystals of red ferro-prussiate of
potassa or tourmaline were affected by the earth's magnetism
(2581.), or that they had the power of affecting each other
(2582.). Neither could I find that Plücker's effect with cal-
careous spar, or red ferro-prussiate of potassa, was either an
attractive or repulsive effect, but one connected with position
only (2550. 2560.). All which circumstances tend to convince
me that the force active in his experiments, and that in my re-
sults with bismuth, &c., is the same¹.
2608. A small rhomboid of Iceland spar was raised to the
highest temperature in the magnetic field which a spirit-lamp
could give (2570.); it was at least equal to the full red heat of
copper, but it pointed as well then as before. A short thick
tourmaline was heated to the same degree, and it also pointed
equally well. As it cooled, however, it became highly magnetic,
and seemed to be entirely useless for experiments at low tem-
peratures; but on digesting it for a few seconds in nitromu-
riatic acid, a little iron was dissolved from the surface, after which
it pointed as well, and in accordance with Plücker's law, as
before. A little peroxide upon the surface had been reduced by
the flame and heat to protoxide, and caused the magnetic
appearances.
:
'The optic axis is the direction of least optic force; and by Plücker's expe-
riments, coincides with what I consider in my results as the direction of mini-
mum magnecrystallic force. It is more than probable that, wherever the two
sets of effects (whether really or only nominally different) can be recognized in
the same body, the directions of maximum effect, and also those of minimum
effect, will be found to coincide.-November 23, 1848.
128
[SERIES XXII.
Magneoptic force.
2609. There is a general and, as it appears to me, important
relation between Plücker's magneto-optical results and those I
formerly obtained with heavy glass and other bodies (2152.
&c.). When any of these bodies are subject to strong induction
under the influence of the magnetic or electric forces, they ac-
quire a peculiar state, in which they can influence a polarized
ray of light. The effect is a rotation of the ray, if it be
passed through the substance parallel to the lines of magnetic
force, or in other words, in the axial direction; but if it be
passed in the equatorial direction, no effect is produced. The
equatorial plane, therefore, is that plane in which the condition
of the molecular forces is the least disturbed as respects their
influence on light. So also in Plücker's results, the optic axis,
or the optic axes, if there be two, go into that plane under the
same magnetic influence, they also being the lines in which
there is the least, or no action on polarized light.
2610. If a piece of heavy glass, or a portion of water, could
be brought beforehand into this constrained condition, and then
placed in the magnetic field, I think there can be no doubt that
it would move, if allowed to do so, and place itself naturally, so
that the plane of no action on light should be equatorial, just as
Plücker shows that a crystal of calcareous spar or tourmaline
does in his experiments. And, as in his case, the magnetic or
diamagnetic character of the bodies, makes no difference in the
general result; so in my experiments, the optical effect is pro-
duced in the same direction, and subject to the same laws, with
both classes of substances (2185. 2187.).
2611. But though thus generally alike in this great and
leading point, there is still a vast difference in the disposition of
the forces in the heavy glass and the crystal; and there is a still
greater difference in this, that the heavy glass takes up its
state only for a time by constraint and under induction, whilst
the crystal possesses it freely, naturally and permanently. In
both cases, however, whether natural or induced, it is a state of
the particles; and comparing the effect on light of the glass
under constraint with that of the crystal at liberty, it indicates
a power in the magnet of inducing something like that condition
in the particles of matter which is necessary for crystallization ;
and that even in the particles of fluids (2184.).
2612. If there be any weight in these considerations, and if
Ост. 1848.]
129
Magnecrystallic action.
the forces manifested in the crystals of bismuth and Iceland
spar be the same (2607.), then there is further reason for be-
lieving that, in the case of bismuth and the other metals named,
there is, when they are subjected to the power of the magnet,
both an induced condition of force (2584.), and also a pre-ex-
isting force (2577.). The latter may be distinguished as the
crystalline force, and is shown, first, by such bodies exhibiting
optic axes and lines of force when not under induction; by the
symmetric condition of the whole mass, produced under circum-
stances of ordinary occurrence; and by the fixity of the line of
magnecrystallic force in the bodies shown experimentally to
possess it.
2613. Though I have spoken of the magnecrystallic axis as a
given line or direction, yet I would not wish to be understood
as supposing that the force decreases, or state changes, in an
equal ratio all round from it. It is more probable that the
variation is different in degree in different directions, dependent
on the powers which give difference of form to the crystals.
The knowledge of the disposition of the force can be ascertained
minutely hereafter, by the use of good crystals, an unchangeable
ordinary magnet (2485. 2528.), or a regulated electro-magnet,
flat-faced poles (2463.), and torsion (2500. 2530.).
2614. I cannot conclude this series of researches without
remarking how rapidly the knowledge of molecular forces grows
upon us, and how strikingly every investigation tends to develope
more and more their importance, and their extreme attraction
as an object of study. A few years ago magnetism was to us an
occult power, affecting only a few bodies; now it is found to
influence all bodies, and to possess the most intimate relations
with electricity, heat, chemical action, light, crystallization, and,
through it, with the forces concerned in cohesion; and we may,
in the present state of things, well feel urged to continue in
our labours, encouraged by the hope of bringing it into a bond
of union with gravity itself.
Royal Institution.
October 20, 1848.
.
VOL. III.
K
130
[SERIES XXII.
Magnecrystallic action.
¶. vi. NOTE.—On the position of a crystal of sulphate of iron in
the magnetic field.
Received December 7, 1848.-Read December 7, 1848.
2615. Though effects of the following
nature are general, yet I think it con-
Fig. 6.
venient to state that I obtained them
chiefly by the use of magnetic poles
(2247.), the form of which is given in
the plan and side-view annexed (fig. 6.).
The crystals submitted to their action
were suspended by cocoon silk, so as to
be level with the upper surface of the poles.
.
2616. A prismatic crystal of protosulphate of iron was
selected, which was nearly 09 of an inch in length, 0·1 in
breadth, and 0.05 in thickness; by examination the magnecry-
stallic axis was found to coincide with the thickness, and there-
fore to be perpendicular, or nearly so (2546.), to the plate.
Being suspended as above described, and the magnet (2247.)
excited by ten pair of Grove's plates, the crystal stood trans-
verse, or with its magnecrystallic axis parallel to the axis of
magnetic force, when the distance between the poles was 2.25
inches or more; but when the distance was about 2 inches or
less, then it stood with its length axial, or nearly so, and its
magnecrystallic axis therefore transverse to the lines of magnetic
force. In the intermediate distances between 2 and 2.25 inches,
the prism assumed an oblique position (2634.), more or less
inclined to the axial line, and so passing gradually from the one
position to the other. This intermediate distance I will for the
present call n (neutral) distance.
2617. If the poles be 2 inches apart and the crystal be
gradually lowered, it passes through the same intermediate
oblique positions into the transverse position; or if the crystal
be raised, the same transitions occur; at any less distance the
changes are the same, but later. They occur more rapidly
when the crystal is raised than when it is lowered; but this is
only because of the unsymmetric disposition and intensity of the
lines of magnetic force around the magnetic axis, due to the
horse-shoe form of the magnet and shape of the poles. If two
DEC. 1848.]
131
Protosulphate of iron.
cylinder magnets with equal conical terminations were employed,
there is no doubt that for equal amounts of elevation or de-
pression, corresponding changes would take place in the position
of the crystal.
2618. These changes however are not due to mere diminution
of the magnetic force by distance, but to differences in the forms
or direction of the resultants of force. This is shown by the
fact that, if the crystal be left in its first posision, and so point-
ing with the length axially, no diminution of the force of the
magnet alters the position; thus, whether one or ten pair of
plates be used to excite the magnet, then distance (2616.)
remains unchanged; and even descending to the use of an ordi-
nary horse-shoe magnet, I have found the same result.
2619. Variation in the length of the prismatic crystal has an
important influence over the result. As the crystal is shorter,
the distance n diminishes, all the other phænomena remaining the
A crystal 0.7 of an inch long, but thicker than the last,
had for its maximum n distance 1.7 inch. A still shorter crys-
tal had for its maximum n distance 1·1 inch. In all these cases
variation of the force of the magnet caused no sensible change.
same.
2620. Variation in that dimension of the crystal coincident
with the magnecrystallic axis affected the n distance: thus, in-
crease in the length of the magnecrystallic axis diminished the
distance, and diminution of it in that direction increased the
distance. This was shown in two ways; first, by placing a
second prismatic crystal by the side of the former in a sym-
metric position (2636.), which reduced the n distance to between
1·75 and 2 inches; and next, by employing two crystals in suc-
cession of the same length but different thicknesses. The
thicker one had the smaller n distance.
2621. Variation in the depth of the crystal, i. e. its vertical
dimension, did not produce any sensible effect on the n di-
stance: nor by theory should it do so, until the extension up-
wards or downwards brings the upper or lower parts into the
condition of raised or depressed portions (2617.).
2622. Variation in the form of the poles affects then distance.
As they are more acute, the distance increases; and as they are
more obtuse up to flat-faced poles (2463.), the distance dimi-
nishes.
2623. With the shorter crystals, or with obtuse poles, it is
K 2
132
[SERIES XXII.
Magnecrystallic action.
often necessary to diminish the power of the magnet, or else
the crystal is liable to be drawn to the one or other pole. This,
however, may be avoided by employing a vertical axis which is
confined below as well as above (2554.); and then the difference
in strength of the magnet is shown to be indifferent to the
results, or very nearly so.
2624. These effects may probably be due to the essential
difference which exists between the ordinary magnetic and the
magnecrystallic action, in that the first is polar, and the second
only axial (2472.) in character. If a piece of magnetic matter,
iron for instance, be in the magnetic field, it immediately be-
comes polar (i. e. has terminations of different qualities). If
many iron particles be there, they all become polar; and if they
be free to move, arrange themselves in the direction of the axial
line, being joined to each other by contrary poles; and by that
the polarity of the extreme particles is increased. Now this
does not appear to be at all the case with particles under the
influence of the magnecrystallic force; the force seems to be
altogether axial, and hence probably the difference above, and
in many other results.
2625. Thus, if four or more little cubes of iron be suspended
in a magnetic field of equal force (2465.), they will become
polar; if also four similar cubes of crystallized bismuth be simi-
larly circumstanced, they will be affected and point. If the
iron cubes be arranged together in the direction of the equatorial
line, they will form an aggregate in a position of unstable equi-
librium, and will immediately, as a whole, turn and point with
the length axially; whereas the bismuth cubes by such approxi-
mation will suffer no sensible change.
2626. The extreme (and the other) associated cubes of the
elongated iron arrangement now have a polar force above that
which they had before; and the whole group serves, as it were,
as a condnctor for the lines of magnetic power; for many of
them concentrate upon the iron, and the intensity of power is
much stronger between the ends of the iron arrangement and
the magnetic poles, than it is in other parts of the magnetic
field. Such is not the case with the bismuth cubes; for how-
ever they be arranged, the intensity of force in the magnetic
DEC. 1848.]
133
Proto-sulphate of iron.
field is, as far as experiments have yet gone, unaffected by
them; and the intensity of the molecules of the crystals appears
to remain the same. Hence the iron stands lengthways between
the poles; the bismuth crystals, on the contrary, whether ar-
ranged side by side, as respects the magnecrystallic axis, so as
to stand as to length equatorially; or end to end, so as to stand
axially, are perfectly indifferent in that respect, vibrating and
setting equally both ways.
2627. A given piece of iron when introduced into a field of
equal magnetic force, and brought towards the pole, adheres to
it and disturbs the intensity of the field, producing a pointed
form of pole in one part with diverging lines of force: a cry-
stal of bismuth vibrates with sensibly equal force in every part
of the field (2467.), and does not disturb the distribution of the
power.
2628. Considering all these actions and conditions, it appears
to me that the occurrence of the n distance with a body which
is at the same time magnetic and magnecrystallic, may be traced
to that which causes them and their differences, namely, the
polarity belonging to the magnetic condition, and the axiality
belonging to the magnecrystallic condition. Thus, suppose an
uniform magnetic field three inches from pole to pole, and a bar
of magnetic matter an inch long, suspended in the middle of it;
by virtue of the polarity it acquires, it will point axially, and
carry on, or conduct, with its mass, the magnetic force, so much
better than it was conducted in the same space before, that the
lines of force between the ends of this bar and the magnetic
poles, will be concentrated and made more intense than any-
where else in the magnetic field. If the poles be made to
approach towards the bar, this effect will increase, and the bar
will conduct more and more of the magnetic force, and point
with proportionate intensity. It is not merely that the magnetic
field becomes more intense by the approximation of the poles,
but the proportion of force carried on by the bar becomes
greater as compared to that conveyed onwards by an equal space
in the magnetic field at its side.
2629. But if a similar bar of magnecrystallic substance be
placed in the magnetic field, its power does not rise in the same
manner, or in the same great proportion, by approximation of
the poles. There can be no doubt that such approximation in-
134
[SERIES XXII.
Magnecrystallic action.
creases the intensity of the lines of force, and therefore increases
the intensity of the magneto-crystallic state; but this state does
not appear to be due to polarity, and the bar does not convey
more power through it than is conveyed onwards elsewhere
through an equal space in the magnetic field. Hence its direc-
tive force does not increase in the same rapid degree as the
directive force of the magnetic bar just referred to.
2630. If then we take a bar which, like a prism of sulphate
of iron, is magnetic, and also magnecrystallic, having the mag-
necrystallic axis perpendicular to its length, such a bar, properly
suspended, ought to have an n distance of the poles, within
which the forces ought to be nearly in equilibrium; whilst at a
greater distance of the poles, the magnecrystallic force ought
to predominate; and at a lesser distance, the magnetic force
ought to have the advantage; simply, because the magnetic
force, in consequence of the true polarity of the molecules,
grows up more rapidly and diminishes more rapidly than the
magneto-crystallic force.
2631. This view, also, is consistent with the fact that variation
of the force of the magnet does not affect the n distance (2618.
2619.); for, whether the force be doubled or quadrupled, both
the magnetic and magneto-crystallic forces are at the same time
doubled or quadrupled; and their proportion therefore remains
the same.
2632. The raising or lowering of the crystal above or below
the line of maximum magnetic force is manifestly equivalent in
principle to the separation of the magnetic poles; and therefore
should produce corresponding effects: and that is the case
(2617.). Besides that, when the crystal is raised above the level
of the poles, such resultants of magnetic force as pass through
it, are no longer parallel to its length, but more or less curved,
so that they probably cannot act with the same amount of
power in throwing the whole crytsal into a consistent polarized
magnetic condition, as if they were parallel to it: whereas, as
respects the induction of the magneto-crystallic condition, each
of the particles appears to be affected independently of the
others; and, therefore, any loss of an effect dependent upon
joint action would not be felt here.
2633. M. Plücker told me, when in England in August last,
that the repulsive force on the optic axis diminishes and in-
DEC. 1848.]
135
Proto-sulphate of iron.
creases less rapidly than the magnetic force, by change of di-
stance; but is not altered in its proportion to the magnetic
force by employing a stronger or weaker magnet. This is
manifestly the same effect as that I have been describing; and
makes me still more thoroughly persuaded that his results and
mine are due to one and the same cause (2605. 2607.).
2634. I have said that, within the n distance, the crystal of
sulphate of iron pointed more or less obliquely (2616.); I will
now state more particularly what the circumstances are. If the
distance n be so adjusted, that the prismatic crystal, which is at
the time between the magnetic poles, shall make an angle of
30° (or any quantity) with the axial line; then it will be found
that there is another stable position, namely, the diametral posi-
tion (2461.), in which it can stand; but that the obliquity is
always on the same side of the axial line; and that the crystal
will not stand with the like obliquity of 30° on the opposite
side of the magnetic axis.
2635. If the crystal be turned 180° round a vertical axis, or
end for end, then the inclination, and the direction in which it
occurs, remain unchanged; in fact, it is simply giving the
crystal the diametral position. But if the crystal be revolved
180° round a horizontal axis; either that coinciding with its
length, which represents its maximum magnetic direction; or
that corresponding with its breadth, and therefore with the
magnecrystallic axis; then the inclination is the same in amount
as before, but it is on the other side of the axial line.
2636. This is the case with all the prismatic crystals of sul-
phate of iron which I have tried. The effect is very determinate;
and, as would be expected, when two crystals correspond in the
direction of the inclination, they also correspond in the position
of their form and direction of the various planes.
2637. All these variations of position indicate an oblique
resultant of setting force, derived from the joint action of the
magnetic and magnecrystallic forces; and would be explained
by the supposition, that the magnecrystallic axis or line of
maximum magnecrystallic force, was not perpendicular to the
chief planes of the crystal (or those terminating it), but a little
inclined in the direction of the length.
136
[SERIES XXII.
Magnecrystallic action.
2638. Whether this be the case, or whether the maximum
line of magnetic force may not, even, be a little inclined to the
length of the prism; still, the n distance supplies an excellent
experimental opportunity of examining this inclination, how-
ever small its quantity may be; because of the facility with
which the influence of either the one or the other may be made
predominant in any required degree.
Royal Institution,
December 5, 1848.
2639. Note. (2591.) Another supposition may be thrown out
for consideration. I have already said that the assumption of
a mere axial condition (2587. 2591.) would account for the set
without attraction or repulsion. Now if we suppose it possible
that the molecules should become polar in relation to the north
and south poles of the magnet, but with no mutual relation
amongst themselves, then the bismuth or other crystal might set
as if induced with mere axial power: but it seems to me very
improbable that polarities of a given particle in a crystal should
be subject to the influence of the polarities of the distant
magnet poles, and not also to the like polarities of the contigu-
ous particles.―January 24, 1849.
137
TWENTY-THIRD SERIES¹.
§ 29. On the polar or other condition of diamagnetic bodies.
Received January 1,-Read March 7 and 14, 1850.
2640. FOUR years ago I suggested that all the phænomena
presented by diamagnetic bodies, when subjected to the forces
in the magnetic field, might be accounted for by assuming that
they then possessed a polarity the same in kind as, but the re-
verse in direction of, that acquired by iron, nickel and ordinary
magnetic bodies under the same circumstances (2429. 2430.).
This view was received so favourably by Plücker, Reich and
others, and above all by W. Weber 2, that I had great hopes it
would be confirmed; and though certain experiments of my
own (2497.) did not increase that hope, still my desire and ex-
pectation were in that direction.
2641. Whether bismuth, copper, phosphorus, &c., when in
the magnetic field, are polar or not, is however an exceedingly
important question; and very essential and great differences, in
the mode of action of these bodies under the one view or the
other, must be conceived to exist. I found that in every
endeavour to proceed by induction of experiment from that
which is known in this department of science to the unknown,
so much uncertainty, hesitation and discomfort arose from the
unsettled state of my mind on this point, that I determined, if
possible, to arrive at some experimental proof either one way
or the other. This was the more needful, because of the con-
clusion in the affirmative to which Weber had come in his very
philosophical paper; and so important do I think it for the
progress of science, that, in those imperfectly developed regions
of knowledge, which form its boundaries, our conclusions and
deductions should not go far beyond, or at all events not aside
¹ Philosophical Transactions, 1850, p. 171.
2
Poggendorff's Annalen, January 7, 1848, or Taylor's Scientific Memoirs,
v. p.477.
138
[SERIES XXIII.
Supposed diamagnetic polarity.
from the results of experiment (except as suppositions), that I
do not hesitate to lay my present labours, though they arrive at
a negative result, before the Royal Society.
2642. It appeared to me that many of the results which had
been supposed to indicate a polar condition, were only conse-
quences of the law that diamagnetic bodies tend to go from
stronger to weaker places of action (2418.); others again
appeared to have their origin in induced currents (26. 2338.);
and further consideration seemed to indicate that the differences
between these modes of action and that of a real polarity,
whether magnetic or diamagnetic, might serve as a foundation
on which to base a mode of investigation, and also to construct
an apparatus that might give useful conclusions and results in
respect of this inquiry. For, if the polarity exists it must be in
the particles and for the time permanent, and therefore dis-
tinguishable from the momentary polarity of the mass due to
induced temporary currents; and it must also be distinguishable
from ordinary magnetic polarity by its contrary direction.
2643. A straight wooden lever, 2 feet in length, was fixed by
an axis at one end, and by means of a crank and wheel made to
vibrate in a horizontal plane, so that its free extremity passed
to and fro through about 2 inches. Cylinders or cores of
metal or other substances, 5 inches long and three quarters of
an inch diameter, were fixed in succession to the end of a brass
rod 2 feet long, which itself was attached at the other end to the
moving extremity of the lever, so that the cylinders could be
moved to and fro in the direction of their length through the
space of 2 inches. A large cylinder electro-magnet was also
prepared (2191.), the iron core of which was 21 inches long,
and 1·7 inch in diameter; but one end of this core was made
smaller for the length of 1 inch, being in that part only 1 inch
in diameter.
2644. On to this reduced part was fixed a hollow helix con-
sisting of 516 feet of fine covered copper wire: it was 3 inches
long, 2 inches external diameter, and 1 inch internal diameter :
when in its place, 1 inch of the central space was occupied by
the reduced end of the electro-magnet core which carried it; and
the magnet and helix were both placed concentric with the
metal cylinder above mentioned, and at such a distance that the
latter, in its motion, would move within the helix in the di-
JAN. 1850.]
139
Induction apparatus employed.
h
༡
་
b
d
wo
W
W
Z
P
a, b, c, frame board; d, d,d, wooden lever, of which e is the axis, f the crank-wheel, and g the great wheel with its handle
h; i the bar connecting the crank-wheel and lever; k a cylinder or core of metal to be submitted to experiment; 7 the rod
connecting it with the lever; m the helix of the electro-magnet; n the iron core and o the exciting battery; p the experimental
helix ; q the galvanometer, 20 feet from the electro-magnet; the commutator; w, w connecting wires; s,s springs of brass or
copper; ta copper rod connecting the two arms of the lever, to give strength. The plan is to a scale of one-fifteenth; the part
at the electro-magnet and experimental helix is in section; the further description is contained in paragraphs 2643, 2644, 2645

and 2648.
140
Supposed diamagnetic polarity. [SERIES XXIII.
rection of its axis, approaching to and receding from the electro-
magnet in rapid or slow succession. The least and greatest
distances of the moving cylinder from the magnet during the
journey were one-eighth of an inch and 2.2 inches. The object
of course was to observe any influence upon the experimental
helix of fine wire which the metal cylinders might exert, either
whilst moving to or from the magnet, or at different distances
from it ¹.
1
2645. The extremities of the experimental helix wire were
connected with a very delicate galvanometer, placed 18 or 20
feet from the machine, so as to be unaffected directly by the
electro-magnet; but a commutator was interposed between
them. This commutator was moved by the wooden lever
(2643.), and as the electric currents which would arrive at it
from the experimental helix, in a complete cycle of motion or to
and fro action of the metal cylinder (2643.), would consist of
two contrary portions, so the office of this commutator was,
sometimes to take up these portions in succession and send
them on in one consistent current to the galvanometer, and at
other times to oppose them and to neutralize their result; and
therefore it was made adjustible, so as to change at any period
of the time or part of the motion.
2646. With such an arrangement as this, it is known that,
however powerful the magnet, and however delicate the other
parts of the apparatus, no effect will be produced at the gal-
vanometer as long as the magnet does not change in force, or in
its action upon neighbouring bodies, or in its distance from, or
relation to the experimental helix; but the introduction of a
piece of iron into the helix, or anything else that can influence
or be influenced by the magnet, can, or ought to, show a corre-
sponding influence upon the helix and galvanometer. My ap-
paratus I should imagine, indeed, to be almost the same in
principle and practice as that of M. Weber (2640.), except that
it gives me contrary results.
2647. But to obtain correct conclusions, it is most essential
that extreme precaution should be taken in relation to many
¹ It is very probable that if the metals were made into cylinders shorter,
but of large diameter than those described above, and used with a corre-
sponding wider helix, better results than those I have obtained would be
acquired.
JAN. 1850.]
141
Apparatus employed.
points which at first may seem unimportant. All parts of the
apparatus should have perfect steadiness, and be fixed almost
with the care due to an astronomical instrument; for any
motion of any portion of it is, from the construction, sure to
synchronize with the motion of the commutator; and portions
of effect, inconceivably small, are then gathered up and made
manifest as a whole at the galvanometer; and thus, without
care, errors might be taken for real and correct results. There-
fore, in my arrangements, the machine (2643. &c.), the magnet
and helix, and the galvanometer stood upon separate tables, and
these again upon a stone floor laid upon the earth; and the
table carrying the machine was carefully strutted to neighbour-
ing stone-work.
2648. Again, the apparatus should itself be perfectly firm
and without shake in its motion, and yet easy and free. No iron
should be employed in any of the moving parts. I have springs
to receive and convert a portion of the momentum of the whole
at the end of the to and fro journey; but it is essential that
these should be of hammered brass or copper.
2649. It is absolutely necessary that the cylinder or core in
its motion should not in the least degree disturb or shake the
experimental helix and the magnet. Such a shake may easily
take place and yet (without much experience) not be perceived.
It is important to have the cores of such bodies as bismuth,
phosphorus, copper, &c., as large as may be, but I have not found
it safe to have less than one-eighth of an inch of space between
them and the interior of the experimental helix. In order to
float, as it were, the core in the air, it is convenient to suspend
it in the bight or turn of a fine copper wire passing once round
it, the ends of which rise up, and are made fast to two fixed
points at equal heights but wide apart, so that the wire has a
V form. This suspension keeps the core parallel to itself in
every part of its motion.
2650. The magnet, when excited, is urged by an electric
current from five pairs of Grove's plates, and is then very
powerful. When the battery is not connected with it, it still
remains a magnet of feeble power, and when thus employed may
be referred to as in the residual state. If employed in the
residual state, its power may for the time be considered con-
stant, and the experimental helix may at any moment be con-
142
[SERIES XXIII.
Supposed diamagnetic polarity.
nected with the galvanometer without any current appearing
there. But if the magnet be employed in the excited state,
certain important precautions are necessary; for upon connect-
ing the magnet with the battery and then connecting the ex-
perimental helix with the galvanometer, a current will appear
at the latter, which will, in certain cases, continue for a minute
or more, and which has the appearance of being derived at once
from that of the battery. It is not so produced, however, but is
due to the time occupied by the iron core in attaining its maxi-
mum magnetic condition (2170. 2332.), during the whole of
which it continues to act upon the experimental helix, producing
a current in it. This time varies with several circumstances,
and in the same electro-magnet varies especially with the period
during which the magnet has been out of use. When first
employed, after two or three days' rest, it will amount to eighty
or ninety seconds, or more. On breaking battery contact and
immediately renewing it, the effect will be repeated, but occupy
only twenty or thirty seconds. On a third intermission and
renewal of the current, it will appear for a still shorter period;
and when the magnet has been used at short intervals for some
time, it seems capable of receiving its maximum power almost
at once. In every experiment it is necessary to wait until the
effect is shown by the galvanometer to be over; otherwise the
last remains of such an effect might be mistaken for a result of
polarity, or some peculiar action of the bismuth or other body
under investigation.
2651. The galvanometer employed was made by Ruhmkorff
and was very sensible. The needles were strengthened in their
action and rendered so nearly equal, that a single vibration to
the right or to the left occupied from sixteen to twenty
seconds. When experimenting with such bodies as bismuth
or phosphorus, the place of the needle was observed through a
lens. The perfect communication in all parts of the circuit was
continually ascertained by a feeble thermo-electric pair, warmed
by the fingers. This was done also for every position of the
commutator, where the film of oxide formed on any part by two
or three days' rest was quite sufficient to intercept a feeble
current.
2652. In order to bring the phænomena afforded by magnetic
and diamagnetic bodies into direct relation, I have not so much
JAN. 1850.]
143
Magnetic and diamagnetic cores.
.
noted the currents produced in the experimental helix, as the
effects obtained at the galvanometer. It is to be understood,
that the standard of deviation, as to direction, has always been
that produced by an iron wire moving in the same direction as
the experimental helix, and with the same condition of the com-
mutator and connecting wires, as the piece of bismuth or other
body whose effects were to be observed and compared.
2653. A thin glass tube, of the given size (2643.), 5 by
inches, was filled with a saturated solution of protosulphate of
iron, and employed as the experimental core: the velocity given
to the machine at this and all average times of experiment was
such as to cause five or six approaches and withdrawals of the
core in one second; yet the solution produced no sensible indi-
cation at the galvanometer. A piece of magnetic glass tube
(2354.), and a core of foolscap paper, magnetic between the
poles of the electro-magnet, were equally inefficient. A tube
filled with small crystals of protosulphate of iron caused the
needle to move about 2°, and cores formed out of single large
crystals, or symmetric groups of crystals of sulphate of iron,
produced the same effect. Red oxide of iron (colcothar) pro-
duced the least possible effect. Iron scales and metallic iron
(the latter as a thin wire) produced large effects.
2654. Whenever the needle moved, it was consistent in its
direction with the effect of a magnetic body; but in many cases
with known magnetic bodies, the motion was little or none.
This proves that such an arrangement is by no means so good
a test of magnetic polarity as the use of a simple or an astatic
needle. This deficiency of power in that respect does not inter-
fere with its ability to search into the nature of the phænomena
that appear in the experiments of Weber, Reich and others.
2655. Other metals than iron were now employed and with
perfect success. If they were magnetic, as nickel and cobalt,
the deflection was in the same direction as for iron. When the
metals were diamagnetic, the deflection was in the contrary
direction; and for some of the metals, as copper, silver and
gold, it amounted to 60° or 70°, which was permanently sus-
tained as long as the machine continued to work. But the
deflection was not the greatest for the most diamagnetic sub-
stances, as bismuth or antimony, or phosphorus; on the con-
144
[SERIES XXIII.
Supposed diamagnetic polarity.
trary, I have not been able to assure myself, up to this time,
that these three bodies can produce any effect. Thus far the
effect has been proportionate to the conducting power of the
substances for electricity. Gold, silver and copper have pro-
duced large deflections, lead and tin less. Platina very little.
Bismuth and antimony none.
2656. Hence there was every reason to believe that the
effects were produced by the currents induced in the mass of the
moving metals, and not by any polarity of their particles. I
proceeded therefore to test this idea by different conditions of
the cores and the apparatus.
2657. In the first place, if produced by induced currents, the
great proportion of these would exist in the part of the core
near to the dominant magnet, and but little in the more distant
parts; whereas in a substance like iron, the polarity which the
whole assumes makes length a more important element. I
therefore shortened the core of copper from 5½ inches (2643.) to
2 inches, and found the effect not sensibly diminished; even
when 1 inch long it was little less than before. On the contray,
when a fine iron wire, 5½ inches in length, was used as a core, its
effects were strong; when the length was reduced to 2 inches,
they were greatly diminished; and again, with a length of
1 inch, still further greatly reduced. It is not difficult to con-
struct a core of copper, with a fine iron wire in its axis, so that
when above a certain length it should produce the effects of iron,
and beneath that length the effects of copper.
2658. In the next place, if the effect were produced by
induced currents in the mass (2642.), division of the mass would
stop these currents and so alter the effect; whereas if produced
by a true diamagnetic polarity, division of the mass would not
affect the polarity seriously, or in its essential nature (2430.).
Some copper filings were therefore digested for a few days in
dilute sulphuric acid to remove any adhering iron, then well-
washed and dried, and afterwards warmed and stirred in the air,
until it was seen by the orange colour that a very thin film of
oxide had formed upon them: they were finally introduced into
a glass tube (2653.) and employed as a core. It produced no
effect whatever, but was now as inactive as bismuth.
2659. The copper may however be divided so as either to
interfere with the assumed currents or not, at pleasure. Fine
I
JAN. 1850.]
145
Effects of division.
copper wire was cut up into lengths of 5 inches, and as many
of these associated together as would form a compact cylinder
three-quarters of an inch in diameter (2643.); it produced no
effect at the galvanometer. Another copper core was prepared
by associating together many discs of thin copper plate, three-
quarters of an inch in diameter, and this affected the galva-
nometer, holding its needle 25° or 30° from zero.
core.
2660. I made a sold helix cylinder, three-quarters of an inch
in diameter and 2 inches long, of covered copper wire, one-six-
teenth of an inch thick, and employed this as the experimental
When the two ends of its wire were unconnected, there
was no effect upon the experimental helix, and consequently
none at the galvanometer; but when the ends were soldered
together, the needle was well affected. In the first condition,
the currents, which tended to be formed in the mass of moving
metal, could not exist because the metal circuit was interrupted ;
in the second they could, because the circuit was not inter-
rupted; and such division as remained did not interfere to
prevent the currents.
2661. The same results were obtained with other metals. A
core cylinder of gold, made of half-sovereigns, was very power-
ful in its effect on the galvanometer. A cylinder of silver,
made of sixpenny pieces, was very effectual; but a cylinder
made of precipitated silver, pressed into a glass tube as closely
as possible, gave no indications of action whatever. The same
results were obtained with disc cylinders of tin and lead, the
effects being proportionate to the condition of tin and lead as
bad conductors (2655.).
2662. When iron was divided, the effects were exactly the
reverse in kind. It was necessary to use a much coarser galva-
nometer and apparatus for the purpose; but that being done,
the employment of a solid iron core, and of another of the same
size or weight formed of lengths of fine iron wire (2659.),
showed that the division had occasioned no inferiority in the
latter. The excellent experimental researches of Dove¹ on the
electricity of induction, will show that this ought to be the case.
2663. Hence the result of division in the diamagnetic metals is
altogether of a nature to confirm the conclusion, that the effects
¹ Taylor's Scientific Memoirs, v. p. 129. I do not see a date to the paper.
VOL. III.
I
146
[SERIES XXIII.
Supposed diamagnetic polarity.
produced by them are due to induced currents moving through
their masses, and not to any polarity correspondent in its general
nature (though opposed in its direction) to that of iron.
2664. In the third place (2656.), another and very important
distinction in the actions of a diamagnetic metal may be experi-
mentally established according as they may be due either to a
true polarity, or merely to the presence of temporary induced
currents; and as for the consideration of this point diamagnetic
and magnetic polarity are the same, the point may best be
considered, at present, in relation to iron.
2665. If a core of any kind be advanced towards the domi-
nant magnet and withdrawn from it by a motion of uniform
velocity, then a complete journey, or to and from action, might
be divided into four parts; the to, the stop after it; the from,
and the stop succeeding that. If a core of iron make this
journey, its end towards the dominant magnet becomes a pole,
rising in force until at the nearest distance, and falling in force
until at the greatest distance. Both this effect and its pro-
gression inwards and outwards, cause currents to be induced in
the surrounding helix, and these currents are in one direction
as the core advances, and in the contrary direction as it recedes.
In reality, however, the iron does not travel with a constant
velocity; for, because of the communication of motion from a
revolving crank at the machine (2643.), it, in the to part of the
journey, gradually rises from a state of rest to a maximum
velocity, which is half-way, and then as gradually sinks to rest
again near the magnet:-and the from part of the journey
undergoes the same variations. Now as the maximum effect
upon the surrounding experimental helix depends upon the
velocity conjointly with the intensity of the magnetic force in
the end of the core, it is evident that it will not occur with the
maximum velocity, which is in the middle of the to or from
motion; nor at the stop nearest to the dominant magnet,
where the core end has greatest magnet force, but somewhere
between the two. Nevertheless, during the whole of the
advance, the core will cause a current in the experimental helix
in one direction, and during the whole of the recession it will
cause a current in the other direction.
2666. If diamagnetic bodies, under the influence of the domi-
nant magnet, assume also a polar state, the difference between
JAN. 1850.]
147
Commutator action varied.
them and iron being only that the poles of like names or forces
are changed in place (2429. 2430.), then the same kind of
action as that described for iron would occur with them; the
only difference being, that the two currents produced would be
in the reverse direction to those produced by iron.
.
2667. If a commutator, therefore, were to be arranged to
gather up these currents, either in the one case or the other, and
to send them on the galvanometer in one consistent current, it
should change at the moments of the two stops (2665.), and then
would perform such duty perfectly. If, on the other hand, the
commutator should change at the times of maximum velocity
or maximum intensity, or at two other times equidistant either
from the one stop or from the other, then the parts of the
opposite currents intercepted between the changes would exactly
neutralize each other, and no final current would be sent on to
the galvanometer.
2668. Now the action of the iron is, by experiment, of this
nature. If an iron wire be simply introduced or taken out of
the experimental helix with different condition of the commu-
tator, the results are exactly those which have been stated. If
the machine be worked with an iron wire core, the commutator
changing at the stops (2665.), then the current gathered up and
sent on to the galvanometer is a maximum; if the commutator
change at the moments of maximum velocity, or at any other
pair of moments equidistant from the one stop or the other,
then the current at the commutator is a minimum, or 0.
2669. There are two or three precautions which are necessary
to the production of a pure result of this kind. In the first
place, the iron ought to be soft and not previously in a magnetic
state. In the next, an effect of the following kind has to be
guarded against. If the iron core be away from the dominant
magnet at the beginning of an experiment, then, on working
the machine, the galvanometer will be seen to move in one
direction for a few moments, and afterwards, notwithstanding
the continued action of the machine, will return and gradually
take up its place at 0°. If the iron core be at its shortest
distance from the dominant magnet at the beginning of the ex-
periment, then the galvanometer needle will move in the contrary
direction to that which it took before, but will again settle at
0°. These effects are due to the circumstance, that when the
L 2
148
[SERIES XXIII.
Supposed diamagnetic polarity.
iron is away from the dominant magnet, it is not in so strong
a magnetic state, and when at the nearest to it is in a stronger
state, than the mean or average state, which it acquires during
the continuance of an experiment; and that in rising or falling
to this average state, it produces two currents in contrary
directions, which are made manifest in the experiments de-
scribed. These existing only for the first moments, do, in their
effects at the galvanometer, then appear, producing a vibration
which gradually passes away.
2670. One other precaution I ought to specify. Unless the
commutator changes accurately at the given points of the
journey, a little effect is gathered up at each change, and may give
a permanent deflection of the needle in one direction or the
other. The tongues of my commutator, being at right angles
to the direction of motion and somewhat flexible, dragged a
little in the to and from parts of the journey: in doing this
they approximated, though only in a small degree, to that which
is the best condition of the commutator for gathering up (and
not opposing) the currents; and a deflection to the right or left
appeared (2677.). Upon discovering the cause and stiffening
the tongues so as to prevent their flexure, the effect disappeared,
and the iron was perfectly inactive.
2671. Such therefore are the results with an iron core, and
such would be the effects with a copper or bismuth core if they
acted by a diamagnetic polarity. Let us now consider what the
consequences would be if a copper or bismuth core were to act
by currents, induced for the time, in its moving mass, and of
the nature of those suspected (2642.). If the copper cylinder
moved with uniform velocity (2665.), then currents would exist
in it, parallel to its circumference, during the whole time of its
motion; and these would be at their maximum force just before
and just after the to or inner stop, for then the copper would be
in the most intense parts of the magnetic field. The rising
current of the copper core for the in portion of the journey
would produce a current in one direction in the experimental
helix, the stopping of the copper and consequent falling of its
current would produce in the experimental helix a current con-
trary to the former; the first instant of motion outwards in the
core would produce a maximum current in it contrary to its
former current, and producing in the experimental helix its in-
JAN. 1850.]
149
Analysis of the actions.
ductive result, being a current the same as the last there pro-
duced; and then, as the core retreated, its current would fall, and
in so doing and by its final stop, would produce a fourth current
in the experimental helix, in the same direction as the first.
2672. The four currents produced in the experimental helix
alternate by twos, i. e. those produced by the falling of the first
current in the core and the rising of the second and contrary
current, are in one direction. They occur at the instant before
and after the stop at the magnet, i. e. from the moment of maxi-
mum current (in the core) before, to the moment of maximum
current after, the stop; and if that stop is momentary, they
exist only for that moment, and should during that brief time
be gathered up by the commutator. Those produced in the
experimental helix during the falling of the second current in
the core and the rising of a third current (identical with the
first) in the return of the core to the magnet, are also the same
in direction, and continue from the beginning of the retreat to
the end of the advance (or from maximum to maximum) of the
core currents, i. e. for almost the whole of the core journey;
and these, by its change at the maximum moments, the com-
mutator should take up and send on to the galvanometer.
2673. The motion however of the core is not uniform in
velocity, and so, sudden in its change of direction, but, as before
said (2665.), is at a maximum as respects velocity in the middle
of its approach to and retreat from the dominant magnet; and
hence a very important advantage. For its stop may be said to
commence immediately after the occurrence of the maximum
velocity; and if the lines of magnetic force were equal in position
and power there to what they are nearer to the magnet, the
contrary currents in the experimental helix would commence at
those points of the journey; but, as the core is entering into a
more intense part of the field, the current in it still rises though
the velocity diminishes, and the consequence is, that the maxi-
mum current in it neither occurs at the place of greatest velocity,
nor of greatest force, but at a point between the two. This is
true both as regards the approach and the recession of the core,
the two maxima of the currents occurring at points equidistant
from the place of rest near the dominant magnet.
2674. It is therefore at these two points that the commutator
should change, if adjusted to produce the greatest effect at the
150
Supposed diamagnetic polarity. [SERIES XXIII.
galvanometer by the currents excited in the experimental helix,
through the influence of, or in connexion with, currents of
induction produced in the core; and experiment fully justifies
this conclusion. If the length of the journey from the stop out
to the stop in, which is 2 inches (2643. 2644.), be divided into
100 parts, and the dominant magnet be supposed to be on the
right-hand, then such an expression as the following, 5050,
may represent the place where the commutator changes, which
in this illustration would be midway in the to and from motion,
or at the places of greatest velocity.
2675. Upon trial of various adjustments of the commutator,
I have found that from 7723 to 88/12, gave the best result with
On the whole, and after many experiments, I
a copper core.
conclude that with the given strength of electro-magnet, distance
of the experimantal core when at the nearest from the magnet,
length of the whole journey, and average velocity of the machine,
8614 may represent the points where the induced currents in
the core are at a maximum and where the commutator ought to
change.
2676. From what has been said before (2667.), it will be seen
that both in theory and experiment these are the points in which
the effect of any polarity, magnetic or diamagnetic, would be
absolutely nothing. Hence the power of submitting by this
machine metals and other bodies to experiment, and of elimina- ·
ting the effects of magnetic polarity, of diamagnetic polarity,
and of inductive action, the one from the others: for either by
the commutator or by the direction of the polarity, they can be
separated; and further, they can also be combined in various
ways for the purpose of elucidating their joint and separate
action.
2677. For let the ar-
rows in the diagram re-
present the to and from
journey, and the inter- a---O-

b
sections of the lines a,
or c, d, &c. the periods
in the journey when the
commutator changes (in
which case c, d will correspond to 50/50, and e, f to 86|14),
then a, b will represent the condition of the commutator for the
JAN. 1850.]
151
Analysis of the actions.
But the line a,
with which no
maximum effect of iron or any other polar body. If the line
a, b be gradually revolved until parallel to c, d, it will in every
position indicate points of commutator change, which will give
the iron effect at the galvanometer by a deflexion of the needle
always in the same direction; it is only when the ends a and b
have passed the points c and d, either above or below, that the
direction of the deflection will change for iron.
b indicates those points for the commutator
effect will be produced on the galvanometer by the induction of
currents in the mass of the core. If the line be inclined in one
direction, as i, k, then these currents will produce a deflection
at the galvanometer on one side; if it be inclined in the other
direction, as l, m, then the deflection will be on the other side.
Therefore the effects of these induced currents may be either
combined with, or opposed to, the effects of a polarity, whether
it be magnetic or diamagnetic.
2678. All the metals before mentioned (2655.), namely, gold,
silver, copper, tin, lead, platina, antimony and bismuth, were
submitted to the power of the electro-magnet under the best
adjustment (2675.) of the commutator.
The effects were
stronger than before, being now at a maximum, but in the same
order; as regarded antimony and bismuth, they were very
small, amounting to not more than half a degree, and may very
probably have been due to a remainder of irregular action in
some part of the apparatus. All the experiments with the
divided cores (2658, &c.) were repeated with the same results as
before. Phosphorus, sulphur and gutta percha did not, either
in this or in the former state of the commutator, give any indi-
cation of effect at the galvanometer.
2679. As an illustration of the manner in which this position
of the commutator caused a separation of the effects of copper
and iron, I had prepared a copper cylinder core 2 inches in
length having an iron wire in its axis, and this being employed
in the apparatus gave the pure effect of the copper with its
induced currents. Yet this core, as a whole, was highly mag-
netic to an ordinary test-needle; and when the two changes of
the commutator were not equidistant from the one stop or the
other (2670. 2677.), the iron effect came out powerfully, over-
ruling the former and producing very strong contrary deflections
at the needle. The platinum core which I have used is an im-
152
Supposed diamagnetic polarity. [SERIES XXIII.
perfect cylinder, 2 inches long and 0·62 of an inch thick: it
points magnetically between the poles of a horseshoe electro-
magnet (2381.), making a vibration in less than a second, but
with the above condition of the commutator (2675.) gives 4° of
deflection due to the induced currents, the magnetic effect being
annulled or thrown out.
2680. Some of the combined effects produced by oblique
position of the commutator points were worked out in confirm-
ation of the former conclusions (2677.). When the commutator
was so adjusted as to combine any polar power which the bis-
muth, as a diamagnetic body, might possess, with any conducting
power which would permit the formation of currents by induc-
tion in its mass (2676.), still the effects were so minute and
uncertain as to oblige me to say that, experimentally, it is with-
out either polar or inductive action.
2681. There is another distinction which may usefully be
established between the effects of a true sustainable polarity, either
magnetic or diamagnetic, and those of the transient induced
currents dependent upon time. If we consider the resistance in
the circuit, which includes the experimental helix and the galva-
nometer coil, as nothing, then a magnetic pole of constant
strength passed a certain distance into the helix, would produce
the same amount of current electricity in it, whether the pole
were moved into its place by a quick or a slow motion. Or if
the iron core be used (2668.) the same result is produced, pro-
vided, in any alternating action, the core is left long enough at
the extremities of its journey to acquire, either in its quick or
slow alternation, the same state. This I found to be the fact
when no commutator nor dominant magnet was used; a single
insertion of a weak magnetic pole gave the same deflection,
whether introduced quickly or slowly; and when the residual
dominant magnet, an iron wire core, and the commutator in its
position a, b (2677.) were used, four journeys to and from pro-
duced the same effect at the galvanometer when the velocities
were as 1 : 5 or even as 1: 10.
.
2682. When a copper, silver, or gold core is employed in
place of the iron, the effect is very different. There is no reason
to doubt, that, as regards the core itself, the same amount of
electricity is thrown into the form of induced circulating cur-
rents within it, by a journey to or from, whether that journey
JAN. 1850.]
153
Effects of time-revulsion.
is performed quickly or slowly: the above experiment (2681.)
in fact confirms such a conclusion. But the effect which is
produced upon the experimental helix is not proportionate to
the whole amount of these currents, but to the maximum
intensities to which they rise. When the core moves slowly,
this intensity is small; when its moves rapidly, it is great, and
necessarily so, for the same current of electricity has to travel
in the two differing periods of time occupied by the journeys.
Hence the quickly moving core should produce a far higher
effect on the experimental helix than the slowly moving core;
and this also I found to be the fact.
2683. The short copper core was adjusted to the apparatus,
and the machine worked with its average velocity until forty
journeys to and from had been completed; the galvanometer
needle passed 39° west. Then the machine was worked with a
greater rapidity, also for forty journeys, and the needle passed
through 80° or more west; finally, being worked at a slow rate
for the same number of journeys, the needle went through only
21° west. The extreme velocities in this experiment were pro-
bably as 1:6; the time in the longest case was considerably
less than that of one vibration of the needle (2651.), so that I
believe all the force in the slowest case was collected. The
needle is very little influenced by the swing or momentum of its
parts, because of the deadening effect of the copper plate
beneath it, and, except to return to zero, moves very little after
the motion of the apparatus ceases. A silver core produced the
same results.
2684. These effects of induced currents have a relation to the
phænomena of revulsion which I formerly described (2310.
2315. 2338.), being the same in their exciting cause and prin-
ciples of action, and so the two sets of phænomena confirm and
illustrate each other. That the revulsive phænomena are pro-
duced by induced currents, has been shown before (2327. 2329.
2336. 2339.); the only difference is, that with them the induced
currents were produced by exalting the force of a magnet placed
at a fixed distance from the affected metal; whilst in the present
phænomena, the force of the magnet does not change, but its
distance from the piece of metal does.
2685. So also the same circumstances which affect the phæ-
nomena here affect the revulsive phænomena. A plate of
154
[SERIES XXIII.
Inductive currents-revulsion.
metal will, as a whole, be well revulsed; but if it be divided
across the course of the induced currents it is not then affected
(2529.). A ring helix of copper wire, if the extremities be un-
connected, will not exhibit the phænomena, but if they be con-
nected then it presents them (2660.).
2686. On the whole, the revulsive phænomena are a far
better test and indication of these currents than the present
effects; especially if advantage be taken of the division of the
mass into plates, so as to be analogous, or rather superior, in
their action to the disc cylinder cores (2659. 2661.). Platinum,
palladium and lead in leaf or foil, if cut or folded into squares
half an inch in the side, and then packed regularly together, will
show the phænomena of revulsion very well; and that according
to the direction of the leaves, and not of the external form.
Gold, silver, tin and copper have the revulsive effects thus
greatly exalted. Antimony, as I have already shown, exhibits
the effect well (2514. 2519.). Both it and bismuth can be made
to give evidence of the induced currents produced in them when
they are used in thin plates, either single or associated, although,
to avoid the influence of the diamagnetic force, a little attention
is required to the moments of making and breaking contact
between the voltaic battery and the electro-magnet.
2687. Copper, when thus divided into plates, had its revulsive
phænomena raised to a degree that I had not before observed.
A piece of copper foil was annealed and tarnished by heat, and
then folded up into a small square block, half an inch in the
side and a quarter of an inch thick, containing seventy-two folds
of the metal. This block was suspended by a silk film as before
(2248.), and whilst at an angle of 30° or thereabouts with the
equatorial line (2252.), the electro-magnet was excited; it imme-
diately advanced or turned until the angle was about 45° or 50°,
and then stood still. Upon the interruption of the electric current
at the magnet the revulsion came on very strongly, and the block
turned back again, passed the equatorial line, and proceeded on
until it formed an angle of 50° or 60° on the other side; but
instead of continuing to revolve in that direction as before
(2315.), it then returned on its course, again passed the equa-
torial line, and almost reached the axial position before it stood
still. In fact, as a mass, it vibrated to and fro about the equa-
torial line.
JAN. 1850.]
155
Revulsion—diamagnetic polarity.
.
2688. This however is a simple result of the principles of
action formerly developed (2329. 2336.). The revulsion is due
to the production of induced currents in the suspended mass
during the falling of the magnetism of the electro-magnet; and
the effect of the action is to bring the axis of these induced
currents parallel to the axis of force in the magnetic field. Con-
sequently, if the time of the fall of magnetic force, and therefore
of the currents dependent thereon, be greater than the time
occupied by the revulsion of the copper block as far as the equa-
torial line, any further motion of it by momentum will be coun-
teracted by a contrary force; and if this force be strong enough
the block will return. The conducting power of the copper and
its division into laminæ, tend to set up these currents very
readily and with extra power; and the very power which they
possess tends to make the time of a vibration so short, that two
or even three vibrations can occur before the force of the electro-
magnet has ceased to fall any further. The effect of time, both
in the rising and falling of power, has been referred to on many
former occasions (2170. 2650.), and is very beautifully seen here.
2689. Returning to the subject of the assumed polarity of
bismuth, I may and ought to refer to an experiment made by
Reich, and described by Weber¹, which, if I understand the
instruction aright, is as follows: a strong horseshoe magnet is
laid upon a table in such a position that the line joining its two
poles is perpendicular to the magnetic meridian and to be con-
sidered as prolonged on one side; in that line, and near the
magnet, is to be placed a small powerful magnetic needle, sus-
pended by cocoon silk, and on the other side of it, the pole of a
bar magnet, in such a position and so near, as exactly to coun-
teract the effect of the horseshoe magnet, and leave the needle
to point exactly as if both magnets were away. Then a mass of
bismuth being placed between the poles of the horseshoe magnet
it is said to react upon the small magnet needle, causing its de-
flection in a particular direction, and this is supposed to indi-
cate the polarity of the bismuth under the circumstances, as it
has no such action when the magnets are away. A piece of
1 Taylor's Scientific Memoirs, v. p. 480.
156
[SERIES XXIII.
Supposed diamagnetic polarity.
iron in place of the bismuth produces the contrary deflection of
the needle.
2690. I have repeated this experiment most anxiously and
carefully, but have never obtained the slightest trace of action
with the bismuth. I have obtained action with the iron; but
in those cases the action was far less than if the iron were applied
outside between the horseshoe magnet and the needle, or to the
needle alone, the magnets being entirely away. On using a
garnet, or a weak magnetic substance of any kind, I cannot find
that the arrangement is at all comparable for readiness of indi-
cation or delicacy, with the use of a common or an astatic needle,
and therefore I do not understand how it could become a test
of the polarity of bismuth when these fail to show it. Still I
may have made some mistake; but neither by close reference
to the description, nor to the principles of polar action, can I
discover where.
2691. There is an experiment which Plücker described to me,
and which at first seems to indicate strongly the polarity of
bismuth. If a bar of bismuth (or phosphorus) be suspended
horizontally between the poles of the electro-magnet, it will go
to the equatorial position with a certain force, passing, as I have
said, from stronger to weaker places of action (2267.). If a bar
of iron of the same size be fixed in the equatorial position a little
below the plain in which the diamagnetic bar is moving, the
latter will proceed to the equatorial position with much greater
force than before, and this is considered as due to the circum-
stance, that, on the side where the iron has N polarity, the dia-
magnetic body has S polarity, and that on the other side the
S polarity of the iron and the N polarity of the bismuth also
coincide.
2692. It is however very evident that the lines of magnetic
force have been altered sufficiently in their intensity of direction,
by the presence of the iron, to account fully for the increased
effect. For, consider the bar as just leaving the axial position.
and going to the equatorial position; at the moment of starting
its extremities are in places of stronger magnetic force than
before, for it cannot be doubted for a moment that the iron bar
determines more force from pole to pole of the electro-magnet
than if it were away. On the other hand, when it has attained
the equatorial position, the extremities are under a much weaker
JAN. 1850.]
157
Results of Plücker, Reich, &c.
magnetic force than they were subject to in the same places
before; for the iron bar determines downwards upon itself much
of that force, which, when it is not there, exists in the plane
occupied by the bismuth. Hence, in passing through 90°, the
diamagnetic is urged by a much greater difference of intensity
of force when the iron is present than when it is away; and
hence, probably, the whole additional result. The effect is like
many others which I have referred to in magnecrystallic action
(2487-2497.), and does not, I think, add anything to the experi-
mental proof of diamagnetic polarity.
2693. Finally, I am obliged to say that I can find no experi-
mental evidence to support the hypothetical view of diamagnetic
polarity (2640.), either in my own experiments, or in the repeti-
tion of those of Weber, Reich, or others. I do not say that such
a polarity does not exist; and I should think it possible that
Weber, by far more delicate apparatus than mine, had obtained
a trace of it, were it not that then also he would have certainly
met with the far more powerful effects produced by copper,
gold, silver, and the better conducting diamagnetics. If bis-
muth should be found to give any effect, it must be checked
and distinguished by reference to the position of the commu-
tator, division of the mass by pulverization, influence of time,
&c. It appears to me also, that, as the magnetic polarity con-
ferred by iron or nickel in very small quantity, and in unfavour-
able states, is far more readily indicated by its effects on an
astatic needle, or by pointing between the poles of a strong
horseshoe magnet, than by any such arrangement as mine or
Weber's or Reich's, so diamagnetic polarity would be much
more easily distinguished in the same way, and that no indica-
tion of that polarity has as yet reached to the force and value of
those already given by Brugmann and myself.
2694. So, at present, the actions represented or typified by
iron, by copper and by bismuth, remain distinct; and their
relations are only in part made known to us. It cannot be
doubted that a larger and simpler law of action than any we are
yet acquainted with, will hereafter be discovered, which shall
include all these actions at once; and the beauty of Weber's
suggestion in this respect was the chief inducement to me to
endeavour to establish it.
2695. Though from the considerations above expressed (2693.)
158
Supposed diamagnetic polarity. [SERIES XXIII.
I had little hopes of any useful results, yet I thought it right to
submit certain magnecrystallic cores to the action of the appa-
ratus. One core was a large group of symmetrically disposed
crystals of bismuth (2457.); another a very large crystal of red
ferroprussiate of potassa; a third a crystal of calcareous spar;
and a fourth and fifth large crystals of protosulphate of iron.
These were formed into cylinders of which the first and fourth
had the magnecrystallic axes (2479.) parallel to the axis of the
cylinder, and the second, third and fifth, had the equatorial
direction of force (2594. 2595. 2546.) parallel to the axis of the
cylinder. None of them gave any effect at the galvanometer,
except the fourth and fifth, and these were alike in their results,
and were dependent for them on their ordinary magnetic pro-
perty.
2696. Some of the expressions I have used may seem to
imply, that, when employing the copper and other cores I
imagine that currents are first induced in them by the dominant
magnet, and that these induce the currents which are observed
in the experimental helix. Whether the cores act directly on
the experimental helix or indirectly through their influence on
the dominant magnet, is a very interesting question, and I have
found it difficult to select expressions, though I wished to do
so, which should not in some degree prejudge that question. It
seems to me probable, that the cores act indirectly on the helix,
and that their immediate action is altogether directed towards the
dominant magnet, which, whether they consist of magnetic or
diamagnetic metals, raise them into power either permanently
or transiently, and has their power for that time directed towards
it. Before the core moves to approach the magnet, the magnet
and experimental helix are in close relation; and the latter is
situated in the intense field of magnetic force which belongs to
the pole of the former. If the core be iron, as it approaches the
magnet it causes a strong convergence and concentration of the
lines of magnetic force upon itself; and these, as they so con-
verge, passing through the helix and across its convolutions, are
competent to produce the currents in it which are obtained
(2653. 2668.). As the iron retreats these lines of force diverge,
and again crossing the line of the wire in the helix in a contrary
direction to their former course, produce a contrary current. It
does not seem necessary, in viewing the action of the iron core,
JAN. 1850.]
159
Nature of the inductive actions.
to suppose any direct action of it on the helix, or any other
action than this which it exerts upon the lines of force of the
magnet. In such a case its action upon the helix would be
indirect.
2697. Then, by all parity of reasoning, when a copper core
enters the helix its action upon it should be indirect also. For
the currents which are produced in it are caused by the direct
influence of the magnet, and must react equivalently upon it.
This they do, and because of their direction and known action,
they will cause the lines of force of the magnet to diverge. As
the core diminishes in its velocity of motion, or comes to rest,
the currents in it will cease, and then the lines of force will con-
verge; and this divergence and convergence, or passage in two
directions across the wire of the experimental helix, is sufficient
to produce the two currents which are obtained in the advance
of the core towards the dominant magnet (2671. 2673.). A cor-
responding effect in the contrary direction is produced by the
retreat of the core.
2698. On the idea that the actions of the core were not of this
kind, but more directly upon the helix, I interposed substances
between the core and the helix during the times of the experi-
ment. A thick copper cylinder 2.2 inches long, 0.7 of an inch
external diameter, and 0·1 of an inch internal diameter, and con-
sequently 0.3 of an inch thick in the sides, was placed in the
experimental helix, and an iron wire core (2668.) used in the
apparatus. Still, whatever the form of the experiment, the kind
and amount of effect produced were the same as if the copper
were away, and either glass or air in its place. When the
dominant magnet was removed and the wire core made a magnet,
the same results were produced.
2699. Another copper lining, being a cylinder 2.5 inches
long, 1 inch in external diameter, and one-eighth of an inch in
thickness, was placed in the experimental helix, and cores of
silver and copper five-eighths of an inch in thickness, employed
as before, with the best condition of the commutator (2675.):
the effects, with and without the copper, or with and without
the glass, were absolutely the same (2698.).
2700. There can be no doubt that the copper linings, when
in place, were full of currents at the time of action, and that
when away no such currents would exist in the air or glass
160
Supposed diamagnetic polarity. [SERIES XXIII.
replacing them. There is also full reason to admit, that the
divergence and convergence of the magnetic lines of force
supposed above (2697.) would satisfactorily account for such
currents in them, supposing the indirect action of the cores
were assumed. If that supposition be rejected, then it seems
to me that the whole of the bodies present, the magnet, the
helix, the core, the copper lining, or the air or glass which re-
places it, must all be in a state of tension, each part acting on
every other part, being in what I have occasionally elsewhere
imagined as the electro-tonic state (1729.).
2701. The advance of the copper makes the lines of magnetic
force diverge, or, so to say, drives them before it (2697.). No
doubt there is reaction upon the advancing copper, and the pro-
duction of currents in it in such a direction as makes them
competent, if continued, to continue the divergence. But it
does not seem logical to say, that the currents which the lines
of force cause in the copper, are the cause of the divergence of
the lines of force. It seems to me, rather, that the lines of force
are, so to say, diverged, or bent outward by the advancing
copper (or by a connected wire moving across lines of force in
any other form of the experiments), and that the reaction of
the lines of force upon the forces in the particles of the copper
cause them to be resolved into a current, by which the resistance
is discharged and removed, and the line of force returns to its
place. I attach no other meaning to the words line of force
than that which I have given on a former occasion (2149.).
Royal Institution,
14 Dec. 1849.
161
TWENTY-FOURTH SERIES'.
§ 30. On the possible relation of Gravity to Electricity.
Received August 1,—Read November 28, 1850.
2702. THE long and constant persuasion that all the forces
of nature are mutually dependent, having one common origin,
or rather being different manifestations of one fundamental
power (2146.), has made me often think upon the possibility
of establishing, by experiment, a connexion between gravity
and electricity, and so introducing the former into the group,
the chain of which, including also magnetism, chemical force and
heat, binds so many and such varied exhibitions of force together
by common relations. Though the researches I have made
with this object in view have produced only negative results,
yet I think a short statement of the matter, as it has presented
itself to my mind, and of the result of the experiments, which
offering at first much to encourage, were only reduced to their
true value by most careful searchings after sources of error, may
be useful, both as a general statement of the problem, and as
awakening the minds of others to its consideration.
2703. In searching for some principle on which an experi-
mental inquiry after the identification or relation of the two
forces could be founded, it seemed that if such a relation existed,
there must be something in gravity which would correspond to
the dual or antithetical nature of the forms of force in electricity
and magnetism. To my mind it appeared possible that the
ceding to the force or the approach of gravitating bodies on the
one hand, and the effectual reversion of the force or separation
of the bodies on the other, might present the points of corre-
spondence; quiescence (as to motion) being the neutral condition.
The final unchangeability of gravity did not seem affected by
such an assumption; for the acting bodies when at rest would
ever have the same relation to each other, and it would only be
1
Philosophical Transactions, 1851, p. 1. The Bakerian Lecture.
VOL. III.
M
162
Relation of gravity to electricity. [SERIES XXIV.
at the times of motion to and fro that any results related to
electricity could be expected. Such results, if possible, could
only be exceedingly small; but, if possible, i. e. if true, no terms
could exaggerate the value of the relation they would establish.
2704. The thought on which the experiments were founded
was, that, as two bodies moved towards each other by the force
of gravity, currents of electricity might be developed either in
them or in the surrounding matter in one direction; and that
as they were by extra force moved from each other against the
power of gravitation, the opposite currents might be produced.
Also, that these currents would have relation to the line of ap-
proach and recession, and not to space generally, so that two
bodies approaching would have currents in the opposite direction
as to space generally, but the same as to the direction of their
motion along the line joining them. It will be unnecessary to go
further into the suppositions which arose concerning these points,
or regarding the effect of forced motions either coinciding with,
or across the direction of the earth's gravitation, and many
other matters, than to say that, as the effect looked for was ex-
ceedingly small, so no hope was entertained of any result except
by means of the gravitation of the earth. The earth was there-
fore made to be the one body, and the indicating mass of matter
to be experimented with the other.
2705. First of all, a body, which was to be allowed to fall,
was surrounded by a helix, and then its effect in falling sought
for. Now a body may either fall with a helix or through a
helix. Covered copper wire, to the amount of 350 feet in length,
was made into a hollow cylindrical helix, about 4 inches long,
its internal diameter being 1 inch and its external diameter 2
inches. It was attached to a line running upon an easy pulley,
so that it could be raised 36 feet, and then allowed to fall with
an accelerated velocity on to a very soft cushion, its axis remain-
ing vertical the whole time. Long covered wires were made
fast to its two extremities, and these being twisted round each
other, were attached to a very delicate galvanometer, placed
about 50 feet aside from the line of fall, and on a level midway
with its course. The accuracy of the connexion and the direc-
tion of the set of the needle, were then both ascertained by the
introduction of a feeble thermo-electric combination into the
current. Such a helix, either in rising or falling, can produce
AUG. 1850.]
163
Relation of gravity to electricity.
no deviation at the galvanometer by any current due to the mag-
netism of the earth: for as it remains parallel to itself during
the fall, so the lines of equal magnetic force, which being parallel
to the dip, are intersected by the wire convolutions of the descend-
ing helix, are cut with an equal velocity on both sides of the
helix, and consequently no effect of magneto-electric induction
is produced. Neither in rising nor in falling did this helix pre-
sent any trace of action at the galvanometer; whether the con-
nexion with the galvanometer was continued the whole time, or
whether it was cut off just before the diminution or cessation of
motion either way, or whether the rising and the falling were made
to occur isochronously with the times of vibration of the galva-
nometer needle. So, though no effect of gravity appeared in
the helix itself, still no source of error appeared to arise in this
mode of using it.
2706. A solid cylinder of copper, three-fourths of an inch in
diameter and 7 inches in length, was now introduced into the
helix and carefully fastened in it, being bound round with a cloth
so as not to move, and this compound arrangement was allowed
to fall as before (2705.). It gave very minute but remarkably
regular indications of a current at the galvanometer; and the
probability of these being related to gravity appeared the greater,
when it was found that on raising the helix or core, similar in-
dications of contrary currents appeared. It was some time be-
fore I was able to refer these currents to their true cause, but at
last I traced them to the action of a part of the connecting
wires proceeding from the helix to the galvanometer. The two
wires had been regularly twisted together, but the effect of
many falls had opened a part near the middle distance into a
sort of loop, so that the wires, instead of being tightly twisted
together like the strands of a rope, were separated for 3 feet, as
if the strands were open. In falling, this loop opened out more
or less, but always in the same manner; and the consequence
was that the part of it representing the transverse opening, which
was furthest from the galvanometer, travelled over a larger
space than the corresponding part nearest the galvanometer.
Now had they travelled through equal spaces, the effect of the
magnetic lines of force of the earth upon them would have been
equal, and no effect at the galvanometer would have been pro-
duced; as it was, currents in opposite directions, but of unequal
M 2
164
Relation of gravity to electricity. [SERIES XXIV.
amounts of force, tended to be produced, and a current equal to
the difference actually appeared. Such a case is described in
my earliest researches on terrestrial magno-electro induction
(171.). It is evident that the current should appear in the re-
verse direction, as the helix and wires are raised in the air, and
thus arose the reverse effect described above. Therefore no
positive or favourable evidence was supplied in favour of the
original assumption by this use of a copper core in the helix.
2707. The copper was selected as a heavy body and an ex-
cellent conductor of electricity. On its dismissal, a bismuth
cylinder of equal size was employed to replace it as a substance
eminently diamagnetic, and a bad conductor amongst metals.
Uncertain evidence arose; but by close attention, first to one
point and then to another, all the indications disappeared, and
then the rising or falling of the bismuth produced no effect on
the galvanometer.
2708. An iron cylinder was also employed as a magnetic metal,
but when made perfectly secure, so as to prevent any motion
relative to the helix, it was equally indifferent with the copper
and bismuth (2706. 2707.).
2709. Cylinders of glass and shell-lac were employed as
non-conducting substances, but without effect.
2710. In other experiments the helix was fixed, and the dif-
ferent substances in the form of cylinders, three-fourths of an
inch in diameter and 24 inches long, were dropped through it,
or else raised through it with an accelerated velocity; but in
neither case was any effect produced. Rods of copper, bismuth,
glass, shell-lac and sulphur were employed. Occasionally these
rods were made to rotate rapidly before and during their fall;
and many other conditions were devised and carried into effect,
but always with negative results, when sources of error were
avoided or accounted for.
2711. On further consideration of the original assumption,
namely, a relation between the forces, and of the effects that
might be looked for consequent upon a condition of tension in
and around the particles of the body, which, as we know, are at
the same moment the residence of both gravitating and electric
forces, and are subject to the gravitation of the earth, it seemed
probable that the stopping of the up and down motion (2703.
2704.) in the line of gravity would produce contrary effects to
AUG. 1850.]
165
Relation of gravity to electricity.
the coming on of the motion, and that, whether the stopping
was sudden or gradual; also that a motion downward quicker
than that which gravity could communicate, would give more
effect than the gravity result by itself, and that a corresponding
increase in the velocity upwards would be proportionally effectual.
In such a case a machine which could give a rapid alternating up
and down motion, might be very useful in producing many
minute units of inductive action in a small space and moderate
time; for then, by proper commutators, the accelerated and re-
tarded parts of each half-vibration could be separated and re-
combined into one consistent current, and this current could be
sent through the galvanometer during the time its needle was
swinging in one direction, and afterwards reversed for the time
of a swing in the other direction; and so on alternately until the
effect had become sensible, if any were produced by the as-
sumed cause.

h
o g
10
f
d
00
U
2
D
2712. The machine which I had made for this purpose is that
described in the last Series of these Researches (2643.), the elec-
tro-magnet, the experimental core and the rod which carried them
being removed :-a, b, c, frame-board; d, d, d wooden lever, of
which e is the axis; f the crank-wheel, and g the great wheel
166
Relation of gravity to electricity. [SERIES XXIV.
with its handle h; i the bar connecting the crank-wheel and
lever; q the galvanometer; r the commutator; w, connecting
wires; s, s springs of brass or copper; t a copper rod connect-
ing the two arms of the lever to give strength; u the hollow
helix fixed, or moveable at pleasure. The plan is to a scale of
one-fifteenth. Being on a moveable frame, it could be placed in
any position. The cylinder of metal or other substance to be
submitted to its action, was 5 inches long and three-fourths of
an inch in diameter, and was firmly held between the ends d, d
of the lever arms. The extent of the alternating motion was 3
inches. A hollow cylindrical helix u, 2 inches in length, and
of such internal diameter that the cylinders could complete their
rapid journeys to and fro within it without any danger of stri-
king against its sides, was constructed, containing 516 feet of
covered copper wire; this cylinder could be either fixed immove-
ably or attached firmly to the cylinder under experiment so as
to move with it. The wires from this helix passed to the com-
mutators and from them to the galvanometer. Part of the mo-
mentum of this machine was taken up by springs s, s (2648.),
and converted into the contrary motion; but so much remained
undisposed of thus, that great care was required in fixing and
strutting to render the action of the whole very steady, or else
derangement quickly occurred at the cylinder and helix, and
electro-currents were frequently produced.
2713. The employment of cylinders of iron, copper and other
substances in this machine, was competent to produce electro-
currents in various ways. Thus, iron might produce magneto-
electric currents consequent upon its polar condition under the
influence of the earth: these it would be easy to detect and
separate by the use of adjusted magnets, which should neutralize
or reverse the lines of magnetic force passing through the iron.
Currents like those induced in copper cylinders and good con-
ductors (2663. 2684.), might be produced by the earth's action;
but as the lines of gravitating force and of terrestrial magnetic
force are inclined to each other, these might be separated by
position; and it appeared that there was no source of error that
might not by care be eliminated. I will not occupy time by
describing how this long lesson of care was learned, but pass
at once to the chief results.
2714. The copper cylinder (2712.) was placed in the machine,
AUG. 1850.]
167
Relation of gravity to electricity.
and the helix fixed immoveably around it, the whole being in
such a position that the cylinder should be vertical, and move
up and down parallel to the line of gravitating force within the
helix. However rapidly the machine was worked, or whatever
the position of the commutator, there was no result at the gal-
vanometer. Cylinders of bismuth, glass, sulphur, gutta percha,
&c., were also employed, but with the same negative conclusion.
2715. Then the helix was taken from its fixed support and
fastened on to the copper cylinder so as to move with it, and
now very regular and comparatively large effects were produced.
After a while, however, these were traced to causes other than
gravity, and of the following kind. The helix was fixed at one
end of a lever, at a point 22 inches from its axis, and being 2
inches in diameter its wires on one side were only 21 inches, and
on the other side 23 inches from this axis. Hence, in vibra-
ting these parts travelled with velocities and through spaces
which are as 21: 23. When therefore their paths were across
the lines of magnetic force of the earth, electro-currents tended
to form in these different parts proportionate in amount or
strength to these numbers; and the differences of these currents
being continually gathered up by the commutators, were made
sensible at the galvanometer. This was rendered manifest by
placing the machine so, that though the plane of vibration was
still vertical, the place of the helix was just under the centre of
motion, and the central line of the helix therefore, instead of
being vertical, was horizontal. Now the convolutions of the
helix cut the lines of magnetic force in the most favourable
manner; and the consequence was that the commutators were
not required, for a single motion of the helix in one direction
was sufficient to show at the galvanometer the magneto-electric
currents induced. If, on the contrary, the plane of motion was
made horizontal, then no current was produced by any amount
of motion; for though the helix was as horizontal as, and not
sensibly more so than before, yet the parts of the convolutions
which intersected the magnetic lines of force (being the upper
and the lower parts) now moved with exactly equal velocity, and
no differential result was produced.
2716. The former small result (2715.) was therefore probably
dependent upon an effect of this kind; and this was confirmed
by placing the machine in such a position that the axis of the
168
Relation of gravity to electricity. [SERIES XXIV.
moving copper cylinder and helix should in its medium position
be parallel to the line of the dip, and then no effect was pro-
duced. Other bodies in the same position were equally unable
to produce any effect.
2717. Here end my trials for the present. The results are ne-
gative. They do not shake my strong feeling of the existence
of a relation between gravity and electricity, though they give
no proof that such a relation exists.
Royal Institution,
July 19, 1850,
169
TWENTY-FIFTH SERIES¹.
§ 31. On the magnetic and diamagnetic condition of bodies.
¶ i. Non-expansion of gaseous bodies by magnetic force. ¶ ii.
Differential magnetic action. ¶ iii. Magnetic characters of
Oxygen, Nitrogen, and Space.
Received August 15,-Read November 28, 1850.
¶i. Non-expansion of gaseous bodies by magnetic force.
2718. THERE can be no doubt that the magnetic force, the dia-
magnetic force, and the magneoptic or magnecrystallic force,
will, when thoroughly understood, be found to unite or exist
under one form of power, and be essentially the same. Hence
the great interest which exists in the development of any one
of these modes of action; for differing so greatly as they do in
very peculiar points, it is hardly possible that any one of them
should be advanced in its illustration or comprehension, without
a corresponding advance in the knowledge of the others. Stimu-
lated by such a feeling, I have been engaged with Plücker, Weber,
Reich and others, in endeavouring to make out, with some de-
gree of precision, the mode of action of diamagnetic as well as
magnecrystallic bodies; and the recent investigation (2640. &c.)
and endeavour to confirm the idea of polarity in bismuth and
diamagnetic bodies, the reverse of that in a magnet or in iron
bodies, was one of the results of that conviction and desire.
2719. Having failed however to establish the existence of
such an antipolarity, and having shown, as I think, that the
phænomena which were supposed to be due to it are in fact
dependent upon other conditions and causes, I was induced, in
the search after something precise as to the nature of diamag-
netic bodies, to examine another idea which had arisen in con-
sequence of the development of magnetic and diamagnetic phæ-
nomena amongst gaseous substances: this thought, with some
of the results which have grown out of it during its experimental
examination, I purpose making the subject of the present paper.
¹ Philosophical Transactions, 1851, p. 7.
170
Non-expansion of gases by magnetism. [SERIES XXV.
2720. Bancalari first showed that flame was diamagnetic'.
The effect, as I proved, was due chiefly to the heated state of
gaseous portions of the flame2; but besides that, it appeared that
at common temperatures diamagnetic phænomena could be ex-
hibited by gases; and also that in their production the gases
differed very much one from anothers; so that taking common air,
for instance, as a standard, nitrogen, and many other gases, were
strongly diamagnetic in relation to it, whilst oxygen took on the ap-
pearance of a magnetic body; for they were repelled from, while
it was attracted to, the place of maximum force in the magnetic
field.
super-
2721. Recalling the general law given respecting the action
of magnetic and diamagnetic bodies (2267. 2418.), namely, that
the former tended to go from weaker to stronger places, and the
latter from stronger to weaker places of magnetic power, and
applying it to such bodies as the gases, which are at the same
time both highly elastic and easily changed in bulk by the
addition of very small degrees of force, it would seem to follow,
that if the particles of a diamagnetic gas tended to go from
strong to weak places of action, in consequence of the direct and
immediate effect of the magnetic power on them, then such a
gas should tend to become enlarged or expanded in the mag-
netic field. For, the amount of power by which the particles
would tend to recede from the axis of the magnetic field, would
be added to the expansive force by which they before resisted
the pressure of the atmosphere; that pressure would therefore
be in part sustained by the new force, and expansion would of
necessity be the result. On the other hand, if a gas were mag-
netic (as for instance oxygen), then the force cast upon the par-
ticles, by such a direct and immediate action of the magnetic
power upon them, would urge them towards the axis of the mag-
netic field, and so coinciding with, and being superadded to the
pressure of the atmosphere, would tend to cause contraction
and diminution of bulk.
2722. If such supposititious cases were to prove true, we
should then be able to arrive at the knowledge of the real zero-
point (2416. 2432. 2440.)4, not amongst gases only, but amongst
¹ Philosophical Magazine, 1847, vol. xxxi. pp. 401, 421.
2 Ibid. pp. 404, 406.
3 Ibid.
p. 409.
4 Ibid. p. 420.
AUG. 1850.] Non-expansion of gases by magnetism.
171
all bodies, and should be able to tell whether such a gas as
oxygen were a magnetic or a diamagnetic body, and also able to
range individual gases and other substances in their proper
places. And though I had originally endeavoured to ascertain
whether there was any change in the bulk of air in the magnetic
field, and found none, still Plücker's statement that he had ob-
tained such an effect¹, and the great enlargement of knowledge
respecting the gases which since then we have acquired relating
to their diamagnetic relations, and especially of the great differ-
ence which exists between them, encouraged me to proceed.
2723. I first endeavoured to determine whether there was any
affection of the layer of air (or other gas) immediately in contact
with the magnetic pole, which, either by the consequent expan-
sion or contraction of that layer, could render it able to affect
the course of a ray of light and thus make manifest the changes
occurring within. A metal screen, with a pin-hole in it, was set
up before the flame of a bright lamp in a dark room, and thus
an artificial star or small definite luminous object was formed.
Forty-six feet from it was placed the great horseshoe magnet
(2247.), ready to be excited by twenty pairs of Grove's plates;
the poles were in a line, so that the ray from the lamp passed
for 4 inches close to the surface of the first pole, then through
6 inches of air, and then, for 4 inches, close to the surface of
the second pole. A very fine refracting telescope, belonging to
Sir James South, having an aperture of 3 inches and 46 inches
focal length, received the ray. The telescope was furnished
with a perfect micrometer, so that the smallest change in the
place of the luminous image could be observed on the threads.
The axis of the telescope was just above the level of the mag-
netic poles. Not the smallest change in either the character or
place of the luminous image could be observed, either on the
making or the breaking of the contact between the voltaic bat-
tery and the magnetic wire.
2724. As the chief part of the light which came to the tele-
scope consisted of rays which passed at some distance above the
magnetic poles, these were cut off by a screen, which rising only
one-eighth of an inch above the level of the poles, allowed no ray
1 Annales de Chimie, 1850, vol. xxix. p. 134.
172
Non-expansion of gases by magnetism. [SERIES XXV.
to pass that was not within that distance. The intensity of the
light was of course diminished, and the image was distorted by
inflection; still its place was well marked by the micrometer.
Not the slightest change in that or any other character occurred
in the supervention or the withdrawal of the magnetic force.
2725. The terminals of the magnetic poles were then varied,
so that the ray sometimes passed parallel and close to a long
right-angled edge, or parallel to and between two right-angled
edges, a little above or below them, or over the line joining
two hemispherical poles, placed close together (and also in many
other ways), but in no case did the magnetic action produce any
effect upon the course of the ray.
50
2726. In another form of the experiment the telescope was
dismissed, and a simple card, with a pin-hole th or oth
of an inch in diameter, employed in its place. The image of
the star of light could be seen through the pin-hole in the dark
room, and yet every ray tending to its formation passed within
th of an inch of the surface of the magnetic pole; still no
effect due to the magnetic force could be observed.
2727. By another arrangement of the polar terminations,
analogous to one I had formerly employed when experimenting
on the diamagnetic relations of the gases', I was able to sur-
round them with other gaseous substances than air, and subject
the ray for 2 inches of its course to these gases whilst under the
influence of the magnet. Though the glass of the enclosing
vessel disturbed the image of the object, i. e. the point of light,
yet it was easy to perceive that no additional effect occurred
when the magnetism was superinduced.
2728. Oxygen, nitrogen, hydrogen and coal-gas were thus
employed; but whether any one of these, or whether air itself
was submitted to examination, when in contact with the active
pole of a very powerful magnet, it did not appear to be either
expanded or condensed to such a degree as to cause any sensible
change in its refractive force.
2729. In order to compare the expected result with the real
result due to change of volume, I took a bar of iron 7 inches
long, and placed it so that the ray from the luminous object in
passing to the eye should proceed by the side of the bar at not
more than 1th of an inch from it, and then raised the tempera-
¹ Philosophical Magazine, 1847, vol. xxxi. pp. 414, 415.
1
AUG. 1850.] Non-expansion of gases by magnetism.
173
ture of the bar gradually, until by expanding the air in contact
with it, the course of the ray of light was sensibly affected; to
do this it required to be exalted many degrees. When the air
of the place was at 60° and the iron raised to 100° Fahr., the
effect was not distinct. Hence it seemed, that observation of the
expected change of volume of the air would be rendered far more
sensible by some arrangement, measuring that change directly,
than by such means as those referred to above, dependent on
refractive force; for it is certain that the change of volume, in a
very small quantity of air, raised from 60° to 100°, would be
very evident by the former method. On the other hand, it was
just possible that if the air or gas was affected by the magnet, it
might only be in that film immediately contiguous to the pole;
and also that great differences in the degree of change might
exist along the edge of a solid angle, and along the sides of the
planes forming that angle. Hence the assumed necessity for
examining those parts by a ray of light; and every precaution
was taken, by inclining the course of the ray a little more or less
to the sides or edges of the poles, and by making the sides or
edges very slightly convex, to include every variation of the ex-
periment, that might help to make any magnetic or diamagnetic
effect, whether special or local, or general, manifest; but with-
out effect.
2730. I proceeded, as these attempts had failed, to endeavour
to determine and compare the volume of air subjected to the
magnetic force, before and after its subjection; and there seemed
to be the greater hope of obtaining some results in this way,
provided any such change was a consequence of the action of
magnetic power, because air and gases, at a considerable distance
from the surface of the magnet, are known to be strongly affected
diamagnetically, and because Plücker had already said he had
obtained such change of volume (2722.).
2731. The first instrument constructed for this purpose was
of the following kind. To blocks of soft iron, each 1 inch
thick and 3 inches square, having filed and flattened surfaces,
were prepared; and also a sheet of copper, th of an inch
in thickness and 3 inches square, having its middle part cut
away to within 0-3 of an inch of the edge all round. This plate
or frame was then placed between the iron blocks, and the
174 Non-expansion of gases by magnetism. [SERIES XXV.
whole held together very tightly by copper screws, so as to
make an air-chamber th of an inch wide and 2-4 inches square,
having the faces of the blocks, which were to become the mag-
netic poles, for its sides. Three apertures and corresponding
passages gave access to the interior of this chamber; small stop-
cocks were attached to each. By two of these, any gas, after
it had been properly dried, could be sent into the chamber, or
swept out of it, by any other entering gas; and to the third was
attached a gauge (2732.) for the purpose of indicating and mea-
suring any change of volume which might occur. The edges of
the central copper plate and the heads of the countersunk
screws, were touched with white hard varnish, and the chamber
thus rendered perfectly tight, under every condition to which it
had to be subjected (fig. 1).
Fig. 1.

о
D
Ө
2732. The gauges were formed of small capillary tubes from
1.5 to 3 inches in length, the diameter in the middle of their
length being less than one-half of that at either termination.
Fig. 2.

These were fixed at one end into a small socket, which screwed
on to the third, or gauge-cock mentioned above (2731.). A
minute portion of spirit, coloured by cochineal, being put into
the external end of this gauge, from a slip of wood or glass, im-
mediately advanced to the middle or narrowest part, forming,
as it always should do, a single portion of fluid. By shutting
the cock, this little cylinder could be easily retained in its place
undisturbed during the filling of the air-chamber with gas, and
AUG. 1850.] Non-expansion of gases by magnetism.
175
the adjustment of its pressure to equality with that of the atmo-
sphere. On shutting the other cocks and opening the gauge-
cock, the gauge was then ready to show any change of volume
which the supervention of the magnetic force might cause; but
to give it the highest degree of sensibility, it was necessary
previously to make the liquid cylinder travel right and left of
its place of rest, that the tube might be moistened on each side
of the indicating fluid; an effect easily obtained by inclining the
chamber to and fro, the gravity of the fluid making it pass one
way or the other. But this and many other necessary precau-
tions as to position, temperature, &c., can only be learned from
experience.
2733. When this box was in its place, it stood between the
poles of the great electro-magnet, with the plane of the gas-
chamber in the equatorial position; then square blocks of soft
iron, resting on the magnet poles, were made to abut and bear
against the sides of the box, so that in fact the inner faces of
the air-chamber were the virtual magnetic poles, and being 3
inches square were only th of an inch apart. Hence, what-
ever air or gas was within the chamber, would be subjected to a
very powerful magnetic action, and could have very small
changes in its bulk measured; but it is perhaps necessary to
observe, that it would be contained in a field having everywhere
lines of equal magnetic power (2463. 2465.).
2734. Air was introduced into the box, and when all was
properly arranged, the place of the indicating fluid was observed
by a microscope. Then the magnet was rendered powerfully
active, and there appeared a very slight motion of the fluid, as
if the air were a little expanded; on taking off the magnetic
force the fluid returned to its first place. The same effect re-
curred again and again. The amount of this change was very
small, and there was reason to refer it to the pressure exercised
by the magnet, when in action, upon the sides of the iron box;
for afterwards, when the box was placed in a vice and squeezed,
the same motion in the fluid occurred; and further, when the
square blocks of soft iron (2733.) were kept apart by an under
block of wood, so as not absolutely to touch and press the box,
the effect was reduced to almost nothing.
2735. Oxygen, nitrogen, carbonic acid and nitrous oxide
gases, were then introduced successively into the iron box, and
with exactly the same result as with air. No difference appeared
176
[SERIES XXV.
Non-expansion of gases by magnetism.
between oxygen and the other gases, greatly as they differ in
magnetic and diamagnetic force and relations. Hydrogen and
coal-gas were also subjected to experiment; but when these
gases were in the box there was a gradual recession of the indi-
cating fluid, due, as I found, to the absorption of the gases,
probably either by the varnish or cement or cork used at the
gauge, or at the joints of the box. The delicacy of the gauge
was thus made manifest; but when the effect was taken into
account, it was found that these gases were equally unaffected
in bulk as the other gases by the magnetic influence.
2736. The diameter of the gauge, at the place where the fluid
was placed, was rather less than дth of an inch. An amount
of motion equal to Toth of an inch was easily discerned. Com-
paring these numbers with the capacity of the gas-chamber, it
would appear that if the gas in the latter had expanded or con-
tracted to the extent of 1000th part, the result would have been
visible; or any difference approaching to this amount, between
oxygen and nitrogen or the other gases, would have become
sensible, but no such effects or differences appeared.
100,000
2737. As the establishment of either the occurrence or the
absence of change of volume in gases, when under the magnetic in-
fluence, appeared to me to be of great and almost equal importance,
I was led to consider whether, in the experiment just described,
the circumstance of the gases having been subjected to the mag-
netic power in a field of equal force (2733.) might not have in-
terfered with the production of the effect sought for; for such a
field is that where the diamagnetic phænomena, of solid and
liquid bodies, occur in the most unfavourable manner, and where
indeed they almost entirely disappear. I therefore constructed
another apparatus so that this condition was removed, and in
which, if the particles of the diamagnetic gas, by any unknown
disposition of the powers in action, tended only to pass from
strong to weaker places of force, and being thus incapable of
enlargement in the axial direction, would only show that effect
equatorially, the opportunity for their doing so should be present.
2738. A cylinder of soft iron had the cen-
tral parts removed in a lathe, until it had as-
sumed the form of an hour-glass, or that re
presented in fig, 3, which is to a scale of one-
third. When placed between the poles of
the magnet instead of the former box, it was
Fig. 3.

AUG. 1850.]
177
Non-expansion of gases.
expected that the continuation of the iron throughout woud
prevent any diminution of its length, from the pressure of the
poles (2734.), and that the diamagnetic phænomena would be
abundantly produced in the parts from whence the iron had
been removed. The latter was found to be the fact, for flame
smoke, bismuth and other diamagnetic matter, when placed
there, passed equatorially very freely.
2739. A copper tube, 2.5 inches long, made of metal 0·1 of
an inch thick, was fitted to the iron, so that when in its place
it should occupy the position represented (fig. 3), and could
easily be made perfectly gas-tight by a little soft cement. In
this way it formed an annular air-chamber round the iron, which,
when measured, was found to have a capacity of rather more than
2 cubic inches, and included the most intense part of the mag-
netic field. These stopcocks were fitted into this copper jacket,
by two of which gas was passed into and out of the chamber,
and the third was appropriated to the pressure-gauge as before.
Whilst naked, this apparatus could not be used, because of its
ever-varying temperature, and the consequent disturbance and
ejectment of the fluid in the gauge; but when clothed in three
thicknesses of flannel its temperature was perfectly steady; and
by the further use of wooden keys to turn the cocks the ap-
paratus became unexceptionable.
2740. Before preceeding to employ this apparatus with dif-
ferent gases, and in order to obtain some idea of what might be
expected by comparing one gas with another, I made a prelimi-
nary experiment, dependent on the relative specific gravities of
air and hydrogen, of the following nature. It is easy to diffuse
a trace of ammonia through the air of a jar, by putting a little
paper wetted with a strong solution into it¹; and it is equally
easy to send a jet of hydrogen, containing the smallest portion
of muriatic acid gas, by a horizontal tube into the ammoniated
air. When this is done, the course of the light hydrogen in the
heavy air is rendered very distinctly visible and it is seen, on
leaving the horizontal tube, to turn at once upwards and to as-
cend rapidly, becoming wire-drawn in its course, in consequence
of its small specific gravity compared to air.
2741. Two hemispherical iron pole terminations, associated
with the great magnet, were then placed in contact with each
¹ Philosophical Magazine, 1847, vol. xxxi. p. 415.
VOL. III,
1
N
178
[SERIES XXV.
Non-expansion of gases
'
other, so that they might be surrounded either by air or oxygen¹
and the jet of hydrogen, delivering at the rate of 6 cubic inches per
minute, was placed exactly beneath the axial line, in the centre
of the magnetic field. When there was no magnetic force em-
ployed the hydrogen rose vertically, breaking against the points
where the hemispherical poles touched; but when the mag-
netic power was on, the stream of hydrogen divided into two
parts, moving right and left, and ascended in two streams at a
distance from the point of contact. Now this division took
place at a certain distance below the axial line; and at that point,
notwithstanding the ascensive power of hydrogen in air or oxygen,
it was constrained to go horizontally by the apparently repulsive
power of the magnetic force, and did not in its further course
approach nearer to the axial line, but formed a curve concentric
with it, or nearly so, so that the compound streams of gas
assumed exactly the shape of a tuning-fork.
2742. When air occupied the magnetic field, the division of
the stream of hydrogen was 0.3 or 0.32 of an inch below the
axial line. When oxygen was about the poles, then the division
of the hydrogen took place as far off as 0.55 of an inch below
the axial line. Hence at these distances the power which tended
to make the hydrogen pass from the axial line, equatorially in
the direction of the radius, was equal to the difference of the
specific gravity of hydrogen compared with that of air and oxy-
gen respectively. At lesser distances the power would be much
greater; and indeed, if in any experiment the hydrogen was
delivered nearer to the axial line, it was blown downwards and
away with much force. Calculating with these data, and still
assuming that the diamagnetic gases receded from the axial
line, in consequence of the direct action of the magnet and that
only, causing them to pass from stronger to weaker places of
action, I found, as I thought, reason to believe that the more
diamagnetic gases, occupying the space within the copper box
(2739.), might probably be expanded at least th part of their
volume by the magnetic force. Now the gauges that I employed
were sensible when the fluid in them moved the 10th of an inch
(2736.), yet that space is only the 2,500,000th part of the capacity of
the chamber, and therefore such an expansion as that above
1
1
60,000
00
1 Philosophical Magazine, 1847, vol. xxxi. pp. 413, 414,
AUG. 1850.]
179
by magnetic action.
would have made it move through 0-4 of an inch; a quantity
abundantly sufficient to render the result sensible if the funda-
mental assumption were correct.
2743. Air was first submitted to the power of the great horse-
shoe magnet, urged by twenty pairs of Grove's plates in this
apparatus (2739.). The fluid moved very slightly outwards, as
if a little expansion occurred on putting on the magnetic force,
and returned when the force is taken off. This small effect
was found afterwards to be due to compression, occasioned by
the tendency of the magnetic poles to approximate (2734.).
2744. Oxygen presented exactly the same appearances as com-
mon air and to the same amount, so that no effect, due to mag-
netic or diamagnetic action, was here evident, but only that of
the compression observed in the case of air (2743.).
2745. Nitrogen gave exactly the same results as oxygen and
air. Now nitrogen is probably more diamagnetic than hydro-
gen, and should therefore have given a striking contrast with
oxygen, if any positive results were to be obtained.
2746. Carbonic acid and nitrous oxide gases yielded the same
negative results, and, as I believe, when the apparatus was in an
unexceptionable condition.
2747. There is at the Pharmaceutical Society an excellent
electro-magnet, of the horseshoe form, similar in arrangement
to our own (2247.), but far more powerful, and this through
Mr. Redwood I was favoured with the use of, for the repetition
of the foregoing experiments at the house of the Society. The
iron, which is very soft and good in quality, is a square bar, 5
inches in thickness, and the medium line is 50 inches in length.
It has 1500 feet of copper wire, 0.175 of an inch in thickness,
coiled round it, and arranged (when I used it) in one continuous
length. The moveable terminal pieces for the poles are massive
in proportion to the magnet. Eighty pairs of Grove's plates
were used to excite this magnet, and as it was found, by preli-
minary trials, that these were most powerful when arranged as
four twenties, with their similar ends connected, they were so
used, constituting a battery of twenty pairs of plates, in which
each platinum plate was 4x 9 inches in the immersed part, and
therefore presented 72 square inches of surface towards the active
zinc.
2748. On repeating the former experiments (2743.) the effect
N 2
180
[SERIES XXV.
Non-expansion of gases
of pressure was again evident, and it was manifest that the mag-
net itself, though 5 inches in thickness, was a little bent by the
mutual attraction of its poles. The effect was very small, because
of the unity of the iron core passing through the centre of the
experimental gas-chamber (2738.). It was the only effect indi-
cated by the gauge, and was the same for all the gases; and
when allowance was made for it, nothing remained to indicate
any change in volume of the gas itself.
2749. Air, oxygen, nitrogen, carbonic acid and nitrous oxide
were submitted, in varying order, to the effect of this very pow-
erful magnet, but not the slightest trace of change of bulk in
any of them appeared.
2750. I think that the experiments are in every respect suffi-
cient to decide that these gases, whether they are considered as
magnetic or diamagnetic bodies, or whether they include bodies.
of both classes (for oxygen is in striking contrast to the rest),
are not affected in volume by the magnetic force, whether in
fields of equal power (2737.), or in places where the power is
rapidly diminishing. I think this decision very important in
relation to the true nature of the magnetic force, either as exist-
ing in, or acting upon the particles of bodies; and as in the
magnetic field the force exhibits itself, not as a central but as an
axial power, so the further distinction of the phænomena, into
such as are related to the axial direction (2733.), and, such as
are related to or include the equatorial direction (2737.), is not
unimportant, for they show that the particles do not tend to
separate either parallel to the lines of magnetic power, or in a di-
rection perpendicular to these lines. Without the experiments,
the mind might have considered it very possible that one of these
modes of expansion might have occurred and not the other.
2751. No doubt it is true, that even yet changes in volume in
these directions may occur, provided the change in one direction
is expansion and in the other contraction, and that these are in
amount equal to each other. It was partly in reference to such
possible changes (which may be considered as molecular), that
the experiments with the ray of light were made (2723. 2729.),
and also that in these and other experiments instituted for the
purpose, a polarized ray was employed as the examiner; but the
results were always negative, when by repetition and care sources
of error were removed,
AUG. 1850.]
181
by magnetic action.
2752. The great differences in the degree of diamagnetic sus-
ceptibility and condition which the gases employed in the fore-
going experiments possess or can assume, are such as to make
one ready to suppose, that if they show no tendency in any case
to change in volume under the action of the magnet, so neither
would any other gas or vapour do so, but that all the individuals
belonging to this great class of bodies would be alike in that
respect. In connexion with this conclusion I may state, that I
have on former occasions, and more lately, endeavoured to ascer-
tain, by the use of very delicate apparatus and powerful electro-
magnets, whether any change was produced in the volume of
such fluids as water, alcohol and solution of sulphate of iron,
but could observe no effect of the kind, and I do not believe in
its existence. Still more recently, and in reference to the class
of solid bodies, I have submitted iron as a magnetic metal, and
bismuth as a diamagnetic body, to the same examination; the
metals were employed both in the state of solid cylinders and of
filings or fragments. The cylinders were put into glass tubes
and the particles into glass bottles; gauges, like those described
(2732.), were applied to them, and that part of the containing
vessel which was not filled with metal, was occupied, in one set
of experiments, by air, and in another by alcohol, yet in no case
could the least change in the volume of the iron or bismuth be
observed, however powerful the magnetic force to which they
were submitted.
2753. One other result of a repulsive force seemed possible
even in cases when, according to a former supposition (2751.),
the tendency to expand equatorially might be compensated by
an equal amount of tendency to contract in the axial direction,
namely, that of the production of currents outwards or equatori-
ally, i. e. in lines perpendicular to the magnetic axis, where
pointed poles or the hour-glass core, already described, were
used, and of other currents setting in towards that line along
the inclined surfaces of the polar terminations; in some degree
like those occurring so powerfully, and traced so readily when
flame or hot air is observed in air, or when a stream of one gas
is observed in another gas'.
1
Philosophical Magazine, 1847, vol. xxxi. fp. 402, 404, 409.
182
No currents produced in gases. [SERIES XXV.
2754. When however the gas occupying the whole of the
magnetic field was uniform in nature and alike in temperature,
not the slightest trace of such currents as these could be ob-
served. It is not easy to devise unexceptionable tests of such
motions, because visible bodies introduced into such a mag-
netic field to test the movements of the air there, are them-
selves diamagnetic; and if they form a little isolated cloud, are
moved together and away as a diamagnetic body would be;
but when the whole field was occupied pretty equally by very
light particles of dust or lycopodium, and the magnet in power-
ful action, no signs of currents in the air were visible. Further,
when a faint stream of diffuse cold smoke from a taper spark
was allowed to fall or rise a little on one side of the axial line,
it was determined outwards and equatorially; but though it
went outwards with the most force when equidistant from the
two conical poles, or their representative parts in the double
iron core (2738.), still when it was made to pass near to one
side, it continued to go outwards and equatorially, even when,
from its close vicinity to the iron surface, it had as it were to
move over it; showing that the tendency of the smoke was
outwards in every part of the magnetic field occupied by air or
gas, and that therefore its motion was due to the action of the
magnet on it as a diamagnetic, and not to currents of the air,
which, if existing, would be inwards in one place or direction,
and outwards in another.
2755. When magnetic or diamagnetic fluids were subject to
the magnetic force upon a plate of mica over the poles, according
to the ingenious arrangement of Plücker, they quickly assumed
the different forms correspondent to their nature, but after that
there was no further motion or current in them. The cases are
no doubt different to those where the whole of the magnetic
field is occupied by the same medium; still, as far as it goes, it
helps to confirm the conclusion that no currents are formed.
On putting the same liquids between the poles in glass cells, no
magnetic currents could be observed in them, though fine par-
ticles were introduced into the fluids, for the purpose of making
such changes of place visible, if they occurred.
2756. So there is no evidence, either by the action on a ray of
light (2727. 2729.), or by any expansion or contraction (2750.),
¹ Philosophical Magazine, 1847, vol. xxxi. p. 403.
1
AUG. 1850.]
183
Differential magnetic action.
or by the production of any currents (2754.), that the magnet
exerts any direct power of attraction or repulsion on the particles
of the different gases tried, or that they move in the magnetic
field, as they are known to do, by any such immediate attraction
or repulsion.
Tii. Differential magnetic action.
2757. Then what is the cause of the diamagnetic change of
place? The effect is evidently a differential result, depending
upon the differences of the two portions or masses of matter
occupying the magnetic field, as the air and the streams of other
gas in it', or mercury and the tube of air in it (2407.), or water
and the piece of bismuth in it (2301.); and though exhibited
only in the action of masses, the latter must no doubt owe their
differences to the qualities of the particles composing them. Yet
it is to be observed, that no attempt to separate the perfectly
mixed particles of very different substances has ever succeeded,
though made with most powerful magnets. Oxygen and nitro-
gen differ exceedingly, yet no appearance of the least degree of
separation occurred in very powerful magnetic fields². In other
experiments I have enclosed a dilute solution of sulphate of iron
in a tube, and placed the lower end of the tube between the poles
of a powerful horseshoe magnet for days together, in a place of
perfectly uniform temperature, and yet without the least appear-
ance of any concentration of the solution in that end which
might indicate a tendency in the particles to separate.
2758. The diamagnetic phænomena of the gases, when consi-
dered as the differential result of the action of volumes of these
bodies, may be produced and examined in a very useful manner
by the employment of soap-bubbles, as follows:-A glass tube
was fitted with a cap, stopcock and bladder, so that any given
gas
contained in the bladder might be sent through it, and also
with a foot or stand so that it might be placed in any required
position. The end of the tube was drawn down, bent at right
angles, and cut off straight across at the extremity, being of
1 Philosophical Magazine, 1847, vol. xxxi. p. 409.
2 Ibid. p. 416.
184
[SERIES XXV.
Differential magnetic action.
the size and shape repre-
sented in fig. 4.
Fig. 4.

2759. It is easy to blow
soap-bubbles at the end of
such a tube, of any size up
to an inch in diameter, and
retain them for the time re-
quired by the action of the
stopcock. The soapy water
should be prepared, when
wanted (and not beforehand),
by putting a cutting or two of soap into a little cold distilled water,
for then bubbles of the thinnest and most equable texture can
be blown, which are more mobile than if thicker suds be used,
and if a little care be taken, quite permanent enough for every
useful experiment. The end of the pipe should be perfectly
clean and free from heterogeneous matter (which is often de-
structive of the bubble), and should be wetted both inside and
outside with the soap-water, and left awhile in it before use.
2760. If a bubble be blown with the end of the tube down-
wards, and be half an inch in diameter, it will usually have a
little extra water at the bottom, and will hang from the slender
extremity of the tube by an attachment so small as to allow it
great freedom of motion. Hence it will swing to and fro like a
pendulum; and according as there is more or less water at the
bottom, it will vibrate more or less rapidly, will, as a whole,
gravitate more or less powerfully, and therefore will retain its
perpendicularly dependent position with more or less stability,
-circumstances which are very useful in the employment of the
bubble as a magnetic or diamagnetic indicator.
2761. The regulation of the relative quantity of water which
is in or upon the bubble is easily obtained within certain
limits. If, after the pipe is dipped in the soap-water, the end
be touched with a piece of wood or glass rod, which has also
been kept in the soap-water, more or less of the liquid may be
removed; and by observing the height at which the fluid stands
by capillary action within the tube, which may be varied between
th and an inch, it is easy, after a few experimental trials, to
observe how much is required to make a bubble charged with a
certain amount of water, and how little to give a bubble without
20
AUG. 1850.]
185
shown by bubbles of gas.
any dependent water below; and then it is just as easy, by ar-
ranging the amount of water beforehand, to blow a bubble of any
required character. Even when no drop of water is left at the
bottom, still a range of thickness or thinness in the film itself
can be obtained.
Fig. 5.
2762. As the bubbles contain less and less of water, so are
they rendered more sensitive in their action. They vibrate slower,
and are more easily moved by forces applied laterally to them.
The diamagnetic effect of the soap-water constituting them is
less, and therefore that of the gas contained within them com-
paratively greater. If the bubble is very thin, the dependent
position becomes a position of unstable equilibrium, for any in-
clination of the tube, or any lateral force, however small, then
causes the bubble to pass to one side, and to run up and adhere
to the side of the tube, fig. 5.
The dependent position sup-
plies, in inclosed spaces or at-
mospheres, an exceedingly de-
licate indicator; and even when
the bubble is on the side of the
tube it still forms a very valu-
able instrument, for it freely
moves round the tube as axis;
and as it possesses a certain
degree of steadiness, it can be
held in the magnetic field in
any position, and by its motion to or from the axial line, shows
very well the magnetic or diamagnetic condition of the gas con-
tained in it in relation to the surrounding air.
2763. If the mouth of the tube be turned upwards, bubbles
of the thinnest texture can be blown; but they are then also
very unstable in position, and run to the side of the tube; they
can be used as indicators, as above (2762.). If the mouth of
the tube be made broader, the bubbles, being thin, can be re-
tained standing on the extremity; but as their attachment is
larger, so they require more force to move them sideways, and
they lose in delicacy of indication. It is convenient, in work-
ing with such bubbles, to make them nearly equal in size and
thickness for the same set of comparative experiments. I
usually employ them about half an inch in diameter.

186
[SERIES XXV.
Differential magnetic action
Fig. 6.
2764. On blowing such a bubble with air, in the dependent
position, placing it in the angle of the double pole on a level
with the axial line (fig. 6), and then putting on the magnetic
power by the use of twenty pair of plates,
the bubble was deflected outwards from the
axial line (or equatorially) with a certain
amount of force, and returned to its first
position on the interruption of the electric
current. The deflection was not great, and being due to the
water of the bubble, gave an indication of the amount of that
effect, to be used as a correction in experiments with other gases.
2765. Nitrogen in air.-A bubble of nitrogen went outwards
or equatorially in common air with a force much surpassing the
outward tendency of a bubble of air (2764.), in a very striking
and illustrative manner. It was often driven up from the end
to the side of the tube; and when on the side, if presented in-
wards, it was driven to the outside of the tube, and however the
tube was turned round, kept that position as long as the magnetic
force was maintained. This effect is more striking when it
is considered that four-fifths of the air itself is nitrogen gas.
2766. Oxygen in air.-The effect was very impressive, the
bubble being pulled inwards or towards the axial line sharply and
suddenly, exactly as if the oxygen were highly magnetic. The
result was expected, being in accordance with the phænomena
presented by oxygen and nitrogen in a former investigation of
the diamagnetic phænomena of the gases'.
2767. Nitrous oxide and olefiant gases in air.-The bubbles
went outwards or diamagnetically with a force much greater
than that due to the effect of the water of the bubble, proving
the relation of these gases to air, and according with the results
formerly obtained with streams of these substances 2.
2768. There is no difficulty in applying this method of ob-
servation to experiments with gases in atmospheres of other
gases than air, provided they be such as do not destroy the
bubble; but I do not consume time by detailing the results of
such experiments, which accorded perfectly with those before
obtained³. The description given is quite sufficient to illustrate
the point stated, namely, that the motion of the gases, one in
¹ Philosophical Magazine, 1847, vol. xxxi. pp. 410, 415.

2 Ibid. p. 411.
3 Ibid. pp. 414, 415
AUG. 1850.]
187
of oxygen, nitrogen, space.
another, when in the magnetic field, is a differential result, and
supply sufficient cases for reference hereafter.
2769. The same conclusion, that the effect is a differential
result of the masses of matter present in the magnetic field, is
also manifest from the consideration of the cases of gaseous,
liquid, and solid diamagnetic bodies, advanced in a former part
of these Researches (2405-14.); and a conclusion of the same
kind, as regards magnetic bodies, may also be drawn from ex-
periments then described (2361–68.).
iii. Magnetic characters of Oxygen, Nitrogen, and Space.
2770. The differential action of two portions of gas, or of any
two bodies, may, by a more elaborate method, be examined in a
manner far more interesting and important than that just de-
scribed. The mode of action referred to may even be made the
basis of instruments, by which, probably, most important indi-
cations and measurements of both magnetic and diamagnetic
actions may be obtained, leading to results which are not even
as yet contemplated by the imagination.
2771. If two portions of matter, gaseous or liquid, are tied to-
gether and placed in a symmetric magnetic field, on opposite sides
of the magnetic axis, they will be simultaneously affected. If both
are diamagnetic, or less magnetic than the medium occupying
the magnetic field, both will tend to go outwards or equatorially;
equally if they are alike, but unequally if they differ. The con-
sequence will be, that, if they are placed, in the first instance,
equidistant from the magnetic axis, the supervention of the mag-
netic force will not alter their position, provided they be alike;
but if they differ, then their position will be changed; for the
most diamagnetic will move outwards equatorially, pulling the
least diamagnetic inwards until the two are in such new positions
that the forces acting on them are equipoised, and they will
assume a position of stable equilibrum. Now the distance
through which they will move may be used indirectly, or better
still, the force required to restore them to their equidistant po-
sition may be employed directly to estimate the tendency each
had to go from the magnetic axis; that is, to give their relative
diamagnetic intensities.
2772. That I might submit gases to such a method of exami-
188
[SERIES XXV.
Paramagnetic character of oxygen.
5
nation, I selected a piece of very thin and regular flint-glass tube,
about ths of an inch external diameter, and not more than th
of an inch in thickness, and drawing at the blow-pipe lamp two
equable portions of this tube into the shape and size represented,
fig. 7, in which the barrel part is 14 inch long, I filled one with
16
Fig. 7.

oxygen gas and the other with nitrogen gas, and then sealed
them up hermetically. The end of the prolonged part of each
was touched whilst warm with sealing-wax and a thread fastened
to it, which thread was tied into a loop, also represented of full
size. By these the tubes were to be suspended perpendicularly
from a torsion balance, so that the middle of each should, when
in place, be on a level with the magnetic axis.
.
2773. The torsion balance consisted of a bundle of sixty
equally-stretched cocoon silk fibres, made fast above to a vertical
axis carrying a horizontal index and graduated plate, and below to
a horizontal lever. A cross bar, about 1 inch long, was attached
to one end of this lever, also in the horizontal plane; and on
the extremities of this cross bar, and 8½ inches from the centre
of motion, were hung the two tubes of oxygen and nitrogen
(2772.), counterbalanced by a weight on the other arm of the
horizontal level. The whole was thus so placed and adjusted in
relation to the electro-magnet, furnished at the time with the
double cone core or keeper (2764.), that the middle part of each
tube was level with the middle of the core, and equidistant on
each side from it. Under these circumstances, if any motion
was given to the balance, so as to make its arm vibrate, the
vibrations were made with great slowness, in consequence of the
weight of the whole moving arrangement, and the small amount
of torsion force in the cocoon silk.
2774. The moment the magnetic force was thrown into action
all things changed. The oxygen tube was immediately carried
inwards towards the axis, and the nitrogen tube driven outwards
on the contrary side. The balance swung beyond its new place
of rest and then returned with considerable power, vibrating
many times in the period, which before was filled by a single
AUG. 1850.] Magnetic relations of oxygen and nitrogen. 189
oscillation; and when it had come to its place of rest, or of
stable equilibrium, the oxygen tube was about one-eighth of an
inch from the iron of the core, and the nitrogen tube four-eighths
distant. Ten revolutions of the torsion axis altered only in a
slight degree these relative distances.
2775. The actions which determine the mutual self-adjustment
of the oxygen and nitrogen, as regards their place in relation to
the magnetic axis, are very simple and evident. In the first
place, the glass of the tubes is more diamagnetic than the sur-
rounding medium or air (2424.), and therefore each tends to
move outwards; but being equal in nature and condition to each
other, they tend to move with equal force when at equal distances,
and at those distances compensate each other. If one be driven
inwards, it is subjected to a greater exertion of force by coming
into a more intense part of the magnetic field; and the other,
being at the same time carried outwards, is for a corresponding
reason in a place of less intense action; and therefore, as soon as
the constraint is removed, the system returns to its position of
stable equilibrium, in which the two bodies are equidistant from
the magnetic axis.
2776. The contents also of the tubes are subject to the mag-
netic forces, and as the result shows (2774.), in very different
degrees. Either the oxygen tends inwards much more forcibly
than the nitrogen, or the nitrogen tends outwards more power-
fully than the oxygen; and the difference must exist to a very
great degree, for it is such as to carry the glass of the oxygen
tube up to a position so near the axis that it could not by itself,
or with mere air inside, retain it for a moment without the
aid of considerable restraint. The power with which the tubes
only would retain their equidistant position, combined with the
extent to which they are displaced from this position, shows
the great amount of force which this conjoint action of the
oxygen and the nitrogen leaves free to be exerted in the one di-
rection, namely, from the oxygen inwards or axially, for though
the action be complicated the result is simple. By former ex-
periments, the nitrogen is known to pass equatorially and the
oxygen axially in air', and the nitrogen tube will pass equatori-
ally according to a certain differential force, depending on the
flint glass and the nitrogen on the one hand, and the bulk of air
Philosophical Magazine, 1847, vol, xxxi, p. 409.
190
[SERIES XXV.
Magnetic character of oxygen gas
displaced by them on the other. The oxygen tube in like man-
ner will tend to pass axially by a differential force, the amount
of which will depend upon the tendency of the oxygen to go
axially, of its tube to go equatorially, and of their joint relation
to the air they displace. But both the tubes and their contents
are by their joint relation to the air and their mechanical con-
nexion so related to each other, that when a force (as of torsion)
is employed to restore them to their equidistant position from
the magnetic axis, all consideration of the matter of the tubes
and of the air as a surrounding medium may be dismissed. The
gases within them may be considered as in immediate relation
with each other and the magnetic axis, and disembarrassed from
all other actions: and the force which may be found needful to
place them equidistant, is the measure of their magnetic or dia-
magnetic differences.
2777. Having thus explained the general principles of action,
I will not at present go into their application in the construction
of a measuring instrument or the results obtained with it, further
than is required for the general elucidation of magnetic and
diamagnetic bodies, and the determination of the true zero-point
(2721. 2722.).
2778. The principles just described enabled me to return to a
method of investigation which on a former occasion greatly ex-
cited my hopes (2433.), but which seemed then suddenly cut off
by want of power. Various bodies, whether considered as mag-
netic or diamagnetic substances, admit of two modes of treat-
ment, which promise to be exceedingly instructive as regards
their properties and their destined purposes in natural opera-
tion. A gas may be heated or cooled, and the effect of tempe-
rature, which is known to be very influential', may now be
ascertained without any change in the bulk of the gas; or it
may be rarefied and condensed through a very extensive range,
and the effect of this kind of change upon it ascertained inde-
pendent of temperature or the presence of any other substance.
Solids and liquids do not admit of these methods of examination,
and do not therefore assist in the determination of the zero-
point and of the true distinction of magnetic and diamagnetic
bodies in the same manner that the gases do.
2779. It appeared to me that if a gaseous body were mag-
¹ Philosophical Magazine, 1847, vol. xxxi. pp. 406, 417.
AUG. 1850.]
191
proportionate to the density.
netic, then its magnetic properties ought to be diminished in
proportion as it was rarefied, i. e. that equal volumes of such a
gas at different pressures ought to be more magnetic, as they
are denser; on the other hand, that if a gas were diamagnetic,
rarefaction ought to diminish its diamagnetic character, until,
when reduced to the condition of a vacuum, it should disappear.
In other words, if two opposed portions of the same magnetic
gas, one rarer than the other, were subjected at once to the
magnetic force, the denser ought to approach the axial line, or
be drawn into the place of most intense action; whereas if two
similarly opposed portions of a diamagnetic gas were subjected
to the magnetic action, the more expanded or rarer gas ought to
go inwards to the place of strongest action.
Fig. 8.
2780. Several bulbs of oxygen (fig. 8), similar in
arrangement to those already described (2772.), and
very nearly alike in size, were prepared and hermeti-
cally sealed, after that the quantity of gas within
them had been reduced to a certain degree by the
air-pump. The first contained the gas at the press-
ure of one atmosphere; the second had the gas at
half an atmosphere, or 15 inches of mercury; the
third contained gas at the pressure of 10 inches of
mercury; and the fourth, after being filled with oxy-
gen, was reduced to as good a vacuum as an excel-
lent air-pump could effect. When the first of these
was compared with the other three, the effect was
most striking opposed to the half atmosphere, it
went towards the axis, driving the expanded portion
away; when in relation to the one-third atmosphere,
it went inwards or axially with still more power; and
when opposed to the oxygen vacuum, it took its place as close
to the iron core as in the former case, when contrasted with
nitrogen (2774.); and it was manifest that the diamagnetic power
of the glass tube which inclosed it (2775.), was the only thing
which prevented the oxygen from pressing against the iron core
occupying the centre of the magnetic field.
2781. On experimenting with the other tubes exactly the
same result was obtained. Thus the tube with one-third of an
atmosphere, in association with the vacuum tube, went inwards,
driving the other outwards, i. e. it was more magnetic than the

192
[SERIES XXV.
Magnetic character of oxygen gas.
vacuum; but in association with the one-half atmosphere tube
it went outwards, whilst the denser gas passed inwards. Any
one of the tubes, if associated with another having a rarer atmo-
sphere, passed inwards or magnetically, whilst if associated with
others having denser atmospheres it passed outwards, being
driven off by the superior magnetic force of the denser gas. As
far as I could ascertain in these preliminary forms of experiment,
the tendency inwards or axially appeared to be in proportion to
the density of the gas; but the exact measurement of these
forces will be given hereafter.
2782. Thus oxygen appears to be a very magnetic substance,
for it passes axially, or from weaker to stronger places of force,
with considerable power; a conclusion in accordance with the
result of former observations¹. Moreover it passes more power-
fully when dense than when rare, its tendency inwards being
apparently in proportion to its density. Hence, as the oxygen
is removed, the magnetic force disappears with it, until when a
vacuum is obtained, little or no trace of attraction or inward
force remains. No doubt it may be said that dense oxygen is
less diamagnetic than rare oxygen, or a vacuum. This however
would imply, that the acting force of a substance, as the oxygen,
could increase in proportion as the quantity of the substance
diminished, which is not, I think, a philosophical assumption;
and besides that, other reasons will soon appear to show that
the magnetic condition which disappears as the oxygen is re-
moved, belongs to, and is dependent upon that substance, and
that oxygen is therefore a truly magnetic body.
2783. Nitrogen, being the other and larger part of the atmo-
sphere, was then subjected to experiment, and three tubes, one
containing the gas at a pressure of 30 inches of mercury, another
with the gas at the pressure of 15 inches, and the third reduced
as nearly as it could be to a vacuum, were prepared (2780.).
When these were compared one with another in the magnetic
field, they were found to be so nearly alike as not to be distin-
guishable from each other, i. e. they remained equidistant from
the magnetic axis. I do not mean to imply that nitrogen at
these different pressures is absolutely the same bulk for bulk
(an instrument now under construction will enable me hereafter
to compare and measure with infinitely greater accuracy, and to
¹ Philosophical Magazine, 1847, vol, xxxi. pp. 410, 415:
1
AUG. 1850.] Magnetic character of nitrogen gas.
193
ascertain these points); but as compared with oxygen, the great
and extraordinary differences produced by rarefaction there, have
no corresponding differences here. If there are any, they are
insensible at present, and may for the chief purpose of this
paper and the determination of the zero-point between mag-
netics and diamagnetics, be taken as nothing.
2784. Nitrogen therefore appears to be neither magnetic nor
diamagnetic; if it were either, it could not but fall in its specific
condition as it was rarefied; as it is, it is equivalent to a vacuum.
If a given space be considered as a vacuum, into which oxygen
or nitrogen is to be gradually introduced, as oxygen is added
the space becomes more and more magnetic, i. e. more compe-
tent to admit of the kind of action distinguished by that word;
but the corresponding gradual addition of nitrogen to an empty
space produces no effect of that kind, or the contrary, and the
nitrogen is therefore neither magnetic nor diamagnetic, but like
space itself.
2785. As yet I have found no gas, which, being on the dia-
magnetic side of zero, can at all compare with oxygen in the
range of effect produced by rarefaction. For the present, I may
mention olefiant gas and cyanogen as substances which appear
to proceed inwards, or towards the axial line, as they are more
rarefied. They are therefore not merely at zero, but are in
opposition to oxygen and are diamagnetic bodies. But if we
want a body that is strongly and undeniably diamagnetic, and
which, being added to or introduced into space, will make it
diamagnetic, as oxygen renders it magnetic, then flint glass or
phosphorus present us with such a substance. When these
bodies are made into forms similar to the volumes of nitrogen,
or the vacua in size and shape, and are compared with them on
the torsion balance, they pass outwards with much force; and it
is probably the great diamagnetic force of the glass of the tubes
that prevents the effect of rarefaction from being more evident
in olefiant and other gases.
2786. When a tube has been filled with a particular gas, then
exhausted as much as possible, and sealed up hermetically, it
may be considered as inclosing what is commonly called a va-
cuum. I have prepared many such vacua, and may be per-
mitted to distinguish them by the name of the gas, traces of
which still remain. In comparing these vacua in the magnetic
VOL. III,
()
194
[SERIES XXV.
Magnetic character of space.
field (2773.), they appeared to me to be in all respects alike;
the oxygen vacuum was not more magnetic than the hydrogen,
nitrogen, or olefiant vacuum. Their differences, if any, were far
smaller than the differences which could be produced by the
variations of size and other conditions of the glass bulbs, and
can only be made manifest by the means hereafter to be used
(2783.); and I am fully persuaded that they will ultimately be
nearly alike, ranging close up to and about a perfect vacuum.
2787. Before determining the place of zero amongst magnetic
and diamagnetic bodies, we have to consider the true character
and relation of space free from any material substance. Though
one cannot procure a space perfectly free from matter, one can
make a close approximation to it in a carefully prepared Torri-
cellian vacuum. Perhaps it is hardly necessary for me to state,
that I find both iron and bismuth in such vacua perfectly
obedient to the magnet. From such experiments, and also from
general observations and knowledge, it seems manifest that the
lines of magnetic force (2149.) can traverse pure space, just as
gravitating force does, and as static electrical forces do (1616.);
and therefore space has a magnetic relation of its own, and one
that we shall probably find hereafter to be of the utmost import-
ance in natural phænomena. But this character of space is
not of the same kind as that which, in relation to matter, we
endeavour to express by the terms magnetic and diamagnetic.
To confuse them together would be to confound space with
matter, and to trouble all the conceptions by which we endea-
vour to understand and work out a progressively clearer view of
the mode of action and the laws of natural forces. It would be as
if, in gravitation or electric forces (1613.), one were to confound
the particles acting on each other with the space across which
they are acting, and would, I think, shut the door to advance-
ment. Mere space cannot act as matter acts, even though the
utmost latitude be allowed to the hypothesis of an ether; and
admitting that hypothesis, it would be a large additional assump-
tion to suppose that the lines of magnetic force are vibrations
carried on by it (2591.); whilst as yet, we have no proof or in-
dication that time is required for their propagation, or in what
respect they may in general character assimilate to, or differ
from, the respective lines of gravitating, luminiferous, or electric
forces,
AUG. 1850.]
195
Magnetic zero-magnetic terms.
2788. Neither can space be supposed to have those circular
currents round points diffused through it, which Ampère's theory
assumes to exist around the particles of ordinary magnetic matter,
and which I had for a moment supposed might exist in the con-
trary direction round the particles of diamagnetic matter (2429.
2640. &c.). The imagination, restrained by philosophical con-
siderations, fails to find any thing in pure space about which the
currents could circulate, or to which they could by any associa-
tion be attached; and the difficulty, if already not immeasurable,
would be still greater to those, if there be any, who, assuming
that magnetic and diamagnetic bodies are alike in nature, must
assume that there are like currents in both; for it does not seem
possible to add (for instance) phosphorus having such a magnetic
constitution, to space supposed to be of a similar constitution,
and yet to have as a result a diminution of the magnetic powers
of the space so occupied.
2789. As space therefore comports itself independently of
matter, and after another manner, the different varieties of mat-
ter must, in relation to their respective qualities, be considered
amongst themselves. Those which produce no effect when added
to space, appear to me to be neutral or to stand at zero. Those
which bring with them an effect of one kind will be on the one
side of zero, and those which produce an effect of the contrary
kind will be on the other side of zero; by this division they consti-
tute the two subdivisions of magnetic and diamagnetic bodies.
The law which I formerly ventured to give (2267. 2418.), still
expresses accurately their relations; for in an absolute vacuum
or free space, a magnetic body tends from weaker to stronger
places of magnetic action, and a diamagnetic body under similar
conditions from stronger to weaker places of action.
2790. Now that the true zero is obtained, and the great
variety of material substances satisfactorily divided into two
general classes, it appears to me that we want another name for
the magnetic class, that we may avoid confusion. The word
magnetic ought to be general, and include all the phænomena
and effects produced by the power. But then a word for the
subdivision, opposed to the diamagnetic class, is necessary. As
the language of this branch of science may soon require general
and careful changes, I, assisted by a kind friend, have thought
that a word not selected with particular care might be provi-
o 2
196
Magnetic character of different gases. [SERIES XXV.
sionally useful; and as the magnetism of iron, nickel and cobalt,
when in the magnetic field, is like that of the earth as a whole,
so that when rendered active they place themselves parallel to
its axes or lines of magnetic force, I have supposed that they
and their similars (including oxygen now) might be called para-
magnetic bodies, giving the following division:-
Magnetic {Paramagnetic.
If the attempt to facilitate expression be not accepted, I hope
it will be excused.
2791. From the presence of oxygen in the air, the latter is,
as a whole, a magnetic medium of no small power. Hence all
the comparative experiments on the diamagnetic condition of
other gases, made by passing streams of them through it and
through each other¹, require a correction, which occasionally
may place some of these bodies on the paramagnetic side of
zero. Even solid and fluid substances may be thus affected;
and the preliminary list, which I formerly gave (2424.), will
need alteration in this respect. I hope soon however to have
the means of ascertaining, not only the place of bodies, but also
their relative degrees of force, at the same and at different tem-
peratures, with a degree of accuracy that will serve great pur-
poses in the further development of this branch of science.
2792. Amongst the gases hitherto examined there is nothing
that compares with oxygen. The following are comparatively
indifferent by the side of it :-chlorine and bromine vapour,
cyanogen, nitrogen, hydrogen, carbonic acid, carbonic oxide,
olefiant gas, nitrous oxide, nitric oxide, nitrous acid vapour, muri-
atic acid, sulphurous acid, hydriodic acid, ammonia, sulphuretted
hydrogen, coal-gas, æther vapour and sulphuret of carbon vapour;
for though some, as olefiant and cyanogen gases, appear to be a
little diamagnetic, and others, as nitrous oxide and nitric oxide,
are magnetic, yet their effects disappear in comparison with the
results produced by oxygen.
2793. I hope to give the correct expression of the paramag-
netic force of oxygen (2783.) hereafter, in the meantime I am
tempted to give one or two rough illustrations of its degree in
¹ Philosophical Magazine, 1847, vol, xxxi. pp. 407, 420, &c.
1
AUG. 1850.] Paramagnetic force of oxygen gas.
197
this place, in addition to the former one (2774.). The capacity
of the oxygen bulb, containing one atmosphere, is not quite 0.34
of a cubic inch, and the weight therefore of the oxygen within
0.117 of a grain. I endeavoured to compare this quantity in
the first place with soft iron, and therefore attached a portion
of that metal, having one-tenth of this weight or 0·012 of a grain,
to a fine platina wire fixed into one end of a vessel, correspond-
ing in size to that containing the oxygen, so as to bring the iron
into the middle, and then the bulb was exhausted and hermeti-
cally sealed. Being now opposed to the oxygen tube in the
magnetic field, it was found, as expected, far to surpass the
oxygen in magnetic power. As it was inconvenient further to
reduce the iron or to enlarge the oxygen, another magnetic sub-
stance was employed for the comparison.
2794. One hundred grains of clean, good, crystallized proto-
sulphate of iron were dissolved in distilled water, and diluted
until a glass bulb, of nearly the same size as the oxygen bulb
when filled with the solution, was equal to the oxygen bulb in
force, and stood equidistant from the axial line, as far as I could
judge by the present modes of observation. When the solution
had this strength, it occupied the bulk of 17 cubic inches. As
the bulk of the oxygen is only 0.34 of a cubic inch (2793.),
that volume of this solution would contain very nearly two grains
of crystallized sulphate of iron, equivalent to 0·4 of a grain of
metallic iron; so that, bulk for bulk, oxygen is equally magnetic
with a solution of sulphate of iron in water containing seventeen
times the weight of the oxygen in crystallized protosulphate of
iron, or 3-4 times its weight of metallic iron in that state of
combination.
2795. Again, the oxygen tubes, containing respectively one
atmosphere and a vacuum (2780.), were adjusted about an inch
apart, and placed on each side of the magnetic axis, and the
force of the magnet developed. The oxygen of course approached
the magnetic axis, and the vacuum passed equatorially. A slen-
der glass filament, about 6 inches in length, had been drawn
out at the lamp and fixed to a foot; and the end of this filament
was then employed to press back the oxygen tube into its ori-
ginal place, and render it equidistant from the magnetic axis
with the vacuum tube. In this position the two tubes would,
as respects the glass, neutralize each other (2775.); and con-
198
Paramagnetic force of oxygen gas. [SERIES XXV.
sidering the vacuum as zero, the oxygen alone may be considered
as active, and the force required to hold it out may be looked
upon as the force with which the oxygen, at that distance of
half an inch, tended to go to the magnetic axis. The deflection
of the glass filament or spring, at the place where the oxygen
tube was held by it, was rather more than one inch from its
position when relieved from the pressure of the tube. Being
taken away, it was set up in the horizontal position (after being
turned 90° on its axis, so that the flexure might be in the same
direction, relative to the filament, as before); and the position
of the end being marked, weights were put on it at the place of
former contact with the oxygen tube, until they produced the
same amount of deflection as before. It required rather more
than the tenth of a grain to produce this effect; and this, consi-
dering that the whole oxygen only weighed 0.117 of a grain,
and that no part of it was nearer than half an inch, whilst the
average distance of the mass was above an inch from the mag-
netic axis, gives a high expression for the magnetic power.
2796. It is hardly necessary for me to say here that this
oxygen cannot exist in the atmosphere, exerting such a remark-
able and high amount of magnetic force, without having a most
important influence on the disposition of the magnetism of the
earth as a planet, especially if it be remembered that its mag-
netic condition is greatly altered by variations in its density
(2781.) and by variations in its temperature'. I think I see
here the real cause of many of the variations of that force, which
have been, and are now, so carefully watched on different parts
of the surface of the globe. The daily variation and the annual
variation both seem likely to come under it; also very many of
the irregular continual variations which the photographic pro-
cess of record renders so beautifully manifest. If such expecta-
tions be confirmed, and the influence of the atmosphere be
found able to produce results like these, then we shall probably
find a new relation between the aurora borealis and the mag-
netism of the earth, namely, a relation established, more or less,
through the air itself in connexion with the space above it; and
even magnetic relations and variations which are not as yet sus-
pected, may be suggested and rendered manifest and measureable,
in the further development of what I will venture to call Atmo-
¹ Philosophical Magazine, 1847, vol. xxxi. p. 417.
1
AUG. 1850.]
199
Atmospheric magnetism.
spheric Magnetism (2847. &c.). I may be over-sanguine in
these expectations, but as yet I am sustained in them by the
apparent reality, simplicity and sufficiency of the cause assumed,
as it at present appears to my mind. As soon as I have suffi-
ciently submitted these views to a close consideration and the
test of accordance with observation, and where applicable with
experiments also, I will do myself the honour to bring them.
before the Royal Society.
Royal Institution, August 2, 1850.
200
TWENTY-SIXTH SERIES ¹.
§ 32. Magnetic conducting power. i. Magnetic conduction.
ii. Conduction polarity. iii. Magnecrystallic conduction.
§ 33. Atmospheric magnetism. i. General principles.
Received October 92,-Read November 28, 1850.
¶i. Magnetic conduction.
2797. THE remarkable results given in a former series of these
Researches (2757. &c.) respecting the powerful tendency of cer-
tain gaseous substances to proceed either to or from the central
line of magnetic force, according to their relation to other
substances present at the same time, and yet the absence of
all condensation or expansion of these bodies (2756.) which
might be supposed to be consequent on such an amount of at-
tractive or repulsive force as would be thought needful to pro-
duce this tendency and determination to particular places, have,
upon consideration, led me to the idea, that if bodies possess
different degrees of conducting power for magnetism, that dif
ference may account for all the phænomena; and, further, that
if such an idea be considered, it may assist in developing the
nature of magnetic force. I shall therefore venture to think
and speak freely on this matter for a while, for the purpose of
drawing others into a consideration of the subject; though I
run the risk, in doing so, of falling into error through imperfect
experiments and reasoning. As yet, however, I only state the
case hypothetically, and use the phrase conducting power as a
general expression of the capability which bodies may possess of
effecting the transmission of magnetic force; implying nothing
as to how the process of conduction is carried on. Thus limited
in sense, the phrase may be very useful, enabling us to take, for
¹ Philosophical Transactions, 1851, p. 29.
+
2 Revised by the author and returned by him, November 12, 1850.
OCT. 1850.]
201
Magnetic conduction.
a time, a connected, consistent and general view of a large class
of phænomena; may serve as a standard of meaning amongst
them, and yet need not necessarily involve any error, inasmuch
as whatever may be the principles and condition of conduction,
the phænomena dependent on it must consist among them-
selves.
2798. If a medium having a certain conducting power occupy
the magnetic field, and then a portion of another medium or
substance be placed in the field having a greater conducting
power, the latter will tend to draw up towards the place of
greatest force, displacing the former. Such at least is the case
with bodies that are freely magnetic, as iron, nickel, cobalt and
their combinations (2357. 2363. 2367. &c.), and such a result is
in analogy with the phænomena produced by electric induction.
If a portion of still higher conducting power be brought into
play, it will approach the axial line and displace that which had
just gone there; so that a body having a certain amount of con-
ducting power, will appear as if attracted in a medium of weaker
power, and as if repelled in a medium of stronger power by this
differential kind of action (2367. 2414.).
2799. At the same time that this idea of conduction will thus
account for the place which a given substance would take up, as
of oxygen in the axial line if in nitrogen, or of nitrogen at a
distance if in oxygen, it also harmonizes with the fact, that there
are no currents induced in a single gas occupying the magnetic
field (2754.), for any one particle can then conduct as well as
any other, and therefore will keep its place; and it also agrees,
I think, with the unchangeability of volume (2750.).
2800. In reference to the latter point, we have to consider
that the force which urges such a body as oxygen towards the
middle of the field, is not a central force like gravitation, or the
mutual attraction of a set of particles for each other; but an
axial force, which, being very different in character in the direc-
tion of the axis and of the radii, may, and must produce its effect
in a very different manner to a purely central force. That these
differences exist, is manifest by the action of transparent bodies,
when in the magnetic field, upon a ray of light; and also by the
ordinary action of magnetic bodies: and hence, perhaps, the
reason, that when oxygen is drawn into the middle of the field,
in consequence of its conducting power, still its particles are
202
[SERIES XXVI.
Magnetic conduction.
not compressed together (2721.) by a force that otherwise would
seem equal to that effect (2766.).
2801. So when two separate portions of oxygen or nitrogen
are in the magnetic field, the one passes inwards and the other
outwards, without any contraction or expansion of their relative
volumes; and the result is differential, the two bodies being in
relation to and dependence on each other, by being simultane-
ously related to the lines of magnetic force which pass conjointly
through them both, or through them and the medium in which
they are conjointly immersed.
2802. I have already said, in reference to the transference
onwards of magnetic force (2787.), that pure space or a vacuum
permits that transference, independent of any function that can
be considered as of the same nature as the conducting power of
matter; and in a manner more analogous to that in which the
lines of gravitating force, or of static electric force, pass across
mere space. Then as respects those bodies which, like oxygen,
facilitate the transmission of this power more or less, they class
together as magnetic or paramagnetic substances (2790.); and
those bodies, which, like olefiant gas or phosphorus, give more
or less obstruction, may be arranged together as the diamagnetic
class. Perhaps it is not correct to express both these qualities
by the term conduction; but in the present state of the subject,
and under the reservation already made (2797.), the phrase may
I think be employed conveniently without introducing con-
fusion.
2803. If such be a correct general view of the nature and dif-
ferences of paramagnetic and diamagnetic substances, then the
internal processes by which they perform their functions can
hardly be the same, though they might be similar. Thus they
may have circular electric currents in opposite directions, but
their distinction can scarcely be supposed to depend upon the
difference of force of currents in the same direction. If the
view be correct also, though the results obtained when two bodies
are simultaneously present in the magnetic field may be consi-
dered as differential (2770. 2768.) even though one of them be
the general medium, yet the consequence of the presence of
conducting power in matter renders a single body, when in
space, subject to the magnetic force; and the result is, that
when a paramagnetic substance is in a magnetic field of unequal
Ост. 1850.]
203
Magnetic conduction.
force, it tends to proceed from weaker to stronger places of ac-
tion, or is attracted; and when a diamagnetic body is similarly
circumstanced, it tends to go from stronger to weaker places of
action or is repelled (2756.).
2804. Matter, when its powers are under consideration, may,
as to its quantity, be considered either by weight or by volume.
In the present case, where the effects produced have an imme-
diate reference to mere space (2787. 2802.), it seems proper that
the volume should be considered as the representation, and that
in comparing one substance with another, equal volumes should
be employed to give correct results. No other method could be
used with the differential system of observation (2772. 2780.).
2805. Some experimental evidence, other than that of change
of situation, of the existence of this conducting power, by dif-
ferences in which, I am endeavouring to account for the peculiar
characteristics of paramagnetic and diamagnetic bodies, may well
be expected. This evidence exists; but as certain considerations
connected with polarity preclude me from calling too freely upon
iron, cobalt, or nickel (2832.) for illustrations, and as in other
bodies which are paramagnetic, as well as in those that are dia-
magnetic, the effects are very weak, they will be better compre-
hended after some further general consideration of the subject
(2843.).
2806. I will now endeavour to consider what the influence is
which paramagnetic and diamagnetic bodies, viewed as conduc-
tors (2797.), exert upon the lines of force in a magnetic field.
Any portion of space traversed by lines of magnetic power, may
be taken as such a field, and there is probably no space without
them. The condition of the field may vary in intensity of
power, from place to place, either along the lines or across
them; but it will be better to assume for the present considera-
tion a field of equal force throughout, and I have formerly de-
scribed how this may, for a certain limited space, be produced
(2465.). In such a field the power does not vary either along
or across the lines, but the distinction of direction is as great
and important as ever, and has been already marked and ex-
pressed by the term axial and equatorial, according as it is
either parallel or transverse to the magnetic axis.
204
[SERIES XXVI.
Magnetic conduction.
Fig. 1.
2807. When a paramagnetic conductor, as for instance, a
sphere of oxygen, is introduced into such a magnetic field, con-
sidered previously as free from matter, it
will cause a concentration of the lines of
force on and through it, so that the space
occupied by it transmits more magnetic
power than before (fig. 1). If, on the other
hand, a sphere of diamagnetic matter be
placed in a similar field, it will cause a di-
vergence or opening out of the lines in the
equatorial direction (fig. 2); and less mag-
netic power will be transmitted through the
space it occupies than if it were away.

Fig. 2.

2808. In this manner these two bodies
will be found to affect first the direction
of the lines of force, not only within the
space occupied by themselves, but also in the neighbouring
into which the lines passing through them are prolonged;
and this change in the course of the lines will be in the contrary
direction for the two cases.
space,
2809. Secondly, they will affect the amount of force in any
particular part of the space within or near them; for as every
section across the line of such a magnetic field must be definite
in amount of force, and be in that respect the same as every
other section, so it is impossible to cause a concentration within
the sphere of oxygen (fig. 1) without causing also a simultaneous
concentration in the parts axially situated as a a outside of it,
and a corresponding diminution in the parts equatorially placed,
bb. On the other hand, the diamagnetic body (fig. 2) will cause
diminution of the magnetic force in the parts of space axially
placed in respect of it, cc, and concentration in the near equa-
torial parts, d d. If the magnetic field be considered as limited
in its extent by the walls of iron forming the faces of opposed
poles (2465.), then even the distribution of the magnetism within
the iron itself will be affected by the presence of the paramag-
netic or diamagnetic bodies; and this will happen to a very
large extent indeed, when, from among the paramagnetic class
such substances as iron, nickel or cobalt are selected.
2810. The influence of this disturbance of the forces upon the
place and position of either a paramagnetic or a diamagnetic
Ост. 1850.]
205
Place of conductors in the field.
.
body placed within the magnetic field, is readily deduced upon
consideration and easily made manifest by experiment. A small
sphere of iron placed within a field of equal magnetic power,
bounded by the iron poles, has a position of unstable equili-
brium, equidistant from the iron surfaces, and at such time a
great concentration of force takes place through it, and at the
iron faces opposite to it, and through the intervening axial
spaces. If the sphere be on either side of the middle distance,
it flies to the nearest iron surface, and then can determine the
greatest amount of magnetic force to or upon the axial lines
which pass through it.
2811. If the iron be a spheroid, then its greatest diameter
points axially, whether it be in the position of unstable equili-
brium, nearer to or in contact with the iron walls of the field.
As the circumstances are now more favourable for the concen-
tration of force in the axial line passing through the body than
before, so this result can be produced by much weaker para-
magnetics than iron, and I have no doubt could easily be pro-
duced by a vessel of oxygen or nitric oxide gas (2782. 2792.).
It now becomes indeed a form, though not the best, of that ex-
periment by which the magnetic condition of bodies is considered
as most sensitively tested.
2812. The relative deficiency of power in diamagnetic bodies
renders any attempt to obtain the converse phænomena to those
of iron somewhat difficult; in order therefore to exalt the con-
ditions, I used a saturated solution of protosulphate of iron in
the magnetic field; by this means I strengthened the lines of
power passing across it, without disturbing its equality in the
parts employed, or introducing any error into the principle of
the experiment, and then used bismuth as the diamagnetic body.
A cylinder of this substance, suspended vertically, tended well
towards the middle distance, finding its place of stable equili-
brium in the spot where the paramagnetic body had unstable
equilibrium. When the cylinder was suspended horizontally,
then the direction it took was equatorial; and this effect also
was very clear and distinct.
2813. These relative and reverse positions of paramagnetic
and diamagnetic bodies, in a field of equal magnetic force, accord
well with their known relations to each other, and with the kind
of action already laid down in principle (2807.) as that which
206
[SERIES XXVI.
Magnetic conduction.
they exert on the magnetic power to which they are subjected.
One may retain them in the mind by conceiving that if a liquid
sphere of a paramagnetic conductor were in the place of action,
and then the magnetic force developed, it would change in form
and be prolonged axially, becoming an oblong spheroid; whereas
if such a sphere of diamagnetic matter were placed there, it
would be extended in the equatorial direction and become an
oblate spheroid.
2814, The mutual action of two portions of paramagnetic
matter, when they are both in such a field of equal magnetic
force, may be anticipated from the principles (2807. 2830.), or
from the corresponding facts, which are generally known. Two
spheres of iron, if retained in the same equatorial plane, repel
each other strongly; but as they are allowed to depart out of
that plane, they first lose their mutual repulsive force and then
attract each other, and that they do most powerfully when in an
axial direction.
2815. With diamagnetic bodies the mutual action is more
difficult to determine, because of the comparative lowness of
their condition. I therefore resorted to the expedient, before
described, of using a saturated solution of protosulphate of iron
as the medium occupying the field of equal magnetic force, and
employing two cylinders of phosphorus, about an inch long and
half an inch in diameter, as the diamagnetic bodies. One of
these was suspended at the end of a lever, which was itself
suspended by cocoon-silk, so as to have extremely free motion,
and the adjustments were such, that when the phosphorus cy-
linder was in the middle of the magnetic field, it was free to
move equatorially or across the lines of magnetic force; it how-
ever had no tendency to do so under the influence of the magnetic
force. The other cylinder was attached to a copper wire handle,
and could be placed in a fixed position on either side of the
former cylinder; it was therefore adjusted close by the side of
it, and the two retained together, until all disturbance from
motion of the fluid or of the air had ceased; then the retaining
body was removed, the two phosphorus cylinders still keeping
their places; finally, the magnetic power was brought into ac-
tion, and immediately the moveable cylinder separated slowly
from the fixed one and passed to a distance. If brought back
again whilst the magnet was active, when left at liberty it receded;
OCT. 1850.]
207
Conduction polarity.
but if restored to close vicinity, when the magnetic force was
away, it retained that situation. The effect took place either in
the one direction or the other, according as the fixed cylinder
was on this or that side of the moving one; but the motion
was in both cases across the lines of magnetic force, and was
indeed mechanically and purposely limited to that direction by
the mode of suspension. When two bismuth balls were placed,
in respect of each other, in the direction of the magnetic axis, so
that one might move, but only in the direction of that axis, its
place was not sensibly affected by the other; the tendency of
the free one to go to the middle of the field (2812.) overpowered
any other tendency that might really exist.
2816. Thus two diamagnetic bodies, when in the magnetic
field, do truly affect each other; but the result is not opposed in
its direction to that of paramagnetic bodies, being in both cases
a separation of the substances from each other.
2817. The comparison of the action of para- and diamagnetic
bodies on each other, was completed by using water as the me-
dium in a field of equal magnetic force, and suspending a piece
of phosphorus from the torsion balance. When the magnetic
power was on, this phosphorus was repelled equatorially, as
before, by another piece of phosphorus, but it was attracted by
a tube filled with a saturated solution of protosulphate of iron;
so paramagnetic and diamagnetic bodies attract each other equa-
torially in a mean medium, but each repels bodies of its own
kind (2831.).
Tii. Conduction polarity.
2818. Having thus considered briefly the effects which the
disturbance of the lines of force, by the presence of paramag-
netic and diamagnetic bodies, is competent to produce (2807. &c.),
I will ask attention to that which may be considered as their
polarity: not wishing by the term to indicate any internal con-
dition of the substances or their particles, but the condition of
the mass as a whole, in respect of the state into which it is
brought by its own disturbance of the lines of magnetic force;
and that, both in regard to its condition with respect to other
bodies similarly affected; and also in regard to differences exist-
ing in different parts of its own mass. Such a condition con-
cerns what may be called conduction polarity. Bodies in free
space, when under magnetic action, will possess it in its simplest
208
Magnetic conduction polarity. [SERIES XXVI.
condition; but bodies immersed in other media will also possess
it under more complicated forms, and its amount may then be
varied, being reversed or increased, or diminished to a very
large extent.
2819. Taking the simplest case of paramagnetic polarity, or
that presented in fig. 1 (2807.), it consists in a convergence of
the lines of magnetic force on to two opposed parts of the body,
which are to each other in the direction of the magnetic axis.
The difference in character of the two poles at these parts is
very great, being that which is due to the known difference of
quality in the two opposite directions of the line of magnetic
force. Whether polar attraction or repulsion exists amongst
paramagnetic bodies, when they present mere cases of conduc-
tion (as oxygen, for instance), is not yet certain (2827.), but it
probably does; and if so, will doubtless be consistent with the
attraction and repulsion of magnets having correspondent poles.
2820. When we consider the conduction polarity of a dia-
magnetic body, matters appear altogether different. It has not
a polarity like that of a paramagnetic substance, or one the mere
reverse (in name or direction of the lines of force) of such a
substance, as I, Weber and others have at times assumed (2640.),
but a state of its own altogether special. Its polarity consists
of a divergence of the lines of power on to, or a convergence
from the parts, which being opposite, are in the direction of the
magnetic axis; so that these poles, having the same general and
opposite relations to each other, which correspond to the dif-
ferences in the poles of paramagnetic bodies, have still, under
the circumstances, that striking contrast and difference from the
polarity of the latter bodies which is given by convergence and
divergence of the lines of force.
2821. Let fig. 3
represent a limited
magnetic field with a
paramagnetic body
P, and a diamag-
netic body D, in it,
and let N and S re-
present the two walls
5
5
Fig. 3.
N

S
D
of iron associated with the magnet (2465.) which form its boun-
dary, we shall then be able obtain a clear idea of the direction
OCT. 1850.] Magnetic conduction-conduction polarity.
209
of the lines of magnetic force in the field. Now the two bodies, P
and D, cannot be represented by supposing merely that they have
the same polarities in opposite directions. The 1 polarity of P
is importantly unlike the 3 polarity of D; but if D be considered
as having the reverse polarities of P, then the one polarity of P
should be like the 4 polarity of D, whereas it is more unlike to
that than to the 3 polarity of D, or even to its own 2 polarity.
2822. There are therefore two essential differences in the na-
ture of the polarities dependent on conduction, the difference in
the direction of the lines of force abutting on the polar surfaces,
when the comparison is with a magnet reversed, and the dif-
ference of convergence and divergence of these lines, when com-
pared with a magnet not reversed; and hence a diamagnetic
body is not in that condition of polarity which may be repre-
sented by turning a paramagnetic body end for end, while it
retains its magnetic state.
2823. Diamagnetic bodies in media more diamagnetic than
themselves, would have the polar condition of paramagnetic
bodies (2819.); and in like manner paramagnetic conductors
in media more paramagnetic than themselves, would have the
polarity of diamagnetic bodies.
2824. Besides these differences the bodies must have an
equatorial condition, which, in the two classes of conductors,
would be able to produce corresponding effects. The whole of
the equatorial part of P (fig. 3) is alike in polar relation to the body
P, or to the lines of force in the surrounding space; and there
is a like correspondence in the equatorial parts of D, either to
itself or to space; but these parts in P or in D differ in intensity
of power one from the other, and both from the general inten-
sity of the space. Such equatorial conditions must, I think,
exist as a consequence of the definite character of any given
section of the magnetic field (2809.).
2825. Though the experimental results of these polarities are
not absent, still they are not very evident or capable of being
embodied in many striking forms; and that because of the ex-
treme weakness of the forces brought into play, as compared
with those larger forces exhibited in the mutual action of mag-
nets. Hence it is, that the many attempts to show a polarity in
bismuth have either failed, or other phænomena have been mis-
taken for those properly referable to such a cause. The highest,
VOL. III.
P
210
[SERIES XXVI.
Magnetic conduction.
and therefore the most delicate, test of polarity we possess, is in
the subjection of the polar body to the line of direction of mag-
netic forces of a very high degree, when developed around it;
and hence it is, that the pointing of a substance between the
poles of a powerful magnet is continually referred to for such
a purpose. It would be, and is utterly in vain to look for any
mutual action between the poles of two weak paramagnetic or
diamagnetic conductors in many cases, when the action of these
same poles is abundantly manifest in their relation to the almost
infinitely stronger poles of a powerful horseshoe or electro-
magnet.
Fig. 4.
Ja
2826. I took a tube a (fig. 4), filled with a saturated
solution of sulphate of cobalt, and suspended it between
the poles of the great electro-magnet; it set readily and
well. Another tube, b, was then filled with a saturated
solution of sulphate of iron, and being associated with
the S pole of the magnet, was brought near the cobalt
tube in the manner shown, but not the slightest effect
on the position of a was observable. The tube b was
changed into the position c, to double any effect that
might be present, but no trace of mutual action between the
poles of a and b was visible (2819.).

Fig. 5.
2827. To increase the effect, the magnetic solution tube
was suspended in water, as a good diamagnetic
medium, between flat-faced poles (fig. 5). It
pointed well. Two bottles of saturated solution
of sulphate of iron were placed at d and e, but
they did not alter the position of a; being re-
moved into the positions ƒ and g, neither was
any sensible alteration of the position of a pro-
duced. I made the same kind of experiment
with an air-tube in water, in which case it points
axially (2406.), with the same negative result.
I do not mean to assert that there was abso-
lutely no effect produced in these cases (2819.);
but if any, it must have been inappreciably
small, and shows how unfit such means are to compare with
those which are supplied by the pointing of a body when under
the influence of powerful magnets. If polarity cannot be found
by these methods in paramagnetic bodies so strongly influential

OCT. 1850.]
211
Conduction polarity
as saturated solution of iron, nickel or cobalt, it can hardly be
expected to manifest itself by analogous actions in the much
weaker cases of diamagnetic substances.
2828. When a spherical paramagnetic conductor is placed
midway in a field of equal magnetic force, it occupies a place of
unstable equilibrium, from which, if it be displaced ever so little,
it will continue to move until it has gained the iron boundary
walls of the field (2465. 2810.); this is a consequence of its
particular polar condition. If the sphere were free to change its
form, it would elongate in the direction of the magnetic axis; or
if it were a solid of an elongated form, it would point axially,
both consequences of its polar condition (2811.).
2829. So also in the case of diamagnetic bodies, their peculiar
condition of polarity is shown by corresponding facts, namely,
by a spherical portion having its place of stable equilibrium in
the middle of the magnetic field (2812.), by a fluid portion tend-
ing to expand equatorially and become an oblate spheroid
(2813.), and by the equatorial pointing of an elongated portion
(2812.). If pointed magnetic poles are used, then the effects
are very much stronger, but are exactly the same in kind, and
dependent upon the same causes and polar conditions.
2830. There are another sct of effects produced, which are
either the results of the axial polarity just referred to, or else
may be considered as consequences of the condition of the
equatorial parts of the conductors (2824.). Two balls of iron,
in a field of equal force, if retained in a plane at right angles to
the line of force, i. e. with their equatorial parts in juxtaposition,
separate from each other with considerable power (2814.), and
the probability is that two infinitely weaker bodies of the para-
magnetic class would separate in like manner. Two portions of
phosphorus, being a diamagnetic substance, have been found
also to separate under the same circumstances (2815.).
2831. The motions here are of the same kind, whereas they
might have been expected to be the reverse (2816.) of each other;
still they are perfectly consistent. The diamagnetics ought to
separate, for the field is stronger in lines of magnetic force
between them than on the outsides, as may easily be seen by
considering the two spheres D D in fig. 6; and therefore this
P 2
212
[SERIES XXVI.
Magnetic conduction.
motion is consistent, and is in accordance generally with the
opening or set equatorially, either of separate portions or of a
continuous mass of such substances (2829.), in their tendency
Fig. 6.

D
D
to go from stronger to weaker places of action. On the other
hand, the two balls of iron, P P, have weaker lines of force
between them than on the outside; and as their tendency is to
pass from weaker to stronger places of action, they also sepa-
rate to fulfil the requisite condition of equilibrium of forces.
Finally, a paramagnetic and a diamagnetic body attract each
other (2817.); and they ought to do so, for the diamagnetic
body finds a place of weaker action towards the paramagnetic
body, and the paramagnetic substance finds a place of stronger
action in the vicinity of the diamagnetic body, D P, fig. 6.
2832. I have frequently spoken of iron in illustration of the
action of paramagnetic conductors, and considered the polarity
which it acquires as the same with that of these conductors;
but I must now make clear a distinction, which exists in my
mind, with regard to the polarity of a magnet, and the polarity,
as I have called it, due to mere conduction. This distinction
has an important influence in the case of iron. A permanent
magnet has a polarity in itself, which is possessed also by its
particles; and this polarity is essentially dependent upon the
power which the magnet inherently possesses. It, as well as
the power which produces it, is of such a nature, that we cannot
conceive a mere space void of matter to possess either the one
or the other, whatever form that space may be supposed to have,
or however strong the lines of magnetic force passing across it.
The polarity of a conductor is not necessarily of this kind; is
not due to a determinate arrangement of the cause or source of
the magnetic action, which in its turn overules and determines
the special direction of the lines of force (2807.); but is simply
a consequence of the condensation or expansion of these lines of
force, as the substance under consideration is more or less fitted
OCT. 1850.]
213
Conduction polarity-iron.
to convey their influence onwards. It is evidently a very dif-
ferent thing to originate such lines of power and determine their
direction on the one hand, and only to assist or retard their pro-
gression without any reference to their direction on the other.
Speaking figuratively, the difference may be compared to that
of a voltaic battery and the conducting wires, or substances,
which connect its extremities. The stream of force passes
through both, but it is the battery which originates it, and also
determines its direction; the wire is only a better or worse con-
ductor, however by variation of form or quality it may diffuse,
condense, or vary the stream of power.
2833. If this distinction be admitted, we have to consider
whether iron, when under the influence of lines of magnetic
power, becomes a magnet and has its proper polarity, or is a
mere paramagnetic conductor with conducting powers of the
highest possible degree. In the first place, it would have the
real polarity of the magnet, in the second only that which I
assign to oxygen and other conducting bodies. To my mind
the iron is a magnet. It can be raised as a source of lines of
magnetic power to an extreme degree of energy in the electro-
magnet; and though, when very soft, it usually loses nearly
all this power upon the cessation of the electric current, yet
such is not the case if the mass of metal forms a continuous
circuit or ring, for then it can retain the force for hours and
weeks together, and is evidently for the time an original source
of power independent of any voltaic current. Hence I think
that the iron under the influence of lines of magnetic power
becomes a magnet; and though it then has the same kind of
polarity, as to direction, as a mere paramagnetic conductor,
subject to the same lines of force, still with a great difference;
for as the internal particles of iron become in a degree each a
system producing magnetism, so their polarity is correlated and
combined together into a polar whole, which, being infinitely
more intense, may also be very different in the disposition of its
force in different parts, to that equivalent to polarity, which a
mere conductor possesses.
2834. It appears to me also as very probable, that when iron,
nickel and cobalt, are heated up to the respective temperatures
at which they lose their wonderful degree of power (2347.) and
retain only so small a portion of it as to require the most sen-
214
[SERIES XXVI.
Magnetic conduction-polarity.
sible test to make it manifest (2343.), they then have passed into
the condition of paramagnetic conductors, have lost all ability
to acquire that state of internal polarity they could assume as
magnets, and now have no other polarity than that which belongs
to them as masses of paramagnetic matter (2819.). It is also
probable that in many states of combination these metals may
take up the mere conducting state; for instance, that whilst in
the protoxide, iron may constitute a magnet, in the peroxide it
is only a conductor; and in this respect it is not a little curious
to find oxygen, which as a gas is a paramagnetic body (2782.),
reducing iron down to, and indeed far below its own condition,
weight for weight. In their various salts also and solutions,
these metals may, in conjunction with the combined matter, be
acting only as conductors.
2835. Perhaps I ought not to have called the condition of
concentration or expansion of the lines of magnetic force in the
bodies acting as conductors, a polarity; inasmuch as true mag-
netic polarity depends essentially and entirely on the direction
of the line of force, and not on any mere compression or diver-
gence of these lines. I have done so only that I might point
with the more facility to facts and views that have heretofore
been associated with some supposed polarity in the bodies which,
whether paramagnetic or diamagnetic, I have been considering
as mere conductors, and I hope that no mistake of my meaning
will arise in consequence. I have already asked for such liberty
in the use of phrases (lines of force, conducting power, &c.)
(2149. 2797.) as may, for the time, set me free from the bondage
of preconceived notions; these are, for that very reason, exceed-
ingly useful, provided they are for the time sufficiently restricted
in their meaning, and do not admit of any hurtful looseness or
inaccuracy in the representation of facts.
¶ iii. Magnecrystallic conduction¹.
2836. The beautiful researches of Plücker in relation to mag-
neoptic phænomena cannot have been forgotten, and I hope that
my own experiments on magnecrystallic results (2454. &c.) are
¹ I must refer here to the important paper by MM. Tyndall and H. Kno-
blauch on this subject in the Philosophical Magazine, 1850, vol. xxxvii. p. 1.
M. F.-January 6, 1851.
OCT. 1850.]
215
Magnecrystallic conduction.
remembered in conjunction with his; the phænomena described
by us are, as I believe, due to a common cause, and are the same
in kind; and as far as they are presented by pure transparent
bodies, are I think brought by Plücker into a proper relation to
the positive and negative optic axis of such bodies'. In these
cases a crystalline body sets powerfully, or takes up a particular
position when placed in a field of magnetic force (2464. 2479.
2550.), without reference to its paramagnetic or diamagnetic
character (2562.), and also without assuming any state which it
can on its removal bring away it (2504.).
2837. If the idea of conduction be applied to these mag-
necrystallic bodies, it would seem to satisfy all that requires ex-
planation in their special results. A magnecrystallic substance
would then be one which in the crystallized state could conduct
onwards, or permit the exertion of the magnetic force with more
facility in one direction than another; and that direction would
be the magnecrystallic axis. Hence when in the magnetic field,
the magnecrystallic axis would be urged into a position coinci-
dent with the magnetic axis, by a force correspondent to that
difference, just as if two different bodies were taken, when the
one with the greater conducting power displaces that which is
weaker.
2838. The effect of position would thus be accounted for
(2586.); and also the greater aptness for magnetic conduction
in one direction than in another (2588.2591.): and, what appeared
to me as an anomaly in the supposition, that a line of force could
have reference indifferently to any part of a plane (2600.) dis-
appears. That heat should take away this conducting power
(2570.) seemed perfectly consistent with what we know of the
effect of heat on the magnetic condition of iron, oxygen, &c.,
and also upon the conducting power for electricity in such cases
as platina, sulphuret of silver, &c. Finally, the assumption did
not appear inconsistent with the state which the body seems to
assume for the time during which it is under the magnetic force
(2609. &c.).
2839. But if such a view were correct, it would appear to
follow that a diamagnetic body like bismuth ought to be less
diamagnetic when its magnecrystallic axis is parallel (as nearly
as may be) to the magnetic axis, than when it is perpendicular
'Philosophical Magazine, 1849, vol. xxxiv. p. 450.
216
Magnecrystallic conduction. [SERIES XXVI.
to it. In the two positions it should be equivalent to two sub-
stances having different conducting powers for magnetism, and
therefore, if submitted to the differential balance, ought to pre-
sent differential phænomena, corresponding in kind to those of
oxygen and nitrogen (2774.), or phosphorus and bismuth, or
any other two differing bodies. Though I have given certain
results on a former occasion which seemed to bear on this point
(2551. 2552. 2553.), they are not satisfactory in the present
state of our knowledge, because the difference, if any, would be
small (2552.), and quickly hidden by the employment of a
single pointed pole. Other experiments, formerly described
(2554-2561.), would not show a small difference in diamagnetic
force (though quite fitted for their intended purpose), because
they were made with flat-faced poles, and a field nearly equal in
magnetic power.
2840. The differential torsion balance (2773.) enabled me to
return to this matter with better hopes of success.
A con-
sistent group of bismuth crystals was selected (2457.) and hung
up on one side of the double cone core (2738.), whilst a cylinder
of flint-glass was opposed to it on the other. The flint-glass
was to be a standard of reference, and therefore neither its place
on the balance nor condition was altered during the experiment.
The bismuth group was placed with its magnecrystallic axis
horizontal, and so that it could be turned in a horizontal plane,
that the axis might be at one time parallel to the magnetic axis
(or lines of force), and at other times perpendicular to it, but
without any alteration of the distance of its centre of gravity
from the opposed glass cylinder. Hence, having either one
position or the other, it could still be compared with the cylinder.
2841. The magnecrystallic axis was first made parallel to the
core or magnetic axis, the magnetic power developed, and when
the diamagnetic bodies had taken their position of rest or stable
equilibrum, the place of the balance lever was observed and
recorded by means of a ray of light reflected from a mirror at-
tached to it. Then the bismuth was turned through 90°, or
until its magnecrystallic axis was perpendicular to the axis of
the double cone core; and now, when the magnet was excited,
the place of the bismuth was found to be further out from the
core than before. On being turned through 90° more, so as to
be in a position diametral to the first (2461.), its place was again
Ост. 1850.]
217
Magnecrystallic conduction.
a little nearer to the magnet; and when in the fourth position,
which is diametral to the second, then it was further out. Thus
the crystallized bismuth proved to be diamagnetic in different
degrees, according with certain directions of its magnecrystallic
axis, being more diamagnetic when this axis was perpendicular
or transverse to the lines of magnetic force, than when it was
parallel to them; and thus the expectation founded upon theo-
retical considerations (2839.) was confirmed.
2842. I tried to obtain similar results with a cube of calca-
reous spar (2597.); for it is evident that if its optic axis, being
in a horizontal plane, is first placed parallel to the magnetic
axis and then perpendicular to it, the body ought to be more
diamagnetic in the first position than in the second, inasmuch
as the latter is the position which it takes up under the influence
of its magnecrystallic or magneoptic condition. I could not
however obtain any distinct results, partly because its power is
in all respects very inferior to the bismuth, partly because of the
present imperfection of my torsion balance, and partly because
of the size and shape of the calcareous spar. A sphere or a
cylinder, having the optic axis perpendicular to the axis of the
cylinder, would be more correct as forms of the substances to be
tried.
2843. In concluding this part of the subject relating to the
magnetic conducting power, I will now refer to some of the
cases which I think experimentally established its existence in the
two subdivisions of magnetic bodies (2805.). The place and
position of iron in a field of equal force (2810. 2811.) is no doubt
a result of the extraordinary power which this body has of trans-
mitting the magnetic force across the space which it occupies,
whether the particles of the iron be considered as polar or not
(2832.), and therefore I accept the converse phænomena as to
place and position of a diamagnetic body (2812. 2813.) as pooof
that it has less power of transmitting the magnetic force than
the space it occupies, and from that conclude that it conducts
diamagnetically (2802.).
2844. The separation of paramagnetic bodies in the equatorial
direction is a proof of the manner in which, by their better con-
duction, they disturb the position of the lines of force in the
medium around them (2831.). The separation of two diamag-
218
Magnecrystallic conduction. [SERIES XXVI.
netic bodies, under the same circumstances, is an equal proof of
the manner in which, by difference of conducting power, they
also disturb the disposition of the force (2831.). The equatorial
attraction of a paramagnetic and a diamagnetic body for each
other, when they are in a medium, which in conducting power
is between the two (2831.), is a proof not only of conduction
in both, but also of their reverse condition in respect of each
other and the medium.
2845. The place of a crystal of bismuth, either nearer to or
further from the magnetic axis (2841.), according as its magne-
crystallic axis is parallel or perpendicular to the axial line, is
also a case of the difference of conducting power, and therefore
of the possession of that power by the diamagnetic body. Many
other cases might be quoted in illustration of the existence of
that power which I assume as conducting power (2797.), and
which probably nobody may be inclined to deny. I will sup-
pose that the above are enough to explain my meaning.
2846. It is hardly necessary for me to say that magnetic con-
duction does not mean electro-conduction, or any thing like it.
The very best electro-conductors, as silver, gold and copper, are
below mere space in their ability to favour the transmission of
magnetic force, so deficient are they in what I have called mag-
netic conduction. There is a striking analogy between this
conduction of magnetic force and what I formerly called specific
inductive capacity (1252. &c.) in relation to static electricity,
which I hope will lead to further development of the manner in
which lines of power are affected in bodies, and in part trans-
mitted by them.
§ 33. Atmospheric magnetism ¹*.
¶ 1. General principles.
2847. It is to me an impossible thing to perceive, that two
ninths of the atmosphere, by weight, is a highly magnetic body,
¹ A most important paper by Professor Christie, “On the Theory of the
Diurnal Variation of the Magnetic Needle," appears in the Philosophical
Transactions for 1827, p. 308. Led by the discoveries of Seebeck in thermc-
magnetism and the experiments of Cumming, he was induced to search how
* I ought to refer the readers of my paper to a theory of the cause of the
daily variations by M. A. de la Rive, founded upon the idea of thermo-
electric currents in the atmosphere and earth; it will be found in a memoir
OCT. 1850.]
219
Atmospheric magnetism.
subject to great changes in its magnetic character, by variations
in its physical conditions of temperature and condensation or
rarefaction (2780.), and at the same time subject to these phy-
far the idea of thermo-currents or thermo-magnetic polarity would apply to
the natural phænomena, and concludes (p. 327), that, admitting that the earth
and the atmosphere are substances in which such action can under any circum-
stances take place, these experiments would indicate that any portion of the
earth bounded by parallel planes with the atmosphere surrounding it, would become
similarly polarized if one part were more heated than another. Thus consider-
ing alone the equatorial regions of the earth, we should have two magnetic poles
on the northern side, and on the southern side two poles similarly posited; the
poles of different names being opposed to each other on the contrary sides of the
equator.
entitled 'On the Diurnal Variation of the Magnetic Needle.' Annales de
Chimie, 1849, xxv. p. 310.
A friend has recently called my attention to an observation by M. E. Bec-
querel, which has reference to the present subject, and is in the following
words. "If we reflect that the earth is encompassed by a mass of air, equi-
valent in weight to a layer of mercury of 30 inches, we may inquire whether
such a mass of magnetic gas, continually agitated and submitted to the regular
and irregular variations of pressure and temperature, does not intervene in some
of the phænomena dependent on terrestrial magnetism. If we calculate in fact
what is the magnetic force of this fluid mass, we find that it is equivalent to
an immense plate of iron, of a thickness a little more thanth of a millimetre
of diameter (?), and which covers the whole surface of the globe." This
passage is at pp. 341, 342, of vol. xxviii. Annales de Chimie, 1850, being
contained in an excellent memoir, in which the author has well worked out
those differential actions of different media, which I developed generally five
years ago:-Experimental Researches, 2357. 2561. 2406. 2414. 2423. &c. By
such means he has rediscovered the magnetic character of oxygen and taken
measurements of its force, being evidently unacquainted with the account that
I gave of this substance in relation to nitrogen and other gases three years ago,
n a letter published in the Philosophical Magazine for 1847, vol. xxxi. p. 401,
and also in Poggendorff's Annalen and elsewhere;—hence the observations
above. I cannot wonder at this, for I myself was not aware of M. E. Bec-
querel's paper until very lately. In my letter of 1847, I speak of oxygen as
being magnetic in common air, p. 410; in carbonic acid, p. 414; in coal gas,
p. 415; in hydrogen, p. 415, its power then being equal to its gravity. I say
that air owes its place to the oxygen and nitrogen in it, p. 416, and tried to
separate these constituents by attracting the oxygen and repelling the nitrogen.
At the end of the paper I hesitate in deciding where the true zero between mag-
netic and diamagnetic bodies is to be placed, and refer to the atmosphere as
being liable to affections under the magnetic influence of the earth. It was
these old results which led me on to the present researches. M. F.-Nov. 28,
1850,
220
[SERIES XXVI.
Atmospheric magnetism.
sical changes in a high degree, by annual and diurnal variations,
in its relation to the sun, without being persuaded that it must
have much to do with the disposition of the magnetic forces upon
the surface of the earth (2796.), and may perhaps account for a
large part of the annual, diurnal and irregular variations, for
short periods, which are found to occur in relation to that power.
I cannot pretend to discuss this great question with much un-
derstanding, seeing that I have very little of that special know-
ledge which has been accumulated by the exertions of the great
and distinguished labourers, Humboldt, Hansteen, Arago, Gauss,
Sabine, and many others, who have wrought so zealously at ter-
restrial magnetism over the surface of the whole earth. But as
it has fallen to my lot to introduce certain fundamental physical
facts, and as I have naturally thought much upon the general
principles which tend to establish their relation to the magnetic
actions of the atmosphere, I may be allowed to state these prin-
ciples as well as I can, that others may be placed in possession
of the subject. If the principles are right, they will soon find
their special application to magnetic phænomona as they occur
at various parts of the globe.
2848. The earth presents us with a spheroidal body, which,
consisting of both paramagnetic and diamagnetic substances,
disposed with much irregularity as regards its large divisions of
earth and ocean, are also equally irregularly disposed and inter-
mingled in its smaller portions. Nevertheless it is, on the whole,
a magnet, and, as far as we at this moment are concerned, an
original source of that power. And though we cannot conceive
at present that all the particles of the earth contribute, as sources,
to its magnetism, inasmuch as many of them are diamagnetic,
and many non-conductors of electric currents, yet it is difficult
to say that any large portion is not concerned in the production
of the force; hereafter it may be necessary, perhaps, to consider
certain parts as mere conductors, i. e. as parts merely permeated
by the lines of force, originating elsewhere, but for the present
the whole may be assumed, according to the theory of Gauss, as
a mighty compound magnet.
2849. The magnetic force of this great system is disposed with
a certain degree of regularity. We have the opportunity of re-
cognising it only as it is exhibited in one shell or surface, which,
being very irregular in form, is always the same to us, for we
OCT. 1850.]
221
Atmospheric magnetism.
rarely, if ever, pass out of it; or if we do, as in a balloon, only
to an insensible extent. This is the surface of the earth and
water of our planet. The magnetic lines of force which pass in
or across this surface are made known to us, as respects their
direction and intensity, by their action on small standard mag-
nets; but their average course or their temporary variations
below or above, i. e. in the air above, or the earth beneath, are
only dimly indicated by variations of the force at the surface of
the earth, and these variations are so limited in their information,
that they do not tell us whether the cause is above or below.
.
2850. The lines of force issue from the earth in the northern
and southern parts with different but corresponding degrees of
inclination, and incline to and coalesce with each other over the
equatorial parts. Their general disposition is represented by the
system, which emanates from a globe having within one or two
short magnets adjusted in relation to the axis. There seems
reason to believe, from the analogy of such globes to the earth,
that the lines of magnetic force which proceed from the earth
return to it; but in their circuitous course they may extend
through space to a distance of many diameters of the earth, to
tens of thousands of miles. Messrs. Gay-Lussac and Biot, in
their ascent in a balloon, perceived some indication of a dimi-
nution in the intensity of the magnetic force at a height of about
four miles from the surface; but we shall shortly perceive that
they might be at the time in the midst of influences sufficient
to account for all the effect, so that none of it might be occa-
sioned by removal from the earth as a magnet. The increase of
the intensity of the magnetic force, as we proceed from the
equator towards the poles, accords with the idea of the enor-
mous extension of this power.
2851. These lines proceed through space with a certain de-
gree of facility, of which a general idea may be gained from
ordinary knowledge, or from experiments and observations for-
merly made (2787.). Whether there are any circumstances
which can affect their passage through mere space, and so cause
variations in their condition; whether variations in what has
been called the temperature of space could, if they occurred,
alter its power of transmitting the magnetic influence, are ques-
tions which cannot be answered at present, although the latter
does not seem to be entirely beyond the reach of experiment.
222
[SERIES XXVI.
Atmospheric magnetism.
2852. This space forms the great abyss into which such lines
of force as we are able to take cognizance of by our observing
instruments, which issue from the earth, proceed, at least at all
parts of the globe where there is a sensible dip. But, as it were,
between the earth and this space, there is interposed the atmo-
sphere; which, however considerable we may estimate it in
height, is so small when compared to the size of the earth, or to
the extent of space beyond it into which the lines of force pass,
that the idea of its being a changeable, active something inter-
posed between two systems far more extensive and steady in their
nature and condition, will not lead to any serious error. It is at
the bottom of this atmosphere that we live and make all our
inquiries, whether by observation or experiment.
2853. The atmosphere consists, as far as we are concerned at
present, of four volumes of nitrogen and one volume of oxygen,
or by weight, of three and a half parts of the former and one
part of the latter. These substances are nearly uniformly mixed
throughout, so that, as regards their manner of investing the
earth, they act magnetically as a single medium; nor does there
seem to be any tendency in the terrestial magnetic forces to
cause their separation', though they differ very strikingly in
their constitution as regards this power.
2854. The nitrogen of the air does not appear to be either
paramagnetic or diamagnetic; if removed from zero, in either
of these respects, it is only to a very small extent (2783. 2784.).
Whether dense or rare, it has apparently the same relation to
and equality with space, as far as the present means of obser-
vation have proceeded. As respects the other element of change,
namely, temperature, I concluded, from former imperfect expe-
riments2, that nitrogen became more diamagnetic when heated
than before; but as it was then mixed with the oxygen of the air,
and the results were mingled together, I have, for the purposes
of the present research, repeated the experiments far more care-
fully.
2855. A small helix of platinum wire, fixed at the end of
thicker copper wires, could be placed in any position beneath
the poles of the great electro-magnet, and being ignited by a
voltaic battery, served to raise the temperature of the gas around
it. The magnetic poles were raised; were terminated by hemi-
¹ Philosophical Magazine, 1847, vol. xxxi. p. 416. 2 Ibid. p. 418.
OCT. 1850.] Effect of heat on air-carbonic acid gas.
223
spheres of soft iron 0.76 of an inch in diameter and 0.2 of an
inch apart; and were covered by a glass shade, resting upon a
thick flat bed of vulcanized caoutchouc. A tube passed through
the bed, rising up to the top of the shade, by which any required
gas could be introduced. A very thin plate of mica, about 3
inches square, was covered with an attenuated coat of wax on
the upper side, and fixed horizontally over the magnetic poles
within the shade. The small platinum helix was so placed as to
be beneath the space, between the poles, and a little on one side
of the axial line, so that a current of hot air rising upwards from
it, could pass to the mica plate, and by melting the wax show
where it came against the mica.
2856. All acted exceedingly well, air being in the glass shade.
When there was no magnetic power on, the hot air from the
ignited helix rose perpendicularly, and melted a neat round por-
tion of the wax, showing the place of the current under natural
circumstances; but when the magnet was thrown into action.
then the wax on the mica remained unchanged, the hot air
being thrown so far away from the axial line, and so cooled by
its forcible mixture with the neighbouring air, as to be unable
to melt a spot of wax anywhere. The moment the magnetic
power was suspended, the column of hot air rose vertically and
regained its original position.
2857. Carbonic acid gas was then sent into the shade, until
twice as much as the contents of the shade had passed through
the pipe (2855.); but as it was heavy and the common air could
make its way out only at the bottom of the shade, there was no
doubt air mixed with the carbonic acid, which at last remained
about the poles. The platinum coil being now heated, the co-
lumn of hot gas rose vertically, as before. On putting on the
magnetic force it was deflected from the axial line, passing equa-
torially, and melted the wax about half an inch off from the
former place. Believing that even this effect might be due to
the air mingled with the gas, other two volumes of carbonic acid
gas were directed into and through the vessel. After this the
magnetic force caused much less deflection of the rising column.
Two volumes more of carbonic acid were sent through, and now
the hot current of gas rose so nearly vertical that there was
scarcely any sensible difference of its place when the magnetic
power was in full action, or when it was entirely absent.
224
[SERIES XXVI.
Effect of heat on nitrogen.
Hence I conclude that carbonic acid gas is very little affected in
its diamagnetic relations by a difference of temperature equal
to that between natural temperatures and a full red heat.
2858. Nitrogen. This gas was prepared by passing common
air slowly over burning phosphorus, and after being washed for
twelve or fourteen hours, was sent into the shade so as to displace
the carbonic acid. As it was lighter than the latter, it per-
formed that service very well, and the portion remaining in the
vessel probably contained no other oxygen or air than that it
carried in with it. This nitrogen being then heated by the
platina coil, was almost as indifferent to the magnet as the car-
bonic acid. The heated column rose (nearly) to the same spot
against the mica, whether the magnetic power was active or not.
It went outwards or equatorially a very small degree when the
magnet was active, but this I attributed to a little oxygen still
left with the nitrogen; and indeed nitric oxide gas shows oxygen
in nitrogen so prepared. The platina coil was raised to as high
a temperature as it could well support without fusion, and yet
there was only this small effect sensible: hence I conclude that
hot nitrogen is not more diamagnetic than cold nitrogen, and that
indeed its magnetic relation is noways affected by such change
of temperature.
2859. I raised the French shade (2855.) an inch for a moment,
and then instantly placed it down again; and now, on making
the magnet active and the coil hot, there was so much effect of
dispersion of the gas within, that the melted spot of wax ap-
peared nearly an inch outside of the standard place, yet only
a very small portion of air or of oxygen could have entered the
vessel under these circumstances.
2860. The nitrogen of the air is therefore, as regards the
magnetic force, a very indifferent body; it does not appear to be
either paramagnetic or diamagnetic; neither does it present any
difference in its relation, whether it be dense or rare, or at high
or low temperatures. I formerly found that the diamagnetic
metals, when heated, did not seem to change in their relation to
the magnet (2397.), and this now appears to be the case with
such neutral or diamagnetic bodies as nitrogen and carbonic acid
gases.
2861. The oxygen of the air differs in a most extraordinary
degree from the nitrogen. It is highly paramagnetic, being,
OCT. 1850.] Atmospheric magnetism--oxygen.
225
same.
.
bulk for bulk, equivalent to a solution of protosulphate of iron,
containing, of the crystallized salt, seventeen times the weight
of the oxygen (2794.). It becomes less paramagnetic, volume
for volume (2780.), as it is rarefied, and apparently in the sim-
ple proportion of its rarefaction, the temperature remaining the
When its temperature is raised, the expansion conse-
quent thereon being permitted', it loses very greatly of its para-
magnetic force; and there is sufficient reason, from a former re-
sult with air², to conclude, that when its temperature is lowered
its paramagnetic condition is exalted. How much its paramag-
netic intensity might be increased by lowering it to the tempera-
ture of freezing mercury, as at the north or south poles of the
earth, we cannot at present tell. Though a gas, it is apparently
like the solid metals, iron, nickel or cobalt, when they are within
the range of temperature which affects their magnetic forces;
and it may, perhaps, like them, rise by cooling to a very high state.
2862. These relations it preserves when mingled with nitrogen
in the air, as long as its physical and chemical conditions remain
unchanged; but it is not irrelevant to remark, that every opera-
tion by which this active part of the atmosphere changes in its na-
ture and passes into combinations, takes away its paramagnetic
powers, whether the result be solid, liquid or gaseous.
2863. Hence the atmosphere is, in common phrase, a highly
magnetic medium. The air that stands upon every square foot of
surface on the earth, is equivalent, in magnetic force, to 8160 lbs.
of crystallized protosulphate of iron (2794. 2861.). This me-
dium is, by every change in its density, whether of the kind in-
dicated by the barometer, or caused by the presence or absence
of the sun, changed in its magnetic relations. Further, every
variation of temperature produces apparently its own change of
force, in addition to that caused by the mere expansion or con-
traction in volume, and none of these alterations can happen
without affecting the magnetic force emanating from the earth,
and causing variations, both in its intensity and direction, at the
earth's surface. Whether these changes are in the right direc-
tion and sufficient in quantity to supply a cause for the variations
of the terrestrial magnetic power, is the point now to be con-
sidered, for the illustration of which I will endeavour to construct
Philosophical Magazine, 1847, vol. xxxi. p. 417.
2 Ibid. p. 406.
VOL. III.
1
226
Atmospheric magnetism. [SERIES XXVI.
a type case, and then apply it, as well as I can, to the natural
facts.
2864. Let us assume the existence of two globes of air di-
stinct from the surrounding atmosphere, by a difference of tem-
perature or by a difference of density: the assumption is not
too extravagant for an illustration, since Prout showed that there
were masses of air, larger or smaller, floating about in the atmo-
sphere, and singularly distinct from the surrounding parts, by
temperature and other circumstances. Not to complicate the
expression, we will leave out of view, at present, the attenuation
upwards, and will consider one of these globes as colder or
denser than the contiguous parts, and that it is in a portion of
space which without it would present a field of equal magnetic
force, i. e. having parallel lines of equal intensity of force pass-
ing across it.
2865. The air of such a globe will facilitate the transmission
of the magnetic force through the space which it occupies
(2807.), making it superior, in that respect, to the surrounding
atmosphere or space, and therefore more lines of magnetic force
will pass through it than eleswhere (2809.). The disposition of
these lines, in respect of the line of the dip of the place, will be
something like what is represented in fig. 7 (2874.), and con-
sequently the globe will be polarized as a conductor (2821. 2822.)
of the paramagnetic class. Hence the intensity of the magnetic
force and its direction will vary, not only within but without the
globe, and these will vary in opposite directions, in different
places, under the influence of laws which are perfectly regular
and well known.
2866. First, as regards the intensity, which before was uniform
(2864.). If the intensity is to be considered as expressing the
amount of force which passes through any given place, then, in
consequence of the definite amount of power which belongs to
any section, as a a, of a given amount of lines of magnetic force
(2809.), a concentration of these lines towards the middle, P,
will cause an increase of intensity at that part, and a diminution
at some other parts, as b b, from whence the influence of the
power has been partly removed. Hence, supposing the normal
condition to exist at a, if a test of intensity were carried from
a to P, it would gradually enter parts b and c, in which the
intensity was less than the normal condition, and these might
OCT. 1850.]
227
Effect of cooled air-needle indications.
be either without or within the globe P, or both (according to
its temperature relative to the surrounding air, its size and other
circumstances); it would then arrive at parts having the normal
intensity; and lastly, at parts, P, having an intensity greater
than the surrounding space; as it went outwards, on the op-
posite side of P, corresponding variations would occur in the
reverse order.
2867. On transporting the test upwards, in the direction of
the dip from e, where the intensity may be considered as nor-
mal, it would gradually occupy positions at ƒ g, &c., in which
the intensity would increase until it arrived at P, after which
it would pass through places of less and less intensity, until at
p it would again find the force in the normal state. If the test,
in being carried upwards, be not taken along the line of the dip,
then it will of course pass through variations like those described
on the line a P, growing more and more in extent until the di-
rection coincide with the line a P, which is at right angles to
the dip and where they are at a maximum. Hence, to pass up-
wards through such a globe of cold air in our latitude, where the
dip is 70° nearly, and at the equator, where it is 0°, would be a
very different matter, and the necessary natural results of such
a difference ought to appear hereafter.
2868. But a magnetic needle or bar is not a test of such in-
tensity, i. e. it will not tell these differences, or it may tell them
in a contrary direction. To understand this point, we have to
consider that a needle vibrates by gathering upon itself, because
of its magnetic condition and polarity, a certain amount of
the lines of force, which would otherwise traverse the space
about it; and assuming that it underwent no change by change
of temperature, it would be affected in proportion to any variations
in the intensity of these lines, provided everything else remained
the same. But being under natural circumstances surrounded
by the atmosphere, which is a medium liable to variation in its
magnetic condition, both by heat and rarefaction, and by these
variations affects the intensity or quantity of the the force, it will
vary in its indications by variations in these conditions. Thus,
for instance, if it were in a large sphere of oxygen, I expect that
it would, by its number of vibrations or otherwise, indicate a
certain intensity; if the oxygen were expanded, that it would
indicate a higher intensity, although the same amount of lines
Q 2
228
[SERIES XXVI.
Atmospheric magnetism.
of force and magnetic energy were passing through the oxygen
as before. If the oxygen were made dense, then becoming a
better conductor, I presume it would convey onwards more of
the force and the magnet less, for the power would be partly
transferred from the unchanging magnet to the improving con-
ductor around it.
2869. These experiments can hardly be made with oxygen
except by means of extremely delicate apparatus, but like effects
are easily shown experimentally in selected analogous cases.
Thus let a thin small tube of flint-glass, about 1 inch long and
an inch in diameter, be filled with a saturated solution of pro-
tosulphate of iron, and suspended horizontally by cocoon-silk
(2279.) between the poles of the electro-magnet, in a vessel
which may either contain air or water, or other media (2406.).
In air it will point axially, and will be analogous to a needle
under the earth's influence, and it will point with a certain amount
of force. Fill the vessel with water, and now it will point with
more force than before, though the water is a worse magnetic
conductor than the air which was previously there; and it is
precisely because the water is a worse conductor that the liquid
magnet or test indicates more power. Increase the conducting
power of the surrounding medium by adding sulphate of iron to
it, and the indication of strength by the tube goes on diminishing,
first returning to the degree of power it had in air, and then
descending to lower gradations, for it returns with less and less
force to its axial position when disturbed from it. So the mag-
netic needle employed for measuring intensity or magnetic force
(for the same meaning is at present understood by the two terms),
indicates, in a certain manner, the power thrown upon itself,
and, I conclude, accurately, provided the condition of the sur-
rounding medium remains magnetically unchanged: but if it be
placed in different media or in an altering medium, I expect that
it will not measure accurately the intensity in them, i. e. it will
not measure directly the amount of force passing relatively
through them. The difference in air under different conditions
would be very small, still it is that difference which concerns us
in atmospheric magnetism; and it is very important to know,
whether, when the magnet indicates an increased intensity of
force, it is altogether due to a real increase of the amount of the
power at its source as it comes to us from the earth, or in part
Ост. 1850.]
229
Cooled air-needle indications.
to a change in the magnetic constitution of the space around
the magnet hitherto unknown to us.
2870. If what is now often indifferently called magnetic force
or intensity have its results distinguished as of two kinds, namely,
those of quantity and those of tension, then we shall more readily
comprehend this matter. At present a needle shows both these
as magnetic force, making no distinction between them, yet they
produce effects on it often in opposite directions; for as they
increase or diminish they both affect the needle alike; but as it
is assumed that the tension can change whilst the quantity
remains the same, and the quantity can be altered, yet the ten-
sion remain unaffected, the result by the needle will then be
uncertain. If the tension in a given region be increased by
diminishing the conducting power, the needle will show increased
force; if it be increased by an increase of magnetic power in
the earth from some internal action, the needle will still show
increased force, and will not distinguish the one effect from the
other. If the quantity in a region be increased by increasing
the conducting power, the needle will show no such increase;
on the contrary, it will indicate diminution of force, because the
tension is diminished; or if the quantity be diminished by dimi-
nishing the conducting power, it will show increased force. The
force might even lose in quantity and gain in tension in such
proportions that the needle should show no change; or it might
gain in quantity and lose in tension, and the needle still be en-
tirely indifferent to the whole result.
2871. If my view be correct, then the magnet is not, as at
present applied, a perfect measure of the earth's magnetic force;
for that may not change when the magnet by the influence of
the different conditions of day and night, or of summer and
winter, may show a difference. How far these uncertainties in
its indication may affect the value of the observations made on
the horizontal and vertical components of the earth's magnetic
force as indications of that which they are expected to tell us, I
do not know; but involving, as the effects do, two very different
conditions, namely, variation of the conducting power and varia-
tion of the amount of force at its source, the one of w hich is
chiefly in the atmosphere and the other in the earth, it seems
to me to be of great consequence to the development of the
theory of terrestrial magnetism, to have some method, if pos-
230
[SERIES XXVI.
Atmospheric magnetism.
sible, of distinguishing these two points or effects from each
other.
2872. Referring again to the model globe, fig. 7 (2874.), it
appears to me, that if a magnet be used as the intensity test, it
will indicate a less intensity at P rather than a greater one, for
the very reason that the conducting power of the whole globe
has been increased; and also, though the apparent diminution
of intensity will probably be greater there than elsewhere, that
the effect will occur in other parts, especially those on the right
and left, and even at b and b, where the power transmitted, in-
stead of being more, as at P, is really less than the portion trans-
mitted in the normal or equable state of the magnetic field.
With a diamagnetic globe of air, i. e. one warmer or more rare-
fied than the surrounding space (2877.), though it would convey
less power as being a worse conductor, still it should cause the
magnet to set with greater force, and so give an indication of
increased intensity, and that also both within and equatorially
without the globe.
2873. If it be true that the changes of the medium (2869.)
can thus affect the magnet, and that such changes can rise up
to a sensible degree in the gases, then the magnet might make a
different number of vibrations in a given time in oxygen and
nitrogen gases of the same density, for they are very different
in their magnetic relations. It should make the greatest num-
ber in nitrogen; perhaps a delicate torsion balance would be a
still more sensible test of such a result; but it is probable that
the space around the needle should be large, and it would be
requisite to ascertain that the two media opposed equal mecha-
nical resistance to the vibrating needle.
2874. The variation of the direction caused by the typical
globe (2864.) might be oblique to the horizontal and vertical
planes, and consequently give results of declination and inclina-
tion, either separately or together. The direction would not
vary in a central line parallel to the general dip of the surround-
ing space (fig. 7). Along another central line perpendicular to
this (i. e. any line in the equatorial plane), a P, there would also
be no variation of the direction, but in any other position there
would be variations. Thus in the line i r, as the free needle
passed from i to k, its lower end would be carried inwards to-
wards the central line of dip P; this effect, after attaining a
OCT. 1850.]
231
Cooled air-needle indications.
maximum, perhaps at 7, would gradually diminish again, and by
the time the needle had reached r the dip would be normal.
Fig. 7.
pl

α
b c
P
Ъ
a
---
f
Corresponding effects would occur on the opposite side of the
axial line pe; and if a needle be considered as in any place the
dip of which is thus affected, and then be conceived as travelling
in a circle round the axial line p e, it would always be in the
surface of a cone, the apex of which is below.
2875. On the other hand, if the variations of the dip below
the equatorial plane a P be considered, they will be equal in
amount, but in the reverse direction, so that the magnetic needle,
when deflected from its normal position, would have its upper
end inclined inwards towards the axial line pe; or if moved
round the axial line would always be in a conical surface, the
apex of which is above.
2876. So the dip would vary in such a globe of air in every
azimuth; and it would also vary in opposite directions in the
upper and lower parts of the globe, and of the affected sur-
rounding space.
2877. If we assume the exist-
ence of another typical globe of
air (2864.), having a higher tem-
perature than the surrounding
atmosphere, then its condition
will be that of a diamagnetic con-
ductor, and will be represented by
Fig. 8.
Fig. 9.

fig. 9 (2807.); and it will have power to affect both the intensity
232
[SERIES XXVI.
Atmospheric magnetism.
and the direction of the lines of force, in conformity with the ac-
tion of the former globe, but in the contrary order. As regards
the action of these globes, consequent upon the direction of the
lines of force in and about them upon a needle coming within
their influence, it may, in part, be represented by a magnet
placed either in the direction of the needle for the cold globe,
or in the reverse direction for the warm one; but as the lines
of force of the combined system of the earth and such a magnet
are very different in their arrangement to the lines of the earth
affected by masses of warm or cold air having only conduction
polarity (2820.), it would be too much to say that they corre-
spond, or that the effects on the intensity or direction would be
the same for similar distance from the centre of the globe of air
and the representative magnet.
2878. In endeavouring to proceed, from these hypothetical
and comparatively simple cases, which are given only to lead the
mind on from the results of experiment to the supposed condi-
tion of matters as regards our atmosphere and the earth, we have
to consider, that though there will be an effect, and though the
intensity and direction of the magnetic force, upon the surface
of the earth, must vary with changes of temperature and density
of the atmosphere, still it will be in a manner very different from
that represented by the typical globe of air, for the latter is a
case which will never occur, though the variations of the natural
case are almost infinite. Still the comparison holds in principle,
and we may expect that as the sun leaves us on the west, some
effect, correspondent to that of the approach of a body of cold
air from the east, will be produced, which will increase and then
diminish, and be followed by another series of effects as the sun
rises again and brings warm air with him.
2879. The atmosphere diminishes in density upwards, and
that diminution will affect the transmission of the magnetic
force, but as far as it is constant, the effect produced by it will
be constant too. The portion of the atmosphere which lies
under the heating influence of the sun, as compared to its depth,
will more resemble a slice of air wrapped round the earth than
a globe. Still the inflection of the lines of force, both above and
below this stratum, will occur, extending into space above and
Ост. 1850.]
233
Distribution of magnetic force.
into the earth beneath (2848.), according to the known influence
of magnetic power and its perfectly definite character (2809.).
We are placed at the bottom of this layer of air, but as the
atmosphere is denser there than higher up, and is also in many
cases more affected there by changes of temperature, we are
probably in a position where the inflections and variations due
to the assumed causes exist in a considerable degree.
2880. There are innumerable circumstances that will break
up, more or less, any general or average arrangement of the air
temperature. For instance, the diversity of sea and land causes
variations of temperature differently in different times of the
year, and the extent to which this goes may be learned from
the beautiful isothermal charts of Dove, now fortunately to be
had in this country'. These variations may be expected to give,
not merely differences in the regularity, direction and degree of
magnetic variation; but because of vicinity, differences so large
as to be manifold greater than the mean difference for a given
short period, and they may also cause irregularities in the times
of their occurrence.
2881. On considering the probable results of the magnetic
action of the atmosphere, it appears to me that if the terrestial
magnetic force could be freed from all periodical and small per-
turbations, and its dispositions ascertained for any given time,
it might still include certain effects constituting a part of atmo-
spheric magnetism. For instance, there is more air, by weight,
over a given portion of the surface of the earth at latitudes from
24° to 34°, than there is either at higher latitudes or at the
equator; and that should cause a difference from the disposition
of the lines of force which would exist if there were an equality in
that respect, or if the atmosphere were away. Again, the tem-
perature of the air is greater at the equatorial parts than in
latitudes north or south of it; and as elevation of temperature
diminishes the conducting power for magnetism, so the propor-
tion of force passing through these parts ought to be less, and
that passing through the colder parts greater, than if the tem-
perature of the air were at the same mean degree over the whole
surface of the globe, or than if the air were away. Again, there
is a greater difference in range of temperature of the air at the
Report of the British Association, 1848, Reports, p. 85.
234
Atmospheric magnetism. [SERIES XXVI.
equator as we rise upwards than in other parts, and hence the
lower part is not so good a conductor proportionately to the
upper part, or to space, as elsewhere, where the difference is
not so great; the magnetic power, therefore, should be in some
degree weakened there, the lines of force being diverted, more
or less, from the warm air and thrown into other parts, as the
cooler atmosphere and space above, or the earth beneath, ac-
cording to the principles before explained (2808. 2821. 2877.).
.
2882. The result of annual variation that may be expected
from the magnetic constitution and condition of the atmosphere
seems to me to be of the following kind. Assuming that the
axis of rotation of the earth was perpendicular to the plane of its
orbit round the sun, and dismissing for the present other causes
of magnetic variation than those due to the atmosphere, the
two hemispheres of the earth, and the portions of air covering
them, would be affected and warmed alike by the sun, or at
least would come into a constant relative state, dependent upon
the arrangement of land and water; and the lines of magnetic
force having taken up their position under the influence of the
great dominant causes, whatever they may be, would not be
altered by any annual change due to the atmosphere, since the
daily mean of the atmospheric effect in a given place would at
all parts of the year be alike. Under such circumstances the
intensity and direction of the magnetic forces might be con-
sidered constant, presuming no sensible change to take place by
the difference in distance from the sun which would occur in
different parts of the orbit; and, as regards the two magnetic
hemispheres, each would be the equivalent of and equal to the
other, and they may for the time be considered in their mean or
normal state.
2883. But as the axis of the earth's rotation is inclined
23° 28′ to the plane of the ecliptic, the two hemispheres will
become alternately warmer and colder than each other, and then
a variation in the magnetic condition may arise. The air of the
cooled hemisphere will conduct magnetic influence more freely
than if in the mean state, and the lines of force passing through
it will increase in amount, whilst in the other hemisphere the
warmed air will conduct with less readiness than before, and
the intensity will diminish. In addition to this effect of tem-
Oct. 1850.]
235
Annual variation considered.
!
perature, there ought to be another due to the increase of the
ponderable portion of the air in the cold hemisphere, conse-
quent upon its contraction and the coincident expansion of the
air in the warmer half, both of which circumstances tend to in-
crease the variation in power of the two hemispheres from the
normal state. Then as the earth rolls on in its annual journey,
that which at one time was the cooler becomes the warmer hemi-
sphere, and consequently in its turn sinks as far below the ave-
rage magnetic intensity as it before had stood above it, whilst
the other hemisphere changes its magnetic condition from less
to more intense.
2884. As the sum of the magnetic forces which crop out from
the earth wherever there is a dip on one side of the magnetic
equator must correspond to the sum of like force on the other
side (2809.), so they would not become more intense in one
hemisphere, or more feeble in the other, without a corresponding
contraction on the one hand, and enlargement on the other. ·
The line of no dip round the globe may therefore be expected to
move alternately north and south every year, or some effect equi-
valent to that take place. The condition of the two hemispheres
under this view may be conceived by supposing an annual un-
dulation of the force to and fro between them, during which,
though neither the character nor the general disposition of the
power be altered, there is in our winter a concentration and in-
crease of intensity in the northern parts coincident with a dif-
fused and diminished intensity in the south, and in summer the
reverse.
2885. In respect of direction, alterations may also be antici-
pated. In the first place, and assuming that the magnetic poles
and the poles of the earth coincide, the dip would increase in
the cooling hemisphere towards the middle and polar parts; but
it ought to diminish towards the magnetic equator, to accord
with the concentration of the hemisphere of stronger power and
enlargement of the weaker one; whilst on the other hand the
dip ought to diminish at the polar and middle parts of the warm-
ing hemisphere and increase towards the magnetic equator.
The magnetic equator would shift a little north and south of its
mean place during each year, simultaneously with the whole
system of magnetic lines. But as the magnetic poles do not
coincide with those of the earth, or with what may be called the
236
[SERIES XXVI.
Atmospheric magnetism.
poles of the changing temperatures, so a cause of difference in
direction will here arise.
2886. Again, it may be that as oxygen is cooled, its paramag-
netic power may increase in a more rapid proportion than that
of the change of temperature, so that the chief alteration of the
disposition of the earth's force may be in the extreme northern
and southern parts; and in combination with the holding power
of the earth (2907.), may even cause a change the reverse of that
expected above in lower latitudes. If in our winter the lines of
force were to close together in the polar parts and to open out
in lower latitudes, the balance of magnetic force would just as
well be sustained as if all the lines in our hemisphere were to be
compressed and strengthened, and be compensated for by a
corresponding change in the south. In the former case, each
hemisphere would balance its own forces, in the latter they
would be balanced against each other. There can, I think, be
no doubt, that as far as the mass of the earth and the space
above our atmosphere are unchangeable in relation to annual
and diurnal variation, so far they would tend to restrain any
variation which might depend only on the varying temperature
and state of the air; holding as it were the two sides of the va-
riations, the increase and diminution of intensity, or the right
and left hand in change of direction, nearer together than they
otherwise would be.
2887. Further, if it be supposed that the whole of a hemi-
sphere is affected at once in the same direction by change of
temperature, it will not be affected alike, but differently in dif-
ferent latitudes, because of the difference in amount of that
change.
2888. The difference of land and water (2880.) will still fur-
ther break up any expected uniformity of the general result, and
cause that certain parts of the cooling hemisphere shall increase
in power more in proportion than other parts; and when
these parts lie on opposite sides of the magnetic meridian of any
given place, they would probably have power to cause an altera-
tion in the declination of the needle at that place.
2889. As the annual changes of temperature are less at the
equator than in parts more north or south, so there, probably,
little or no annual variation would occur: none indeed as regards
the varying temperature or expansion of the air, but only that
Ост. 1850.]
237
Annual variation.
portion which is consequent upon the alternate changes of the
parts on its opposite sides (2884.).
2890. Another effect, which may be considered as an annual
variation, but which is connected with the diurnal change, may
be expected. As the daily changes in temperature of the atmo-
sphere, influential upon a given place in north or south medium
latitudes, are greater in extent in summer than in winter, so the
corresponding magnetic variations may be expected to vary also,
being larger in the northern hemisphere, when the sun is on
the north side of the equator, and less when he is present in the
southern hemisphere, and producing like correspondent change
there.
"
2891. From a most important investigation by Colonel
Sabine¹, founded on the results of observations at Toronto and
Hobarton, the facts appear to be that the magnetic intensity is
greater in both hemispheres in those months which are winter in
the northern hemisphere, and summer in the southern. Similar
results are greatly wanted for other localities, and would show
whether the different disposition of land and sea has anything
to do with the question, or whether the results at Toronto and
Hobarton are true exponents of hemispherical effects. As-
suming Toronto and Hobarton as being such exponents, the
dip in both hemispheres is greater (i. e. greater north dip at
Toronto and south dip at Hobarton) in those months which are
winter in the northern, and summer in the southern hemisphere.
Whether there is any annual variation of the dip or total force
in the equatorial parts of the globe is very important to deter-
mine. It would be well worth while to take up a station for
the express purpose; the instruments are very simple, and the
observations would require only a single observer. They are
described in the paper referred to. Unfortunately such obser-
vations are not even made in Great Britain.
2892. The manner in which the diurnal variation may be
produced or affected by the action of the sun on our atmo-
sphere as the earth revolves in its beams has been already
generally referred to. The whole portion of atmosphere ex-
¹ On the means adopted for determining the Absolute Values, Secular
Change, and Annual Variation of the Magnetic Force, Philosophical Trans-
actions, 1850, p. 201.
238
[SERIES XXVI.
Atmospheric magnetism.
posed to the sun receives power to refract the lines of magnetic
force which traverse it, and the whole of that which covers the
darker hemisphere assumes an equally altered, but contrary state
relative to the mean condition of the air. It is as if the earth
were inclosed within two enormous magnetic lenses competent
to affect the direction of the lines of force passing through them.
2893. I have already said that the action of the atmosphere
thus affected might in some degree be compared at night time
to that of an enormous, diffuse, and very feeble ordinary mag-
net, having the position that it would naturally take according
to the line of dip, passing over us from east to west, and inclu-
ding us for the time within its influence: in the daytime the ac-
tion would be like that of the similar journey, not of a correspond-
ing magnet reversed in direction, but of a corresponding globe
of diamagnetic matter (2821.). Assuming the maximum heat
and cold to occur at midday and midnight, we might expect
that the maximum effects would also occur near those periods
as regards the variations of intensity (2824. 2866.); for, other
things being the same, the central parts of the heated and cooled
masses are those where the difference of intensity should be
greatest.
2894. It might be expected that this variation in the intensity
would be greatest at those parts of the globe over which the sun
passes vertically, or nearly so; but that may depend upon two
circumstances at least; first, whether the difference in the day
and night temperature is greater there than at other places, because
the extent of the variation may be dependent in part upon that
difference; and next, whether the amount of effect to be ex-
pected is the same for the same difference in number of degrees
of temperature at every part of the scale (2886.). If the con-
ducting power of oxygen (2800.) should be found by future ex-
perimental measurements (2960.) to increase in a greater pro-
portion for a fall of a given number of degrees at lower tem-
perature than at high ones (including the effect of contraction
for that fall (2861.)), then it may be that parts more distant from
the sun will be more affected than those under it; or if the con-
trary be the case, less affected than otherwise would be expected.
2895. With regard to the daily variations, as respects the
direction of the lines of terrestrial magnetic force, or the inclina-
tion and declination of the magnetic needle, the principles of
OCT. 1850.]
239
Diurnal variation.
the changes that may be expected to occur have been already
referred to (2879.); and it remains for me to compare these ex-
pectations with a few simple cases of observation, in such a
general manner as will tend to show whether the direction of
action is, both in theory and fact, the same; and whether there
is any probability that the effect has been assigned to its true
cause; for this purpose I will confine myself entirely at present
to a part of the daily variation, namely, the effect of the sun and
air as the luminary arrives at and passes over the meridian.
.
2896. Profiting by the last volume which has issued from the
powerful mind and careful hands of Colonel Sabine', I will take
the case of Hobarton. The observatory there is in latitude 42°
52'5 south, and longitude 147° 27'-5 east of Greenwich. The
absolute declination is 9° 60'8 east, and the dip is 70° 39' south.
In order to have the place of the sun and the time of maximum
and minimum temperatures at hand, I have transferred the
mean temperature for January (summer) for seven years, 1841–48,
and the mean temperature for June (winter) for the same pe-
riod, corresponding to every hour in the day and night, from
pp. lxxxiv. and cviii. to fig. 10, Plate I., where the middle series
of numbers represents the hours, the line next below them a base
line of temperature at 30° Fahr., and the two curves still lower
down the mean hourly temperature for summer and winter.
The short lines show generally the direction of the needle east
or west of its mean position, the upper end being of course the
north extremity. The positions about noon are distinguished
by full lines, being those required for more immediate illus-
tration.
2897. The north end of the magnetic needle at Hobarton is
most east at 2 o'clock, and most west about 21 o'clock. Being
at the extreme west at the latter hour, it passes through the
full range of variation, or to the extreme east in five hours, or
by 2 o'oclock, and then requires the remaining nineteen hours to
return to the utmost west. The maximum east and west decli-
nation is at 2 and 21 o'clock for summer, and at 3 and 22 o'clock
for winter. The vertical positions show at what hours the decli-
nation was 0, and correspond with Sabine's zero. From 21 to
2 o'clock the needle passes from one extremity of its variation
to the other, the north or upper end travelling in the reverse
1
¹ Magnetic and Meteorological Observations, Hobarton, vol. i. 1850.
240
[SERIES XXVI.
Atmospheric magnetism.
1
direction to the sun, so that it and the sun cross the meridian
together in opposite directions, nearly about or a little before
noon. About 2 o'clock the needle is arrested, and after that
time returns west, following the sun. It will be proper to state,
that the north end of the needle, the motion of which has just
been described, is the end towards the equator, and also, the
upper end of a dipping-needle at Hobarton. This distinction
will receive more significance presently.
2898. Hence the cause which affects the needle appears to be
far more powerful, and more concentrated in time when the sun
is present than when he is away. In this there is accordance
between the time of the effect and the time when the sun could
exert most influence on those magnetic conditions of the atmo-
sphere, which are for the present supposed to govern that effect.
2899. It will be seen by examination of fig. 10, that the time
of maximum temperature is not when the sun is on the meridian,
but two hours after it, both in summer and winter. But in re-
ference to temperature and its effect on the magnetic condition
of the air, and through that on the needle, it is not the local
temperature which is supposed to influence the needle, but that
which effects enormous masses of air, above as well as below,
and of which the temperature at the spot, however important it
may become when we can properly interpret it, gives us as yet
little or no knowledge. Still there are some points on which
temperature has a more direct bearing. Thus the amount of
variation of temperature is in summer double what it is in winter,
and the amount of variation in the declination increases in the
same proportion (2890.). The minimum temperature in winter
is later than in summer, and the extreme western declination of
the needle is also later at the same period.
2900. The varying direction of the magnetic lines of the earth
is made known to us by observations in two planes, one the
horizontal plane, to which the position east and west is referred,
constituting declination, and the other a vertical plane passing
through the line of mean declination, and supplying observa-
tions of inclination. The direction of the line of force referred
to this plane might change so as either to increase or diminish
the inclination, and it does increase at some places for the same
hour of local time for which it diminishes at others; thus it in-
creases at Greenwich whilst it diminishes at St. Helena, which
Ост. 1850.]
241
Diurnal variation-direction.
is nearly in the same meridian. At Hobarton it changes rapidly
at the east and west extremes of the variation, i. e. about 2 and
21 o'clock. From noon it diminishes until about 3 o'clock; it
then continues nearly the same in summer, when the variation
is greatest until 18 or 19 o'clock, from that time it increases
until about 22 o'clock, and is nearly a maximum from thence
till noon.
Hence it will be understood, that the inclination is
generally greatest during the rapid journey of the north end of
the needle from west to east between 21 and 2 o'clock, and
least in the other or prolonged half of the journey; and though
this is partly broken up in the night effect, to be considered
hereafter, still as a general result it always appears.
2901. All this may be roughly represented by fig. 11 (2909.),
in which E. W. represents the path of the sun between the
tropics as he comes up with the hours 21, 22h, &c. in his daily
journey, and e the path described by the north or upper end of
the needle, freely suspended at Hobarton, and therefore showing
both declination and inclination, i. e. the whole direction.
Looking down upon such a needle, its upper end will take the
course indicated by the arrow, and its position at any given
hour is shown sufficiently by the leading lines.
2902. This relation of the motion of the needle to that of the
sun has long been known: it has great significance in relation
to my hypothesis of the physical cause of these variations. As
regards the part of the action which I am considering, it is as if
the pole of a magnet came on with the sun, of like nature to the
upper end of the Hobarton needle, and at first drives that end
west. Towards 19 o'clock the tendency westward diminishes,
but the tendency south increases. At 21 o'clock, the increase
in the sun's power, acting not directly from the sun but from a
region in the atmosphere beneath it, is not sufficient to compen-
sate for his more unfavourable position; the earth's force brings
the needle back as regards declination, and then it passes east-
wards, but the southerly motion or inclination still increases;
about 24 o'clock, or ncon, the sun is as to east or west declina-
tion indifferent, but powerful in southern action, making the
inclination then, or soon after, a maximum. Then as the sun
goes west of the needle, its power in driving the pole behind it
eastward, will increase for a time, whilst the power producing
inclination will diminish, until at 2 or 3 o'clock the earth's force
VOL. III.
Ꭱ
242
[SERIES XXVI.
Atmospheric magnetism.
will regain preponderance as the sun's power diminishes by
distance, and the needle will return towards its least dip and
mean inclination.
2903. All this may be represented experimentally by carrying
a magnetic pole north of the dipping-needle, so as to represent
the place of the sun-heated air to Hobarton, provided that pole
be of the same kind as the north or upper pole of the needle.
I have already stated (2877. 2863.), that when a portion of air
is heated in a field of magnetic power, it looses in magnetic con-
duction power, and if in association with air less heated deflects
the lines, assuming the state which I have distinguished as that
of diamagnetic conduction polarity; then presenting the very
polarity, or rather the very inflection of the lines of force, which
would affect the needle, as it is affected. As the sun rises and
passes north of such a place as Hobarton, the atmosphere under
his coming influence becomes more and more heated and ex-
panded; and referring to the model globes of air (2864. 2877.),
it is as if such a warm mass passed with the sun through all the
regions of the equator, extending also far north and south of it ;
and, having Hobarton within its influence, produced the effects
there observed.
2904. In such a view one sees a reason for the short time
occupied in the return of the needle from west to east as the
sun passes immediately over its meridian, and for the long time
during which it is passing from east to west as the influence of
the sun is slowly withdrawn, and then again slowly renewed
during the remaining part of his journey, exception being made
for the present of the paramagnetic effects due to cold.
2905. I will now consider the Toronto case of diurnal varia-
tion as it is presented to us in the volume of magnetical observa-
tions, issuing from the same authority and hands as the former
volume¹, and also in further observations down to 1848, sent to
me by the kindness of Colonel Sabine. The position of the
observatory is in lat. 43° 39′ 35″ N. and long. 79° 21′ 30″ W.
The absolute declination is 1° 21' 3" W., and the mean or ab-
solute dip is 75° 15′ N., so that as regards Hobarton it is on the
other side of the equator, and nearly on the other side of the
world. The results for the months of June and December are
¹ Magnetical and Meteorological Observations. Toronto, 1840, 1841, 1842,
Sabine.
OCT. 1850.]
243
Diurnal variation—direction.
placed in a diagram corresponding to that for Hobarton (2896.),
employing the Toronto time for the hours, Plate I. fig. 12.
2906. The north end of the needle is that universally referred
to in speaking of the declination; its course at Toronto, during
the immediate sun effect, is as follows:-Having gradually moved
east from 16h, it is at extreme east at 20 o'clock, and then returns
from the east to extreme west in six hours, after which it moves
eastward from the sun. But if we convert this into the motion
of the equatorial extremity of the needle, for that is the upper
end if the needle be free, and concerns us most in the com-
parison with Hobarton, then it will be seen that this end is most
west at 19 or 20; and leaving that position at that hour, it
travels quickly eastward, passing through the full range of varia-
tion or to extreme east in six hours, or until 2ª, and then returns,
following the sun.
2907. Looking at these results, I might repeat the words
used in illustration of the Hobarton effects, but for the sake of
brevity will simply refer to them. As before, the amount of
variation in the declination is in summer double what it is in
winter. The difference of temperature is three times greater.
The extreme west and east declination is both in summer and
winter at 20 and at 2 o'clock, so that the magnet holds to the
time in both seasons; but the maxima and minima of cold, as
shown before, vary in the two seasons, for the former is at
4 o'clock in summer and 2 in winter, whilst the latter is at
16 o'clock in summer, and 20 o'clock in winter. But this is a va-
riation with consistency; for it will be seen by a moment's inspec-
tion that in winter the maximum of heat has moved towards the
time of most powerful action in the one direction, and the minimum
has moved towards it in the other. The passage of the sun,
therefore, over the meridian, and the period of rapid motion
of the needle from west to east, still coincide.
2908. The other element of direction is the inclination. Its
variation is very small, but changes thus. A principal maxi-
mum dip occurs at 22 o'clock, and the extreme minimum dip
at 4 o'clock.
2909. So all the effects may again be generally represented
by an ellipse (fig. 13) as they were for Hobarton; and I may
refer to the words then used, substituting Toronto for Hobarton
and north for south (2901.). As the sun comes up from the
R 2
-244
[SERIES XXVI.
Atmospheric magnetism.
east in his course between the two places, he drives, by the
altered atmosphere beneath him, the upper ends of their needles
before him, and outwards from the line of his path, as if he
Fig. 13.
TORONTO
W.
noon
23
22
g1
20
Fig. 11.
HOBARTON
were a north pole to the Hobarton magnet, and a south pole
to the Toronto magnet. By 22 o'clock, the earth's force, and
the action of the air due to the sun's position, permit a re-
turn to the east, though the inclination for a time increases
(2902.); both swing rapidly round from west to east as he
passes over the meridian, and then having obtained their maxi-
mum position eastward, soon follow after him under the influ-
ence of the earth's force, less and less counteracted by the re-
treating sun. So striking is the similarity between Hobarton
and Toronto, that Colonel Sabine has already especially distin-
guished and described it¹, and has shown, that, lying down the
direction of motion in both cases by curves, and bringing the
two curves together by their faces, they coincide almost exactly,
with this single difference, that the Hobarton changes precede
those at Toronto by an hour, or rather more, of local time.
:
2910. We cannot represent this day effect experimentally upon
two such needles as those at Hobarton and Toronto by one pole
of a magnet, though we can do it with each separately with dif-
ferent poles but we see at once from the hypothesis, the rea-
son why the sun acts in this manner (2877.), and how it is that
the region of influential atmosphere that accompanies him in
his journey round the globe, acts with one effect in the northern
1 Hobarton Magnetical Observations, 1850, p. xxxv.
Ост. 1850.]
245
Diurnal variation-direction.
latitude and another in southern positions (2903.). The rea-
sons also for the short time of the day journey and the lengthened
period of the night return (2904.), are manifest. The occurrence
of disturbances or secondary waves of power in the night time,
and the condition both of the chief variation and the subordinate
oscillations in summer and winter, will be considered hereafter.
2911. Greenwich.-The following results are taken from the
volume of Greenwich observations for 1847. The latitude is
51° 31' N., and being removed nearly 80° in longitude from
Toronto, the station is well contrasted with it and also with
Hobarton. The mean declination is 22° 51′ 18″ W., and the
mean inclination is 69° N. As it is the upper end of the dip-
ping-needle which we have to consider for the purpose of a ready
comparison with the sun's observed day action (2906.), I will
describe those parts of its course and place for Greenwich time
which concern us now. Moving westward before 19¹ and 20,
it then returns towards the east, and in six hours, or by 1 or 2h,
has completed the great sun swing, after which it returns west,
following the luminary. The vertical force is given as greatest
between 3 and 4 o'clock, and least between 11 and 13 o'clock.
The south end of the needle therefore is more upright at the
former time and less at the latter; and as the latter occurs during
the prolonged return part of the journey from east to west, in-
cluding the night hours, so we perceive that the upper end of
the needle performs its daily journey in an irregular closed curve,
which the ellipse for Toronto, fig. 13 (2909.), may generally re-
present; it passes from east to west slowly during the night
hours, approaching the equator at the same time, and then it
returns from west to east with far greater rapidity, performing
this part of its journey at a greater distance from the equator
and nearer to the pole.
2912. Washington, U.S.-Latitude 38° 54' N.; longitude
77° 2′ W.; the mean declination 1° 25′ W.; the mean dip
71° 20′ N. The south or upper end of the needle is in the
morning at extreme west, about 20 to 22 o'clock, and at extreme
east about 2 o'clock; it then returns slowly west, with the
night action as in former cases, regaining extreme west at 20 to
22 o'clock. This is exactly the same movement for declination,
in relation to the place of the sun, as for the former localities.
I have not the variation of the dip, but theory would lead one
246
[SERIES XXVI.
Atmospheric magnetism.
to conclude that it is greatest between 22 and 2 o'clock, and
least in the evening and night time. The total amount of decli-
nation variation is greatest in summer, as before, being 9'-87 in
July and only 4' in December. The greatest difference in the
earth's temperature is also in July, being then nearly 20° Fahr.,
whereas in December and January it is only 10° Fahr. The
shortest period between the extreme temperature, including
therefore the quickest change of temperature, is from 16 or 18 to
2 o'clock, and consequently includes noon. All these conditions
combine to produce the greatest magnetic action, and it is in the
direction pointed out by the hypothesis.
2913. Lake Athabasca.-Latitude 58° 41′ N.; longitude 111°
18′ W. of Greenwich; mean declination 28° E. The ob-
servations are only for five months, but as the position is in
a high latitude and may be important for future considerations,
I give the results here. The extreme western position of the
upper end of the needle is about 17 or 18 o'clock, and its ex-
treme eastern position about 1 or 2 o'clock; so that as far as
declination is concerned, the action of the sun and atmosphere
is as in former cases. The amount of declination variation is
very great, being in October 21'32; in November 10'8; in
December 9'78; in January 16'29, and in February 14'87.
2914. Fort Simpson.-Latitude 61° 52′ N.; longitude 121° 30′
W. of Greenwich; mean declination 38° E. These observations
are only for two months, i. e. April and May 1844. The ex-
treme western place of the upper or south end of the needle was
at 19 o'clock, and its extreme eastern position at 2 o'clock.
The result therefore is in perfect accordance with the preceding
observations and conclusions. The amount of variation, as given
in the horizontal plane, is very large, being 36'26 in April and
32' in May.
* 2915. St. Petersburgh.-Latitude 59° 57' N.; longitude 30°
15' E. of Greenwich; mean declination 6° 10' W; the dip 70°
30′ N. The observations are the mean of six years, and show
that the upper end of the needle is extreme west in regard of
noon, about 19¹ and 20¹ for the months of March to August,
and that for the other months there is a western position about
the same hours. The extreme east position is, for all the months,
about half-past 1 o'clock, so that the sun's effect in passing
over at the noon period is as in former cases. The greatest
OCT. 1850.]
247
Diurnal variation-direction.
amount of variation is 11'52 in June; in winter it dwindles
away to as little as 1'77. From theory the dip may be expected
to increase during the day hours and diminish at night.
2916. Thus these cases, which, including the chief feature of
diurnal variation and sun action, were selected as a first and
trial-test of the hypothesis, join their evidence together, as far as
they go, in favour of that view which I am offering for their
cause; nor have I yet found any instance of even an apparent
contradiction in regard to the sun action. They assist the mind
greatly in forming a precise notion of the manner in which the
influence of the sun and air is supposed to act, not only in simi-
lar cases, but in respect of other consequences, i. e. in all that
properly comes under the term of atmospheric magnetism; I will
therefore now restate more particularly the principles which, ac-
cording to the hypothesis, govern them, in hopes that I may be
fortunate enough to assist in developing by degrees the true phy-
sical cause of the magnetic variations in question.
2917. Space, void of matter, admits of the transmission of
the magnetic force through it (2787.2851.). Paramagnetic and
diamagnetic bodies either increase or diminish the degree in
which the transmission takes place (2789.). This, their influ-
ence, I have expressed, for the time, by the phrase of magnetic
conducting power, and I think have given sufficient first experi-
mental evidence of the existence of the power and its effects in
disturbing the lines of magnetic force (2843.). The atmosphere
is, by the oxygen it contains (2861. 2863.), a paramagnetic me-
dium, and has its conducting force greatly diminished by eleva-
tion of temperature (2856.) and by rarefaction (2782. 2783.), as
has also been fully proved by experiment. The sun is an agent
which both heats and rarefies the atmosphere, and in its diurnal
course, the place of greatest heat and rarefaction must, speaking
generally, be beneath it. The irregularities in the condition of
the earth's surface and other causes do produce local departures
from an exact relation of place, but they probably disappear
partly, if not altogether, in the upper regions of the air.
2918. Assuming that the air under the sun is most changed
magnetically, and confining the attention to a spot where the
sun is vertical, for the purpose of considering the condition of
the atmosphere there and at other parts in relation to it, the sup-
position of a globe of air over the spot will of course find no fit
248
[SERIES XXVI.
Atmospheric magnetism.
application (2877.). We are first to suppose the sun far away
and the atmosphere in a mean state as to temperature, and then
consider the sun as present in the meridian of a given place;
and it is the degree of alteration in temperature and expansion
of the air beneath and around the place of the sun, and the man-
ner in which the change comes on and passes away, which con-
cern us. In relation to the surface of the earth, that alteration
will be greatest somewhere beneath the sun, and will diminish
in every direction around, becoming nearly nothing as to direct
action at that part or circle of the earth where the sun's rays are
tangent. In relation to elevation, it is a question yet whether
the effect is greatest in amount at the surface, diminishing up-
wards. As regards the atmosphere, it must of course end with
it, though as respects space itself (2851.), a reservation-thought
may arise. With regard to any alteration occasioned by the
sun's influence in the opposite hemisphere, though there is none
produced directly, yet indirectly there is that due to the falling
of the temperature of the air, from the condition to which the sun,
whilst above the horizon, had brought it. This change must
be more tardy, irregular and disturbed, by local and other cir-
cumstances, than the opposite alterations produced by the direct
influence of the luminary; and is that which occasions, by the
hypothesis, the second maximum or minimum or other recur-
ring night actions, made manifest by the needle in the hours
when the sun is away.
2919. The lines of force which issue from a magnet are, as it
were, located and fixed by their roots in a way well understood
experimentally by those who have worked upon this subject.
In the same manner the lines which issue from the earth more
or less suddenly, according to the amount of inclination, are held
beneath by a force of location; and because of the unchanging
action of the earth in respect of atinospheric effect, are restrained
more or less from alteration beneath during the changing action
of the atmosphere. This fixation in the earth is a chief cause
of certain peculiarities in the atmospheric phænomena as we ob-
serve them; and is productive of that rotation of the line of force
about the mean position which we have already considered
during the sun swing, and shall meet with again under the ac-
tion of cold air. This condition of fixation at the lower parts of
the lines of force occurs at every station where there is any dip
OCT. 1850.]
249
Diurnal variation—direction.
at all, and gives for each the point of convergence round which
the motion of the upper end of the needle takes place (2909.
2932.).
Fig. 14.
H
f
2920. So the atmosphere, under the influence of the sun, lies
upon the earth altered most at the
part beneath the luminary.
It has
received power to affect the lines of
magnetic force differently to the
manner in which it affected them in
the sun's absence. It has become a
great magnetic lens, able to refract
the lines, and the manner in which
it does so appears to be of the fol-
lowing nature. All the lines pass-
ing through this heated and ex-
panded air, surrounded by other
air not so much heated, will, be-
cause of its being a worse magnetic
conductor than the latter (2861.
2862.), tend to open out (2807.);
and the mass of heated air, as a
whole, will assume the condition of

•
N
S..
diamagnetic polarity. If, therefore, for the sake of simplicity,
the magnetic and astronomical poles of our earth be supposed
as coincident, and fig. 14 represent a section taken through them
and the place of the sun, then N and S will be the magnetic
poles, and the different curves cutting the outline of the circle
will sufficiently represent the course of the magnetic lines as
they occur at or about the surface of the earth, H being the
sun, and a the place immediately beneath it, which is also coin-
cident with the magnetic equator. By this diagram we shall
have an illustration of the hypothetical effect on the inclination
of the needle.
2921. Considering the point a first, and assuming as yet that
the maximum of change in the air is always at the surface of the
earth, we shall find that there the lines of force will open out,
preserving in some degree their parallel or concentric relation.
Consequently a magnetic needle, free to move in every direction,
and therefore taking up its position in the line of force, ought
not, if placed at this spot, to be altered in its position. It ought
250
[SERIES XXVI.
Atmospheric magnetism.
to show perhaps a diminution of magnetic force transmitted
through that spot; but, for the reason before given (2868.), I
conclude it would indicate a greater intensity, the increased
power thrown upon it through the diminution of the conducting
power of the air in that place causing it to act as a more power-
ful needle.
2922. Proceeding to a point b, there the lines of force have
dip. The same physical effect will be produced upon them here
as before, i. e. the portions in the atmosphere will open out;
but neither here nor in the former case will they continue to
have the same curvature as before, for towards and in the earth,
where they have their origin, they are restrained more or less
from altering by the unchanging action of the earth (2919.) ;
whilst at their more advanced parts, as at c, they enter into
portions of the atmosphere which are nearer to the most intense
lines of solar action, H C, probably also into the region of most
intense action, and also into space, circumstances which cause
more displacement of the lines, tending to separate by the ten-
sion of the parts altered in the air, than can happen in the earth
(2848.). So the magnetic line of force at b will not move par-
allel to itself, but being inclined a certain degree to the horizon,
when in the normal condition, will be more inclined, i. e. will
have more dip given to it by the presence of the sun. This is
the fact made manifest by the needle when indicating the posi-
tion of the line as to inclination (2908.) at Hobarton, Toronto
or elsewhere, by the motion of its upper end; for it is manifest
that whatever happens on one side of the place of the sun and
magnetic equator, when, as in our supposition (2920.), they
coincide, will happen on the other.
2923. The case may be more simply stated, for the facility of
recollection, by saying that the effect of the sun is to raise the
magnetic curves, over the equatorial and neighbouring parts,
from their normal position, in doing which the north and south
dip are simultaneously affected and increased.
.
2924. At the place d like effects on the inclination must be
produced, and theoretically it should be affected in the same
direction even at N. and S. At the point a the inclination is
supposed to be not at all altered, but going either north or south,
the changes appear and increase. It is not probable that the
maximum alteration will be at N. or S., but the latitude where
Ост. 1850.]
251
Diurnal variation-direction.
it will occur must depend upon the many conjoined circumstances
that belong to the case of a globe round which a magnetic lens,
such as I have endeavoured to describe, is continually revolving.
2925. Instead of assuming that the sun is at H, let us suppose
that we are looking at the diagram in a vertical position and
towards the east; the sun coming up from the east and passing
over our heads, and bringing with it that condition of our atmo-
sphere which is the cause of the change. As it does so, all the
magnetic curves would rise; the inclination would increase at
b, d, and every place where there was any beforehand in opposite
directions on the two sides of a; this would go on until the sun
was in the zenith, and then as it passed away and sank behind
us the lines would draw in again and the dip diminish to what
it was at first. The maximum of dip would be when the sun
was near the zenith, and the minimum when he was quite away.
2926. But if the resultant of force be above in the atmosphere
(2937.), which is by far the most probable, as it is the whole
atmosphere which acts by heat diamagnetically, then the results
would be modified; for if over a, the lines of force might be
depressed, and any inclination there would be diminished; at b
it might not for the moment be affected; whilst in higher lati-
tudes it would be increased, according as the line of force from
the resultant in the atmosphere, wherever that might be, fell
outside of the angle formed by the inclination with the horizon
of a given place or within it. St. Helena, the Cape of Good
Hope, and Hobarton, furnish instances of the three cases.
2927. At the same time the total force would undergo a change
in its amount; that transmitted through a given space would be
least when the sun was in the zenith, and most when he was
away (2863.). The total variation in the force should be greatest
at α,
and diminish from thence towards north and south. The
daily variations of the inclination are so imperfectly known to
us at present, that we cannot say how far the natural changes
will accord with these expected variations, but as far as the
observations go they agree with the theory.
2928. If the sun, instead of being over the equator, is at a
tropic and so vertical, for instance, over b, then the effects will
be modified; and the resultant still being assumed as above, the
lines of force which before were not affected may be expected
to descend and lessen the inclination, whilst other lines in higher
252
[SERIES XXVI.
Atmospheric magnetism.
latitudes, which before were increased in inclination, may now
be but little affected, and other lines in still higher latitudes
have, as before their inclination, increased. On the other side
of the equator, the tendency of the lines would be to increase in
inclination.
Fig. 15.
n
m
C
2929. Proceeding to that part of the expected change of posi-
tion of the free needle which produces variations of declination,
let er in fig. 15 represent the sun's
path in the equator, and t c, t' c' the
same at the tropics; let mr be a
magnetic meridian, and a a', ii', o o'
places of equal north and south incli-
nation on opposite sides of the equa-
tor. The curves of magnetic force
seen in front in fig. 14, are now in-
the plane of the magnetic meridian,
but may be considered as rising on
opposite sides of the equator and
coalescing over it. If the air on all
sides were in its mean condition and
ť
100
But if
the sun entirely away, these curves would be in the vertical
plane mr; or if the sun near midday was so placed that the
resultant of the heated and changed atmosphere was in the
meridian m r, though effects of inclination would occur (2922.),
still the curves would remain in the same vertical plane.
the resultant were either to the east or the west of m r, variations
of declination would be produced. For suppose the sun to be
advancing from the east or r; because it gives the air a diamag-
netic condition, the lines of force would tend to expand (2877.),
and therefore move westward, as represented in the meridian
ns; and the deflection caused thereby would be greatest upon
the surface of the earth, because it is there that the curves as
they enter the earth are held and restrained in respect of their
normal position (2919.). As the warmed atmosphere came on,
the western deflection would increase to a certain extent, and
then diminish to nothing when the resultant was in the meridian ;
but as the latter passed on, the deflection would grow up on the
eastern side of n s, and, after attaining a maximum, would di-
minish and cease as the warm air retreated.
2930. If the sun's path was in the northern tropic, t c, and
OCT. 1850.]
253
Diurnal variation-direction.
the resultant in the atmosphere therefore to the north of the
stations a or i, though that would make a difference in the
amount of the declination variation, it would not alter its direc-
tion, for still, the curves a a' and ii' would bear to the west as the
sun came up, and would be on the meridian when the resultant
was there also. There would be more effect produced at i than
at i', but the contrary character of the dip, in respect of the sun's
place, would not alter the direction of the declination variation.
2931. A cold region of air acting, as at the coming on of night,
upon the lines of magnetic force of the earth, would, by virtue of
its paramagnetic character (2865.), produce corresponding effects
both of inclination and declination, but in the contrary direction.
2932. Thus the lines of force which issue from the earth at
all places upon its surface where there is any dip, will, by the
hypothesis, under the daily influence of the sun, describe by
their ascending parts a closed curve or irregular cone, the apex
of which is below. As a fact this result is perfectly well known,
but its accordance with the hypothesis is important for the latter.
The mean position of the free needle will be in the axis of this
curve or cone, and its return, either in declination or inclination,
to the mean is an important indication of the amount and position
of the variable forces which influence it at such times.
2933. My hypothesis does not at all assume that the heated or
cooled air has become magnetic so as to act directly on the
needle after the manner of a piece of iron, either magnetically
polar or rendered so under induction. There is no assumed
polarity of the oxygen of the air other than the conduction
polarity (2822. 2835.) consequent upon a slight alteration of the
direction of the lines of force. The change in the magnetic
conducting power causes this deflection of the lines; just as a
worse conductor of heat introduced into a medium of better
conducting power disturbs the previous equable transfer of heat,
and gives a new direction to that which is conducted; or as in
static electricity, a body of more or less specific inductive capacity
introduced into a uniform medium disturbs the equable lines of
force which were previously passing across it.
2934. The sole action of the atmosphere is to bend the lines
of force. The needle being held by these lines and, when free,
being parallel to them, changes in position with the changes of
the lines. It is not necessary even that the lines, which are
254
[SERIES XXVI.
Atmospheric magnetism.
immediately affected in direction by the altered air, should be
those about the needle, but may be very distant. The whole of
the magnetic lines about the earth are held by their mutual
tension in one connected sensitive system, which has no slug-
gishness anywhere, but feels in every part a change in any one
particular place. There may be, and is continually, a new
distribution of force, but no suppression. So when any change
in direction happens, near or distant, the needle in a given place
will feel and indicate it, and that the more sensibly according to
the vicinity of the place and the kind of change induced; but
the disposition of the whole system has been affected at the same
moment, and therefore all the other needles will be affected in
obedience to the change in the lines of force which govern them
individually.
2935. The needle is a balance on which all the magnetic power
around a given locality fastens itself, even to the antipodes, and
it shows for each place every variation in their amount or dispo-
sition, whether that occurs near or far off. Its mean position
is the normal position; and as regards atmospheric changes,
the fixation of the lines of force in the earth (2919.) is that which
tends to give the lines a standard position (exclusive of secular
changes), and so bring them and the needle back from their
disturbed to their normal state. Hence, whilst considering the
causes which disturb either the declination or the inclination,
arises the importance of keeping in mind the mean position or
place of the needle (2932.), and not merely the direction in which
it is moving.
2936. So the well-known action of the sun on the needle is,
by my hypothesis, very indirect; the sun at a given place affects
the atmosphere; the atmosphere affects the direction of the
lines of force; the lines of force there affect those at any distance
and these affect the needles which they respectively govern.
2937. I have, for the sake of convenience in considering a
special action of the atmosphere, spoken of the resultant in the
atmosphere dependent on the sun's presence; and will do so a
little while longer without implying any direct action of this
resultant, or that portion of air which yields it, upon the needle
(2933.), for the sake of considering at what probable height it is
situated in the air. That it cannot be on the surface of the earth,
is shown by the depression of the lines and diminution of the
OCT. 1850.]
255
Diurnal variation-direction.
dip at St. Helena and Singapore during the middle of the day;
and that it is not even under the sun, is shown by the manner
in which the greatest action precedes, in some degree, the sun,
as at Hobarton and Toronto, and other places by different
amounts of time; neither the time when the sun is on the meri-
dian, nor the time when the observed temperature is highest
(for that is after the sun), is the time of greatest action, but one
before either of these periods. The changes in the temperature
of the air produced by the sun, will not take place below and
above at the same time. The upper regions of the atmosphere
over a given spot are affected by the sun at his rising and after-
wards, before the air below is heated; and therefore the effect
from above would be expected to precede that below. The
temperature observed on the earth does not show us, for the
same time, the course of the changes above, and may be a very
imperfect indication of them. The maximum temperature below
is often two, three, or four hours after the sun, whereas, whatever
heat the sun gives by his rays directly to the atmosphere, must
be acquired far more rapidly than that. It is very probable
and almost certain, that at 4 or 5 o'clock A.M. in the summer
months, the upper regions may be rising in temperature, whilst
on the surface of the earth, through radiation and other causes,
it is falling. The well-known effect of cold just before sunrise
in some parts of India, and even in our country, is in favour of
such a supposition. We must remember that it is not the
absolute temperature of the air at any spot that renders it influ-
ential in producing magnetic variations, but the differences of
temperature between it and surrounding regions. Though the
upper regions be colder than the lower, their changes may be as
great or greater; they happen at a range of temperature which
is probably more influential than a higher range (2967.); and,
what is of importance, they occur more quickly and directly
upon the presence of the sun. The quantity of heat which the
atmosphere can take directly from the sun's rays, is indicated by
the different proportions we receive from him when he is either
vertical or oblique to us, and so sending his beams through less
or more air; and when he has departed, the upper parts of the
air are far more favourably circumstanced for rapid cooling by
radiation than the portions below. So that the final changes
may be as great or greater than below, and we may learn little
256
[SERIES XXVI.
Atmospheric pressure.
of them, or their order, or time, by observations of temperature
at the earth's surface. In addition therefore to observations of
magnetic effect, as depression of the lines of force at St. Helena,
&c., there are apparently reasons deducible from physical causes,
why the chief seat of action should be above in the atmosphere.
2938. In the midday effect the upper end of the needle passes
the mean position (2935.) on its return to the east generally
before the sun passes the meridian going westward. At Toronto
it is about an hour in advance; at St. Helena and Washington
an hour and a half; at Greenwich and Petersburg two hours;
at Hobarton and the Cape of Good Hope the passage is about
noon. Such results appear to indicate that the place of maximum
action is in advance of the sun; and it probably is so in some
degree, but not so much as at first may be supposed, as will
appear I think from the following considerations.
occur.
2939. The precession of the time of maximum action may
depend in part upon some such condition as the following. As
the sun advances towards and passes over a meridian, the air is
first raised in temperature and then allowed to fall, and these
actions produce the differences in different places on which the
magnetic variations depend. But they depend also upon the
suddenness with which or the vicinity at which these differences
Thus two masses of air, having equal differences of
temperature, will affect the lines of force more if they be near
together, and to the needle, than if they be far apart. And again,
if a body of air were of a certain low temperature at one part,
and, proceeding horizontally, were to increase rapidly to a certain
high temperature and then diminish slowly to the first low tem-
perature, such a body passing across a set of lines of magnetic
force would affect them in opposite directions at a fore and after
part; but it would affect them most on the rapidly altering side.
2940. Now the air as heated by the sun must be in this
condition. According to analogy with solid and liquid bodies,
being exposed to heat and then withdrawn, the changes of
temperature that it would undergo would be more rapid in the
elevation than in the falling, and so the changes in the pre-
ceding would be more rapid than in the following parts. To
this would be added the effect of the atmosphere warmed
by the earth; for as that is slower in attaining heat, as is
shown by the time of maximum temperature, so its effects
OCT. 1850.]
257
Diurnal variation-direction.
being gradually communicated to the air above, as the sun
passed away, would tend to retard its fall and enlarge the dif-
ference already spoken of. Applying these considerations to
the natural case, the strongest effect and the greatest variation
should be towards the west, and the following or lesser action
towards the east of the sun; and the mean condition of the
needle for the whole change would be in advance of that body.
2941. Mr. Broun has made observations of the daily variation
at different heights, namely, at Makerstoun and the top of the
Cheviot Hills, where the height differs by nearly half a mile,
and finds, I believe, no difference in the intensity, but that the
progress is first at the higher station. It would be very inter-
esting to have an observatory up above, but to give the results
required it should have air and not solid matter beneath it.
Fig. 16.
2942. There is another circumstance which importantly influ-
ences the times of the passages of the declination variation. If
two places north and south of the equator have equal dip and
contrary declinations, i. e. if both their upper ends point east or
west, then the effects ought to correspond and form a pair. But
if both have east or west declination, according to the usual mode
of marking this effect by the north end of the magnet, then the
variations already described should come on as the sun passes
midway between them, but there should be a difference in time.
As the luminary appcars and approaches, the needles a and b
(fig. 16) will most probably be
affected together; but, as he
draws nigh, if the places have
eastern declination, the one
that is south will be soonest
affected, and for the time most
strongly, but will in a period
more or less extended, be fol-
lowed by the corresponding
action at the other place. For
as each needle will have return-
ed from the first half of its
series of changes to 0° by the
time the sun is on its magnetic
meridian, and as it will arrive
at this meridian, as regards the

VOL. III.
a
b
S
258
[SERIES XXVI.
Atmospheric magnetism.
south needle, before it does so for the north needle, so the south
magnet should precede the other in its changes. If the declina-
tion of both were westerly, then the north needle would precede
the south.
2943. The hypothesis advanced, besides agreeing with the
facts regarding the direction of the needle's motions, as is the
case generally, and if my hopes are well-founded, will be the
case also in more careful comparisons; should also agree in the
amount of force required for the observed declinations at given
hours. I have endeavoured to obtain experimental evidence of
the difference of action of oxygen and nitrogen on needles sub-
jected to the earth's power, but have not yet succeeded. This
however is not surprising, since a saturated solution of proto-
sulphate of iron has failed under the same circumstances.
delicate apparatus may perhaps yield a positive result.
More
2944. That small masses of oxygen should not give an indi-
cation of that which is shown by the atmosphere as a whole is
not surprising, if we consider that the mass of air is exceeding
great, and includes a vast extent of the curves on which it, by
the hypothesis, acts; and yet that the effect to be accounted for
is exceeding small. The extreme declination at Greenwich is
12', equal to about 4' 24" of east and west alteration on the free
needle, so that that is the whole of what has to be accounted for.
One could scarcely expect such an effect to be shown by small
masses of oxygen and nitrogen acting on only a few inches in
length of the magnetic curves passing through them, unless one
could use an apparatus of extreme and almost infinite sensibility;
but from what I have seen of oxygen when compared at dif-
ferent degrees of dilution (2780.), or at different temperatures
(2861.), I am led to believe that the effects on it produced by
the sun in the atmosphere will ultimately be found competent
to produce these variations.
2945. Where the air is changed in temperature or volume,
there it acts and there it alters the directions of the lines of
force; and these by their tension carry on the effect to more
distant lines (2934.), whose needles are accordingly affected.
The transferred effect will be greater or less according as the
distances are less or greater, and hence a change near at hand
may overpower that at a distance, and a cloud close to a station
may for the moment do more than the rising sun.
These are
OCT. 1850.] Diurnal variation-Annual variation.
259
the irregular variations; and the extent of their influence is well
shown by the photographic records of Greenwich and Toronto.
The volume of Greenwich Observations for 1847 contains a pho-
tographic record of the declination changes, February 18—19,
1849. Between 6 and 7 o'clock there is a variation of 16' occur-
ring in 18 minutes of time, or at the rate nearly of l′ for each
minute of time. The course of the mean variation for the same
date and time is 1'95 in two hours, or at the rate of 1 second for
each minute of time, so that the irregular variation (which may
be considered as a local variation in respect of the sun's power
for the time) is sixty times that due to the effect of the great
resultant; moreover it was in the reverse direction, for the tem-
porary variation was from east to west, whilst the mean variation
was from west to east.
2946. Another mode of showing how much the action of nearer
portions of the atmosphere may overpower and hide the effect of
the whole mass, is to draw the line of mean variation for the
twenty-four hours through such a photographic record as that just
referred to, and then it will be seen in every part of the course how
small the mean effect on the needle is, compared to the irregular
or comparatively local effect for the same moment of time. The
magnet with which these observations were made, is a bar of
steel 2 feet long, 1½ inch broad and a quarter of an inch thick,
and therefore not obedient to sudden impulscs; it is probable
that a short, quick magnet would show numerous cases in which
the irregular variation would be several hundred of times greater
than the mean. Still all these irregularities and overpowering
influences of near masses are eliminated by taking the mean of
several years' observations, and thus a true result is obtained, to
which the hypothesis advanced may be applied and so tested.
2947. Returning for a short time to the annual variation
(2882.), I may observe, that it has been a good deal considered
in discussing the daily variation. The arrangement of the mag-
netic effects by Colonel Sabine at Hobarton, Toronto, St. Helena,
and elsewhere, into monthly portions, proves exceedingly in-
structive and important, especially for places between and near
the tropics. It supplies that kind of analysis of the annual
variation which is given by the hours for the daily variation.
$ 2
260
[SERIES XXVI.
Atmospheric magnetism.
Every month, by a comparison of its curve with those of other
months, tells its own story, at the same time that it links its
predecessor and successor together.
2948. I shall have occasion to trace these monthly means
hereafter; but in the meantime refer to the effect of the sun's
annual approach and recession indicated by these means, as
according with the hypothesis in respect of near and distant
actions (2945.). Hobarton and Toronto are in opposite hemi-
spheres, so that the sun whilst approaching one recedes from
the other, and the amount of variations therefore changes in
opposite directions. Below is the average for each month, de-
rived in the case of Hobarton from a mean of seven years, and
in that of Toronto from a mean of two years.
January
February
March
April
May
Hobarton.
Lat. 42° 52'5 S. Toronto. Lat. 43° 39' 35 N.
11.66
11.80
9.50
7.26
4.56
6.51
6.40
8.50
9.52
10.34
FEE
June
3.70 Winter.
July
August
September
October
November
December
4.61
5.89
8.24
11.01
12.05 Summer
11.81 .
11.99
12.70 Summer.
12.68
9.72
7.59
5.75
4-47 Winter.
The two stations are in latitudes differing only 47' from each
other; and the extreme difference of the atmospheric effect be-
tween summer and winter differs as little, being at Hobarton,
which has the highest latitude, 8'-35, and at Toronto 8'23.
2949. According to Dove, the northern hemisphere is warmer
in July than the southern hemisphere by 17°.4 Fahr., and colder
in winter by only 10°7; the numbers being as follows:-
July.
Northern hemisphere 710 620-3 the whole globe.
Southern hemisphere 53.6)
January. Northern hemisphere 48.854°-15 the whole globe.
Southern hemisphere 59.5 J
The mean for the whole year is 59°.9 for the northern hemisphere,
OCT. 1850.]
261
Annual variation.
and 56°5 for the southern. Therefore, as Dove further shows,
the whole earth is in July, when the sun is shining over the ter-
raqueous parts, 8° higher in temperature than in January, when
it is over the watery regions: and from the influence of the
same cause, the mean of the southern hemisphere is 3°4 below
the mean of the northern half of the globe. The difference be-
tween January and July is for the northern hemisphere 22°.2,
and for the southern only 5°.9. These differences are so pecu-
liar in their arrangement and so large in amount, that they
must have an effect upon the distribution of the magnetic forces
of the earth, but the data are not yet sufficient to enable one
to trace the results. Sabine indicates a probability from his
analysis of observations, that the sum of the earth's magnetic
force is increased in intensity when the sun is in the southern
signs, i. e. in our winter (2891.). I should have expected from
theory that such results would have been the case, at least in
those parts where the dip was not very great; because a colder
atmosphere ought to conduct the lines of magnetic force better,
and therefore the systems round the earth ought at such a time
to condense, as it were, in the cooler parts. It would be doubt-
ful, however, whether the needle would show this difference,
because the lines of power would not be restrained above, as in
the case formerly supposed (2922.), but could gather in from
space freely. From what has been said, however, it will be evi-
dent that such a conclusion can only be drawn with any degree
of confidence from observations made pretty equally over both
hemispheres.
2950. If we should ever attain a good knowledge of the an-
nual variation for several stations in different parts of both hemi-
spheres, it would help to give data by which the depth at which
the magnetic power is virtually situated might be estimated; for,
as this power is expected to undergo undulations over very large
portions of the earth's surface by the annual changes of tempe-
rature (2884.), so they would differ in character and extent ac-
cording as the origin of the lines should prove to be more or less
deeply situated.
2951. With regard to the many variations of magnetic force,
not periodic or not so in relation to the sun, which yet produce
262
[SERIES XXVI.
Atmospheric magnetism.
the irregular and overruling changes already referred to (2945.),
dependent, as I suppose, on local variations of the atmosphere,
I may be allowed to notice briefly such points as have occurred
to my mind.
2952. The varying pressure of the atmosphere, over a given
part of the earth's surface, ought to cause a variation in the mag-
netic condition of that part of the earth. It is represented to
us by a difference of 3 inches of mercury, or one-tenth of
the weight of the atmosphere. Now the oxygen in a given
space is paramagnetic in proportion to its quantity (2780.), and
therefore it does not seem possible that that quantity over a
given space of the earth's surface, whether it be recognized by
volume as above, or by weight as in a given volume at the earth's
surface, should be varied to the extent of one-tenth of the whole
sum without producing a corresponding alteration in the distri-
bution of the magnetic force; the lines being drawn together and
the force made more intense by an increase of the quantity or of
the barometric pressure, and the reverse effects produced at the
occurrence of diminished pressure.
2953. At any spot which is towards the confines of that space
where the air is increasing or diminishing in pressure, there
will probably occur variations in the directions of the lines of
force, and these will be more marked at such places as happen
to be between two others, in one of which atmosphere is accu-
mulating, whilst from the other it is retreating. Whether these
changes (which I think must occur) produce by vicinity, effects
large enough to become sensible in our magnetic instruments,
is a question to be resolved hereafter. To suggest the cause is
useful, because to know of the existence, nature, and action of a
cause, is important to the arrangement of the best means of ob-
serving and evolving its effects.
2954. Winds and large currents of air above may often be
accompanied by magnetic changes if they endure for a time
only. A constant stream like the trade-wind, may have a con-
stant effect; but if, when the arrangement of the lines of mag-
netic force through the atmosphere is in a given state con-
sequent upon the condition of the atmosphere at that time, a
wind arises which mixes regions of cold and warm air together,
or makes the air more dense in one region than another, or pro-
ceeding from one to another, balances regions which before were
Ост. 1850.]
263
Irregular variations.
in different conditions, then every such change will be accom
panied by a corresponding change in the disposition of the mag-
netic force, to which we may perhaps hereafter be able to refer
by means of our instruments. Even tides in the air ought to
produce an effect, though it may be far too small to be rendered
sensible.
2955. The precipitation of rain or snow is a theoretical reason
for the change of magnetic relations in the space where it takes
place; because it alters the temperature where such precipita-
tion occurs, and relieves it from a quantity of diluting diamag-
netic or neutral matter. A chilling hail-storm might affect the
needle in a summer's day. Clouds may have a sensible influence
in several ways; acting at one time by their difference from
neighbouring regions of clear air, and at other times by absorb-
ing the sun's rays, and causing the evolution of sensible heat at
different altitudes in the atmosphere at different places, or pre-
venting its evolution more or less at the surface of the earth.
Those masses of warmer or colder air of which meteorologists
speak, which being transparent are not sensible to the eye, will
produce their proportionate effect. And hypothetically speaking,
it is not absolutely impossible that the hot and partially deoxy-
genated air of a large town like London, may affect instruments
in its vicinity; and if so, it will affect them differently at dif-
ferent times, according to the direction of the wind.
2956. If one imagines on the surface of the earth a spot which
shall represent the resultant there of the atmospheric actions
above, and can conceive its course as it wanders to and fro,
under the influence of the various causes of action which have
been in part referred to, whilst it still travels onwards with the
affect
sun, one may have an idea of the manner in which it may
the various observatories scattered over the earth. I believe
that its course, as regards the east and west direction of its
wanderings, is partly told in the photographic registerings of
Greenwich and Toronto, being there mingled in effect with other
causes of variation. This spot may be concentrated or diffuse
it may pass away and reappear elsewhere; there may even be
two or more at once sufficiently strong to cause vibrations of the
needle between them.
e;
2957. The aurora borealis or australis can hardly be indepen-
pent of the magnetic constitution of the atmosphere, occurring
264
Atmospheric magnetism. [SERIES XXVI.
as it does within its regions, and perhaps in the space above.
The place of the aurora is generally in those latitudes the air of
which has a distinct magnetic relation, by difference of tempera-
ture and quantity, to that at the equator, and the magnetic cha-
racter both of the aurora and of the medium in which it occurs
ties them together; therefore, to be aware of and to understand
in some degree the latter, will probably direct us to a better com-
prehension of the former. The aurora is already connected with
magnetic disturbances and storms; it may in time connect them
with changes in the atmosphere in a manner not at present an-
ticipated, and as the suggestion is founded upon principle it seems
deserving of consideration.
2958. Can the magnetic storms of Humboldt be due to atmo-
spheric changes? This is a question on which I would offer the
following observations. Supposing a magnetic rest in the at-
mosphere, and that all local or irregular variations remained un-
changed for the time, then if a change happened in one place it
would be felt instantly everywhere else over the whole earth,
and in proportion to the distance from the place of change. It
would be felt instantly, because the impulse would not be con-
veyed chiefly or importantly through the matter of the earth or
air, but through the space above, for the lines there are affected
by changes in that part of them which passes through the at-
mosphere, and, as I conceive, would affect the other lines in space
round our globe, which would in turn affect those parts of their
lines, which, passing downwards to the earth, govern the needles
below. In space, I conceive that the magnetic lines of force, not
being dependent on or associated with matter (2787. 2917.),
would have their changes transmitted with the velocity of light,
or even with that higher velocity or instantaneity which we sup-
pose to belong to the lines of gravitating force, and if so, then a
magnetic disturbance at one place would be felt instantaneously
over the whole globe.
2959. But the difficulty is to conceive an atmospheric change
sufficiently extensive and sudden to make itself perceived every-
where at the same time amongst the comparatively local varia-
tions that are continually occurring. Still, if there were a lull
in these disturbances by the opposition of contrary actions or
otherwise for the same moment of time at two or more places,
those places might show a simultaneous effect of disturbance,
Ост. 1850.]
265
Magnetic storms.
and that even when the cause might be very little or not at all
sensible in the place where it occurred. A simultaneous change
over an area of 600 or 800 miles in diameter, might produce less
alteration in the middle of that area than at the extremities of
radii of 1000 miles.
2960. It becomes a fair question of principle to inquire how
far masses of the air may be moved by the power of the mag-
netic force which pervades them. When two bulbs of oxygen
in different states of density are subjected to a powerful magnet
with an intense field of force, the mechanical displacement of
one by the other is most striking. Whether in nature the
enormous volumes of air concerned, and the difference in inten-
sity of the earth's magnetic force at the different latitudes where
these may be supposed to be located, combined with the differ-
ence of temperature, are sufficient to compensate for the small
portions of oxygen in the air and the smaller variations in den-
sity, is a matter that cannot at present be determined. The
differential result of motion, as has been shown, is very great
where the direct result, as of compression, is not merely very
small but nothing (2774. 2750.), and the atmosphere is a region
where the differential action of enormous masses is concerned.
2961, Now in the matter of difference of intensity, Gay-Lus-
sac and Biot conclude from their observations ¹, that the mag-
netic force is the same at a height of four miles as at the surface
of the earth. M. Kupffer, however, draws from Gay-Lussac's
results the conclusion, that there was a little diminution, and
Professor Forbes, from his experiments made in different parts
of Europe², concludes that there is a decrease of the force up-
wards. Such decrease may be a real consequence due to the
difference of distance from the source of the terrestrial magnetic
force; or, as is more likely, it may be due to the different
proportions of oxygen there and at the surface of the earth.
According to Gay-Lussac's account of the air brought from
above, it was as 0.5 to 10, compared with the density below.
Hence the paramagnetic power, added to space in the place
above, from whence the air was taken, would not be more
than one-half of that added by the presence of the denser atmo-
sphere below. This I think ought to make a change in the dis-
¹ Annales de Chimie, Ann. xiii. vol. lii. p. 86.
2 Edin. Phil. Trans. 1836, vol. xiv. p. 25,
266
[SERIES XXVI.
Atmospheric magnetism.
tribution of the magnetic force; it would almost certainly do so
at the equator, where the lines of force are parallel to the gene-
ral direction of the atmosphere (2881.); and I think it would
do so, as to the horizontal component, in the latitude where
Gay-Lussac and Biot made their aërial voyages. It is also just
possible that the observers may have been in such relation to
the heated or cooled air about them as to have had the difference
observed produced, or rather affected, by some of the circum-
stances just described (2951.).
2962. Whether the result obtained by Gay-Lussac and Biot
indicate a change of power due to distance or not, this we know,
that there are great changes from the magnetic equator toward
the north and south; and that, as Humboldt and Bessel say,
it is doubled in proceeding from the equator to the western limits
of Baffin's Bay. And when so little as one-third of a cubic inch
of oxygen can exert a force equal to the tenth of a grain, subject
to the action of our powerful magnet, we may well conceive that
the enormous sum of oxygen present, in only a few miles of heated
or cooled atmosphere, can compensate for the great difference of
magnetic force, and so by change of place, cause currents of winds
having their origin in magnetic power. In such a case we should
have a relation of magnets to storms; and the magnetic force of
the earth would have to do with the mechanical adjustments and
variations of the atmosphere, sometimes causing currents which
without it might not exist, and at other times opposing those
which might else arise, according as the great differential rela-
tions by which it would act (2757.) should combine with or op-
pose the other natural causes of motion in the air. Such move-
ments would react upon the magnetic forces, so that these would
readjust themselves, and so there would be magnetic storms,
both material and potential, in the atmosphere, as there are sup-
posed to be of the latter kind in the earth.
2963. In bringing this communication to a close, I have to
express my obligations to two kind and able friends, Colonel
Sabine and Professor Christie, for the interest they have taken
in the subject, and on the part of the former for the extreme
facilities afforded me in the use of observations and the data de-
rived from them; but in doing so I must be careful not to convey
any idea that they are at all responsible for the peculiar views
I have ventured to put forth. I may well acknowledge that much
OCT. 1850.]
Ост.
267
Atmospheric magnetism.
which I have written has been upon very insufficient considera-
tion; but hoping that there might be some foundation of truth
in the account of the physical cause of the variations which I
have ventured to suggest, I have not hesitated to put it forth,
trusting that it might be for the advantage of science. The mag-
netic properties and relations of oxygen are perfectly clear and
distinct, and are established by experiment (2774. 2780.); and
it is no assumption to carry these properties into the atmosphere,
because the atmosphere, as a mere mixture of oxygen and ni-
trogen, is shown to possess them also (2862.) 1. It varies in its
magnetic powers, by causes which act upon it under natural cir-
cumstances, and make it able to produce some such effects as
those I have endeavoured generally to describe.
2964. If it be a cause, in part only, of the observed magnetic
variations, it is most important to identify and distinguish such
a source of action, even though imperfectly; for the attention is
then truly and intelligently directed in respect of the action and
the phænomena it can produce. The assigned cause has the ad-
vantage of occurring periodically and for the same periods, as a
large class of the effects supposed to be produced by it; and if
the agreement should appear at first only general, still that
agreement will greatly strengthen its claim to our attention. It
has the advantage of offering explanations and even suggestions
of many other magnetic events besides those which are periodical,
and it presents itself at a time when we have no clear knowledge
of any other physical cause for the variations, but are constrained
vaguely to refer them to imaginary currents of electricity in the
air or space above, or in the earth beneath.
2965. The causes, both of the original power and of its secu-
lar variations, are unknown to us. But if, accepting the earth
as a magnet, we should be able to distinguish largely between
internal and external action, and so separate a great class of
phænomena from the rest, we should be enabled to define more
exactly that which we require to know in both directions, should
be competent to state distinctly the problems which need solu-
tion, and be far better able to appreciate any new hints from na-
ture respecting the source of the power and the effects that it
presents to us.
2966. The magnetic constitution of oxygen seems to me won-
¹ Philosophical Magazine, 1847, vol. xxxi. pp. 406, 409.
268
[SERIES XXVI.
Atmospheric magnetism.
.
.
derful. It is in the air what iron is in the earth. The almost
entire disappearance of this property also, when it enters into
combination, is most impressive, as in the oxynitrogens and oxy-
carbons, and even with iron, which it reduces into a condition
far below either the metal or the oxygen, weight for weight.
Again, its striking contrast with the nitrogen, which dilutes it,
impresses the mind, and by the difference recalls that which also
exists between them in relation to static electricity (1464.) and
the lightning flash. Chlorine, bromine, cyanogen and its con-
geners, chemically speaking, have no magnetic relation to oxy-
gen. In nature it stands in this respect, as in all its chemical
actions, alone.
2967. There is much to do with oxygen relative to atmospheric
magnetism. Its proportion of paramagnetic force at different
temperatuxes and different degrees of rarefaction, will require
to be accurately ascertained, and this I hope to effect by a torsion
balance, in course of construction (2783.). Indeed, I hope that
this great subject may be largely touched and tried by experi-
ment as well as by observation, and therefore gladly make it
part of these experimental researches.
2968. One can scarcely think upon the subject of atmospheric
magnetism without having another great question suggested to
the mind (2442.). What is the final purpose in nature of this
magnetic condition of the atmosphere, and its liability to annual
and diurnal variations, and its entire loss by entering into com-
bination either in combustion or respiration? No doubt there
is one or more, for nothing is superfluous there. We find no re-
mainders or surplusage of action in physical forces. The small-
est provision is as essential as the greatest. None are deficient,
none can be spared.
Royal Institution.
September 14, 1850.
APPENDIX.
Received November 12, 1850.
The following Tables of data obtained at Toronto, St. Peters-
burgh, Washington, Lake Athabasca and Fort Simpson, supplied
to me by the kindness of Colonel Sabine, have not yet been pub-
lished. The data for Hobarton and Greenwich are in the
volumes of observations for those stations.


Toronto.-Longitude 77° 5' W. Latitude 43° 40' N. Approximate declination 1° 25' W. Mean inclination 75° 15' N.
Diurnal variation of the Declination in the several months, from July 1842 to June 1848 inclusive.
Increasing numbers denote a movement of the south or upper end of the magnet towards the West.
Toronto mean
time.
}
Oh.
Noon.
|
1h. 2h. 3h. 4h. 5h. 6h. 7h. 8h.
5h. 6h. 7h 8h. 9h. 10h. 11h.
Daily
12h.
Midn.
13h. 14b. 15h. 16h. 17h. 18h.
19h. 20h. 21h. 22h. 23h.
means.
1
January
February
March
April
May
I
June
•
July
August
I'II
September
October
November
December
0.87 0.00 0.00 0.53 144 2.28 2.89 347 443 453 439 406
0.78 0.00 0.06 0.94 1·58 1.91 273 313 402 444 469 445
1.44 0.01 0.00 0'59 174 2.90 3.82 4'77 563 6·60 647 6·86
1.25 0.00 0.16 102 276 412 5 14 6 31 705 7'14 7.60 7.66
1.16 0.00 0.29 1'56 3'24 5'11 608 6:27 618 675 736 7°49
1.37 0.00 0.02 0.94 2 53 4'35 5 45 611 6.10 6·66 6·66 6·87
153 0.09 0.00 0.84 2.18 3'98 520 5'77 6.31 6.34 731 7.38
0.00 0.73 2.61 452 6 12 7.60 752 805 8.97 8.51 840
0.03 0.00 0.76 2.92 462 6'04 6.78 6.83 7.62 7.84 783 708
0.48 0.00 0.31 1.38 2.38 306 3.84 4°33 4'92 576 5.68 548
0.75 0.00 0.34 1.37 2.21 2.91 3.96 489 5°16 5*70 5*54 5:26
၀:၀၀
1*200*18 0·00 0·61 1·67 2·56 3·30 3·89 4°39 4·62 495 448
3.66
342 363 3'87 446 384
388
444 548
5.80 479 303
330
431
381 3'54 407 3'97 486
495
5'20
5'97
570
464 253
343
604
6'42 6.55 6'34 6.69 6.59
710
8:30
9'38
940
7'15 422
521
7.39
740
677
767
8.14
7:50
500
451
409
732 7.65 7.82 8.08 8:33 9:46
7:26 6.72 710 7.80 9.70 11.02
6.50 6.37 6.36 729 9'03 11 34
7.06 642 6.37 6.86 8.53 10 54
7.69 7.65 783 8:24 9'50 12'09
7.66 7.53 7'77 845 8.38 979
521 489 5'16 582 574 550
379 380 4'51 444 4'99 495
349 304 356 392 402 3.81 418 4°50
10 09
10 20
9'10
6.87 374
609
12.16 12.03
10:28
6.90 3°52
6°39
12 34
12'09
10'54
767 404
6.12
1201 12 22
10'69
|
7.65 427
613
13.89 13 79
11 51
731 373
7'31
•
11 16 10'24
8.60
5'34 225
6:37
6.39 7°32
702
5*17 2.63
3.89
5'70 6'31
608 4'57 235
3.92
5′22 4'67 2.83
330
January
February
March
April
May
June
July
August
September
October
November
December
Mean Diurnal variation of the Inclination in the several months, from July 1842 to June 1848.
Increasing numbers denote increasing inclination.
Ι ΟΙ I'11 129 130 1'12
I'12 1'17 127 137 I'19 075
047
037
0'54 058 045 033 028 022 O'21 036
045 049 044 041 030 027
054 104 106 043
044
069
070 0.79 0.86 0.39
045
0.56
0.76
084
053 050 050 046 046 047
0.59 0.64 0.61 0.60 0.66 0.74
0.86 0.87 0.89 0.92 104 100
090 091 098 103 105 108
062
081
0·95 | 1'00 1°05] 0°50
0.80
0.90
103 116 116 061
0*70
0.62
0.56 0.66 0.78 0.83 0.87
0.81
0.80
0.88
103 114093 057
053
064 065 073 074 0.84
0.89
1'00
1'09
125 126 1·13 0·62
0.68
0·62
0.38
0.70 0.70 0.75 0.57 0.65 0.68
045 040 033 022 022 032
033 0.31 0.21 0.22 0.12 0.07 0.00
0.34 028 0'22 0.14 0.08
0.95
128
164 185 171
075
055
0.85
104 115 111 048
0'08 0'42
0.14 0.89 100 0°32
0.09
057 057 058 053 054 055
0.00 0.17
0.63 0.81
0.34 0.66 0.81 0.31
0.93 113 110 054
1*02 077 0°53 0.22 0.00 0.09 0.16 0.21 0.25 0.33 034 038
0.86 0.61 0.36 0.12 0.01 0.00 0.09 012 019 026 027 031
1'02 077 047 0°14 0'000'00 0'12 022 024 035 040 044
099 077 0.54 0.17 0.05 0.00014 035 049 053 0'49 0.61
0·830°52 0.22 0.06 0.00 0.11 0.27 0°33 047 062 0.64 0.66
0.89 0.60 0.26 0.05 0.00 0.00 0.16 034 053 068 073 083
0.67 0.55 0.17 0.07 0.00 0.06 0.17 0°24 039 040051 0.56
0.85 0.51 0.21 0.00 0.02 0.04 0.25 040 042 044 048 055
135 082 0.35 0.10 0.00 0.10 0°29 049 053 055 0.57 0.63
0.93 0.67 0.39 0.14 0.00 0.06 0.21 0.30 037 039 040 049
094 075 045 022 011 0.18 0.12 0.18 0.20 0.20 023 033
o'91 0·88 0.51 0.27 0.05 0.01 0.02 0.16 0.21 0.27 0.33 0.30
0'450'51
Hourly means o'94 069 037 013 002 005 017 028 036 042 045 051 055


Toronto.-Mean Diurnal variation of the Total Force in the several months, from July 1842 to June 1848.
Increasing numbers denote increasing Force. Mean Total Force at Toronto 13.9.
The figures express the changes in parts of the whole Force.
Daily
| |
9h. 10h. 11. 12h. 13h. 14h. 15h. 16h. 17h. 18h. 19h. 20h. 21. 22h 23h. means.
|
Toronto
mean time} Oh.
1h. 2h. 3b. 4h. 5h. 6h. 7h. gh.
March
ΟΙ Ι
02,0
April.
May
June
July
021
...
02 I
013
Means
'00 '00 '00 '00 '00 '00 '00 '00 '00
January 005 ΟΙΙ 017 023 022 024 023 023 023 020
ΟΙΟ
019 015 OIO 009 004 003 004 005 008 009
February. 006 012 019 022 024 026
026
ΟΙΟ
026 027 025 023 019 017 009 005 003 004 006 009 010 016 004 000
004
019 026 029 031 031 031 028 025
2014 005 002 0021 002
003 ΟΙΟ 013 013 007 002 000 014
O12 020 031039 045 045 044 039 034 027 020 012 008
009 006 006 019
004 013 015 031 038 042 038 035 029 025 017 OII 004 002
003 008 017 025 029 031 030 028 022 018 014
ΟΙΙ 006 002 002
015 019 030 038 044 047 043 039
031 026
015 007 004
August 027 034 044 042 057 057 051 046 041 032 023 010 006 001
September 029 043 053 060 060 056 052 050 044 038 034 029 019 007
004 009 018 022 028
October
027 032 032 033 033 034 031 026 023 018 007 003 005 002
000 005
014 018
November 007 014 022 026 028
026 028 025 025 028 024 018 015 OII 007 004 ΟΟΙ 003 OOO 003 007 009 008
002 001 003 ΟΙΙ
December 004 ΟΙΟ 019 020 023 02 J 021 021 019 018 017 012 ΟΙΟ 008 006 007 003 003 007 006 006 006 OOI OOO OII
ΟΙΙ 018 026 032 036 037 035 033 029 025 020 015 008 005 003
002 004
008 013 014 014 008 005 006 017
Mean Temperature of the Air in the several months, from July 1842 to June 1848, in degrees of Fahrenheit's scale.
00 *00 '00 '00 *00 '00 '00 '00 '00 '00 '00 '00 *00 '00 *00 '00
ΟΙΟ 003 OOO
000
012
003
003
ΟΟΙ 013
002
000
007 003 000 009 ΟΙΙ 013 012 012
003 008
ΟΙΟ
010 015 013 009 003
OOI 006 ΟΙΙ 014 014 ΟΙΟ
002 005 OII 016 017 015
003 000
006 018 026 026
000 000
015
005
002 OOO 013
014
ΟΙΟ 002
020
024
019
019
02 I
026
ΟΟΙ
015
015
016
021 030
ΟΙΙ
ΟΙΙ 008 006 017
1298
May
June
...
January.. 278 283 28.6 28.5 28.0 27.1 26.3 25.8 25.5 25.3 26.3 24.6 25.6 235 234 21.6 232 230 237 236 239 248 260 27.1 25.48
February.274 28.2 28.5 28.5 280 26.9 25.6 24.6 238 23°2 227 222 22°0 217 213 209 205 202 200 199 209 229 24'9 26.3 23.80
March 338 344 350 349 343 336 319 305 295 286 280 273 27.3 268 263 262 258 255 250 25'9 278 299 316 32.8 29.71
April...... 476 48.5 490 490 486 479 461 435 418 407 398 393 391 389 379 373 370 366 36.8 392 415 436 452 46.6 42.55
590 599 602 60 3 603 599 581 552 526 507 49°7 488 480 469 46°3 456 451 452 47'6 506 530 552 56.8 580 53°04
66.7 67.5 679 68.3 68.5 68.1 66.6 639 606 584 570 561 557 548 541 533 527 529 55.6 58.5 608 62°7 64°4 656 60·86
July 729 737 745 748 747 74 3 727 692 651 62'9 618 607 598 58.9 58.3 57.6 569 569 598 634 660 68 2 701 71'5 66 02
August 730 739 74'5 748 746 741 725 684 653 636 624 616 607 600 594 587 58.3 58.1 59.6 63°2 663 687 706 721 66:43
September 639 645 64'9 649 647 637 611 58.3 571 560 549 542 538 53°3 527 52°2 516 511 517 542 570 59'5 615 629 57'90
October... 497 503 505 50'3 496 478 458 447 43'9 43°1 42°3 416 410 40°4 40'1 39'9 395 394 396 404 42.8 456 475 489 44°35
November 395 400 401 399 390 377 369 363 35'9 357 353 349 343 340 337 334 332 333 336 33.6 346 362 37.7 38.8 36.15
December 299 304 307 305 29.8 28.9 28.2 27.9 27.5 273 270 269 26·6 260 257 255 255 255 251 250 254 266 27′9 29°1 27′44
Means ... 49°27 49'97 50′37 50*39 50*01 49°17 47.65 45 69 440542-9642′27 41′5241*1640*41 39′93 39°35 39′11 38 97 398441°4643′33 45°32 47 02 48°31 44°48


St. Petersburgh.-Longitude 38° 18' East. Latitude 59° 57′ North. Mean declination 6° 10' West.
Mean Diurnal variation of the Declination in the several months, from 1841 to 1845 inclusive.
Increasing numbers denote a movement of the south or upper end of the magnet towards the West.
Noon.
Midn.
hmh mh mh mh mh mh mh mh mh mh mh mh mh mh mh mh mh mh mh mh mh mh mh m
Mean time... 0 211 212 213 214 215 216 217 218 219 2110 2111 2112 211|13 21|14 2115 211|16 21||17 213|18 211|19 2120 21 21 21 22 21 23 21 Means.
May
June
Ο
8.73
January.. 027 000 0·36 1·24 159 1.99 2·39 3·28 403 4·65 456 465 443 372 377 3.10 2.57 222 2:35 217 2:08 1.86 142 102 249
February. 084 0.00 0.09 0'57 155 2.84 354 363 403 518 567 549 527 452 4 34 465 434 390 403 377 3.50 3 23 261| 1'46 3′29
March 0.89 0.00 0.04 115 2.88 416 5′36 629 673 678 740 7·84 669 6:51 576 611 6·38 6·16 6·65 6·56 673 6.38 496 279 505
April...... 159 000 0.36 2.17 403 554 704 793 8:33 8.02 930 917 8.68 8.46 859 917 930 9:48 1001 10.68 9'75 758 461 701
1'02 0.00 0.62 2.13 3.68 549 6'96 7:44 718 6.82 744 8.24 8.55 8.73 8.82 9.66 10 23 10 7211*12 1139 11 12 9'92 749 3'54 7'01
1'77 0'000'00 1°37 2°92 452 5°76 6·25 625 6·56 713 713 7:49 8.28 8.68 9.70 10 23 10 94 11°30 1139 11 52 10 10 7:35 412 670
146 004 000 III 2.39 394 496 527 598 5.98 678 749 766 771 842 855 9:30 952 983 975 904 846 6.96 3.90 6.02
0.27 0.00 0.40 244 416 594 704 673 749 727 735 7:27 8:02 811 8:06 8.55 9.30 9.88 1019 1019 9'44 842 567 315 647
September 057 0.00 0.84 2:57 4:30 633 678 749 7'97 806 8:33 7:49 704 7:31 7.40 6.78 7:04 691 727 731 713 6:25 412 195 572
October
Ο
0.31 0.00 0.48 177 3'59 408 487 576 602 6.56 691 620 571 518 478 4:39 4:16 3'99 421 483 509 465 332 159 410
November 0.09 0.00 0.36 155 190 271 279 315 381 439 447 4:34 368 3:06 275 2:35 2.22 182 182 190 177 177 093 057 2:26
December 0.53 0.00 0.36 124 182 2:39 2.79 2.97 403 456 456 452 368 310 2.88 2.53 204 182 177 177 182 168 128 093 2:29
Means 0.80 0.00 0.33 1·61| 2°9c| 4°16′ 5′02 5′52 5′99 6·24 6·66| 6·65| 6·41| 6·22 6·20 6·25 6·42 643 6·67 6·75 6·66 6:04 447 247 4.87
July
August
...
Mean Temperature of the Air in the several months, from 1841 to 1845 inclusive.
O
·
·
•
•
•
·
Fahrenheit's scale.
10.67
19-7419-761
19918-7918-7918-
January.. 20-28 2071 20 67 20:41 1982 1989 1973 1971 1974 1976 1967 19-49 1938 1933 1929 19 19 19-0418-90 1879 1879 1874 18.81 19.24 1998
February. 18.34 18.58 18.70 18.65 18-27 17:35 16.88 16.52 16 32 16.0915.95 15.67 15 55 15 48 15 39 15 19 14 97 14.88 14 76 14.65 15 19 15 66 16.61 17:35
March 25.61 26 30 26.97 27 01 27.01 26 13 24 74 23.88 23.2022 4421 94 21 31 2070 2007 19.62 19 26 18.84 18.54 18 34 18.74 19.87 21 38 22.95 24°53
April. 37.85 38 07 38.58 38.81 39 53 38.63 36 54 34 62 33 35 32 38 31°42 30°7230′07 29°55 29.08 28.61 28.36 28 42 29°213063 32 1633 75 35 39 36 79
53°46 53.80 54 31 54 72 55 10 54 29 52 2349 844791 46 1945 38 43 9043 16 42°37418341°4741 5642 7344*1946 0647-8849 5751 1752 65
6303 63 48 63.8364 36 64 97 64 0761 90 59 97 58 1956 48 55 0454 07 53 26 52 58 5200 51 50 52 27 53 33 5495 56 57 58 21 59 72 59 02 62.15
66.44 66'93 67 21 67 46 67.93 67 26 65 28 63 61 62 01 60 57 59 56 58-86 58.05 57 33 56.86 56 48 56.68 57 53 58.86 60 5962 0663 43 64 7665 90
August 67.10 68.00 68.56 68 69 69 23 68.56 65 73 63 70 62 26 60 8960 08 59′22 58 14 57 60 57 20 56 57 56 14 56 73 57 65 59 45 61 29 63 12 64'7166.06
September 54 50 55 6655 91 55 78 55.83 54 56 52 62 51 16 50 15 49 43 48 89 48-3147 75 47 25 46.85 46 44 46 26 46 06 46 17 47 2148 76 50 56 52.20 53:37
October 41.9244.80 42.7641 9841 78 40 92 40*30 39.89 39 56 39 31 38.86 38.52 38 32 38 14 38.00 37.85 37 73 37 67 37 53 37 71 38 28 39°11 40°124104
November 29°73 30 22 30.88 29 75 29 26 28.96 28.83 28.67 28.58 28 41 28 52 28.49 28°47 28°45 28 42 28 27 28 13 28.04 28.00 27.95 28.07 28 42 28.83 29 37
December 26.04 26°45 26′40 26-27 26°1325′91257026 02 25*52 25°48 25°48 25°32 25 2125*1224 96 24-85 24-85|24′92 25.03250325*1425°25|25′39|25′79|
May
June
July
...
•
•
•
•
•
❤
·
•
•
272
[SERIES XXVI.
Appendix.
Latitude 38° 54′
Mean dip 71° 20′
Washington, U.S.-Longitude 77° 2' West.
North. Mean declination 1° 25′ West.
North.
Mean Diurnal variation of the Declination in minutes, and
temperature in Fahrenheit's scale, of the months of the
years 1840, 1841, 1842, which are specified.
Increasing numbers denote a movement of the south or upper
end towards the East.




Noon.
hm hm hm hm hmh mh mh mh mh mh mh mMean.
Mean time 0 12 212 4 12 6 12 8 12 10 12 12 12 14 12 16 12 18 12 20 12 22 12
ΙΟΙ
Jan. 1841-42. 4-10 5.20 3.96 2.52 0.87 0·68 1.01 1.62 1·66 1·71 0·91 0·29 2:04
Feb. 1811-42. 3.55 5.28 422 2.89 159 0.94 0.84 126 0·81 0·82 060 035 176
Mar. 1841-42 634 7:51 626 425 2.88 2.31 2.50 300 171 113 0.00 176 3'30
Apr. 1841-42. 6.56 8.33 642 441 322 197 2:24 135 073 046 000 218 315
May 1811-42 772 8.57 636 445 382 347 325 305 2.63 033 000 425 3'99
June 1841-42. 8.55 9'47 800 533 491 424 405 4:32 344 063 000 453 479
July 1840-41. 8.42 9.87 807 575 457 3:52 3.60 3.40 2.99 0.98 0.00 3.62 4°56
Aug. 1840-41.1094 1081 795 6.00 403 3'55 448 464 404 135 000 5.89 530
Sept. 1840-41. 876 844 543 4:45 2.62 3.31 2.83 2.86 2.44 0.87 0.00 422 385
Oct. 1840-41. 565 583 435 247 141 058 141 180 151 135 000 175 234
Nov. 1840-41. 469 479 333 160 051 074 114 141 082 071 0.00 1.83 179
Dec. 1840-41. 3'93 490 3:39 1'92 010 036 0.62 153 093 200 roz o'87 179
Noon.
Temperature.

h mh mhmhmh mh mh mh mh mh mh mh m
Mean time ... 0 12 2 12 4 12 6 12 8 12 10 12 12 12 14 12 16 1218 12 20 12 22 12
о
Jan. 1841-42. 38.28 4083 40 18 36.68 35 47 34 24 32 37 32 10 3171 30533163 36.96
Feb. 1841-42.40°03 42.51 42 28 38 22 35.38 33.86 32 58 31°2230°51 30 18 31 44 36-72
Mar. 1841-42.51 39 53 61 53 28 49 96 46 20 44 37 42 48 41 2640-06 39 87 42 28 48.06
Apr. 1841-42. 57.68 59.81 60 2057 21 52 18 49 12 47'91 46′9146°1246 49 49 93 54°02
May 1841-42.66 37 68-48 68-69 65.93 59.83 56 70 55 1953 34 52 42 55 50 59 72 63°23,
June 1841-42. 79 32 81-85 82-75 76-8972 29 68.70 66.83 66 0465 07 68-26 73 6377 37
July 1841
8113 81 53 84 6081 33 74-9371*5668 7868 0966 78 70*6475*19 78.38
Aug. 1840-41.78 70 80 7380 0975 93 71 48 68 0066 8265 12 64 1765-6965 73 76-09
Sept. 1841
74.66 76.50 76.30 72 3068 59 64.90 62 70 61.90 610061 29 65 73 7102
55 30 5700 56 20 52 94 48 40 46.60 44′9043 7042*3041 70 4500 51.61
48.00 49 20 48 50 47 3044 2043 2041 80 40*70 39 40 38.80 39.50 44.10
39°20 41°30 40 60 37′95 36′26 34°70 3350 33 16 32 2031·6031·69 36·00
Oct. 1841
Nov. 1841
Dec. 1841
...
...
...
...
·
D
·
D
·


Lake Athabasca.—Longitude 111° 18′ West. Latitude 58° 41′ North. Mean declination 28° East.
Diurnal variation of the Declination in the months of October, November and December 1843, and Jan. and Feb. 1844.
Increasing readings denote a movement of the south or upper end of the magnet towards the West.
VOL. III.
Dec.... 304 6'16 557
1844.
Oct.. 1*137°49 6°23 18°95 21°32 855 13:35 9.90 10°72 7°03 2°29
Nov.... 3'73 5*17 674 9'07 10'35 10.80 9.40 8.80 7.63 654 110
565 9°23 7′61 9.78 6·73 6·58 5°33 194
2.70
0'00
Mean
h mh mh mh mh mh mh mh mh mh mh m
time. 12 55 13 55|14 55|15 55 16 55 17 55 18 55 19 55 20 55|21 5522 55
1843.
5 minutes
to noon.
h m
23 55
5 minutes
to mid-
night.
h m
Mean time.
h mh mh mh mh mh mh mh mh mh mh m
0 551 552 553 554 555 556 557 558 559 55 10 55 11 55
13 days obs. in
Oct. 1843.
25 days obs. in
Nov. 1843.
473.30
0·00 0·29 0·02 0·980-492-88 188 3.75 347 3.308′42
0°49
0*55
1*06 1*571°932 732 943 344 52497 543 708 304
0.03 0.00 0.83 2.372 633.814-183°574357 19 405
3.63
6.05
25 days obs. in
Dec. 1843.
Jan.... 5.69 8.48
Feb....
... 427 4'93
6.97 | 12°57 16′29|10′05 9′97|10°02 9′96 7′95 499
10-5514-8014-87 12-10
846 10.55 14.80 14 87 14.06 12 10 12.76 8.64 2.82
2.10
2.93
1-483-243-764-524-96
0*390.00 2.75 1672 473 634 725 155°443′97 6.71
1.55 0.00 1.483°243 764 524.96 548 558 499 6.98 5'40
2*18
25 days obs. in
Jan. 1844.
25 days obs. in
Feb. 1844.
Fort Simpson.-Longitude 121° 30' West. Latitude 61° 52′ North.
Diurnal variation of the Declination in the months of April and May 1844.
Increasing numbers denote a movement of the south or upper end of the magnet towards the West.
15 minutes
Mean
past mid-
night.
h m
time.} 12 15
15 minutes
past noon.
Mean time.
h mh mh mh mh mh mh mh mh mh mh m
13 15 14 15 15 15 16 15 17 15 18 15 19 1520 1521 1522 1523 15
h m
0 15
h mh mh mh mh mh mh mh mh mh mh m
1 152 153 154 155 156 157 158 159 15 10 15 11 15
1844.
T
April
May
..
5.82
1'56
6·03 17:45 25-16 22.90 36.80 36-26 37.60 30 14 25-27 18.77 8.27
7'77 11'71 15.63 17 19 23 73 28 22 32.69 29·8020*29|15′51 9′49
171 15-63 17-19 2373
28.2.
"2232-6929-8020*2915"
5'72
9*49 4'74
2.160·001-371-230′43
2.160.00 1*37 1230430304044621′26 2·86 5′55
750-700-750-800-000-191-906-
20 days obs. in
Apr. 1844.
18 days obs.in
00-191-906-723'51 229 167 May 1844.
274
TWENTY-SEVENTH SERIES'.
§ 33. On Atmospheric Magnetism—continued.
Received November 19,-Read November 28, 1850.
Tii. Experimental inquiry into the laws of atmospheric magnetic
action, and their application to particular cases.
2969. BELIEVING that experiment may do much for the deve-
lopment of the general principles of atmospheric magnetism, and
produce rapidly a body of facts on which philosophers may
proceed hereafter to raise a superstructure, I endeavoured to
find some means of representing practically the action of the
atmosphere, when heated by the sun, upon the terrestrial mag-
netic curves. The object was to obtain some central arrange-
ment of force which should deflect these curves or lines as they
are deflected in a diamagnetic conductor or globe of hot air
(2877.), and then apply the results obtained by such an arrange-
ment as a partial test to the various cases supplied by the mag-
netic observatories scattered over the earth. At first I endea-
voured, for the sake of convenience, to attain this desired end
by means of a horseshoe magnet, employing the lines which
passed from pole to pole to disturb and re-arrange the earth's
force; but the comparative weakness of the terrestrial force near
the magnet, and the great prominence of the poles of the latter,
gave rise to many inconveniences, which soon caused me to
reject that method and have recourse to a ring-helix and voltaic
apparatus. Considering the new use to which this helix is to
be applied, the interest of the results, and the instruction that
may be drawn from them, I shall be excused for being somewhat
elementary in the description of its character and action.
2970. The helix consisted of about 12 feet of covered copper
wire formed into a ring having about twenty-five convolutions,
and being 1½ inch in external diameter. The continuations of
the wire were twisted together so as to neutralize any magnetic
Pilosophical Transactions, 1851, p. 85,
Nov. 1850.] Experimental deflection of lines of force.
275
effect which they could produce, and were long enough to reach
to a voltaic arrangement, and yet allow free motion of the helix.
The requisite amount of magnetic power in the helix may be
judged of by the following considerations :-Suppose a declina-
tion needle freely suspended; and then the helix placed at a
distance in the prolongation of the needle with its axis in a line
with the latter, and with that side towards the needle which will
at small distances cause repulsion. The needle will point, in the
magnetic meridian, with a certain amount of force; but as the
helix is brought near it will point with less force, and within a
certain distance will no longer point in the magnetic meridian,
but either on one or the other side of it. There is a given
distance within which the needle, when in the magnetic meridian,
is in a position of unstable equilibrium, but beyond which it has
a position of stable equilibrium, the distance varying with the
strength of the exciting electric current. The power of the helix
should be such, that when end on to the needle the latter has a
position of stable equilibrium in the meridian. One pair of
plates is quite sufficient to make the helix as magnetic as is
needful for distances varying from 4 to 24 inches. When a
needle is properly arranged with either a magnet or a helix to
the north or south of it as above described, if the magnet or
helix be moved west the near end of the needle will move east
and contrariwise.
2971. As is well known, such a helix has a system of magnetic
lines, which, passing through its axis, then opens out and turning
round on the outside re-enters again at the axis, the circles of
magnetic force being everywhere perpendicular to the electric
current traversing the convolutions of the helix; and now I had,
at a moment's notice, a source of lines of magnetic power exactly
of the kind required to produce, in association with those of the
earth, a disposition of the forces coinciding either with those of
paramagnetic or diamagnetic polarization (2865. 2877.).
2972. For let fig. 17 represent a section parallel to Fig. 17.
the axis of the ring-helix, then the two circles may
represent the disposition of the magnetic force in
that section, and the arrow-heads may serve to indi-
cate that magnetic direction which belongs to lines of
force issuing out of the north end of a magnet. If
such a system be suddenly produced in the midst of the earth's
T 2
276
Atmospheric magnetism. [SERIES XXVII.
·
lines, it acts upon them according to the position of the helix in
relation to the direction of the earth's power. Choosing the two
positions in which the axis of the helix is parallel to the natural
direction of the power, as shown by a free needle, at the place
of observation, then two contrary effects are produced, which, as
regards the lines exterior to the helix system, correspond to the
polarity of paramagnetic and diamagnetic conductors. If, for
instance, the helix is so placed that the polarity of its magnetic
lines, exterior to and in the plane of the ring, accords with that
of the earth's force, as in fig. 18, then
the earth's lines are deflected as re-
presented, and a magnetic needle
placed at a, which had taken up its b
position by the earth's influence, will
not tend to alter its position as the
helix approaches it, though it will be
acted on with more power.
In other
Fig. 18.
C
parts of the line, b a c, it will alter its position, standing as a
tangent to the curvature, and therefore will be deflected some-
times one way and sometimes another, as it is carried along the
line (or through the neighbouring lines), in place of remaining
parallel to itself, as it would do if the electro-magnetic helix were
away.
2973. On the other hand, if the helix were turned round into
the second position (2972.), then the effect upon the direction of
the neighbouring lines of force would be
as in fig. 19. Needles placed at d and e
would again be deflected from the natu-
ral position given to them by the earth,
but they would be deflected in a con-
trary direction to that which would be
taken if they were in corresponding situ-
Fig. 19.
d
f
ations under the former arrangement. This figure and state of
things represents the paramagnetic disposition of the forces, as
the former did the diamagnetic condition.
2974. It is not pretended that the whole of these arrangements
of forces are like those of the cases of paramagnetic and diamag-
netic conductors. Independent systems are here introduced into
the midst of the earth's magnetic power, and the central part of
each arrangement must therefore be excepted; there are also
Nov. 1850.] Experimental deflection of lines of force.
277
attractions inwards and repulsions outwards, when the needle is
at a and f, which do not take place in the cases of mere magnetic
conduction. But external to these helix systems, the arrange-
ment imposed upon the lines of force from the earth is in ac-
cordance with that produced by diamagnetic and paramagnetic
conductors, and at distances from 2 inches to 2 or 3 feet; the
lines of force thus altered, and those contorted by the sun and
atmosphere in the great field of nature, are comparable in their
direction, and may be considered as representing each other.
2975. In order to obtain a simple result of the action of such
a centre of force on the magnetic lines of the earth, I adjusted
a rod in the direction of the dipping-needle, and also a plane at
the foot of it parallel to the magnetic equator at London. Then
suspending a small magnet, half an inch long, from cocoon-silk,
so that when hanging it should be parallel to the magnetic
equator, it was adjusted so as to be near to the plane at the foot
of the rod representing dip. The ring-helix (2970.) was then
associated with the voltaic pair, so that contact could be com-
pleted at any moment, and being always retained parallel to
itself and to the plane of the magnetic equator, could be brought
into the vicinity of the needle on all sides, above or below, and
its action upon it observed. As the object was to represent the
sun's action, the current was so sent through the helix that its
upper face would repel the north end of a magnetic needle; for
then a magnet, outside of and in the plane of the ring, would
not tend to have its position changed, and the disposition of the
forces of the earth under the influence of the helix was as in
fig. 18, or like that of a diamagnetic conductor.
2976. In making observations of this kind, and especially if
the ring-helix is purposely retained at a considerable distance
from the needle, it is better not to connect the helix permanently
with the battery and then carry it towards and by the needle,
but rather to choose the place where the helix action is to be
observed, and when the helix is there to make contact with the
battery; the motion and direction of the needle is then easily
observed; or if it still, through reason of distance, be feeble,
making and breaking contact a few times isochronously with the
vibrations of the needle soon raises the effect to any degree
required.
2977. There are certain positions in respect of the needle as
278
[SERIES XXVII.
Atmospheric magnetism.
a centre which must be clearly comprehended. The magnetic
axis is a line through the centre of the free regular needle parallel
to the direction of the earth's lines of force, whatever that may
be, at the place where the experiments may be made. The
magnetic equator plane is a plane passing through the centre
of the needle perpendicular to the magnetic axis. The plane
of the magnetic meridian is that plane which coincides with the
magnetic axis, and also with the direction in which the declina-
tion needle points. This position always occurs with the magnets
that are employed for observation, being a consequence of the
method in which they are supported; it would not be taken by
a needle placed at right angles on its mechanical axis, the latter
being in the magnetic axis.
2978. When the ring-helix, situated as before explained
(2975.), was anywhere in the plane of the magnetic meridian,
it exerted no action on the declination needle tending to change
its position. When the helix was anywhere in the plane of the
magnetic equator, it exerted no action on the needle to make it
change its direction. These are the only places in which the
helix does not affect the position of the needle.
2979. These two planes of no variation divide the space
around the magnet into four quadrants, and the helix being in
any one of these, affects the needle, altering its declination.
The deflection of the line of force for two neighbouring qua-
drants is in the contrary direction, so that as the helix passes
from the neutral line into one or the other quadrant, the declina-
tion of the needle changes.
2980. If the helix be above or below the magnetic equator and
be carried round the magnetic axis travelling along a line of
latitude, then the needle makes one large oscillation to the right,
and another to the left during the circuit. Supposing that the
experiment commences with the helix above the equator, and in
the plane of the magnetic meridian north of the needle, if it then
proceeds by west to south and on by east to its original position
the north end of the needle will first go westward; will then
stop and return eastward, passing the mean position, and will
finally return westward and settle in its first or original direction.
All the time the helix is to magnetic east of the needle it will
cause the same deflection, and also as long as it is in the west;
the deflection will be more or less, but not change in direction
Nov. 1850.] Experimental deflection of lines of force.
279
as regards the neutral place. The position of the helix north or
south of the needle is of no consequence as to the direction of
the declination, provided it remain on the same side of the mag-
netic meridian, though it is to the amount. If the helix be
below the magnetic equator the direction of the declination is
reversed, but then again it does not change whilst the helix re-
mains east or west of the needle and its plane of mean declination.
2981. If we carry the helix round the needle in a plane per-
pendicular to the planes of the magnetic equator and meridian,
so as to traverse in succession the four quadrants, then the
needle makes two to and fro vibrations (instead of one) during
the circuit. Thus, beginning with the helix in the neutral
position over the needle and going round by west and below,
and then upwards on the east side to its first position, the north
end of the needle will first pass westward, then eastward, then
westward, after that eastward, and finally westward to its original
or neutral position.
2982. As the helix is carried from the neutral planes (2978.)
into any of the quadrants, the power of affecting the declination
of the needle is first developed, and then increases every way,
from the edges of the quadrant until it attains its maximum
force at the middle. Hence the maximum deflection east or
west is when the helix is in the middle of each quadrant. There-
fore, when the helix is carried from the middle of one quadrant
to the middle of the next, only one motion in the needle appears;
as for instance, an increasing westerly declination, though the
direction of the declination in relation to the mean position has
been reversed in that time, and there was a moment when the
needle had no extra declination, but was in that mean position.
So also as the helix moves over one quadrant from one neutral
plane to another, though the declination of the needle produced
by it has not changed in direction, but has been, for instance,
all the time west, still the needle will have exhibited two motions,
going first west during the increase of the power, and then east
whilst it is diminishing; and hence it is that though there are
four departures of the needle from and return to the neutral or
mean position, whilst the helix circumscribes it in an east and
west vertical plane (2981.), there are only two complete journeys
of the needle.
2983. The amount of the deflection diminishes as the distance
of the helix from the needle increases; and the contrary.
280
[SERIES XXVII.
Atmospheric magnetism.
2984. Two other needles were slung (2975.) very oblique to
the magnetic axis, one with its north end upwards and the other
with its north end downwards, and these were submitted to the
action of the helix as the former had been (2978.). They were
affected exactly in the same manner, showing no difference; i. e.
a given end always moved the same way for the same change in
position of the helix. If the helix was very near, then one pole
was a little more influenced than the other in certain positions;
but its removal further off took away that difference (which is
easily accounted for (2970.)) and produced pure results. The
place of the helix above or below the prolongation of the line of
the needle made no difference, provided it was in the same place
as regarded the magnetic equator of the earth's lines of force
passing through the needle.
2985. For the purpose of establishing the nature of the action
which such a helix, always in the given or diamagnetic position
(2975.), would exert upon the inclination, a small dipping-needle
was submitted to its action and the following results obtained.
The needle could move in the plane passing through the mag-
netic meridian of London.
2986. There was no deflection of the needle when the helix
was in the plane of the magnetic equator, or in a plane perpen-
dicular to that containing the mechanical axis of the needle. In
every other position it affected it; so that these two planes divided
the sphere of action into four segments, as before.
2987. As the helix passes from one quadrant to another, the
direction in which the needle is deflected changes as before
(2982.). If the helix is in the upper north segment or the lower
south segment, the upper or south end of the needle is deflected
towards the south; if the helix be in the upper south or lower
north segments, the upper or south end of the needle is deflected
towards the north. If the helix be carried round the needle in
the direction of the plane of motion, which in this case is that of
the magnetic meridian, the end of the needle starting from a
mean or unaffected position will move first one way, as for
instance, north and then south; north again and south again,
and finally north to regain its place of rest: so that there are
two extreme deflections of the end in each direction, as before,
in the case of the declination magnet (2982.).
2988. In other words, when the helix was anywhere below the
magnetic equator, the lower or north end of the needle tended
Nov. 1850.]
281
Experimental illustrations.
to point outwards from it or outside of it, being as it were repelled
by the axis of the helix, but drawn by the outer curved lines of
force, fig. 20 (2992.). Or if the helix were above the equator,
then the upper or south end of the needle went outwards from
the helix, moving exactly in the same direction in relation to the
helix as the lower pole did before.
2989. The support of the needle was turned round 90°, which
therefore removed the plane in which the needle could move 90°
from the magnetic meridian. This carried the plane of no action
on the needle 90° round, so that it now coincided with the mag-
netic meridian; and the plane, which, standing east and west,
was before neutral, was no longer a plane of indifference, but in
fact passed at the middle of the segments through the places of
strongest action.
.
2990. Here with inclination, as before with declination, it is
not the direction in which the needle stands that determines
what action the helix may have upon it; for it may be loaded
or otherwise restrained, as all horizontal needles are; but it is
the direction of the lines of force at the needle which, with the
helix, governs all. The helix may be above or below the pro-
longation of the needle indifferently; for if it still continues on
the same side of the line of force, under the influence of which
the needle acts, then the end of the needle moves in the same
direction, though it may travel towards the helix in one instance
and from it in another.
2991. I suspended a needle so that it was free to move in
every direction, and now I obtained the simple natural effect of
the helix, or a diamagnetic globe (2877.) on a given line of force,
and it is well to have it in mind. For, though we are obliged
for the sake of practical observation to divide the position into
two parts, declination and inclination, yet, the results in each
case are much better compared and remembered when the simple
law of change in the whole line of force is ready in the mind for
reference. The equatorial plane and the magnetic axis are now
the only parts in which the helix can be without affecting the
position of the needle; the first gives places (for the helix) with
a stable position for the needle, and the second such as have
either stable or unstable positions, according to the helix distance.
2992. If the helix be out of the plane and axis, then the end
of the needle nearest to it leans from it as if repelled. If the
282
[SERIES XXVII.
Atmospheric magnetism.
helix be carried round in a circle of latitude, the end of the
needle moves round before it just like the upper end of the
needles at Hobarton and Toronto, in respect of the sun, during
the midday hours. Instead of moving the helix round the
needle, we may carry the needle into different positions as re-
gards the helix, and then fig. 20 will re-
present the result. A result exceedingly
simple, and in perfect accordance with the
diamagnetic disposition of the forces pro-
duced by the helix (2972.), as the two
dotted lines indicate.
N
N
Fig. 20.
N
N
2993. As an expression of the facts for
use in applying them to the explanation
and illustration of natural phænomena, it
may be said in respect of declination, that
the helix being above the needle in a
plane having dip, and therefore above its
magnetic equator, if on the east of a needle.
having north dip, it will send the south or
upper end west, or if on the east of a needle having south dip
(being of course then itself inverted (2972.)), it will cause the
north or upper end to pass westward; seeming to repel the end
of the free needle or part of the line of force nearest to it. In
reference to the inclination, it may be said, that the helix being
above the needle, tends to send the upper end of the needle or
line of force from it. If the helix is north of the magnetic axis,
it will tend to send the upper end of the needle south; if it is
south, the upper end will go north. As in the case of the de-
clination, it is as if the end of the free needle or line of force
nearest to it was repelled. In fact every case is included in this
result, that if the helix be diamagnetically adjusted (2975.) for a
free needle, whether it is above or below the needle, or on this
side or that, the nearest end of the needle will be as if repelled
provided the helix is not in a neutral position.
2994. I repeated all these experiments with the helix reversed,
so as to give the effect of a paramagnetic globe of air (2865.
2973.). I need only say, that the effects were precisely the same
in nature and order, only in the reverse direction. They will
be required in the explication of the night and early morning
actions, due to the cooling of the atmosphere (3003. 3010.).

Nov. 1850.1
283
Experimental illustrations.
2995. In these experiments, that the laws of deflection might
appear in their simplicity, the needle was suspended in the air,
and the representation of the sun's action carried round it in all
directions. But in nature the air is only above the needle,
and the earth as a magnet is beneath it. In the natural case
also, there is the fixation of the lines in the earth (2919.), which
tends, by holding them below the surface, to give them an amount
of deflection at the surface, far beyond what they would have if
they were as free to move in the earth beneath as in the space
above¹; and though this deflection would coincide with that
produced by the helix alone, still it was important to verify its
effect. I therefore took a bar magnet 30 inches long, and weak
in condition, and suspended the needle above it in various parts,
so as to have the effect of north or south dip to any degree, or
no dip at all near the middle parts. The effect of absence of air
from beneath was also in a certain degree represented: and to
make this point more striking, I occasionally put masses of iron
on and under the middle part of the magnet. The results with
the helix were now influenced greatly in the amount of the de-
flection, but not in the direction. When the helix affected the
direction of the needle, it was according to the above laws.
2996. In the consideration of natural phænomena, the mag-
netic axis, and also the planes of the magnetic equator and
meridian, being circles or planes of no deflection, are very im-
portant. Changing as they do with every change, either of
place or declination or dip, they require some ready means of
illustration, and can hardly be comprehended in their effects
without a model. I have prepared a globe on which, after
marking the places of the observatories, I have drawn the mag-
netic meridians of these places as they were last estimated. I
have then in another colour drawn for each place its magnetic
equator, making that a great circle parallel to the equatorial
plane of the dipping needle at the place. I have also marked
on the globe the mean path of the sun for each month, and by
the use of adjustible pins to indicate the hours before and after
1
Referring to the typical globe of cold air (2874.), it is manifest that if the
space below the horizontal lines a, c, &c. were occupied by matter holding the
lines in it, then the deflections now represented on the lower parts would
appear above the holding surfaces, and to a much greater degree, though ex-
tending downwards to a much smaller space.
284
[SERIES XXVII.
Atmospheric magnetism.
noon of any given place, I have the means of ascertaining with
sufficient accuracy when the sun is in any particular quadrant,
or what part of the quadrant; when it passes a neutral line and
what its position in relation to the place of observation is, in a
manner which no diagrams or figures could supply. I have
found the globe very useful; and I accustom myself to place it
always in a certain position, namely, with the axis of rotation
horizontal, the north pole to my right hand, and the astrono-
mical meridian of the place of observation towards the zenith.
The observer can then regard it as from the place of the rising
sun.
2997. Though we thus have the experimental conditions of a
needle under an action like that resulting in nature from the
presence of the sun (2920.), I do not pretend that they can be
applied without modification to natural phænomena, but only
that they give very important aid in the study of the latter and
the rationale of their action. The atmosphere, instead of being
illimitable, wraps the earth round as a garment; the influence,
as it extends from the region of action, must, in respect of that
portion which is conveyed through its mass (2920.), curve with
its curvature, and give a result in any particular place, which
only refined calculations founded upon careful observations can
determine accurately. In regard to the development of the air
action, it would, I think, be very interesting to ascertain, even
roughly, the daily variations of a magnet at the bottom of a deep
mine, half-way up, and at the mouth of the shaft. The results
might tell us much about the holding power of the earth and the
depths to which the deflections of the magnetic lines of force
penetrate, and might even give us a rough expression of the
changes of the internal power (or the absence of such changes)
when freed from those dependent upon the atmosphere.
2998. Another reason why the experimental results must not
be applied too closely is as follows. If the lines of force of the
earth were perfectly regular, then the change produced amongst
them by the sun and air would be regular also. But as the
natural system is not regular either between the tropics, as at
Sister's Walk and Longford in St. Helena, or in the higher
latitudes, as at Hudson's Bay, so apparent inconsistences may
and must result. The probability is that the greatest irregula-
rities in the arrangement of the earth's magnetism are in and
Nov. 1850.]
285
Experimental illustrations.
near the surface of the earth, and that above they tend to adjust
with each other into a more regular order. Still the irregulari-
ties must extend their influence very far upwards, so that the
contortions of the magnetic meridians or lines of force are not
likely to be effaced, or much diminished, at the region coinciding
with the place of the atmosphere's effect.
2999. But though the lines are irregular in the large space
affected by the sun, the result will be expansion of the whole
as a system and diamagnetic polarity. The lines of force below
will be affected by those above; and so, though a perfect simi-
larity between different places is not to be expected, still the
kind of change at the earth's surface is not likely to be so uncer-
tain as it might at first appear. Therefore, I believe the globe
(2996.) will be found very useful in giving information regarding
the probable effects of the magnetic meridian and equator, due
to the place of the sun in the two chief quadrants for any given
month of the year, or hour of the day.
3000. The passage of the magnetic meridian is important, and
appears far more so after the experiment described (2978.) than
it did on a former occasion (2942.). Being very often inclined
to the astronomical meridian, it must have great influence in
deciding when the daily declination changes in its direction.
The place of greatest action, and its travelling north or south
along a line of magnetic force according as the declination was
west or east in relation to the helix as a sun, was confirmed by
an experiment; and the further observation (a consequence of
the former), that when the sun was equidistant from a place
more north or south than itself, its action was far stronger on
that side at which its path and the declination direction made
an acute angle than on the other side where it was obtuse, was
also confirmed. Thus if the helix, moving from east to west,
were passing a place north of it having western declination,
then the action was stronger on the western side of the place than
on the east for equal distances of the helix from the magnet.
3001. The passage of the magnetic equator by the sun is also
important, since the direction of the diurnal variation of the
experimental needle is then altered; and this is of the more
consequence, because by the great degree of natural declination
in many places, even far north and south, this passage is thrown
forward towards the astronomical meridian, either on the east
286
[SERIES XXVII.
Atmospheric magnetism.
side or the west, and comes into effect during the more influen-
tial hours of the sun or the cold. In all those places too where
the dip is little, as at St. Helena, and in or near the sun's path,
it may be important in influencing the amount of action. From
the change of place of the sun between the tropics, and the
variety of dip and declination at different places, the passing of
the neutral planes by the sun and acting region must take place
under an extreme variety of conditions; the unravelling of which
I think will be much assisted by knowledge such as that which
the preceding experiments and principles give. The sun may
be
astronomically either north or south of the needle, and yet the
declination of the needle not change in direction (2980.); or if
there were much mean declination, as at Greenwich, then it
might be astronomically east or west of it, and yet the declina-
tion produced not change its direction. The sun region may
be south of a place and yet send its upper end further south
(2990.); for all will depend upon its position in relation to the
magnetic meridian and the magnetic axis, which are in most
cases very far removed from those that are astronomical: added
to all these causes of variety, there is the fixation of the lines of
force in the earth (2919.), which tends to give a further diversity
to them.
3002. In the former paper I considered only the effect of air
raised in temperature above the mean condition (2895.), illus-
trating it by the sun's effect in the middle of the day; now I
purpose considering that which will be produced by the cold of
night, which reduces the air of a given region below the mean
air temperature of that place. When a portion of air is so cooled,
its conduction power is increased; in conjunction with the warmer
air of surrounding regions it deflects the lines of magnetic force
passing through both, as indicated by the type globe (2864. 2874.),
and acquires what I have called conduction polarity (paramag-
netic), meaning thereby simply that the lines of force draw toge-
ther in the middle of the cooled air.
3003. Theoretically, the effect of a cold region of air coming
up from the east would be to make the magnetic lines of force,
as they leave the earth, advance or bend towards it, because
those in and about the cold air are inflected into it; and as those
immediately west of the cold region move into or towards it, so
those further west, being in part relieved from their tension, will
Nov. 1850.]
287
General principles of action.
also move east, and thus an effect, the reverse of that of the sun
(2877. 2972.), or the same as that of the helix in the paramag-
netic position (2973. 2994.), will be produced. The upper ends
of needles at places having dip show this deflection of the upper
part of the lines of force, because they move by, with, and in
them.
3004. So as cold approaches, the lines will lean towards it
until it is in the position of maximum action in the eastern qua-
drant; then they will return (in declination) before the cold, until
both it and the line (or needle) are in the magnetic meridian;
after which, as the cold travels on westward, the needle will
follow it west until the cold has attained its place of maximum
action in the west quadrant (2982.); and then, as the cold re-
treats, the needle will return east to its mean place; assuming
that there is no other action for the time than that of the cold
region. The upper end of the free needle, therefore, at any
given place will tend towards the cold region, just as before it
tended from a warm region; and as the declination is affected,
so also the inclination will be. If the cold be on the magnetic
meridian of a place within the tropics, as St. Helena or Singa-
pore, it will increase the dip there, whilst at the same moment
it is diminishing the dip at places south or north of it having
considerable dip, a result which follows directly from the inflec-
tion of the lines of force into or towards the cold region.
3005. The chief regions of heat and cold on the same parallel
of latitude, do not follow each other at equal intervals of time.
It is difficult to make a judgement regarding their interval in
the atmosphere above; but the maximum of cold on the earth
for the twenty-four hours, is assumed by many as being seven-
teen hours after the preceding noon, and only seven hours from
the coming noon. This brings into consideration the joint effect
of hot and cold regions in deflecting the lines of force, especially
during the forenoon and middle of the day. If a cold region be
only three and a half hours west of a place at the same time that
the warm region is three and a half hours east of it, it is very
manifest that the joint effect of the two, for both act then to
cause the same deflection, will be far greater than that of the
heat or cold alone, or than any corresponding effect at other
periods, for neither twelve hours after, nor at any other time
will there be an equivalent condition of circumstances; and so
288
[SERIES XXVII.
Atmospheric magnetism.
it is also for other combinations of hot and cold regions, the
effect of which will vary both by position and by their extent.
A free needle is held in tension by the lines, which are them-
selves governed by the hot and cold regions of atmosphere;
it probably never occupies its mean place, but is always in
the resultant of these ever-present and ever-varying causes of
change.
3006. As the earth revolves under the sun, each place would
have, speaking generally, a maximum and a minimum of tem-
perature for its atmosphere in the twenty-four hours. But
looking at the globe as a whole, there would be one maximum
and two minima, i. e. there would be a maximum region some-
where beneath the snn in his path, and a minimum in each of
the polar regions; which, as regards the twenty-four hours,
would not be at the pole, but in some place of high latitude, and
perhaps, as before, seven or eight hours before noon. These
cold regions will be very seriously affected in their extent and
place and power by the position of the sun between the tropics;
for as he advances to one tropic the cold region there will dimi-
nish in extent and force, whilst the other will grow up in im-
portance; and whilst they thus vary in their power of influencing
the general direction of the lines of force, they will vary in their
own position also, and have at different times very various rela-
tions of place to the sun in different months, and so produce
very various effects. It is these differences which are made
manifest to us, as I believe, in the night and morning actions
at the numerous observatories scattered over the globe.
3007. I will proceed to apply these views, and the additional
knowledge gained by experiment, to the localities formerly con-
sidered, and to some new ones between the tropics, for the pur-
pose of explaining, if I can, the principles of night action; of
retardation, more or less, of the effects in relation to local time;
of the difference in direction of the declination variation in dif
ferent months, for the same place at the same hours, as pointed
out by Colonel Sabine; of the diminution of dip in one place,
and increase of it at another for the same local time. In doing
so, it will be necessary to refer continually to that place which
may be considered, in respect of the station, as the centre of hot
or cold action for the time. I will endeavour to use the word
region for that purpose, meaning thereby not the whole extent
Nov. 1850.]
289
St. Petersburgh-cold effect.
of heated or warmed air, nor the centre, but the chief place of
the altered portion. It is very manifest that in some days in
March or September, all the air that is east of the meridian at
21h or 22h may be considered warm in comparison of that which
is then west of the same meridian, and that a resultant of action,
which shall be the same for all places, cannot exist.
3008. We are to remember that the eastening and the west-
ening of the upper end of the needle, of which I always speak,
is produced in two ways. The needle travels as positively by
the withdrawal of a direct cause of action as it does under the
immediate direct action of that cause, but in the contrary direc-
tion (2982.). A westening may be the result either of the
coming up of the sun on the east of the place of observation, or
of its withdrawal in the west, after he has passed over the meri-
dian and produced the great east swing.
3009. St. Petersburgh has a mean declination of 6° 10′ W.,
and a dip of 70° 30′ N.; therefore, though the magnetic and
astronomical meridians are not very oblique to each other, still
the sun or warm region reaches the former from 20' to 40' before
the latter, and hence the time of the great sun-swing, which is
from 20 to 1 o'clock, is made earlier than it otherwise would be.
The magnetic equator of the needle (2977.) forms an angle of
about 40° with the earth's equator, and being thus tilted, it
disposes the two quadrants chiefly concerned in the daily varia-
tion (2979.), so, that in the St. Petersburgh summer the warmest
region is not only far nearer to the needle, but passes through
the strongest places of action of the quadrants, whereas in winter
it is further off, and also in much weaker positions. Hence a
cause, as I believe, of the great difference in the amount of va-
riation of declination, and also of its character: in November,
December and January, it is from 4'47 to 4'65 only, whilst
in June it is 11'52'. See the Tables, p. 271, and the Curves,
Plate II.
3010. In December or January, being St. Petersburgh winter,
1 The eastening and westening of a free dipping-needle are not properly
represented by the movements of a horizontal needle, inasmuch as at places
with different dip the angle is read off on planes differently inclined to the dip
itself, and in high latitudes the effect is greatly exaggerated. But though
different places may not be compared without a correction, the variations for
the same place as St. Petersburgh are comparable and proportionate.
VOL. III.
U
290
Atmospheric magnetism. [SERIES XXVII.
the sun-swing east almost disappears. It is over by 1 o'clock',
after which the upper end of the needle follows the sun until 9",
having passed its mean position at 5h. It then stops, after which
it moves east until 16 or 17; then again stops, or nearly so,
until 21", and then the sun-swing comes on, carrying it to ex-
treme east. So here there are two very important points to
explain, namely, why the needle moves eastward after 9¹, and
why it does not travel westward from 13 to 20¹, but, on the
contrary, is travelling eastwards or standing still: the explana-
tion, according to my view, is as follows:-St. Petersburgh is a
place in which, from its position, the upper cold, consequent
upon the daily withdrawal of the sun, would produce a para-
magnetic action (2994. 3003.). This action, as the sun set,
would begin to appear on the east, and I conclude that at 9"-11h
the cold region coming up from the east, not on the latitude of
the sun's path, which is far to the south, but probably near to
that of St. Petersburgh itself, is able at 9-11 o'clock, during
which the needle is stationary, to counteract any remaining
tendency westward, and after that to draw the line of force and
the needle end eastward until 17 o'clock, and to hold it there,
after which the sun sends it eastward in the great swing. That
the cold, considering its probable position, may well direct the
needle end eastward till 17, and the sun region not send it
westward from 17h to 20h or 21h, is seen, I think, to be a very
natural consequence of the probable position of the two regions
between these hours. For letting the sun (whose place we know)
represent the warm region at 17ª, he is then in the eastern qua-
drant below the horizon, so that if he could affect the needle
through or round the earth (2995.), it would be to easten it, and
it continues in that quadrant until 19h. Then at 19h, when he
enters the quadrant, in which he begins to exert a westening
action on the sun, he is in such a position as respects the needle
at St. Petersburgh (as is seen by a line drawn over the surface of
the globe (2996.) and compared with the magnetic meridian and
dip), and in so inefficient a part of the quadrant (2982.), and
also so far off, that it has no power to send the needle west-
ward, but only in association with the retreating cold region to
¹ The St. Petersburgh observations are at 21 minutes after each hour; but
I mention the hour without the minutes as sufficient for a general statement.
Nov. 1850.] St. Petersburgh—cold effect at night.
291
hold it there, until at 21", or thereabout, the sun-swing from
west to east occurs as in other cases. After this the needle
follows the sun from 1 o'clock, being, as the hours advance,
gradually arrested and taken up by the cold region of the next
twenty-four hours, as already described.
3011. I have considered the cold eastening as continued until
as late as 17", which would imply probably that until that hour
the cold region was east of St. Petersburgh. It is very difficult
to speak, even in a general manner, of the places or times of
things so little identified as yet, as the warm and cold regions in
the upper atmosphere; but referring to the temperatures on the
earth at St. Petersburgh, I may point out, that the extreme cold
is, in the month of January, as late as 19 and 20 o'clock, and
five hours later than it is in the summer months. I may also
point out here, for use in the summer months, that the maximum
heat varies three hours in the opposite direction; so that whilst
from the highest to the lowest temperature in the day is only
eleven hours in summer, it is nineteen hours in winter, as may
be seen by the Temperature Table, p. 271. As the day comes
on, therefore, in January the highest temperature is only five
hours after the lowest, which accords generally with the assumed
cause of the effects on the needle¹.
3012. As I am endeavouring to make St. Petersburgh a gene-
ral case of night action for the explanation of corresponding
effects at other places, so I may notice that the night action
must contain a portion of sun effect which combines with that
of the cold. The action of the sun is known by observation to
be very extended; in the case of St. Petersburgh, the sun, when
at the southern tropic and on the meridian, is between 80° and
90° from the station, and yet we see by the observations and
curves how large an effect he produces (3009.). Wherever the
sun may be, he is by his motion causing changes which are felt
simultaneously over the whole globe; and at 9 and 10 o'clock he
is in an effectual part of that quadrant which would send the
¹ In relation to the cold of the upper atmosphere and the occurrence of its
maximum (at certain levels at least), not at midnight but hours after, how
often do we in this country see a clear bright night, and then just before the
sun rises, the formation of a veil of clouds high up, and, upon his appearing,
their dissolution and passing away! In these cases the clouds show the time
of greatest cold above by their formation, and by their dissolution its quick
reversion and change into increasing warmth.
U 2
292
[SERIES XXVII.
Atmospheric magnetism.
needle eastward if the earth were replaced by air, and in the
representative experiments with a helix (2995.) does so send it
eastward when a magnet is interposed. The night action ought
therefore to be greatest in winter, as it is, because the cold is
then most intense, and also because the action of the distant sun
coincides with it. It is very probable that many of the curious
contortions of the night action which appear in the curves of
Hobarton, Toronto and elswhere, may depend upon the manner
in which, at different hours, these two causes (probably with
others) combine together.
3013. Though the declination varies little or nothing between
17h and 21¹, no westening then appearing (3010.), still I should
expect a marked action on the inclination at that time, and con-
clude that it will be on the increase; but I have not been able
to obtain a table of the daily variation of inclination.
3014. In the month of February the same remarks apply;
but as the sun is now coming from the southern signs and
drawing nearer to St. Petersburgh its power is increasing, and
this is shown by making the cold eastening for 15h, 16 and 17h
less in extent than before by more than half a minute (of a de-
gree), and by absolutely overcoming it and making a return
westwards between 17 and 18h, before the swing to the east
comes on. In March the effect is still more striking; the para-
magnetic eastening is arrested at 14ª, and the following diamag-
netic westening extends to 20h; then follows the swing. In
April the westening by the warm region is as early as 13" and
continues to 20", being very strong. It is interesting to look at
the Table of Temperatures for these months, even as they are
obtained at the earth's surface. As the months come on the
eastening from the cold ceases sooner and sooner, being in
January and April 17h and 13h respectively. The minimum of
temperature also retreats, being for the same month 20¹ and 16¹.
On the contrary, the maximum of heat advances from the winter
to the summer months, being also greatly increased; and the
effect on the sun-swing is seen both in the advanced time of
change and the increased amount of variation.
3015. In May and June the night or cold eastening has dis-
appeared, or is shown only by a little hesitation; and from
midnight the coming on of the sun region sets the needle end
west. If we look at the globe (2996.), we should be led to ex-
Nov. 1850.] St. Petersburgh—cold effect at night.
293
pect that it would do this. The sun is then in the northern
tropic nearly, wheeling round St. Petersburgh and comparatively
near to it; and a free dipping needle would in twenty-four hours
make one revolution in the same direction as the sun region,
but at the opposite end of the line, joining the two together. If
the needle were at the astronomical pole of the earth, having
great dip, it would describe almost a circle with nearly uniform
motion; but being really much nearer to the warm region in
one part of the uniform daily course of the latter than another,
the radius vector joining it with the region then makes a much
greater angle in a given time than when it is further off, and
hence the greater rapidity of the motion between 20 and 1h,
and the production of what I have familiarly called the sun-
swing from west to east.
3016. It will be seen from the Table of Curves (Plate II.),
that we have at St. Petersburgh a fine example of that kind of
result which Colonel Sabine calls attention to so strongly in
his paper upon the St. Helena phænomena; and those oc-
curring at Hobarton, Toronto and elsewhere; namely, a declina-
tion variation in different directions for the same hours in different
months. Thus, in the present case, the needle end goes east-
ward for the hours 13h to 20h in October, November, December,
January and February, whilst it goes west for the same hours
in April, May, June, July and August: March and September
curves fall midway. But this difference is now I hope by the
hypothesis accounted for (3010. 3015.), and I trust that equally
satisfactory reasons will appear for St. Helena (3045.) and other
places (3022. 3039. 3065.).
3017. The paramagnetic character of the eastening effect by
cold in the winter months after 10 o'clock, would probably be
illustrated by inclination observations for the same time; for if
the cold region passes to the south of St. Petersburgh the incli-
nation will be decreased by the paramagnetic action, but increased
by the diamagnetic resultant; and the manner in which these
two elements of direction, i. e. inclination and declination, are
combined at any given moment, is very important to the full
elucidation of the magnetic effect of the atmosphere. I have
not been able to give these data for St. Petersburg. The
total force variations would also help greatly to clear up the
1 Philosophical Transactions .847, p. 51.
294
[SERIES XXVII.
Atmospheric magnetism.
subject. Indeed it is not fair to endeavour to explain the re-
sults of the assigned cause by taking only one element of three
into consideration. What we require ultimately to know, is all
the changes of a free needle in position and in respect of power.
All are important, and all should be considered at once.
I pre-
sume that the theory of the variations cannot advance very far
without their joint consideration.
3018. Greenwich presents a fine case of the night episode, and
the different directions of the magnetic variation for the same
hours in different months. In these respects it is very much
like St. Petersburgh, but has great additional interest, because
of the large western declination', and the effect produced by it
on the places of the active quadrants (2979. 3000.), and the
times of the variation phænomena. On setting up its position
on the globe (2996.), it will be seen that the equatorial plane is
not likely to be much concerned in the midday action, and that
the sun or warm region passes nearly across the middle of the
two chief quadrants in summer; which with its nearness at the
same time, ought to make the midday swing to east very great.
In winter it is further off and in much weaker parts of the qua-
drant, so that the swing ought to be far less, and such is the
case. The greatest summer variation is 11'30, and the least
winter variation only 5'88. In April, May, June, July and
August, the great west declination of the south or upper end of
the needle is at 19h 20', and the chief east position at 1¹ 20′.
The latter position remains the same all the year round, but the
extreme westening is in the other seven (cold) months at 9¹ 20′
and 11" 20´², or verging towards midnight; it then surpassing the
morning west deflection. Thus the sun's effect in summer, in
weakening the cold night effect (3005.), is very evident; and so
also is the manner in which the night action grows up, until very
prominent, in the winter months, through the strengthening of
the cold action (3006.), when the sun is towards the southern
tropic and in the weaker parts of the segments. The assumed
principles of this action have been already given in the case of
St. Petersburgh (3010. &c.).
1 Mean declination 22° 51′ W.
Mean inclination 69° N.
h
2 See the Curves, Plate II. The observations are only for every two hours,
so that no degree of nicety can be expected in assigning the time of any given
change.
Nov. 1850.]
295
Greenwich-day and night effect.
3019. The magnetic meridian is much to the east of the astro-
nomical meridian, where the warm region passes it, especially in
winter, for then the sun crosses it about 10 o'clock, and in sum-
mer about 11 o'clock. Hence the swing ought to be earlier in
winter then in summer, though, because of the slower angular
motion of the warm region in relation to Greenwich (3015.), it
ought then to occupy a longer time; and yet, as above said
(3018.), be, by reason of distance, of smaller amount. All this
appears to accord remarkably with the fact. The swing begins
at 17h in the winter but not until 19h in the summer, and ending
at the same hour at both seasons, namely, 1 o'clock, is much
longer in its occurrence in winter than in summer. It begins
earlier, because the magnetic meridian is sooner passed than in
summer; and the reason also appears why the extension in time
is at the beginning rather than at the termination of the swing;
for, because of the declination, the warm region is at the same
hours much less east of the magnetic meridian in the morning
and much further west of it in the afternoon, in winter than in
summer; hence the swing is thrown forward in time in winter;
and though prolonged, its termination coincides with the ter-
mination in summer, as far at least as these two-hour observa-
tions can indicate.
3020. As the region precedes the sun, the degree of mean de-
clination here ought to make the day-swing come on early, i. e.
earlier then at Hobarton, and especially earlier than at Toronto,
unless other causes of variation interfere. Now the beginning
is earlier than at Toronto, but the end the same. Both the
beginning and the end is an hour earlier than at Hobarton.
The latter difference I believe due to the difference of mean de-
clination at Toronto, I think, we shall find another cause in-
fluencing the time (3032.).
:
3021. We are to remember also that in winter the sun or
warm region passes the magnetic meridian two hours before he
passes the astronomical meridian; and therefore his effect in
giving west position to the south or upper end of the needle
ceases long before it does in summer, and perhaps even before
it ceases to come nearer; and so the eastern after-effect on it
ought to be greater, which it is. This eastern effect should be
strengthened also, because the action of the warm region on the
needle ought to be comparatively great after passing the mag-
296
[SERIES XXVII.
Atmospheric magnetism.
netic meridian; for its path forms an obtuse angle with the
meridian before the passage and an acute one afterwards (3000.),
and therefore it is more powerful. To all these causes of action
will be added the effect for the time of the cold in the distant
west (3005.).
3022. The case of difference of direction before 19h (3016.) is
very marked at Greenwich, as may be seen by looking at the
Curves for the months, Plate II. The south or upper end of
the needle goes west in May, June, July and August, from
12h to 19h, i. e. from midnight to five hours before noon;
but in October, November, December and January, it is east-
ening at the same hours. Considering first a summer month,
as June, the upper end of the needle is westward as the sun
comes onward (as it ought to be) until 19h, when he is almost
in the middle of his passage through the east quadrant; and in
respect of distance and angular relation to the magnetic meridian,
the warm region is then, probably, in the place of greatest power
to produce westening of the needle end'. In the next six hours
the needle passes to extreme east, performing, according to the
observations, a fourth of the whole swing in the first two hours,
a half in the next two, and a fourth in the remaining two, the
journey being no doubt with first rapidly increasing and then
rapidly diminishing velocity. In this transit of the region, the
sun is for about two-thirds of the time in the eastern quadrant,
and one-third in the western; and his path in the latter third
forms almost the base of an equilateral triangle with Greenwich,
having the magnetic meridian for one side, so that all that time
it is close to and therefore has strong action on the needle (3000.).
The sun is at 1h in such a position as respects this angle, that if
we assume the region to be somewhat in advance of it, the latter
would be in that place where it could exert its maximum east-
ening effect; and therefore after that, as it recedes westwards,
would let the needle return from east to west, as it does, fol-
lowing it. The needle continues to go west, passing its mean
place for the month about 7; in the meantime, before that, at
a little after 6 o'clock, the sun has left the western segment by
¹ It must not be forgotten, that the return from an extreme east or west
position is not when the sun or warm region passes by a neutral line, or from
one quadrant to another, but when it passes its point of greatest action in a
quadrant (2982.).
Nov. 1850.]
297
Greenwich-day and night effect.
passing the magnetic equator; it has not yet set to Greenwich,
and if it have any action, it will, because of the segment it is
now in (2979.), still be to carry the needle end westward. The
end in fact continues to go westward, slowly only, after 10 o'clock,
gaining a little from 10 to 15h; and then, as the sun comes up,
passing more rapidly west, as it ought to do, until 19h, and
finally making the great swing to the east as before. The whole
progression here is very simple, and apparently a natural result
of the assumed cause. Effects of cooling no doubt come in;
but the cold region has diminished in intensity and extent
(3006.), has retreated northward, and its action appears in com-
bining with the former to produce only variations in the velocity
of the change.
3023. Then for the winter, let us consider January; and, as
the eastening is a maximum in all the months at 1 o'clock, after
the sun's passage across the meridian, let us begin the cycle
there. At 1h the upper end of the needle is at extreme east,
and the amount of the variation not half what it was in summer,
the sun being now far off. The sun and warm region pass the
magnetic meridian about 21" or 22h; and therefore, in the hours
before and after that, should produce the full west to east effect.
At 1 o'clock the needle returns west, following the retreating sun,
and does so quickly for seven or eight hours, or up to 9h,
during which time the warm region, and also the carly morning
cold region, are in quadrants and positions, which, if they have
any action at all like that referred to in the experiments (2975.
2995.), would then set or hold the needle end west of its mean
position. Then an action of the following kind supervenes; the
needle remains stationary until 11", after which it goes esat at
midnight and until 15h; again remains stationary, or nearly so,
for two hours; then eastens again, slowly at first and afterwards
more rapidly, until 1b, when it has atttained its maximum east-
ening and the place from whence it set out.
3024. This night action is another case of the action of a cold
region like that considered in respect of St. Petersburgh (3010.).
It appears to me that at 11h the immediate sun action and return
west after it, were over; that the cold region which was coming
round from the east did then act by its paramagnetic condition
(combined with the complementary effects of the sun's action
on the other side of the globe), and set the needle eastward, as
298
[SERIES XXVII.
Atmospheric magnetism.
it would be competent to do (2994. 3010.) until 14h or 15h. In
eastening, the needle does not arrive at the mean place, but is
still l' west of it; and the reason why it hangs there from 15h
to 17h and then begins to go east again, more and more under
the sun's action, is probably that, as the sun rises in the southern
tropics, his distance and position bring the resulting distant
warm region gradually into action with that of the nearer cold;
that at first he stops the action of the latter, and then as he ad-
vances combines with and finally replaces it; causing the usual
swing to come on, slowly at first and then quickly, from west to
east by 1h. How this would happen is well seen, both as re-
spects the place of the sun in the southern hemisphere, and in
the two magnetic segments, by reference to the globe (2996.)
and the diagram of the curves of variation, Plate II.
3025. Considering another and an intermediate month as
March; at 1h the upper end of the needle is at extreme east;
then until 9h it follows the sun as before (3023.). From 9h to
11h it is stationary; then the paramagnetic action of cold from
the east occurs, and the needle moves east until 13h. It is then
stopped, and two hours sooner then before; for the sun now ap-
pears to Greenwich as early as 6 o'clock, and in a more favour-
able position for effect, both as regards the magnetic meridian
and the segment in which it has for the time its place; and so
the needle is actually sent west for a couple of hours. It is then
almost held steady until 19h, after which the great sun-swing
occurs. The holding west and yet the absence of more west-
ening between 15" and 19", is not inconsistent with the southern
place of the warm region, and it is probable that at that time the
dip is increasing; an effect which would accord very harmoniously
with the conditions of matters at the time.
3026. Other months are on this or that side of March in
respect of their effects; the corresponding month on the opposite
side of the year (September) is the same as March, except in
that portion of effect which is consequent upon a month follow-
ing one that is warmer or colder than itself (3053.). Greenwich
therefore satisfactorily illustrates the application of the hypothesis
to the case of a difference in direction for the same hour in dif-
ferent months (3016. 3022.); and also the occurrence of the
night effect, and its transition into the very marked eastening of
the early morning.
Nov. 1850.]
299
Hobarton-Toronto.
"
3027. The cases of Hobarton and Toronto are so similar,
though in opposite hemispheres, that they may be considered
together. A very important comparison of the phænomena at
both places has been already made by Colonel Sabine in relation
to the variations of declination, inclination, and total force'.
When examined by the globe (2996.) the distribution of the
quadrants is nearly alike, the sun being in two chief east and
west quadrants, from about 18 to 6 o'clock, or during the day,
The sun is in more influential parts of the quadrants in summer
than in winter, and the effect is seen in the difference of the
amount of declination variation. At Hobarton it is 12'05 in
summer and only 3'6 in winter. At Toronto it is 14' in summer
and 5′-2 in winter. The night action at both is alike in character,
and has been sufficiently explained according to the hypothesis
in the former cases (3010. 3024.).
3028. Colonel Sabine has given the data by which the varia-
tions of the inclination and of the total force at Hobarton and
Toronto may be compared with and applied to the hypothesis;
but I hesitate to enter upon them in this general view, inasmuch
as these and the declination variations should be closely con-
sidered and compared together at every hour for each particular
place. The inclination variation at Hobarton is greatest in its
summer, being then 2'18, and least in winter, or 1'28, as was
to be expected. The great variation occurs in the daytime, as
with the declination; the dip being most as the sun region passes
over the meridian. The greatest dip is not at the same hour for
all the months; it occurs at 23 o'clock for December, February
and March, at 24 o'clock for September, at 1 o'clock for June
and July; as it moves on so do the points of least dip on each
side of it, so that the whole curve advances in time in the order
of these months. There is also another affection of it, for the
quickest transition is from most to least dip in some months, as
December, February, and from least to most dip in other months,
as June, July, September. At Toronto the dip variation, though
peculiar in some points, may be said to have the same general
character.
3029. For the variation of the total force at both places, I will
1 Hobarton Observations, 1850, vol. i. p. lxviii., &c.; also Philosophical
Transactions, 1847, p. 55, and 1850, pp. 201, 215, &c. See the Curves,
Plate II., and Tables for Toronto, pp. 269, 270.
300
[SERIES XXVII.
Atmospheric magnetism.
at present only refer to Colonel Sabine's volumes, and the ob-
servations he has made thereon.
3030. These is a remarkable difference between the time of
the day changes at Hobarton and Toronto, to which Colonel
Sabine has called attention. It consists in the occurrence of
those at the latter place, about an hour before those of the former.
If this had depended upon the declination, then the change
should have taken place first at Hobarton, for there the sun
arrives at the magnetic meridian before he comes to the astro-
nomical meridian, and for like hours of local time he is in a
better position in the quadrant in the afternoon than at Toronto;
still it is the later of the two.
3031. If the time of the sun-swing from west to east be con-
sidered, the middle of it ought to be somewhere near the period
when the warm region is passing the magnetic meridian (2982.),
and in that way supplies an approximative expression of the
relative positions of the region and the sun. The swing is at
Hobarton from 21 to 2 o'clock, or five hours, and the magnetic
meridian is passed by the sun nearly in the middle of the time,
or 23h 20' o'clock. But according to the supposition just made,
this is also the time at which the warm region ought also to pass,
and so the sun and the region in this place appear to arrive at
the meridian together. At Toronto the sun-swing is about four
hours in winter, or from 21 to 1 o'clock, and five hours in sum-
mer, or from 20 to 1 o'clock. Of the latter five hours the middle
is 22 o'clock, at which time the region ought to pass over the
magnetic meridian, and as that coincides nearly with the astro-
nomical meridian, it appears that the region is about 1 hour
before the sun. By a similar comparison for winter, the region
would then appear to be about an hour before the sun¹.
3032. I am inclined to refer much of this precession of the
warm region at Toronto to the geographical distribution of land
and water there. The Atlantic is on the east and the continent
of America on the west of the station, and as Dove's charts and
results intimate, the temperature may rise higher and sooner
¹ In reference to the position in advance of the sun, of the resultant of those
actions which set the needle end westward, we must remember that the prece-
ding cold, being perhaps seven hours only to the west, is by its action on the
general system of the curves aiding the westening of the needle, whilst the
sun is in the east and even over the meridian (3005.).
Nov. 1850.]
301
Hobarton-Toronto.
over the land than over the water, and so throw the warm region
in respect of Toronto in advance of the time or of the sun. In
the case of Hobarton the arrangement is different; and, in fact,
what land there is is between the advancing sun and the station,
and would tend to hold the warm air region back, and tend to
cause its time to coincide with that of the sun. Even the greater
difference in summer than in winter at Toronto appears to be
explicable in the same manner, by reference to the relative posi-
tion of the sun at the two seasons to the land and water arrange-
ment.
3033. Though the temperature on the earth's surface is a very
uncertain indication of that above (2937.), yet as far as it goes
it harmonizes with this view. The maximum temperature oc-
curs sooner after midday at Hobarton than at Toronto; in the
former place it is at 2 o'clock and very regular, and the mini-
mum at 16-19 o'clock, being earlier in summer and later in win-
ter. At Toronto the maxima are from 2 to 4 o'clock, and the
minima at 16-18 o'clock. The maxima are later in summer than
in winter; the minima are as at Hobarton, being later in winter
than in summer. The mean temperature is lower at Toronto
than at Hobarton, being as 44°.48 and 53° 48: the range of varia-
tion is also greater, being at Toronto 43° and for Hobarton
only 18°.
3034. It is probable that effects of retardation and accelera-
tion, in respect of the passage of the local part of the warm re-
gion for a given place, may occur in many parts of the globe,
and these will require to be ascertained for every locality and
for the different seasons there. A place having the reverse
position of Toronto would have a reversed or retarded effect; and
hence it might happen that needles in the same latitude might
be affected at very different local times, and yet all be regularly
affected every twenty-four hours. The region would in that
time make its diurnal revolution, but vary in the velocity of its
different parts at different periods of its journey, and that in a
different degree and order for different latitudes, and for different
parts of the same parallel of latitude. Even the time during
which the effect (as for instance the sun-swing) continued would
probably be altered; one place holding the influence longer and
another dismissing it sooner, analogous to two conditions of
stable and unstable equilibrium.
302
[SERIES XXVII.
Atmospheric magnetism.
3035. Cape of Good Hope'.-This station is in longitude
18° 33' east and latitude 33° 56' south. The mean declination is
29° west and the dip 53° 15′ south. The amount of dip, com-
bined with the position of the place, gives a magnetic equator,
which passes nearly through the astronomical poles, and so the
sun's path in every part of the year intersects it almost at right
angles and at the same hour, namely, about 20' past 7 o'clock in
the morning and evening, or at 19h 20′ and 7h 20'. But because
of the great declination, the sun is in the astronomical meridian
two hours before he arrives at the magnetic meridian in Cape
winter, and half an hour or more before in Cape summer.
3036. The sun passes obliquely through both the chief qua-
drants and across their central parts pretty equably; but be-
cause of the western character of the mean declination he is
much nearer the Cape when in the eastern than when in the
western quadrant for all the months, and so the coming up
effect, i. e. the westening before the midday swing commences,
ought to be more powerful than the eastening after it is over, and
such is the case. This is in beautiful and striking contrast to
Greenwich, which, having the same kind of mean declination
and nearly in the same degree, is on the north of the sun's path,
and therefore the luminary passes its magnetic meridian before
12 o'clock, and for a time still approaches the station: the re-
sult is the reverse effect to what we have at the Cape; for the
eastening effect at the end of the midday swing is more powerful
than the westening effect before it, as is well seen by the curves
given in Plate II.
3037. Selecting July as the month in which the effect of
winter occurs at the Cape, we find that the day-swing is very
feeble, as it ought to be, the sun being in the northern tropic
and far away; and the swing east is at an end by three o'clock
when the sun has passed by about one hour over the magnetic
meridian. The upper or north end of the needle then westens
for two hours, following the sun until 5, when the luminary is
low to the Cape and at its setting. After that the needle end
eastens slowly until 10, then a little more quickly until mid-
night (passing the mean position at 11h); quicker still until 16h
or 17h, and still more quickly until 19, when it has attained its
maximum east position. This effect I believe to be due to the
¹ See Tables, pp. 317, 318, and curves of variation, Plate II.
Nov. 1850.]
303
Cape of Good Hope.
cold, which in these hours is approaching from the east, and
setting by its paramagnetic action (3003.) the needle end east-
ward. On the surface of the earth the maximum cold in this
month is at 17h or 18h, and as far as it goes this result accords
with the effect above described. At 19h, the sun in rising not
only stops the eastening but quickly drives the needle back
again, and the latter very rapidly goes westward until about 23", at
which time the sun-swing from west to east comes on, being over
by 2 or 3¹, completing the daily variation, after which the
needle goes west, following the sun as before. In this sun-wing
is seen the effect of an inclined magnetic meridian (3000.); for
though the sun is, at the beginning, only an hour east of the
astronomical meridian, he is full three hours to the east of the
magnetic meridian. As the swing occupies about four hours,
the warm region is probably near the magnetic meridian about
half-past 12 or 1 o'clock.
3038. January presents a case of Cape summer.
The day-
swing is then from 21h to 1 or 2h. After 2¹ the needle upper
end follows the sun westward until 6¹, and then moves a little
eastwards for two hours; after this it moves slowly westward
again, the whole effect being as if a cold region had occurred on
the east, had passed over and gone away west, and the tempe-
rature below at this time is within 2° of the minimum. This
night effect of drawing the needle westward (3004.) proceeds
slowly until 15 or 16h, being assisted by the rising temperature
on the east urging the end still more rapidly west until 20¹,
when having reached its maximum in that direction, it at 21h
turns back and is driven to extreme east in the sun-swing,
through an amount of variation more than twice as great as
that produced in July or Cape winter.
3039. I think the above is a true explanation of the reverse
motion of the needle in the months of July and January, or
Cape winter and summer. In winter the paramagnetic effect
of cold air is on between 12h and 19h, remaining longer on the
east side of the magnetic meridian; as it passes forward, both it
and the sun region conspire at 19h to carry the needle westward,
for though they have opposite actions they are then also on
opposite sides of the magnetic meridian (3005.). In the summer
the cold region has much less power, occurs earlier', soon passes
¹ The minimum temperature below is three hours earlier.
304
[SERIES XXVII.
Atmospheric magnetism.
over, for the summer sun is behind it, and then rather aids the
sun in carrying the needle weswtard.
h
3040. Some of the other months are still more striking in
summer effect. February has a swing through 8' from west to
east between 21h and 1b; then from 1h to 3h it scarcely changes;
from 3h to 6h it follows the sun west; from 6h to 16h it varies
but little, showing the merest trace of east effect about 8h;
and after 16h it passes west more and more rapidly, so that
by 21h it is at a maximum west, ready to swing back as the
sun region passes over. The other and intermediate months
are easily traced, and found to be beautifully consistent with the
same principles of the hypothesis. As is evident, in almost
every case each month partakes of the character of the preceding
month in some degree, though not so much in this case of the
Cape as in some others (3053.). The curves of December and
January are more equal.
3041. The time of the sun-swing illustrates exceedingly well
the effect of the inclined magnetic meridian (3000.). In No-
vember, December and January, the swing is from 20h to
between 1h and 2h. In these months the sun crosses the astro-
nomical meridian about half an hour before he arrives at the
magnetic meridian. In October, February and March, the
swing is later, being from 21h to 2h or 3h, for the sun then passes
the magnetic meridian an hour or more later than the astrono-
mical or time meridian. In September, April and May, the
swing is still later, being from 22h to 2h or 3h, and the sun is
still longer than before in reaching the magnetic meridian. In
June, July and August, the swing is latest, being from 23h to 3h,
and the sun is proportionately late in arriving at the magnetic
meridian. What I describe as the passage of the sun is of course
true of the warm region which precedes it; but I prefer referring
to the visible type rather than to the invisible reality, because it
ties the considerations of time more simply together.
3042. The inclination at the Cape varies singularly in the
twenty-four hours, depending, I think, upon its mean degree.
It is such that the warm and cold resultants of action for the
Cape will sometimes be above the line of the dip and sometimes
below it, not only for different times of the year, but I think in
some seasons, even at different times of the day. It would re-
quire much attention to unravel the whole effect. In June,
Nov. 1850.] Cape of Good Hope-St. Helena.
305
July and August, when the sun and its warm region are greatly
to the north of the Cape, it appears that the dip is increased as
the region passes, which would give a rotation of the upper end
of the needle like that at Hobarton (2909.); but in November,
December, January, February, March and April, the dip
diminishes at that time, and the resulting rotation of the pole is
of the contrary kind, or like that at St. Helena (3057.) and
Singapore (3061. 3067.).
3043. The daily variations of intensity at the Cape are
remarkable. In the months October to April it is at a chief
maximum at 19h or 20h; by noon it is reduced to a minimum as
the sun passes over; gradually rises to a second maximum about
4h or 5h, and then, after sinking a little about 8 or 9h, reaches
the chief maximum about 18h or 19h next morning. In the
months from May to September the chief maximum is at 21h
or 22h, which is followed by a minimum at 1 or 2h, due to the
day effect. Then comes on the 5b maximum, and after thirteen
hours or more the second minimum as low almost as the former,
and only three hours before the chief maximum; so that this
maximum is placed between minima close on each side of it.
3044. These are exactly the months during which the upper
end of the needle moves eastward in early morning up to 19h,
and that is just the hour when the minimum intensity occurs.
From 18h or 19h to 21h the intensity rises to a maximum, pre-
cisely as the lines of force are moving westward before the sun
region, prior to their quick return east; and as they return in
their quick journey so the intensity falls to a minimum again,
and is at that minimum at 1h or 2b, just as the swing is over.
Here is a very close connexion, and it is curious to see the
needle end at east with minimum power at 18", and again also
at 1h, remembering that in that time it has swung from east to
west and back to east again.
3045. St. Helena¹.-This is a station which Colonel Sabine
has distinguished as of the highest interest; being near the line
of least force, within the tropics, and with little magnetic incli-
nation2. It was here also that he called attention to the striking
fact, that the course of the needle is in some months in one
direction, and in other months in the contrary for the same hours
¹ See Tables, pp. 319, 320, and curves of variation, Plate II.
Magnetical Observations, St. Helena, 1840 to 1843.
VOL. III.
2
X
306
[SERIES XXVII.
Atmospheric magnetism.
of the day¹. De la Rive attempted to explain this fact2, but
Sabine has stated that this explanation is not satisfactory³.
3046. St. Helena being a small island in the south Atlantic
ocean is removed about 1200 miles from the nearest land.
The longitude is 5° 40′ west, the latitude 15° 56′ south; the
mean declination 23° 30′ west, and the mean dip 22° south.
Hence there are three quadrants concerned in the day action of
the sun, especially when that luminary is south of the equator.
The sun is south of St. Helena itself in the months of November,
December, January and February, or for nearly that time; it is
north of the island for the rest of the year. At one time the
sun passes the astronomical meridian before it arrives at the
magnetic meridian, and at another time the contrary is the case.
In addition to these peculiar circumstances, St. Helena is a place
of great local differences, and also its dip is so low that the sun's
day effect is almost constantly to depress and lessen it.
3047. In June and July the sun rises to St. Helena in the
south-east quadrant; about an hour after, it passes into the
north-east quadrant, and crosses it toward the southern end,
being then at mid-distance in the quadrant about one-third of
the length, or nearly 60° from the southern termination. It
leaves this quadrant about 1h 20m, crossing the magnetic meri-
dian at that time (and consequently so long after passing the
astronomical meridian), and entering the third or north-west qua-
drant traverses it obliquely towards its northern extremity. In
our winter, December and January, the sun also rises to St. Helena
in the south-east quadrant, as before; but it now remains in it
until 22h, being for much of the time in strong places of action ;
it enters the north-east quadrant to the south of St. Helena, and
does not remain in it two hours, being then only in the weakest
part of it; it leaves it again before arriving at the astronomical
meridian, then enters the north-west quadrant, gliding along
near to its southern side, and is within two-thirds of an hour of
leaving it when it sets to St. Helena.
3048. As June presents the aspect of circumstances ap-
proaching nearest to that of a station further south, as Hobarton
or the Cape, so I will consider the variations for it first. The
1 Philosophical Transactions, 1847, p. 51.
2 Annales de Chimie et de Physique, March 1849, tome xxv. p. 310.
• Proceedings of the Royal Society, May 10, 1849, p. 821.
Nov. 1850.]
307
St. Helena.
north or upper end of the needle is then nearly at its mean
place at midnight or 12h: it advances east (slowly at first) until
16h, and then more and more rapidly up to 19h, when it stops
and goes as quickly west until about 22h, after which it changes
but little until 3ª, when it moves west till 5, and then slowly
east up to 12¹, and then onwards to 16¹ and 19h, as already
said. The eastening from midnight and before, I refer to the
paramagnetic action of the cold, which comes up from the east
as before (3003. 3025. 3037.); the rapid increase of the eastening
from 16 to 19h is consistent with the increasing cold of the early
morning, and also with the circumstance, that the sun and its
representative region are then passing from the south-east into
the north-east quadrant, and must be not far from the neutral
line, for that is the time of quickest transit of the needle. As
the sun advances into the north-east quadrant, it first stops the
eastening, as at 19h, and then converts it into westening (3014.),
which goes on consistently with all former observations until
22h; the needle is then retained a little west of its mean position
until 1¹, at which time it has not yet attained coincidence with
the magnetic meridian, and after this hour it is determined east
a little until 3¹. This effect, from 22¹ to 3h, I consider as the
sun-swing to the east; and I think, examining the globe (2996.),
its small amount in declination is quite consistent with the rela-
tive positions of St. Helena and the warm region, combined
with those of the active and neutral parts of the quadrants tra-
versed during the time. From 3h to 5h the needle end moves
westward, following the sun; and that effect harmonizes with
the idea that the previous holding of the needle in an eastern
position, from 22h to 3", is the sun effect: then the slow
eastening from 5h to midnight and beyond, is the cold effect
coming on.
3049. Colonel Sabine has shown that the months of May,
June, July, and August, may be classed together, so that I will
not speak of each. Whilst they show the analogies they have
between themselves, they also indicate the transitions to and
from the other months. Let us consider September. From 7h,
through midnight on to 16h, the needle stands nearly at the
mean. From 16h to 18h, the upper or north end eastens through
the effect of the early morning cold. That the eastening should
be fully effected an hour sooner than before (3048.) is quite con-
•
x 2
308
Atmospheric magnetism. [SERIES XXVII.
sistent with the principles, for the path of the sun and its dia-
magnetic region is far nearer to the station than before, being
now about the equator. From 18h to 22h it sends the end west-
ward in conformity with all former observations, and then comes
on the sun-swing from west to east, between 22h and 24", and
a hold at extreme east an hour longer. The shortness in time
of this transit is, I think, a beautiful point. The sun is still
north of St. Helena, but is now so much nearer that he passes
through the same angle east and west, in respect to the place of
observation, in less than half the time of the former sun effect
in June (3041.). After this the needle end travels west from
1" to 6", following the sun as on other occasions; and then from
6¹ to 9h moves a little east by the evening cold in the east,
and remains near the mean position until the greater cold before
sunrise (3005. 3011.) takes it more east between 16h and 18h of
the coming day.
.
3050. In looking at the curves of variation (Plate II.), it will
be seen that the curve for the next month, October, is remarkable
for being like in general character with, and yet far removed in
place from, that of September; and this effect appears due to the
circumstance that the sun has now arrived at the latitude of
St. Helena, or nearly so. According to my supposition, there
has been a feeble night effect (3010.); and at midnight the
needle is at the mean position and moving slowly westward,
when the greater cold which precedes the sunrise coming into
action on the east, counterbalances and arrests the western pro-
gress, and even draws the needle, as before, east a little for a
couple of hours, till 18h. Even the sun region is at 16h in that
quadrant (the south-east one), that if it could act on the needle
it would combine with the cold in the next or north-east quadrant
in setting it eastward. By 18h both the preceding cold region
and the following sun region are so far advanced in their re-
spective quadrants that they combine to carry the needle end
west as before, until 20¹, and then comes on the swing from
west to east until 24h. Why this begins sooner, lasts longer,
and is above four times the extent of the September swing,
appears to be that the sun region comes up upon the latitude of
St. Helena, and so acts in respect of the magnetic meridian
more powerfully, and also sooner and longer; also that because
of the mean declination west it arrives at equidistant points
Nov. 1850.1
309
St. Helena-cumulative effects.
from and passes over the magnetic meridian sooner; and also
from the effect of an accumulative action added to it from former
months (3053.).
3051. At 1 o'clock the needle begins to turn from extreme
east, i. e. sooner than in the former months, oecause the mag-
netic meridian is sooner passed, and follows the sun until 4ª,
when it stops, and then the evening or night action due to cold
appearing in the east, carries the needle back eastward till 10,
and then as it advances in the quadrant lets the needle return
back again (3004.) until between 12h and 13h, when the latter is
in its mean position. The cold region then appears to draw it
westward until 16h, when its distance increasing, it releases the
needle and lets it return east until 18 o'clock, when the latter is
still west of its normal position, and then the sun region rising
up, helped perhaps by the cold that immediately precedes it,
which is probably now over or beyond the magnetic meridian,
sets it toward the west prior to the sun-swing.
3052. In December and January the sun is south of the station.
This makes no difference in the general character of the curve
for these months; nor should it according to the hypothesis, ex-
cept in this point, that though the sun is very near to St. He-
lena and has the cumulative effects of the preceding months
(3050. 3053.) added to its own effect at the time, still it is in
weaker parts of the quadrant, and whilst in the chief segment is
almost up in the corner and near the place where the two neu-
tral planes cross each other; hence its effect ought to be less,
and so it is; for the sun-swing of November and February is
larger than that of December and January. The sun-swing
happens in December at the same time as for October, though
in the latter month it crosses the magnetic meridian after, and
in the present before midday: still there is only half an hour's
difference from one to the other, and the observations are per-
haps not close enough to allow one to separate its peculiar effect
out of an interval of four hours. Besides, accumulative causes
may interfere. The places of the December curve are altogether
a little more west than those for October.
3053. The cumulative effect of preceding months is very im-
portant and well-shown at St. Helena (3050.). Thus, taking the
September curve and comparing it with that for October or the
following month, we have a great difference of a certain kind;
310
Atmospheric magnetism. [SERIES XXVII.
then again comparing September with the month in which the
sun is returning from the southern tropic instead of proceeding
to it, and has arrived at the same position as it had in October,
another striking difference appears. March is the nearest month
for the second comparison. Up to 20h its curve changes like
the October curve, but the upper end of the needle is all the
time about half a minute east of its place in October. At 20h
the needle in October begins to swing from west, and reaches
extreme east at 24" in March it westens until 21h, then returns
and reaches extreme east at 1; so that the swing is an hour
later, and during that time the end is from half a minute (of space)
to a minute more west than in October. This difference I believe
to be due to the cumulative effect of the months between October
and March, during which time the heat has been diminishing in
the northern hemisphere, and increasing in the south. Similar
results in other months make it probable that the effect of the
atmosphere, though induced by the sun, lags behind the lumi-
nary considered as in his astronomical position all the year round;
and that therefore in advancing to and receding from a tropic,
he seems to do less in the first instance and more in the second
than is due to his place for the time.
3054. But where circumstances are apparently equal, a differ-
ence also arises. Thus from March to April in one direction,
and from September to October in the other, might be expected
to be alike, except for a little of the lagging effect (3053.), which
would appear on both sides: nevertheless March and April are
in Sabine's curves between September and October, and near to-
gether, whilst the other two are far apart. This effect I refer to
the different conditions of the two hemispheres as regards heat
(Dove). From September to October the sun is passing from a
hemisphere having a mean temperature in summer 17°-4 above
that of the other hemisphere for its winter; but in March and
April it is departing from a hemisphere having a mean summer
temperature of only 100.7 above that of the other hemisphere
for its winter (2949.); and these respective differences must
tend to separate September and October, and bring together
March and April, as is seen to be the case by the curve charts,
Plate II.
3055. I need not go further into the declination variation of
St. Helena: the lines for the other months are subject to the
Nov. 1850.]
311
St. Helena-dip.
observations already made. Colonel Sabine's important query
of the cause of difference in direction for different months (3045.),
appears to me at present to be answered for this station, as well
as for the other stations, in very various latitudes where it makes
its appearance (3016. 3022. 3039.).
3056. The dip at St Helena is a daily variation very simple
in character, being a maximum at 7h and a minimum at 22¹ and
23h, with only one progression. It proceeds to its minimum
therefore in the middle of the sun-swing, i. e. the upper end of
the needle proceeds to west, and descends from 16 to 19h or 20h,
during which time therefore the dip is decreasing; then it re-
turns east until it reaches the neutral position, the dip decreasing
the while still more. The needle still continues to go east to
complete the sun-swing, but now the dip increases; at 24h or 1h
the needle returns (in declination) after the sun westward, but
still with increasing dip; at 5 or 6 the westening has almost
ceased, and an hour after the dip is at its maximum.
3057. So as the sun and its region pass over they diminish
the dip by depressing the upper ends of the lines of force, and
as they pass away the lines rise (2926. 2937.) and the dip in-
creases. The ellipse or curve, therefore, which represents the
motion of the upper end of the needle at St. Helena, as the sun
comes up from the east, is above westward and downward, and
back below to east; then rising to be repeated in the next
twenty-four hours. This is the reverse direction to the repre-
sentative ellipse for Hobarton, having like south dip in a greater
degree. But that is in perfect consistency with the hypothesis;
for as the region is located above in the air, it is above the angle
which the dip makes with the horizon at St. Helena, and there-
fore ought to depress the line of force and lessen the dip. At
Hobarton, the region being in the tropical parts, is within the
angle formed by the line of dip with the horizon, and therefore
deflects the lines of force upwards and increases the dip, and so
the portions of ellipse at the two places, which correspond in
time and direction as to declination, have contrary variations of
inclination.
3058. Singapore¹.-This is a very interesting station: being
¹ See Tables, pp. 321, 322, and the curves of variation, Plate II. The data
for Singapore are deduced from the recent very valuable labours of Captain
Elliot.
312
[SERIES XXVII.
Atmospheric magnetism.
in longitude 103° 53′ E., it has only 1°16′ N. latitude, and so is
close to the equator. Its declination too is only 1° 40′ E., and
its inclination 12° S. It is also near the line of weakest force
round the earth. The magnetic equator of the needle is almost
parallel to the earth's equator, and the quadrants (2929.) are dis-
tributed with great simplicity, the magnetic and astronomical
meridian nearly coinciding. In our summer the sun passes
through the east and west northern quadrants during the day-
time; in our winter through the east and west southern qua-
drants; and in certain months through all four quadrants, follow-
ing nearly the neutral line of the magnetic equator.
3059. Hence if the line of force were free, i. e. if it had no
hold in the earth (2919.), we should expect from the hypothesis
little or no change in the needle, especially in the month when
the sun was over the magnetic equator; but because there is dip,
and the lines of force which govern the needle are to the south
tied up in the earth (2929.), whilst they are free to move in the
air and space towards the north, so there is variation both of
the declination and inclination in a perfectly consistent manner;
and keeping this in mind, I think we shall have no difficulty in
tracing the monthly results according to the hypothesis.
3060. In the first place, the curves of day variation are so like
those of St. Helena, month for month, that the account given of
them there will suffice for the present occasion (3048.). The
sun-swing occurs at the same period, and the effect, dependent,
as I suppose, on the character of the two hemispheres, is pro-
duced (3054. 2949.). There are however striking differences in
the latter part of the sun turn, and also in the night hours, from
5h to 14h. The amount of variation appears small; but this is
chiefly due to the circumstance that the horizontal plane on
which we read it almost coincides with the free needle, and so
the correction before referred to (3009. note) necessary to give
the true value of the variation is here very small.
3061. Considering June first, as at St. Helena, the upper
needle end moves east as before until 19", under the influence of
the morning cold, after which it stops and is sun-driven west
until 22h, when it swings downwards and beneath to east by 3¹;
then follows the sun west until 7h; it then stops and returns,
creeping more and more east because of the coming cold (3065.).
In July the needle eastens a little more before 19h; westens until
Nov. 1850.]
313
Singapore.
23h, and then eastens until 4h. The sun-swing is thus thrown
an hour later than in June, which I believe to be connected with
the accumulation of heat over the land (3054.), combined with
the lagging effect of the sun (3053.). In August the needle end
eastens until 19h; more than in July, and most of all the months;
it then westens strongly before the sun until 23, after which
the sun-swing comes on and continues until 5h, as if the warm
region were behind the sun, perhaps even 2h. The time of the
swing is much prolonged, and not unnaturally, as the place is
at the equator and therefore under the sun. In September the
eastening is less, the westening is less, and the sun-swing is less.
April is like September, except that the latter shows the effect
of the previously warmed hemisphere (3053.).
3062. Then there are four months in the year, November, De-
cember, January and February, when the sun is south of Sin-
gapore, and altogether during the day in the southern quadrants
(3058.). As the sun comes on from 16h or 17h, the upper part
of the line of force moves westward (the lower being fixed in the
earth) until 19 or 20 o'clock. The sun is at this time in the
south-east quadrant, and it might be excepted perhaps that
the motion of the north or upper end of the needle should be to
the east if there were any change at all. But there are two or
three reasons, from the hypothesis, why this should not be. For
that effect there should first of all be no dip; and in the next place,
if there were no dip, the sun is so nearly in the neutral line of
the magnetic equator, that the deflection, if any, would have been
very small. On the other hand, the lines of force have dip to
the south, and being therefore held in the earth, that travelling
of the sun along the neutral line, which in its coming up would
have sent the whole line of force west, and so caused no variation
of declination, can now only send the northern parts, as they rise
out of the earth and are carried on with the general system of
lines, west, and so cause that western travelling of the needle
which does occur. Besides this, though the sun be south of that
neutral line and also of Singapore, there is reason to suppose
that the middle or resultant of the warm region is north even of
both (3063.), which would aid the westening of the needle just
described.
3063. For if we call to mind Dove's results, they show that
the northern hemisphere, as a whole, is warmer than the south-
ern (2949.). Again, if we look at the meridian of Singapore, we
314
[SERIES XXVII.
Atmospheric magnetism.
shall find that there is far more continent on the north of it,
to produce a higher temperature, than to the south; and even
by the local tables of temperature below, we shall find that May,
June, July and August are the hottest months for Singapore, and
November, December, January and February the coldest; all
tending to make us suppose that the warm region of the atmo-
sphere is relatively north of the sun's place, and perhaps even
of Singapore (3067.).
3064. At 20h the sun-swing from west to east comes on, and
continues until 2h, after which the needle moves west, following
the sun, until 10h or 11h when it is near the mean; it still goes
on westening very slowly until 17h, when the morning sun ac-
tion takes it up and drives it more quickly west, until about 20h,
when the sun-swing east occurs. The curve in these months is
very simple in its character; the night or cold effect appears to
be but small, being indicated rather by a hesitation than by a
distinct movement east.
3065. The easterly movement of the needle end in May, June,
July and August, and the westerly movement in November,
December, January and February, for the same hours, up to 19
o'clock, are in striking contrast; and I have attributed the differ-
ence to the effect of a cold region coming on from the east
during the former months (3061.), which is absent in the latter
months. In reference to this point, we have again to consider
that the warm region is on the north of the equator (3063.), and
that as the sun moves north and south it also will move with it,
but still keeping north of it. Hence the two cold regions, which
come up to the meridian in higher latitudes (3006.) before the
sun, will not be in the same relation to Singapore, for the one on
the south will be nearer to it than the one on the north, or at all
events more powerful. So when the sun is near and at the
southern tropic, the warm region probably passes over Singapore,
at which time, therefore, whilst it is the nearest, the most power-
ful and most direct in position, the cold regions will be least in
force at the station, and also least favourably disposed by posi-
tion. But when the sun is at the northern tropic, then the
power of the warm region is diminished, both by distance and
direction, and the southern cold region grows up into importance
by increased strength and closer vicinity, and so produces the
eastening before 19h.
3066. A striking difference in the direction of the night curves,
Nov. 1850.]
315
Singapore-inclination-total force.
from 5h to 14h, at St Helena and Singapore may be observed.
At the former place the needle end tends first east and then
west, whilst at the latter it moves first west and then east. The
difference is, I believe, due to the appearance of night cold ac-
tion at St. Helena, to a greater extent than at Singapore. Sin-
gapore shows that action in June, July and August, as just de-
scribed (3065.), but only in a weak degree and at a late hour.
At St. Helena, which is in latitude 16° S., the cold effect should,
for the reasons given above (3065.), appear in more power, and
hence the eastening at 6ª and after; and that this is the cause is
indicated also in a degree by the tables of temperature; for
whilst at Singapore the difference between the maximum and
minimum in the twenty-four hours is only from 3° to 4°, at St.
Helena it is from 4°.5 to 7°, and four-fifths or even five-sixths
of this depression occurs by 9 o'clock: so that four or five hours
before that, there was in the east a cold region coming up and
producing the eastening effect recorded in the curves.
3067. The inclination variation at Singapore is beautifully
simple, and such as might be expected from the hypothesis; the
sun or warm region, when passing the meridian, always being
over the lines to depress them. It is alike in all the months,
being greatest at night-time and least at mid-day; it is nearly
the same from 8 to 18h; then as the sun comes up it decreases
quickly until 23¹ or 24", after which, as the sun passes away, it
increases nearly as quickly until 7 or 8h. The amount of varia-
tion is greatest when the sun is over or to the south of Singa-
pore.
It is least in June and July, when he is near the north-
ern tropic. In December and January, when he is near the
southern tropic, it is considerably more than in June and July,
which again seems to show that the warm region is chiefly north
of the sun (3063.).
3068. The total force variation is simple, being a maximum
from 9h 12h, and a minimum at 22h or 23h, near noon. The
greatest variation is in April and October, or at the equinoxes,
and the least in December and June, when the sun is at the tro-
pics. The force is the least towards noon, when I suppose that
the air above is in the worst condition of conduction, and would
cause a magnet in it to show more power. But how that may
affect the curves beneath on the surface of the earth, where they
are compressed together, is doubtful, and the whole matter of
316
Atmospheric magnetism. [SERIES XXVII.
intensity is too uncertain and has too many bearings for me
to consider it usefully here.
3069. I hope soon to give further experimental data for the
purpose of illustrating and testing the view of the physical
cause of the magnetic variations which I have put forth, namely,
those I expect to obtain by the differential balance, and others
concerning the sensible influence of oxygen in causing, under
different conditions, deflection of the lines of magnetic force.
Royal Institution,
November 16, 1850.


Cape of Good Hope.-Longitude 18° 30′ E. Latitude 33° 56′ S. Declination 29° 05′ W. Inclination 53° 15′ S.
Mean Diurnal variation of the Declination in each month of the years 1841 to 1846.
Increasing numbers denote a movement of the north or upper end of the magnet towards the East.
Noon.
Mean time Oh. 1h. 2¹. 3h. 4b. 5b. 6h. 7h. Sh.
April
May
June
...
Midn
Daily
9h. 10h. 11h. 12h. 13h. 14h. 15h. 16h. 17h. 18h. 19h. 20h. 21h. 22h. 23h. means.
**
| |
January.. 411 543 5°50 504 464 429 396 416 443 436 427 4′13 398 379 3°56 3°32 3'09 2.67 2.01 1.15 0.37 0.36 139 2'93 3'28
| | | |
|
February. 551 748 8.21 7·86 706 6·11 574 583 5'90 582 5'74 569 5'78 5'73 5'55 550 5.38 527 490 3.36 1.26 0.00 0.82 2'96 493
March
|
534 674 729 6'93 6'17 548 532 5'33 542 5'39 528 5:40 5 34 5:52 5'59 5'54 5'52 5:39 495 322 1'04 0.02 126 344 466
| |
4'07 500 476 421 375 3'53 342 3'39 344 345 351 356 353 3'98 3'96 407 417 432 415 3.29 1°32 0.00 0.39 0.06 3'30
183 249 281 292 2.50 215 217 231 2.33 230 245 241 264 2.83 2.87 3.10 3.24 3′36 3·80 | 3′91 |│2.31 | 0·68 | 0·00 0·62 | 2°42
| |
0.74 127 1.87 | 1·87 | 1°36 | 105 III 119 1.24 134 149 1·63 1'74 2.00 2.04 2.25 2·22 2.28 2.59 3′21 2.38 0.86 0.00 0.10 | 1*58
July 0'60 1.18 1.96 209 1'54 1'06 1′06 1'09 1.19 131 1'46 174 203 2.22 223 232 2'46 2.61 | 3.08 3.56 2.74 135 0.28 0.02 171
August
| | |
0.62 152 2.50 3 23 293 2 22 2 27 2°34 2.46 2.56 249 2.64 2'77 2'91 301 3°32 345 363 435 4'98 3.65 174 0.36 0.00 271
September 158 2.64 322 327 2.94 2.57 2.64 273 2.75 276 2.82 2.84 2.91 305 306 319 322 3.36 433 4'10 243 084 000 0'49 2.65
October. 4'90 5.81 5'96 5'23 429 3.69 3.84 405 409 417 418 416 416 415 396 379 363 340 2.78 137 0.14 0.00 127 318 3'59
|
| |
November 519 6.15 6.36 5'98 5'43 4'98 508 526 5.32 5:39 537 5:37 5 34 513 484 455 415 341 2.05 0.68 0.00 0.57 2.19 3.88 428
December 4.64 548 5.51 508 447 441 424 442 4.54 460 466 467 462 436 407 374 3.38 2.63 142 039 004 055 205 3:56 | 362
Mean Diurnal variation of the Inclination in each month of the year, from April 1841 to June 1846.
denote increasing inclination.
Inclination 53° 15′ South.
I'IO
Ο
Increasing numbers
| | | | |
| | | |
January..0030.00 | 0°34 | 056 | 0.72 | 100 | 125 135 146 151 150 1°41 137 140 130 122 118 1°10 094 0.99 0.97 0.92 0.66 0.23 | 0·98
|
February. 013 000 0'44 105 155 1'91 2'01 2 14 2 14 2'09 2'94 1'94 170 163 165 156 1.63 1.70 1.66 1.94 2 26 | 2·08 | 145 | 0·66 | 1°56
March
Ο
O'II |
| I
0.00 0.46 105 145 186 2.09 2.21 2.16 2.02 194 179 179 146 135 146 145 150 151 169 181 166 1.00 0.41 1.38
| |
| |
April...... 000049 105 155 176 189 216 221 211 2.06 188 165 145 118 118 107 122 112 110 110 148 153 092 033 135
May
| | | |
| | | |
0.00 0.38 0.70 0.86 108 116 127 131 149 1'59 1°39 | 1°32 1.16 0.89 0.93 0.89 0.76 0.68 0.30 0.15 0'53 066 0.56 0.12 0.84
June 0.41 0.53 0.58 0.76 0.64 079 096 1.22 134 140 1°29 1′22 1°04 | 0′96 | 0·89 | 0.81 0.73 0.78 0.36 0.00 0.07 0.38 0.36 0'430'75
July 0.62 0.64 0.59 0.64 0.77 0.87 118 120 1°46 1°43 1'43 1'21 1'07 0.95 0.77 0.87 0.67 0.60 0.28 0.00 0.18 0.51 0.64 0.56 0.80
August 0.12 0.38 0.76 0.99 116 127 134 160 155 152 145 130 116 104 0.84 0.83 0.63 0.68 0.27 0.00 0.13 033 043 030 0.84
September 000 0'23 0.66 109 1.40 165 178 168 175 175 140 127 091 097 0.56 0.81 0.51 0.73 0.18 0.31 0.07 0.35 0.03 0.12 0.84.
October..
|
0.00008 053 117 175 198 1.98 189 188 175 160 1.50 1.28 123 120
20 110 109 107 107 109 104 077 036 005 114.
0.14
November 0 14 000 0'29 064 112 153 141 146 148 133 125 108 0.99 0.94 0.90 0.87 0.87 0.94 0.80 0.62 046 026 0.06 0.00 0.81
December 0.13 0.30 0.87 1°22 | 140 | 1°53 1·78 2.01 | 2°04 | 181 | 170 | 1°57 | 150 | 1°48 1°47 150 150 140 1'05 0·81 0°48 0*150*02 | 0·00 1*15
Means
...
| | |
0'14 025 0·61 0·96 | 123 | 145 | 1·60
1·69 174 1·69 | 149 | 1°44| 1°28 | 1′18 | 1°09 || 108
1.02 1.02 0.79 0.72 0.79 0.80 0.54 0.27 104
I


'00
5h. 6h.
'00 '00 *00 '00 '00
'00 '00 '00
Cape of Good Hope.-Mean Diurnal variation of the Intensity in each month of the year, from April 1841 to June 1846.
Increasing numbers denote increasing intensity.
The numbers express the changes in parts of the whole Force. Approximate Total Intensity 7.5.
Noon.
Mean time Oh. 1h. 2b. 3b. 4h
Daily
Midn.
|
|
7h 8h. 9h. 10h. 11. 12h. 13h. 14h. 15. 16. 17h. 18h. 19h. 20h. 21h. 22b. 23h. means.
00 '00 '00 '00
'00
'00 '00 '00 '00 '00
00 '00 '00 '00
003
March
January
018 031 041 047 048 039 036 038 040
February. 000 Ooo 020 047 069 083
OOO 007 027 052 070 079
044
045 047 049 050 052
061
071 079 078 056 028 005 042
076
072
068
069
071
071
074
075
078 076
077
080
092
115
127
105
062 026 068
074
069
064
064
067
066
070 068
066| 068|
068
068
081
103
119
094
047
011 063
April……….
000
017 040 058 070 071
068
065
060 059
059
060 060 059 060 063
061
060
065 083
102
093
May
003
000 008 019 036 038
035 028 025 023
021
02 I
008
OOO!
003 015 029 030
026
02 I 017
014
009 004 005 016 032 033
026
023 018
013
022
017 ΟΙΟ OIC
OIO 007 007
020 020
019 019
018
013
059 021
050 020 025
059
007] 009
007 008
007 ΟΙΟ 008 004
009 008
039 017 015
June
July
007 OOO
026 056 063
003 030 041
005 027 043 041
023 016
August 028 013 007 ΟΙΟ 028 035 029 024 019 016 017 016 016 016 017 013 013 009
009 044 061 064 044 023
September 007 000 005 015 023 028 021 2017 013 012 013 012 019 015 020 014 019 008 005 018 051 057 050 023 019
October..
009 033 057 070 064 053 047 045 047 047 049 051 055 056
088 084 060 025 005 050
November 000
000 005 021 038 049 057 048 044 043 044 044 047 050 053 057 052 074 090 096 082 054 022
December 000 003 015 029 037 035 034 030 027 026 028 031 035 036 038 042 047 060 074 076 066 042 013
Means
0401
005 005 017 032 046 050 045 040 036 035 036 036 038 038 040 040 040 043 047 058 072 064 042
000
056
056 056 060 073
Mean Temperature of the Air from April 1841 to June 1846 inclusive. Fahrenheit's scale.
January.. 73-1673-3073-0372:43 71 52 70-3067-9466-1165-4565-0164-51
June
•
•
•
•
64-1063-7763-5463-3263-0662-8563-1865-2067-24
•
•
•
•
•
•
•
•
•
·
007 047
000
034
017 461
·
·
•
68-7870-0571-4672-5967-58
February. 74 0474 07 73 63 72 85 71 74 70 3668 2066 69 66 13 65 75 65 34 64 93 64 54 64 23 64.00 63 6063 41 63 1264 46 66°33 67 94 69°72 716273*1067'91
March 71 74 72 40 72 1971-4069 9668 0765 98 64.98 64°38 63 69 63 2062 8562 37 62 06 61 69 61 4461 1560 97 61 3163 0365 39 67 48 69.50 710065.76
April......68 39 68.94 68.90 68 06 66 56 64 22 62 69 62 13 61 54 60 98 60 46 59 87 59°53 59 27 5900 58.80 58.40 58 28 58 1759 4961-82 64 1465 95 67 35 62 62
May 62.32 62 55 62 43 61 7460 49 58.99 58 08 57 41 56.81 56.39 55 85 55 48 55 37 55 21 55 05 54 81 54 59 54 32 54 04 54 44 56 42 58 48 60.0961 29 57.61
58.45 58.79 58.78 58 32 57'01 55 58 54 79 54 25 53 71 53 25 52 77 52 32 52 16 51-8651 69 51 53 51 21 50 95 50 80 50.83 52 2054 42 56 17 57 42 54 14
59'15 59 66 59'65 59 21 57 77 56°13 55 15 54 47 53-83 53 34 52.86 52 37 52°08 51.7251 42 51 19 50.96 50.83 50 51 50 88 52 67 54 94 56.87 58 28 54°41
August 58.86 59 23 59 07 58 61 57 61 55 91 5501 54 35 53 91 53 60 53 1752 91 52 71 52 31 52 075187 51 54511951 1551 88 53 1955 57 57 05 58 30 5463
September 61-60 61-7961 68 60 87 59 65 58 02 56 78 5609 55 62 55 22 54 58 54 47 54 36 53 95 53 64 53 31 53 10 53 20 53 13 54 94 56.90 58.61 59'94 60'94 56'77
October... 65 48 65 71 65 46 64 66 63.38 61 56 59 51 58-68 58 05 57 51 57 14 56 74 56 70 56 33 56 11 55.88 55-64 55 63 57 14 59'08 6100 62 7564 0765'04 59'97
November 68.00 68 03 67.63 66 98 66 1964 82 62 49 61 12 60 38 59.99 59 52 59 12 58.82 58 43 58.00 57 69 57 48 58 14 60 55 62.5063 9665 27 66 50 67.50 62.46
December (71-02 71*2370-8470-2169-6368·2365*6963′94|63 1962-64 62-07615961*1860-8260*4960*17 59′91 60-8363-4165-8067-1768-4269'62 70°4265′35


July
...
•
•
•
•
•
·
·
•
U
•
·
•
•
D
•
•
•
•
·
•





St. Helena.-Longitude 5° 40' West. Latitude 15° 56' South. Declination 23° 36′ West. Inclination 21° 40' South.
Mean Diurnal variation of the Declination for the years 1841 to 1845 inclusive.
Increasing numbers denote increasing eastening of the north or upper end of the needle. Mean Declination 23° 36'6 W.
Noon.
Midn.
Daily
Mean time Oh. 1b. 2h. 3h. 4b. 5h. 6h. 7h 8h. 9h. 10h. 11h. 12h. 13h. 14h. 15. 16. 17. 18h. 19h. 20h. 21h. 22h. 23h. means.
-
173 168
2.83 2.75
270
January.. 372 319 241 203 2.09 1.84 192 241 2.80 2.90 2.86 2.81 2.63 2°43 223 201
February. 453 451 411 339 2.80 2.55 2.61 302 321 335 348 352 342 322 312 298
March
| | |
376 4'11 348 2 57 215 220 2.48 2.64 2.69 2.68 2.85 2.84 2.80 2.77 2.68 2.70 2.69
April...... 328 248 165 127 103 101 123 150 156 1.60 171 1·81 | 1′96 | 192 | 1'92 2.00 2.16 2 22
May
June
|
157
1.50 0.59 0.00057 175 315 213
2.64 114 0.00 0.31 1.52 3.34 285
2.96 1'90 0.26 0.00 113 272 249
247 2.15 0.62 0.00 0.82 2'57 170
| | | |
0'71 044 0'57 071 055 021 025 048 0.56 0.72 0.78 0.90 1'02 1.09 III 118 132 204 2.58 1.50 0.32 0.00 0.49 0.88
0.71 0.73 0.88 094 0'44 000 0.10 0.39 0.56 0.73 0.90 106 117 122 125 129 140 166 2 16 3.31 2.69 139 075 0.69 110
July 0'82 071 078 084 0°48 002 000 0'22 046 0.64 0.84 0.98 1'08 114 114 124 131 1'46 2.02 311 2°58 131 0.63 0.67 102
August 0.11 0.00 0°40 0.86 0.82 0.42 0.25 0.52 0.68 0.78 0.88 102 102
| | | |
102 104 118 127 161 237 343 2 52 1'19 0'360'050'99
September 089 0.85 0.65 044 035 028 c28 053 0·62 0.67 0.79 0.78 0.75 0.64 0.61 0.65 0.70 0.95 2.12 1.89 0.85 0.17 000 0'430'70
October... 441 435 343 2.06 1°23 1°32 1.80 204 2.21 234 245 243 | 2°23 | 2.00 192 1.81 172 174 199 049 0.00 0.72 2.08 3.61 2.10
November 3'97 382 3.31 2.52 185 185 2.29 277 299 313 321 3′13 2.96 2.68 2.46 2.22 1'97 1.80 1.53 0.21 0.00 103 222 341 239
|
December 3.65 3.48 2.70 1'94 166 185 215 2.58 2'93 3 12 3.20 3.13 2.89 2.64 240 217 1'93 173 1.38 0.32 0.00 0.86 2.09 332 2.25
May
Ο
Mean Diurnal variation of the Inclination in each month, from January 1841 to December 1845.
Increasing numbers denote increasing inclination. Mean Inclination 21° 40′ South.
January.. 014 046 107 | 1°49 2·18 253 277 291 287 2.83 277 263 240 223 199 185 180 177 165 137 0.88 0.53 0.00 0.02 1″71
February. 0'23 0.61 133 2.00 2.39 2.78 301 315 312 298 2.86 2.73 2.61 246 244 2.21 2.15 2.00 2.04 1.82 140 094 0'10 000 1'97
March
|
O'11 056 133 186 221 247 2.80 2.97 2.99 2.89 2.89 2.67 246 237 2.26 2 12 1'99 2.01 184 153 106 0'430'000'10 183
|
April...... 045 089 1'54 2 14 253 283 305 317 326 2.88 2.97 2.63 241 218 215 2:08 188 177 147 130 094 043 027 000 1.88
| |
0'200'74 116 162 1'90 210 2 22 2.36 2.28 2.21 2 12 1'99 | 177 | 169 | 156 133 121 116 118 109 0.81 0.36 0.00 0.03 1*38
June 0*180°56 104 158 165 191 2°21| 2°26 2 24 2*12 202 198 2:06 177 168 154 1'46 1°36 1′22 098 0.80 0.43 0.09 0.00 138
July
| |
0.30 0.60 106 144 182 201 242 247 240 2.35 2.21 2'04 180 158 152 130 125 1.08 1.00 0.84 0.53 0.27 0.00 0.03 135
August 0.25 0.72 121 161 1′94 2.16 | 2°35 2.40 2°39 2°19 2·12 | 1′98 1.80 1.69 1°58 1.40 1°33 125 113 107 079 054 019 000 1'42
September 0.18 0.70 129 172 2.02 2'19 240 240 2°32 213 2011'99 | 1*80 | 1·68 | 1°47 150 151 144 140 127 0.92 0.60 0.36 0.00 14.7
| | |
|
October... 0'24 074 136 190 2.34 2.56 2.55 2.88 2.65 2.56 2.46 2.28 2.09 2.04 1.89 1.80 170 169 1.63 1.31 0.88 0.37 0.00 0.02 1.66
November 008 0.27 0.74 119 163 2.00 2.35 245 2.38 2.30 2.18 2.07 196 1.83 171 159 166 148 135 092 055 0.23 0.00 0.10 1'38
| |
| |
| |
| | |
December 026 073 106 159 2.08 2.41 2.69 2.78 2.61 245 239 215 2.01 180 172 1.56 148 138 1.26 0.85 0.40 0.10 0.00 0.07 149
Means
220.63
| | | | | |
|
0'22 0·63 1·18 1.68 2.06 2.33 2.57 2.68 2.63 249 2.42 2.26 2.10 1'94 1·83 1·69 | 1·62 1'53 | 143 | 1°20
083 044 0.08 0.03 1'58











Noon.
Mean time Oh. 1h. 2h. 3h. 4h. 5h. 6h. 7h.
'00 *00 '00 '00 '00 '00
St. Helena.-Mean Diurnal variation of the Total Intensity in each month, from January 1841 to December 1845.
Increasing numbers denote increasing intensity.
Midn.
Daily
|
8h. 9h. 10h. 11b. 12h. 13h. 14b. 15h. 16h. 17. 18h. 19h. 20h. 21h. 22h. 23h. means.
'00
February
March
April
162 150
May
June
January 130
129 116 098 081 063 046
117 109 092 077 063 050 029
153 147 124 096 070 055 032 020 ΟΙΟ OOO 006
122 088 068 042 021 ΟΙΟ 005
163 142
115 087 065 049 036 023
141 128 101 064 063 047 028
027 016 004 OOO!
014 007 ΟΟΙ 002 003
'00 '00 '00 '00 '00 '00
ΟΟΙ
'00
'00
*00
'00 *00 '00 '00 '00 '00 '00 '00 '00
002
001
004 000
016
ΟΙ Ι
004 000
015
006
006
004
ΟΟΙ 000
July
August
...
126 117
095 073 051 042 027
139 126
103 077 053 038 026
September 143 131 105 077 056 037
October
135 123 105
105
015 ΟΙΙ
002 002
013
004
ΟΟΙ 000
OOO
026 013
0041
003
007
ΟΙ Ι
007
Ooo
005
ΟΙΙ
020
007
002
009 ΟΙΙ
OI I
OO I
008 015 015 019 019 024 040 055 080
004 002 OOO 002
003 009 023 046 070
004 OOI 016 014 018 018 021 026 040 068 102
007 014 015 016 025 024 024 031 054
008 008 01I 018 019 019 025 034 048
002 003 004 004 004 009 013 022 042
003 005 006. ΟΙΙ 015 018 019 024 038
002 005 009 015 015 016
014 018 024 022 024 023
2013 019
020
019
017 032 058 093
016 017 017 017
109 124 051
095
114 039
132
149 055
090 102 150 051
095
132
159 054
075
IIO
137 043
068
097
116 041
016 018 037 068
103
131 039
ΙΟΙ
022 038 069
01
134 046
123
135 050
026 048 071 087
105 112 048
107 117 045
December
ΠΟΙ
088 070 051 030 015
November I 12 III ΙΟΙ 090 076 055 029 018
116 IIO 105 089 071 051 027 ΟΙΙ 004 OOO OOO 003 003
006 008 ΟΙΟ ΟΙΙ 012 024 046 064 086
136 127 107 084
107 084 066 048 030 016 008 002 002 003 006 009 011 014 015 017 021 032 052 082 110 132 047
Mean Temperature of the Air from 1841 to 1845 inclusive.
၀၀3 ၀၀6 ၀၀၄ ၀II
Means
39
May
June
·
·
•
•
•
D
·
•
·
January.. 67-68 68-05 67.93 67-7967-30 66 04645863-39 62-93 62-62 62 42 62-27 62-06 61.88 61.6661-60 61-49 61.39 61 37 61 84 62-7964-09 65-3866-556398
February. 69 14 69 61 69-85 69 59 68.95 67-8966-5965 43 64 91 64-66 64 46 64 32 64 1363 96 63 7863 5963 51 63 44 63 42 63 62 64 43 65 72 67 08 68 24 65.87
March
69.13
69 57 69 8969'71 691 1068 10 66.86 65 84 65 47 65 1565.00 64.83 64 65 64 50 64 3164 1764 1564 03 64 05 64 29 65'08 66 39 67 35 68 38 66.24
April... 68.54 68.89 68.98 68 64 67 99 66 9865-84 65 15 64 84 64 61 64 45 64 29 64 11 64 02 63.8863.77 63.66 63 51 63 49 63 69 64 50 65 70 66.74 67.8665.60
65.76 66.01 66.09 65.84 65 17 64 11 63 56 63 3262 73 62 13 62.03 61.88 61 67 61 57 61 40 61 24 61*1961 1961 04 6106 62.01 63 22 64 11 65 22 63.05
62.40 62.76 62.73 62 39 61.83 6098 60 14 59 68 59 49 59 34 59 20 59 11 5900 58-86 58 74 58.61 58 56 58 53 58 47 58 52 59 13 60 16 60.98 61.80 60'07
July
60*3760.83 607760 51 59.87 58.98 58 14 57 70 57 48 57 25 57 13 56.91 56.81 56 72 56 6056·51 56 43 56 36 56 31 56.38 57.07 58.09 58.90 59.69 57'99
August 59'68 59'99 60*12 5972 59 11 58 11 57 23 56.83 56.60 56 45 56.32 56 20 56 10 55 98 55 76 55.68 55 53 55 50 55 39 55 56 56 2057 22 58.07 58.96 57 17
September 59.89 60 26 60 18 59 77 59 11 58 03 57 05 56 56 56.35 56 21 56 04 55 91 55 8255 67 55 51 55 37 55 29 55 21 55 21 5544 56 12 57 18 58 31 59'14 57°07
October... 61 5061 98 6191 61 31 60 46 59°31 58 18 57 57 57 64 57 12 56.99 56.84 56 64 56 48 56 30 56 18 56 11 56 01 56 06 56 50 57.38 58.61 59 71 60 73 58°23
November 63 44 63.88 63.97 63 52 62 63 61 32 59 94 59 11 58 76 58 57 58 41 58.24 58.08 57 90 57.71 57.62 57 55 57 43 57 53 5803 58.94 60 2061 3562 35 59.84
65-7264-8863-62 62*17 61*1060-70 60°46 60′27
December 65 1965.81 65.87 65-72 64.88 63 62 62 1761 10 60 70 60 46 60 27 60 12 59′95 59 75 59 57 59 47 59 34 59 31 59 39 59'77 60 69 61 97 6303 64 19 61 77
59′75 59°57 59′47 5931 606961′97 630364-1961-77
...
•
•
·
•
•
·
.
·
•
·
•
•


VOL. III.
Singapore.-Latitude 1° 16' N. Longitude 103° 53' E. Declination 1° 40′ E. (Approx.).
Inclination 12° S. (Approx.)..
Mean Hourly oscillation of the Magnetic Declination for each month of the years 1843, 1844 and 1845.
Increasing numbers denote a movement of the north or upper end of the magnet towards the East.
Noon.
Midn.
Daily
|
Mean time 01. 11. 21h. 31. 41. 51. 61. 71. 8. 9. 10. 11h 12h 13h 14h 15h 16h 17h 18h 19h 20h 21h 22h. 231. means.
March
April
May
June
...
1'43
0.82
116
1
January 204 252 279 272 252 224 211 218 204 1.97 1.84 170 1.63 1.63 1.50 1.43 129 102 0.61 0.00 0.00 0.41 0.82 122 1'59
292 313 306 2.79 2.52 2·31 2°31 2∙18 204 190 190 1'97 | 1′90 | 190 190 1.84 170 1°29 | 0'540'000'000'34 143 | 1·84
February. 2°31
129 143 163 177 163 143 129 109 0.95 0.88 0.82 0.82 0.88 0.88 0.88 0.82 0.82 0.82 0.82 0°48 0'000'07 0'54 102 096
0.34 0.61 0.75 1'02 116 116 0.95 0.82 0·61 0'54 0.61 0.68 0.82 0.95 095 095 0.88 0.82 1*16 095 034 0.00 0.20 041 070
|
|
| |
0.07 0.48 0.82 1'16 1°36 095 1.02 0.88 0.75 0.68 0.75 0.82 1.09 1*16 129 136 136 211 224 143 0.68 0.27 0.00 075
| |
0°20 041 054 061 0'540'34 0.14 0.00 0.00 0.00 0.07 0.20 0.41 0.54 0.61 0.68 0.68 1°36 1.56 0.82 0°41 0·00 0·14 0°46
July
0°07 0'41 0.61 0.88 102 0.88 0.48 0.34 0.27 0.20 0.27 0.34 0.54 0.68 0.82 0.75 0.82 163 1'97 1'29 054 0.14 0.00 0.67
August ... 0.20 0.68 102 156 1.63 184 143 129 1'09 1'02 102 116 122 1°36 1°43 1'50 150 170 2.52 2'79 1'77 0.75 0.14 0.00 1*27
| | | |
September 0.48 0.88 1.36 163 1.63 156 150 129 116 109 102 109 116 122 129 129 136 143 1'97 177 075 0.20 0.00 0.20 1*14
October I'90 231 231 218 197 177 177 163 1.50 1.36 129 129 1°43 136 136 129 122 1'09 1'16 0'54 0.14 0.00 0.27 102 133
| |
| | |
November 245 292 299 2.86 245 211 197 184 170 156 136 136 143 143 136 1°29 116 102 048 0.00 0.00 0.27 0.82 163 1'51
December | | |
2*52 | 2·99|2′99 | 299 2.86 2:45 218 204 1'97 184 170 163 156 1-56 156 1.50 143 116 061 0.00 0.00 0.41 102 177 170
Y
May
June
...
Ο
Mean Diurnal variation of the Inclination in the several months during the years 1843, 1844 and 1845.
Increasing numbers denote increasing inclination. Approximate inclination 12° South.
| | |
|
| | |
|
January.. 0.00 0.43 0.98 1·28 | 190 2.07 2.38 2.57 2.62 271 276 276 2.66 271 271 272 272 272 273 2·52 197 109 0.32 0.02 197
February. 004 0.64 124 1.75 2.00 2.21 2 56 2.82 2'94 302 3'10 307 308 303 298 299 297 297 3'03 2.88 2.35 1.21 0.40 0.00 2*22
March 0.06 0.29 0.75 136 175 1.88 2′22 255 265 270 274 272 272 2.67 271 272 272 275 275 254 184 075 0.11 0.00 191
April 028 0.82 154 2'09 2'47 271 304 300 327 3′36 341 349 343 340 333 329 329 327 315 292 2.18 1.15 0.28 0.00 2.46
0.00 0.32 0.80 1.17 1.62 | 196 2′29 234 242 243 242 2.20 2.38 240 242 246 2.52 | 2′51 | 225 1.87 125 049 0.03 0.00 169
| | |
0.04 0.20 0.57 0.98 144 1.50 220 225 2′19 2·16 2′10 2'07 215 2′21 2°15 2°20 221 2′29 202 171 125 0.69 0.22 0.00 153
0.00 0.15 0.45 0.89 134 176 2.10 2.16 2.19 220 220 2.07 218 219 219 221 2*21|2°27 2*02 1'74 128 069 027 005 153
August
| |
...O'12 0°34 069 101 135 168 199 2°32 221 227 2′26 2.28 | 2·26 2.20 2.18 222 221 222 193 1·68 1.30 0.62 0.14 0.00 1.56
September 041 100 160 194 2 11 232 258 269 278 2.82 2.85 2.84 2.85 279 274 275 275 279 266 2.39 1.66 0.79 0.15 0.00 2.09
October 0.38 117 1'94 2.38 2.48 2.59 2.86 307 323 329 3'34 323 333 323 3 22 3.20 324 320 325 296 2.18 1.14 0.21 0.00 246
| | |
November o'16 063 137 196 2.32 2.68 2.88 2.87 302 308 307 306 306 303 302 295 301 300 315 2.80 201
2.80 2011'04 0'17 0.00 2.26
December o'09 054 113 1.62 192 2.26 253 2.66 2.85 2.86 2.85 2.86 276 276 272 2.69 2·65 2.69 244 2.38 1.81 1.08 0.34 0.00 2.02
0'13 0'54 1'09 154 1.89 2 14 2'47 2.61 2'70 274 276 272 274 272 2.70 2.70 271 272 2·62 | 2'37 1.76 0.89 0.22 0.01 198
Means
July
...
·

March
April..
May
June
ΟΙΟ
ΟΙΙ
July
007 007
...
October. 102
November
December
Means
...
073 050 036 029
080 063 044 030
077 061 044 031 026 021 012
033 022 019 OII
098 075 052 033
021
002
007
008 007
033
002 000 OOI 005 005 009 ΟΙΙ 014 025 049
114 085 055 035 026 020 013 007 003 OOI 000 002 005 008 007 009 ΟΙΙ 012 012
122 094 065 040 029 020
016 ΟΙΙ 005 003 005 002 000 004 009 OII
020
104 081 060 036 020
ΟΙΙ
013 014 OII
006 006
OOO 004 006 006 006 008
096 075 051 026 011 042 004 004 ΟΟΙ Ooo
003 004 004 008
100 081 056 033 019 013
004 004 002
004 006 004 010 015
August IOI 081 055 033 016 009 ΟΙΟ 005 006 000 002 002 004 ΟΙΟ OII ΟΙΙ 016 018
September 093 065 037 029 018 009 009 008 002
003 003 008
014 018 019 017
017 023
024 013 007 003
006
016 019 017
015 009 003 ΟΟΙ OOO ΟΟΙ 000 002
004 000 000 OOI 002 003
007 004 002
004 002 002 001
Singapore.-Mean Diurnal variation of the Total Intensity in the several months during the years 1843, 1844, 1845.
Increasing numbers indicate increase of total intensity.
The numbers express the changes in parts of the whole force. Approximate total intensity 8.21.
Noon.
Midn.
Daily
|
Mean time 04h. 11. 21h. 31h. 41h. 51h. 6h1. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17h 18h 19h. 204h. 214h. 224h. 234. means.
··
'00
'00
'00 '00
'00
'00
'00 '00 '00 '00
'00 '00 '00 '00 '00 '00 '00 *00 '00 '00
January. 086 066 047 030 028 021 015 009 009 003 002 Ooo
February. 099 080 061 042 027 024 013 008 004 OOO
'00
'00 *00 '00
ΟΙΟ
012
022
054
074
099
100
031
082
103 IIO 032
013
015
012
027 057
043 076 IIO
087
112 122 035
139
137 041
025
044 073 097
114
118 036
000
000
000 ΟΟΙ ΠΟΙ
002
020 038 062
085
102
105 031
ΟΙΟ
026 044 070
091
105
110 034
028 046 077 096
115
114 036
000
ΟΟΙ OOO
000
045 079 104
117
115 035
OO I
ΟΙ Ι
ΟΙΙ
037 070 ΙΟΙ 117
006 007 013 012 013 017 034 059 082
020
121 037
095 029
006 008 010 012 014 021 038 065 091 110
112
034
May
June
..
O
0031
098
006 009 013 014 014 019 035 056 078 095 091 030
Mean Temperature of the Air observed on the Standard Thermometer inside the Observatory,
O
O
о
82.1
during the years 1841, 1842 and 1843.
O
O
C
O
80.9
O
81°4
January 79°7 79.5 80.0 79.5 797 791 790 784 78.5 780 781 77.5 77.9 77.3 77.6 76.9 77.4 76.5 77.0 76.3 77.3 77.4 78.6 78.8 78.2
February. 807 816 812 821 812 82.1 80.2 80.6 797 802 792 796 78.6 790 783 78.6 78.2 782 777 782 780 794 796 81.8 79.8
March 814 821 817 82.3 81.6 820 809 815 80.5 81 2 801 810 799 806 79'4 803 79°1 799 787 79.8 79.4 80.6 80.6 815 80.7
April..... 818 818 821 818 819 816 814 812 810 809 80*7 80.2 80.3 80.3 79'9 800 79'5 796 792 798 799 806 811 814 808
82.5
82.7
82.5
81.8
814
80'9
805
80°3
79.9
81.8
82.5 82.9 82.7 83.1 82.5 82.7 82.2 82.0 817 816 814 814 812 812 807 80.7 80.3 80.2 801 804 810 817 81.8 82.6 816
July 824 830 82.8 83.1 82.7 82.7 82.2 82.1 81.8 819 815 815 811 812 807 809 80.3 80.6 80.8 80.8 80.8 819 819 82.6 817
August 817 819 819 819 818 818 814 813 810 812 80.8 80.8 80.4 80.3 80.1 80.1 79.8 79.8 79.5 79.8 80.2 80.8 81.2 81.6 80.9
September 82.1 82.6 82.4 82.3 82.2 82.1 817 816 815 812 81.0 80.8 80.5 803 801 800 797 797 794 794 803 809 814 818 81'0
October.. 81.5 81.3 817 814 817 812 812 80.6 80.7 80.2 80.1 79.8 79.6 798 794 793 790 79'3 78.7 792 795 800 80.7 80.9 80.3
November 811 810 81.3 80.8 81.0 80.6 80.4 801 801 797 797 796 793 791 789 78.7 78.6 78.5 78.4 78.5 79.2 79.6 80.2 80.5 79.8
December 810 81.3 81.3 81.3 80.9 80.8 80.2 800 79'6 794 792 792 790 790 78.6 78.4 781 781 779 78.2 78.7 79.5 80*180*7 796
Means
815 817 818 818 816 815 811 809 80.7 80.5 80.3 801 799 798 79°5 794 792 791 789 791 796 80.2 807 81°3 804




...
323
On Atmospheric Magnetism.
[Royal Institution Proceedings, April 11, 1851.]
ON a former evening (January 24) it was shown that oxygen
gas was magnetic, being attracted towards the poles of a magnet;
and that like other magnetic bodies, it lost and gained in power
as its temperature was raised and lowered, and that the change
occurred within the range of natural temperatures. These pro-
perties it carries into the atmosphere; and the object, this
evening, was to show how far they might be applied to explain
certain of the observed variations of the terrestrial magnetic force.
If a source of magnetic power be considered (as a magnet), it
presents us with a system having polarity; and if the parts which
are called the poles be taken as representing the most concen-
trated condition of the polarity, then the contrary polarities,
manifest externally in relation to the magnet, are perfectly defi-
nite, being exactly equal to each other. If the magnet be
irregular in the disposition of its force, still the same definite
character of the sum of the contrary polarities holds good.
External to the magnet those concentrations which are named
poles may be considered as connected by what are called mag-
netic curves, or lines of magnetic force, existing in the space
around. These phrases have a high meaning, and represent the
ideality of magnetism. They imply not merely the directions of
force, which are made manifest when a little magnet, or a crystal
or other subject of magnetic action is placed amongst them, but
those lines of power which connect and sustain the polarities,
and exist as much when there is no magnetic needle or crystal
there as when there is; having an independent existence ana-
logous to (though very different in nature from) a ray of light
or heat, which, though it be present in a given space, and even
occupies time in its transmission, is absolutely insensible to us
by any means whilst it remains a ray, and is only made known
through its effects where it ceases to exist. The form of a line
of magnetic force may vary exceedingly from a straight line to
every degree of curvature, and may even have double and com-
plicated curvatures impressed upon it. Its direction is deter-
mined by its polarity, the two changing together. Its powers
are such, that a magnetic needle placed in it finds its place of
Y 2
324
[APRIL 1851.
Atmospheric magnetism.
rest parallel to it; a crystal of calcareous spar turns until its
optic axis is transverse to it; and a wire which is unaffected
when moved in or along it, has an electric current evolved the
instant that it passes across it: by these and by other means
the presence of the magnetic line of force and its direction are
rendered manifest.
The earth is a great magnet; its power, according to Gauss,
being equal to that which would be conferred if every cubic yard
of it contained six one-pound magnets; the sum of the force
therefore is equal to 8,464,000,000,000,000,000,000 such mag-
nets. The disposition of this magnetic force is not regular, nor
are there any points on the surface which can be properly called
poles: still the regions of polarity are in high north and south
latitudes; and these are connected by lines of magnetic force
(being the lines of direction) which, generally speaking, rise out
of the earth in one (magnetic) hemisphere, and passing in varied
directions over the equatorial regions into the other hemisphere,
there enter into the earth to complete the known circuit of power.
A free needle shows the presence and direction of these lines.
In London they issue from the earth at an angle of about 69°
with the horizon (being the dip or inclination); and the plane
in which they rise forms an angle of 23° W. nearly with true
north, giving what is called west declination. Where the dip
is small, as at the magnetic equator, these lines scarcely rise out
of the earth and pass but a little way above the surface; but
where it is large, as in northern or southern latitudes, they rise
up at a greater angle, and pass into the distant realms of space,
from whence they return again to the earth in the opposite
magnetic hemisphere; thus investing the globe with a system
of forces like that about an ordinary magnet, which, wherever it
passes through the atmosphere is subject to the changing action
of its magnetic oxygen. There is every reason to believe that
these lines are held in the earth, out of which they arise and by
which they are produced, just as the lines which originate in a
magnet are held by it, though not in the same degree; and that
any disturbance from above affecting them will cause a greater
change in their place and direction in the atmosphere and space
above, than in the earth beneath.
The system of lines of magnetic force around a magnet or the
earth is related by a lateral tension of the whole, analogous in
APRIL 1851.]
325
General principles.
some degree to the lateral tension of lines of static electrical force;
both the one and the other being easily made manifest by experi-
ment. The disturbance of the tension in one part is accompanied
instantly by a disturbance of the tension in every other part; for
as the sum of the external powers of a system, unaltered at
its origin, is definite and cannot be changed; so any alteration
either of intensity or direction amongst the lines of force at one
place, must be accompanied by a corresponding change at every
other. So if a mass of soft iron on the east side of a magnet
causes a concentration of the lines of force from the magnet on
that side, a corresponding expansion or opening out of the lines
on the west side must be and is at the same time produced; or
if the sun, on rising in the east, renders all the oxygen of the air
on that side of the globe less magnetic and less able therefore to
favour the transition of the lines of terrestrial force there, a
greater number of them will be determined through the western
region; and even though the lines of force may be doubted by
some as having a separate existence such as that above assumed,
still no error as to the effects on magnetic needles would in that
case be introduced, for they by experiment would be and are
the same.
The power of a magnetic body as iron or oxygen to favour
the transmission of lines of force through it more than other
bodies not magnetic, may be expressed by the term conduction.
Different bodies, as iron, nickel, oxygen, conduct in various
degrees, and not only that, but the same body as iron or oxygen
conducts in different degrees at different temperatures. When
space traversed by uniform lines of magnetic force is occupied
by a uniform body as air, the disposition of the lines is not
altered ; but if a better conducting substance than the air is
introduced, so as to occupy part of the space, the lines are
concentrated in it, and drawn from other parts, as shown by
P, P in the figure, or if a worse conducting substance is intro-

D
P
duced, the lines are opened out as at D, D. In both cases the
326
[APRIL 1851.
Atmospheric magnetism.
lines of force are inflected, and a small magnetic needle standing
in them at the inflected part would have its direction changed
accordingly. Experimental illustrations of these changes in
direction are given in Mr. Faraday's paper in the Philosophical
Transactions for 1851, Part I. par. 2843, &c.
Now this by the hypothesis is assumed to take place in the
atmosphere. Supposing it all at mean temperature, the lines of
force would have the direction determined by the arrangement
of the power within the earth. Then the sun's presence in the
east would make all the atmosphere in that region a worse con-
ductor, and cause it to assume the character of D; and as the
sun came up to and passed over the meridian and away to the
west, the atmosphere under his influence would bring up changes
in direction like those shown in either D or D; it would there-
fore manifestly set a needle in a given latitude in opposite direc-
tions as it passed by; and as evidently set two needles in north
and south latitudes in opposite directions at the same moment
of time. As the night came on and a temperature lower than
the mean came up from the east and passed over, the lines of
force would be inflected as in P or P, and a reverse variation
of the needle to that which occured before would now take place.
That natural effects of variation must be produced consequent
upon the magnetic nature of oxygen and its daily variations of
temperature is manifest; but whether they cause the observed
variations, or are competent to do so, is a question that can only
be decided after very careful inquiry. Observations are now
made on the surface of the earth with extreme care in many
places, and these are collated, and the average or mean result,
as to direction and intensity of the earth's force, ascertained for
every hour and season; and also many remarkable, anomalous,
and extra results evolved. A theory of the causes of any or all
of these variations may be examined first by the direction which
the varying needle does or ought to assume, and then by the
amount of the variation. The hypothesis now brought forward
has been compared with the mean daily variation for all the
months in the year at north and south stations, as Toronto and
Hobarton, and at many others near to and far from the equator,
and agrees in direction with the results observed far beyond what
the author anticipated. Thus the paths described by the upper
ends of free needles in the north and south hemispheres should
APRIL 1851.]
327
General principles.
be closed curves, with the motion in opposite and certain direc-
tions, and so they are:-the curves described by needles in north
or south latitudes should be larger in summer and smaller in
winter, and so they are:-a night or cold action should grow
up in the winter months, and such is the case: the northern
hemisphere ought to have a certain predominance over the
southern, because of its superior temperature, and that is so :—
the disposition of land and water ought to have an influence,
and there is one in the right direction :-so that in the first
statement and examination of the hypothesis it appears to be
remarkably supported by the facts. All these coincidences are
particularly examined into and stated in the Philosophical Trans-
actions already referred to. The next step will be to ascertain
what is the amount of change in the conducting power of the air
for given changes of temperature, and then to apply that in the
endeavour to ascertain whether the amount of change to be
expected is (as well as the direction) accordant with that which
really occurs.
328
TWENTY-EIGHTH SERIES'.
§ 34. On lines of Magnetic Force; their definite character; and
their distribution within a Magnet and through space.
Received October 22,-Read November 27 and December 11, 1851.
3070. FROM my earliest experiments on the relation of electri-
city and magnetism (1.14. note), I have had to think and speak
of lines of magnetic force as representations of the magnetic
power; not merely in the points of quality and direction, but
also in quantity. The necessity I was under of a more frequent
use of the term in some recent researches (2149. &c.), has led
me to believe that the time has arrived, when the idea conveyed
by the phrase should be stated very clearly, and should also be
carefully examined, that it may be ascertained how far it may
be truly applied in representing magnetic conditions and pha-
nomena; how far it may be useful in their elucidation; and,
also, how far it may assist in leading the mind correctly on to
further conceptions of the physical nature of the force, and the
recognition of the possible effects, either new or old, which may
be produced by it.
3071. A line of magnetic force may be defined as that line
which is described by a very small magnetic needle, when it is
so moved in either direction correspondent to its length, that
the needle is constantly a tangent to the line of motion; or it is
that line along which, if a transverse wire be moved in either
direction, there is no tendency to the formation of any current
in the wire, whilst if moved in any other direction there is such
a tendency; or it is that line which coincides with the direction
of the magnecrystallic axis of a crystal of bismuth, which is car-
ried in either direction along it. The direction of these lines
about and amongst magnets and electric currents, is easily
represented and understood, in a general manner, by the ordi-
nary use of iron filings.
1 Philosophical Transactions, 1852, p. 1.
OCT. 1851.]
329
Definition of lines of force.
3072. These lines have not merely a determinate direction,
recognizable as above (3071.), but because they are related to a
polar or antithetical power, have opposite qualities or conditions
in opposite directions; these qualities, which have to be distin-
guished and identified, are made manifest to us, either by the
position of the ends of the magnetic needle, or by the direction
of the current induced in the moving wire.
3073. A point equally important to the definition of these
lines is, that they represent a determinate and unchanging
amount of force. Though, therefore, their forms, as they exist
between two or more centres or sources of magnetic power, may
vary very greatly, and also the space through which they may
be traced, yet the sum of power contained in any one section
of a given portion of the lines is exactly equal to the sum of
power in any other section of the same lines, however altered in
form, or however convergent or divergent they may be at the
second place. The experimental proof of this character of the
lines will be given hereafter (3109. &c.).
3074. Now it appears to me that these lines may be employed
with great advantage to represent the nature, condition, direction
and comparative amount of the magnetic forces; and that in
many cases they have, to the physical reasoner at least, à supe-
riority over that method which represents the forces as concen-
trated in centres of action, such as the poles of magnets or
needles; or some other methods, as, for instance, that which
considers north or south magnetisms as fluids diffused over the
ends or amongst the particles of a bar. No doubt, any of these
methods which does not assume too much, will, with a faithful
application, give true results; and so they all ought to give the
same results as far as they can respectively be applied. But
some may, by their very nature, be applicable to a far greater
extent, and give far more varied results, than others. For just
as either geometry or analysis may be employed to solve cor-
rectly a particular problem, though one has far more power and
capability, generally speaking, than the other; or just as either
the idea of the reflexion of images, or that of the reverberation
of sounds may be used to represent certain physical forces and
conditions; so may the idea of the attractions and repulsions of
centres, or that of the disposition of magnetic fluids, or that of
lines of force, be applied in the consideration of magnetic phæ-
330
On lines of magnetic force, [SERIES XXVIII.
nomena. It is the occasional and more frequent use of the
latter which I at present wish to advocate.
On
3075. I desire to restrict the meaning of the term line of force,
so that it shall imply no more than the condition of the force in
any given place, as to strength and direction; and not to include
(at present) any idea of the nature of the physical cause of the
phænomena; or be tied up with, or in any way dependent on,
such an idea. Still, there is no impropriety in endeavouring
to conceive the method in which the physical forces are either
excited, or exist, or are transmitted; nor, when these by experi-
ment and comparison are ascertained in any given degree, in
representing them by any method which we adopt to represent
the mere forces, provided no error is thereby introduced.
the contrary, when the natural truth and the conventional repre-
sentation of it most closely agree, then are we most advanced in
our knowledge. The emission and the æther theories present
such cases in relation to light. The idea of a fluid or of two
fluids is the same for electricity; and there the further idea of a
current has been raised, which indeed has such hold on the mind
as occasionally to embarrass the science as respects the true
character of the physical agencies, and may be doing so, even
now, to a degree which we at present little suspect. The same
is the case with the idea of a magnetic fluid or fluids, or with the
assumption of magnetic centres of action of which the resultants
are at the poles. How the magnetic force is transferred through
bodies or through space we know not whether the result is
merely action at a distance, as in the case of gravity; or by some
intermediate agency, as in the case of light, heat, the electric
current, and (as I believe) static electric action. The idea of mag-
netic fluids, as applied by some, or of magnetic centres of action,
does not include that of the latter kind of transmission, but the
idea of lines of force does. Nevertheless, because a particular
method of representing the forces does not include such a mode
of transmission, the latter is not therefore disproved; and that
method of representation which harmonizes with it may be the
most true to nature. The general conclusion of philosophers
seems to be, that such cases are by far the most numerous, and for
my own part, considering the relation of a vacuum to the mag-
netic force and the general character of magnetic phænomena ex-
ternal to the magnet, I am more inclined to the notion that in the
:
OCT. 1851.] their recognition—by a moving wire.
331
transmission of the force there is such an action, external to the
magnet, than that the effects are merely attraction and repulsion
at a distance. Such an action may be a function of the æther;
for it is not at all unlikely that, if there be an æther, it should
have other uses than simply the conveyance of radiations (2591.
2787.). Perhaps when we are more clearly instructed in this
matter, we shall see the source of the contradictions which are
supposed to exist between the results of Coulomb, Harris and
other philosophers, and find that they are not contradictions in
reality, but mere differences in degree, dependent upon partial
or imperfect views of the phænomena and their causes.
3076. Lines of magnetic force may be recognized, either by
their action on a magnetic needle, or on a conducting body
moving across them. Each of these actions may be employed
also to indicate, either the direction of the line, or the force
exerted at any given point in it, and this they do with advan-
tages for the one method or the other under particular circum-
stances. The actions are however very different in their nature.
The needle shows its results by attractions and repulsions; the
moving conductor or wire shows it by the production of a
current of electricity. The latter is an effect entirely unlike that
produced on the needle, and due to a different action of the
forces; so that it gives a view and a result of properties of the
lines of force, such as the attractions and repulsions of the needle
could never show. For this and other reasons I propose to
develope and apply the method by a moving conductor on the
present occasion.
3077. The general principles of the development of an electric
current in a wire moving under the influence of magnetic forces,
were given on a former occasion, in the First and Second Series
of these Researches (36. &c.); it will therefore be unnecessary to
do more than to call attention, at this time, to the special
character of its indications as compared to those of a magnetic
needle, and to show how it becomes a peculiar and important
addition to it, in the illustration of magnetic action.
3078. The moving wire produces its greatest effect and indi-
cation, not when passing from stronger to weaker places, or the
reverse, but when moving in places of equal action, i. e. trans-
versely across the lines of force (217.).
332
On lines of magnetic force, [SERIES XXVIII.
3079. It determines the direction of the polarity by an effect
entirely independent of pointing or such like results of attraction
or repulsion; i. e. by the direction of the electric current pro-
duced in it during the motion'.
3080. The principle can be applied to the examination of the
forces within numerous solid bodies, as the metals, as well as
outside in the air. It is not often embarrassed by the difference
of the surrounding media, and can be used in fluids, gases or a
vacuum with equal facility. Hence it can penetrate and be
employed where the needle is forbidden; and in other cases
where the needle might be resorted to, though greatly embar-
rassed by the media around it, the moving wire may be used
with an immediate result (3142.).
3081. The method can even be applied with equal facility to
the interior of a magnet (3116.), a place utterly inaccessible to
the magnetic needle.
3082. The moving wire can be made to sum up or give the
resultant at once of the magnetic action at many different places,
i. e. the action due to an area or section of the lines of force,
and so supply experimental comparisons which the needle could
not give, except with very great labour, and then imperfectly.
Whether the wire moves directly or obliquely across the lines
of force, in one direction or another, it sums up, with the same
accuracy in principle, the amount of the forces represented by
the lines it has crossed (3113.).
3083. So a moving wire may be accepted as a correct philoso-
phical indication of the presence of magnetic force. Illustrations
of the capabilities already referred to, will arise and be pointed
out in the present paper; and though its sensibility does not
as yet approach to that of the magnetic needle, still, there is no
doubt that it may be very greatly increased. The diversity of
its possible arrangements, and the great advantage of that diver-
sity, is already very manifest to myself. Though both it and
the needle depend for their results upon essential characters and
1
¹ A natural standard of this polarity may be obtained, by referring to the
lines of force of the earth, in the northern hemisphere, thus:—if a person with
arms extended move forward in these latitudes, then the direction of the
electric current, which would tend to be produced in a wire represented by the
arms, would be from the right-hand through the arm and body towards the
left.
OCT. 1851.] their investigation-by experiment.
333
qualities of the magnetic force, yet those which are influential,
and, therefore indicated, in the one case, are very different from
those which are active in the other; I mean, as far as we have
been able as yet to refer directly the effects to essential charac-
ters and this difference may, hereafter, enable the wire to give
a new insight into the nature of the magnetic force; and so
it may, finally, bear upon inquires, such as whether magnetic
polarity is axial or dependent upon transverse lateral conditions;
whether the transmission of the force is after the manner of a
vibration or current, or simply action at a distance; and the
many other questions that arise in the minds of those who are
pursuing this branch of knowledge.
Fig. 1.
3084. I will proceed to take the case of a simple bar magnet,
employing it in illustration of what has been said respecting the
lines of force and the moving conductor, and also for the purpose
of ascertaining how these lines of force are disposed, both
without and within the magnet itself, upon which they are
dependent or to which they belong. For this purpose the fol-
lowing apparatus was
employed. Let fig. 1 re-
present a wooden stand,
of which the base is a
board 17.5 inches in
length, and 6 inches in
breadth, and 0.8 of an
inch in thickness: these
dimensions will serve as
a scale for the other parts.

K
Ľ
H I
P
F
D
A
K
B
A B are two wooden uprights; D is an axis of wood having two
long depressions cut into it, for the purpose of carrying the two
bar magnets F and G. The wood is not cut away quite across
the axis, but is left in the middle, so that the magnets are
about th of an inch apart. From O towards the support A,
it is removed, however, as low down as the axis of revolution, so
as to form a notch between the two magnets when they are in
their places; and by further removal of the wood, this notch is
continued on to the end of the axis at P. This notch, or
opening, is intended to receive a wire, which can be carried
334
[SERIES XXVIII.
On lines of magnetic force.
down the axis of rotation, and then passing out between the two
magnets, anywhere between O and N, can be returned towards
the end P on the outside. The magnets are so placed, that the
central line of their compound system coincides with the axis
of rotation; E being a handle by which rotation, when required,
is given. H and I are two copper rings, slipping tightly on to
the axis, by which communication is to be made between a wire
adjusted so as to revolve with the magnets, and the fixed ends
of wires proceeding from a galvanometer. Thus, let P L repre-
sent a covered wire; which being led along the bottom of the
notch in the axis of the apparatus, and passing out at the
equatorial parts of the magnets, returns into the notch again
near N, and terminates at K. When the form of the wire loop
is determined and given to it, then a little piece of soft wood is
placed between the wires in the notch at K, of such thickness,
that when the ring I is put into its place, it shall press upon
the upper wire, the piece of wood, and the lower wire, and keep
all tightly fixed together, and at the same time leave the two
wires effectually separated. The second ring, H, is then put
into its place on the axis, and the introduction of a small wedge
of wood, at the end of the axis, serves to press the end P into
close and perfect contact with the ring H, and keep all in order.
So the wire is free to revolve with the magnets, and the rings
H and I are its virtual terminations. Two clips, as at C, hold
the ends of the galvanometer wire (also of copper); and the latter
are made to press against the rings by their elasticity, and give
an effectual contact bearing, which generates no current, either
by difference of nature or by friction, during the revolution of
the axis.
3085. The two magnets are bars, each 12 inches long, 1 inch
broad, and 0.4 of an inch thick. They weigh each 19 ounces,
and are of such a strength as to lift each other end to end and
no more. When the two are adjusted in their place, it is with
the similar poles together, so that they shall act as one magnet,
with a division down the middle: they are retained in their
place by tying, or, at times, by a ring of copper which slips
tightly over them and the axis.
3086. The galvanometer is a very delicate instrument made
by Rhumkorff (2651.). It was placed about 6 feet from the
magnet apparatus, and was not affected by any revolution of the
Ост. 1851.]
335
The moving wire-its action.
a
Fig. 2.
3
latter. The wires, connecting it with the magnets, were of
copper, 0·04 of an inch in diameter, and in their whole length
about 25 feet. The length of the wire in the galvanometer I do
not know; its diameter was 15th of an inch. The condition
of the galvanometer, wires, and magnets, was such, that when
the bend of the wires was formed into a loop, and that carried
once over the pole of the united mag-
nets, as from a to b, fig. 2, the galvano-
meter needle was deflected two degrees
or more. The vibration of the needle
was slow, and it was easy therefore to
reiterate this action five or six times, or
oftener, breaking and making contact
with the galvanometer at right inter-
vals, so as to combine the effect of like
induced currents; and then a deflection

i
of 10° or 15° on either side of zero could be readily obtained.
The arrangement, therefore, was sufficiently sensible for first
experiments; and though the resistance opposed by the thin long
galvanometer wire to feeble currents was considerable, yet it
would always be the same, and would not interfere with results,
where the final effect was equal to 0°, nor in those where the
consequences were shown, not by absolute measurement, but by
comparative differences.
3087. The first practical result produced by the apparatus
described, in respect of magneto-electric induction generally, is,
that a piece of metal or conducting matter which moves across
lines of magnetic force, has, or tends to have, a current of elec-
tricity produced in it. A more restricted and precise expression
of the full effect is the following. If a continuous circuit of
conducting matter be traced out, or conceived of, either in a
solid or fluid mass of metal or conducting matter, or in wires or
bars of metal arranged in non-conducting matter or space;
which being moved, crosses lines of magnetic force, or being
still, is by the translation of a magnet crossed by such lines of
force; and further, if, by inequality of angular motion, or by
contrary motion of different parts of the circuit, or by inequality
of the motion in the same direction, one part crosses either more
or fewer lines than the other; then a current will exist round it,
due to the differential relation of the two or more intersecting
.
336
On lines of magnetic force. [SERIES XXVIII.
parts during the time of the motion: the direction of which cur-
rent will be determined (with lines having a given direction of
polarity) by the direction of the intersection, combined with the
relative amount of the intersection in the two or more efficient
and determining (or intersecting) parts of the circuit.
Fig. 3.
3088. Thus, if fig. 3 represent a magnetic pole N, and over it
a circuit, formed of metal, which may
be of any shape, and which is at first
in the position c; then if that circuit be
moved in one direction into the posi-
tion 1; or in the contrary direction into
position 2; or by a double direction of
motion into position 3; or by trans-
lation into position 4; or into position
5; or any position between the first and
these or any resembling them; or, if the
first position c being retained, the pole
move to, or towards, the position n;

n
N
then, an electric current will be produced in the circuit, having
in every case the same direction, being that which is marked in
the figure by arrows. Reverse motions will give currents in the
reverse direction (256. &c.).
3089. The general principles of the production of electrical
currents by magnetic induction have been formerly given
(27. &c.)¹, and the law of the direction of the current in relation
to the lines of force, stated (114. 3079. note). But the full
meaning of the above description can only be appreciated here-
after, when the experimental results, which supply a larger
knowledge of the relations of the current to the lines of force,
have been described.
3090. When lines of force are spoken of as crossing a con-
ducting circuit (3087.), it must be considered as effected by the
translation of a magnet. No mere rotation of a bar magnet on
its axis, produces any induction effect on circuits exterior to it;
for then, the conditions above described (3088.) are not fulfilled.
The system of power about the magnet must not be considered as
necessarily revolving with the magnet, any more than the rays of
light which emanate from the sun are supposed to revolve with the
1
¹ Philosophical Transactions, 1832, p. 131, &c.
OCT. 1851.]
337
outside of a magnet.
sun. The magnet may even, in certain cases (3097.), be consi-
dered as revolving amongst its own forces, and producing a full
electric effect, sensible at the galvanometer.
Fig. 4.
b
3091. In the first instance the wire was carried down the
axis of the magnet to the middle distance, then led out at the
equatorial part, and returned on the outside; fig. 4 will repre-
sent such a disposition. Supposing
the magnet and wire to revolve once,
it is evident that the wire a may be
considered as passing in at the axis
of the magnet, and returning from
b across the lines of force external
to the magnet, to the axis again at c; and that in one revolution
the wire from b to c has intersected once, all the lines of force
emanating from the N end of the magnet. In other words,
whatever course the wire may take from 6 to c, the whole system
of lines belonging to the magnet has been once crossed by the
wire. In order to have a correct notion of the relation of the
result, we will suppose a person standing at the handle E, fig. 1
(3084.), and looking along the magnets, the magnets being
fixed, and the wire loop from 6 to c turned over toward the left-
hand into a horizontal plane; then if that loop be moved over
towards the right-hand, the magnet remaining stationary, it will
be equivalent to a direct revolution (according to the hands of
a watch or clock) of 180°, and will produce a feeble current in
a given direction at the galvanometer. If it be carried back
180° in the reverse direction, it will produce a corresponding
current in the reverse direction to the former. If the wire be
held in a vertical, or any other plane, so that it may be consi-
dered as fixed, and the magnet be rotated through half a revo-
lution, it will also produce a current; and if rotated in the
contrary direction, will produce a contrary current; but as to
the direction of the currents, that produced by the direct revo-
lution of the wire is the same as that produced by the reverse
revolution of the magnet; and that produced by the reverse
revolution of the wire is the same as that produced by the direct
revolution of the magnet. A more precise reference of the
direction of the current to the particular pole employed, and
the direction of the revolution of the wire or magnet, is not at

VOL. III.
Z
338
On lines of magnetic force [SERIES XXVIII.
present necessary; but if required is obtained at once by re-
ference to fig. 3 (3088.), or to the general law (114. 3079. note).
3092. The magnet and loop being rotated together in either
direction, no trace of an electric current was produced. In this
case the effect, if any, could be greatly exalted, because the
rotation could be continued for 10, 20, or any number of revo-
lutions without derangement, and it was easy to make thirty
revolutions or more within the time of the swing of the galva-
nometer needle in one direction. It was also easy, if any effect
were produced, to accumulate it upon the galvanometer by
reversing the rotation at the due time. But no amount of revo-
lution of the magnet and wire together could produce any effect.
3093. The loop was then taken out of the axis of the magnet,
but attached to it by a piece of pasteboard, so that all should be
fixed together and revolve with the
same angular velocity, fig. 5; but
whatever the shape or disposition of
the loop, whether large or small, near
or distant, open or shut, in one plane,
or contorted into various planes; what-
Fig. 5.

ever the shape or condition, or place, provided it moved alto-
gether with the magnet, no current was produced.
3094. Furthermore, when the loop was out of the magnets,
and by expedients of arrangement, was retained immovable,
whilst the magnet revolved, no amount of rotation of the mag-
net (unaccompanied by translation of place) produced any degree
of current through the loop.
Fig. 6.
3095. The loop of wire was then made of two parts; the por-
tion c. fig. 6, on the outside of the
magnet, was fixed at b, and the
portion a, being a separate piece,
was carried along the axis until it
came in contact with the former
at d; the revolution of one part
was thus permitted either with or without the other, yet pre-
serving always metallic contact and a complete circuit for the
induced current. In this case, when the external wire and the
magnet were fixed, no current was produced by any amount of
revolution of the wire a on its axis. Neither was any current
produced when the magnet and wire, c, d, were revolved to-

Ост. 1851.]
339
within and without a magnet.
gether, whether the wire a revolved with them or nor.
When
the magnet was revolved without the external part of c d, or the
latter revolved without the magnet, then currents were produced
as before (3091.).
3096. The magnet was now included in the circuit, in the
following manner. The wire a,
fig. 7, was placed in metallic con-
tact on both sides of the interval
between the magnets at N (or the
pole), and the part c was brought
into contact with the centre at d.
a
Fig. 7.

The result was in everything the same as when the wire a was
continued up to d, i. e. no amount of revolution of the magnet
and part c together could produce any electric current. When
c was made to terminate at e or the equatorial part of the mag-
net, the result was precisely the same. Also, when c terminated
at e, the part a of the wire was continued to the centre at d,
and there the contact perfected, but the result was still the same.
No difference, therefore, was produced, by the use between N
and d, or d and e, of the parts of the magnet in place of an insu-
lated copper wire, for the completion of the circuit in which the
induced current was to travel. No rotation of the part a pro-
duced any effect, wherever it was made to terminate.
Fig. 8.
3097. In order to obtain the power of rotating the magnet
without the external part of the wire, a copper ring, was fixed
round, and in contact with it at the equatorial part, and the
wire c, fig. 8, made to bear by
spring pressure against this ring,
and also against the ring H on
the axis, fig. 1 (3084.); the circuit
was examined, and found com-
plete. Now when the wire c e was

C
α
fixed and the magnet rotated, a current was produced, and that
to the same amount for the same number of revolutions, whether
the part of the wire a terminated at N, or was continued on to
the centre of the magnet, or was insulated from the magnet and
continued up to the copper ring e. When the wire, by expe-
dients, which though rough were sufficient, was made to revolve
whilst the magnet was still, currents in the contrary direction
were produced, in accordance with the effect before described
z 2
340
On lines of magnetic force [SERIES XXVIII.
(3091.); and the results when the wire and magnet rotated
together (3092.), show that these are in amount exactly equal
to the former. When the inner and the outer wires were both
motionless, and the magnet only revolved, a current in the full
proportion was produced, and that, whether the axial wire a made
contact at the pole of the magnet or in the centre.
3098. Another arrangement of the magnet and wires was of
the following kind. A radial insulated wire was fixed in the
middle of the magnets, from the
centre d, fig. 9, to the circumfe-
rence b, being connected there
with the equatorial ring (3097.);
an axial wire touched this radial
wire at the centre and passed out
Fig. 9.

at the pole; the external part of the circuit, pressing on the ring
at the equator, proceeded on the outside over the pole to form
the communication as before. In the case where the magnet
was revolved without the axial and the external wire, the full
and proper current was produced; the small wire, d b, being,
however, the only part in which this current could be gene-
rated by the motion; for it replaced, under these circumstances
the body of the magnet employed on the former occasion (3097).
Fig. 10.
3099. The external part of the wire instead of being car-
ried back over that pole of the magnet at which the axial wire
entered, was continued away over the other pole, and so round
by a long circuit to the galvanometer; still the revolution of the
magnet, under any of the described circumstances, produced
exactly the same results as before.
It will be evident by inspection of
fig. 10, that, however the wires are
carried away, the general result
will, according to the assumed prin-
ciples of action, be the same; for if
a be the axial wire, and b', b", bill
the equatorial wire, represented in
three different positions, whatever
magnetic lines of force pass across
the latter wire in one position, will

B
also pass across it in the other, or in any other position which
can be given to it. The distance of the wire at the place of
Oct. 1851.]
341
surrounding a magnet.
intersection with the lines of force, has been shown, by the
experiments (3093.), to be unimportant.
3100. Whilst considering the condition of the forces of a
magnet, it may be admitted, that the two magnets used in the
experimental investigations described, act truly as one central
magnet. We have only to conceive smaller similar magnets to
be introduced to fill up the narrow space not occupied by the
wire, and then the complete magnet would be realized-or it
may be viewed as a magnet once perfect, which has had certain
parts removed; and we know that neither of these changes
would disturb the general disposition of the forces. In and
around the bar magnet the forces are distributed in the simplest
and most regular manner. Supposing the bar removed from
other magnetic influences, then its power must be considered as
extending to any distance, according to the recognized law; but,
adopting the representative idea of lines of force (3074.), any
wire or line proceeding from a point in the magnetic equator of
the bar, over one of the poles, so as to pass through the magnetic
axis, and so on to a point on the opposite side of the magnetic
equator, must intersect all the lines in the plane through which
passes, whether its course be over the one pole or the other
So also a wire proceeding from the end of the magnet at the
magnetic axis, to a point at the magnetic equator, must intersect
curves equal to half those of a great plane, however small or great
the length of the wire may be; and though by its tortuous course
it may pass out of one plane into another on its way to the equator.
it
.
3101. Further, if such a wire as that last described be revolved
once round the end of the magnet to which it is related, a slip-
ping contact at the equator being permitted for the purpose, it
will intersect all the lines of force during the revolution; and
that, whether the polar contact is absolutely coincident with the
magnetic axis, or is anywhere else at the end of the bar, provided
it remain for the time unchanged. All this is true, though the
magnet may be subject, by induction at a distance, to other
magnets or bodies, and may be exerting part of its force on them,
so as to make the distribution of its power very irregular as
compared to the case of the independent bar (3084.), or may
have an irregular or contorted shape, even up to the horseshoe
form. It is evident, indeed, that if a wire have one of its ends
applied to any point on the surface of a magnet, and the other
342
On lines of magnetic force. [SERIES XXVIII.
end to a point in the magnetic equator, and the latter be slipped
once round the magnetic equator, and the loop of wire be
made to pass over either pole, so as at last to resume its first
position, it will in the course of its journey have intersected once
every line of force belonging to the magnet.
.
3102. A wire from pole to pole which passes close to the
equator, of course intersects half the external lines of force in a
great plane, twice, in opposite directions as regards the polarity;
and, therefore, when revolved round the magnet, has no electric
current induced in it. If it do not touch at the equator, still,
whatever lines it intersects, are twice intersected, and so the same
equilibrium is preserved. If the magnet rotate under the wire,
it acts the part of the central rotating wire already referred to
(3095.); or if any course for the electric current other than a
right line is assumed in it, that course is subject to the law of
neutrality above stated, as will be seen by reference to the in-
ternal condition of the magnet itself (3117.). Hence the reason
why no currents are produced, under any circumstances of motion,
by the application of such conducting circuits to the magnet. I
may further observe, in reference to the intersection of the lines
of force, that if a wire ring, a little larger in diameter than the
magnet, be held edgeways at one of the poles, so that the lines
of force there shall be in its plane, and be then turned 90° and
carried over the pole to the equator (3088.), it will intersect
once all the lines of the magnet, except the very few which will
remain unintersected at the equator.
3103. Whilst endeavouring to establish experimentally the
definite amount of the power represented by the lines of force,
it is necessary to take certain precautions, or the results will be
in error. For instance, ten revolutions of the wire about the
magnet, or of the magnet within the fixed wire (3097.), ought to
give a constant deflection at the galvanometer, and yet without
any change in the position of the wire the results may at different
times differ very much from each other; being at one time 9°,
and at another only 4° or 5°. I found this to be due to difference
of velocity within certain limits, and to be explained and guarded
against as follows.
3104. If a wire moves across lines of force slowly, a feeble
electric current is produced in it, continuing for the time of the
motion; if it move across the same lines quickly, a stronger
Ост. 1851.]
343
Precautions as to time-velocity.
current is produced for a shorter time. The effect of the current
which deflects a galvanometer needle, is opposed by the action.
of the earth, which tends to return the needle to zero. A con-
tinuous weak current, therefore, cannot deflect it so far as a
continuous stronger current. If the currents be limited in dura-
tion, the same effect will occur unless the time of the swing of
the needle to one side be not considerably more than the time
of either of the currents. If the time of the needle-swing be ten,
and the time of ten quick rotations be six, then all the effect of
the induced current is exerted in swinging the needle; but if
the time of ten slow rotations be twelve or fifteen, then part of
the current produced is not recognized by the extent of the
vibration, but only by its holding the needle out awhile, at the
extremity of a smaller arc of declination. Therefore, when quick
and slow velocity was compared, and indeed, in every case of
comparative rotations of the wire and magnet, only that number
of rotations was taken which could be well included within the
time of the needle's journey to one side;-when the needle, there-
fore, was seen to travel on to its extreme distance after the rota-
tion and the inducing currents had ceased. If the needle began to
return the instant the motion was over, such an experiment was
rejected for purposes of comparison. When these precautions
were attended to, and velocities of revolution taken, which occu-
pied times from one-third to three-fourths of that required for
the swing of the needle, when the same number of revolutions
(ten) gave the same amount of deflection, namely, 9°5, with my
apparatus, though the time of revolution varied as 1 : 2, or even
in a higher degree.
3105. Another cause of difference produced by varying velo-
city, is the diminution of the action of the current on the needle,
as the angle which the latter forms with the convolutions of the
coil increases. Hence a constant current produces more effect
on the deflection of the needle for the first moments of time than
afterwards. This effect, however, was scarcely sensible for
swinging deflections of 9° or 10°, produced by currents which
were over before the needle had moved through 4º or 5º.
3106. It has already been shown, that it is a matter of indif-
ference whether the wire revolve in one direction or the magnet
in the other (3091.); and this is still further proved by the cases
where the magnet and the wire revolve together (3092.); for then
344
On lines of magnetic force [SERIES XXVIII.
the currents which tend to form are exactly equal and opposed
to each other, whatever the position of the wire may be. As
the immobility of the needle is a point more easily ascertained
than the extent of an arc, indicated only for a moment, and as
the rotations of the magnet and wire conjointly can be made
rapid and continuous, the proof in such cases is very satisfactory.
3107. Proceeding to experiment upon the effect of the distance
of the wire c, fig. 11, from the
magnet, the wire was made to
vary, so that sometimes it was not
more than 8 inches long (being of
copper and 0.04 of an inch in dia-
meter), and only half an inch from
the magnet, whilst at other times
:
Fig. 11.

it was 6 or 8 feet long and extended to a great distance. The
deflection due to ten revolutions of the magnet was observed, and
the average of several observations, for each position of the wire,
taken these were very close (with the precautions before de-
scribed) for the same position; and the averages for different
positions agreed perfectly together, being 9°5. I endeavoured
to repeat these experiments on distance by moving the wire and
preserving the magnet stationary in the manner before described
(3091.); they were not so striking because time would only allow
of smaller deflections being obtained (3104), but the same num-
ber of journeys through an arc of 180° gave the same deflection
at the galvanometer, whether the course of the wire was close to
the magnet or far off; and the deflection agreed with those ob-
tained when the magnet was rotating and the wire at rest.
3108. As to velocity of motion; when the magnet was rotating
and the wire placed at different distances, then ten revolutions
of the magnet produced the same deflection of the needle, whether
the motion was quicker or slower, and whatever the distance of
the wire, provided the precautions before described were attended
to (3104.). That the same would be true if the wire were moving
and the magnet still, is shown by this; that whatever the velo-
city with which the wire and magnet revolve together, and what-
ever their distance apart, they exactly neutralize and equal each
other (3096.).
3109. From these results the following conclusions may be
drawn. The amount of magnetic force, as shown by its effect in
OCT. 1851.]
345
occurring in air-conclusions.
evolving electric currents, is determinate for the same lines of
force, whatever the distance of the point or plane, at which their
power is exerted, is from the magnet. Or it is the same in any
two, or more, sections of the same lines of force, whatever their
form or their distance from the seat of the power may be. This
is shown by the results with the magnet and the wire, when
both are in the circuit (3108.); and also by the wire loop revol-
ving with the magnet (3092.); where the tendency of currents
to form in the two parts oppose and exactly neutralize or com-
pensate each other.
3110. In the latter case very varying sections outside of the
magnet may be compared to each other; thus, the wire may be
conceived of as passing (or be actually formed so as to intersect)
lines of force near the pole, and then, being continued along a
line of force until over the equator, may be directed so as to
intersect the same lines of force in the contrary direction, and
then return along a line of force to its commencement; and so
two surface sections may be compared. It is manifest that every
loop forming a complete circuit, which is in a great plane passing
through the axis of the magnet, must have precisely the same
lines of force passing into and passing out of it, though they may,
so to say, be expanded in one part and compressed in another ;
or (speaking in the language of radiation) be more intense in one
part and less intense in the other. It is also as manifest, that,
if the loop be not in one plane, still, on making one complete
revolution, either with or without the magnet, it will have inter-
sected in its two opposite parts an exactly equal amount of lines
of force. Hence the comparison of any one section of a given
amount of lines of force with any other section is rendered,
experimentally, very extensive.
3111. Such results prove, that, under the circumstances, there
is no loss, or destruction, or evanescence, or latent state of the
magnetic power by distance.
3112. Also that convergence or divergence of the lines of
force causes no difference in their amount.
3113. That obliquity of intersection causes no difference. It
is easy so to shape the loop (3110.), that it shall intersect the
lines of force directly across at both places of intersection, or
directly at one and obliquely at the other, or obliquely in any
degree at both; and yet the result is always the same (3093.).
346
On lines of magnetic force [SERIES XXVIII.
3114. It is also evident, by the results of the rotation of the wire
and magnet (3097. 3106.), that when a wire is moving amongst
equal lines (or in a field of equal magnetic force), and with an
uniform motion, then the current of electricity produced is pro-
portionate to the time; and also to the velocity of motion.
3115, They also prove, generally, that the quantity of elec-
tricity thrown into a current is directly as the amount of curves
intersected.
3116. In addition to these results, this method of investiga-
tion gives much insight into the internal condition of the magnet,
and the manner in which the lines of force (which represent
truly all that we are acquainted with of the peculiar action of the
magnet) either terminate at its exterior, or at any assumed points,
to be called poles; or are continued and disposed of within. For
this purpose, let us consider the external loop (3093.) of fig. 5.
When revolving with the magnet no current is produced, because
the lines of force which are intersected on the one part, are again
intersected in an opposing direction on the other (3110.). But if
one part of the loop be taken down the axis of the magnet, and
the wire then pass out at the equator (3091.), still the same
absence of effect is produced; and yet it is evident that, external
to the magnet, every part of the wire passes through lines of
force, which conspire together to produce a current; for all the
external lines of force are then intersected by that wire in one
revolution (3101.). We must therefore look to the part of the
wire within the magnet, for a power equal to that capable of
being exerted externally, and we find it in that small portion
which represents a radius at the central and equatorial parts.
When, in fact, the axial part of the wire was rotated it produced
no effect (3095.); when the axial, the inner radial, and the ex-
ternal parts were revolved together, they produced no effect;
when the external wire alone was revolved, directly, it produced
a current (3091.); and when the internal radius wire alone
(being insulated from the magnet) revolved, directly, it also pro-
duced a current (3095. 3098.) in the contrary direction to the
former; and the two were exactly equal in power; for when
both portions of the wire moved together directly, they perfectly
compensated each other (3095.). This radius wire may be re-
placed by the magnet itself (3096. 3118.).
OCT. 1851.]
347
occurring within a magnet.
3117. So, by this test there exists lines of force within the
magnet of the same nature as those without. What is more,
they are exactly equal in amount to those without. They have
a relation in direction to those without; and in fact are continua-
tions of them, absolutely unchanged in their nature, so far as
the experimental test can be applied to them. Every line of
force therefore, at whatever distance it may be taken from the
magnet, must be considered as a closed circuit, passing in some
part of its course through the magnet, and having an equal
amount of force in every part of its course.
3118. When the axial part of the wire is dismissed and the
magnet employed in its place, so as to be included in the circuit,
it is easy to see how it acts the part of the conductor. For
suppose the wire itself to be continued from N to b, fig. 12, by
any of the three paths indicated by
dotted lines, the effect is the same in
all the cases, both by experiment
(3093.) and by principle (3100.).
For whatever the form of the path,
it will in one revolution intersect
Fig. 12.

the same amount of lines of force within the magnet, as are
intersected in the contrary direction by the part of the wire
outside the magnet; and when the magnet is employed to com-
plete the circuit in place of the internal wire, then its substance
produces precisely the same result; for direction and every other
circumstance which influences the result remains the same: one
conductor has simply been substituted for another. The great
mass of the magnet might be supposed able to do something
more than the thin wire, but the reason why it only equals it in
effect will be seen hereafter (3137.). And as the axial wire, in
revolving, does nothing but conduct (3095.), all the effect
being produced by that part which represents a radius be-
tween the axis and the equator (3098.); so the magnet, re-
revolving as a cylinder, is as to its mass like the revolving wire ;
with the exception of so much of it as represents a radius con-
necting together the two points at the pole or axis and at the
equator, where communication with the wire is completed. As
was shown long ago (220.), if a cylinder magnet be revolved,
and the ends of the galvanometer wires a c be applied to the
extremities of its axis, no current is evolved; but if a be applied
348
On lines of magnetic force, [SERIES XXVIII.
to one end, it matters not which, and c be applied at the equator
or any other part on the surface of the cylinder, a current always
in the same direction for the same rotation will be produced.
3119. Further to prove these points, the magnets were cut in
half through the equatorial plane, and then either a disc of
copper placed there, or a wire radius only, or the magnets
brought together again: and these three arrangements were used
in succession to complete the circuit from the axial-wire (3095.)
to a fixed wire at the surface of the equator. Whichever was
employed the current produced was the same, both in direction
and amount. If the cylinder magnet above described (3118.)
be terminated at the ends by attached discs of silver or copper,
the wires applied to their surfaces, as they revolve with the
magnet, produce precisely the same currents as to direction as
if applied to the surface of the magnet itself (218. 219).
3120. In this striking disposition of the forces of a magnet,
as exhibited by the moving wire, it exactly resembles an electro-
magnetic helix, both as to the direction of the lines of force in
closed circuits, and in their equal sum within and without. No
doubt, the magnet is the most heterogeneous in its nature, being
composed, as we are well-aware, of parts which differ much in
the degree of their magnetic development; so much so, that some
of the internal portions appear frequently to act as keepers or
submagnets to the parts which are further from the centre, and
so, for the time, to form complete circuits, or something equiva-
lent to them, within. But these make no part of the resultant
of force externally, and it is only that resultant which is sensible
to us in any way; either by the action on a needle, or other
magnets, or soft iron, or the moving wire. So also the power
which is manifest within the magnet by its effect on the moving
mass, is still only that same resultant; being equal to, and by
polarity and other qualities, identical with it. No doubt, there
are cases, as upon the approach of a keeper to the poles, or the
approximation of other magnets, either in favourable or adverse
positions when more external force is developed, or it may be a
portion apparently thrown inwards and so the external force
diminished. But in these cases, that which remains externally
existent, corresponds precisely to that which is the resultant
internally; for when either the same, or contrary poles, of a
powerful horseshoe magnet were placed within an inch and
a
OCT. 1851.]
349
their definite character.
half of the poles of the bar-magnets, prepared to rotate with the
attached wires (3092.), as before described, still, upon their revo-
lution, not the slightest action at the galvanometer was perceived;
the forces within the magnet and those without perfectly com-
pensating each other.
3121. The definite character of the forces of an invariable
magnet, at whatever distance they are observed from the magnet,
has been already insisted upon (3109.). How much more stri-
kingly does that point come forth now, that, being able to observe
within the magnet, we find the same definite character there ;
every section of the forces, whether within or without the magnet,
being exactly of the same amount! The power of a magnet may
therefore be easily represented by the effects of any section of
its lines of force; and as the currents induced by two different
magnets may easily be conducted through one wire, or be, in
other ways, compared to each other, so facilities may thus arise
for the establishment of standards amongst magnets.
3122. On the other hand, the use of the idea of lines of force,
which I recommend, to represent the true and real magnetic
forces, makes it very desirable that we should find a unit of such
force, if it can be attainable, by any experimental arrangement,
just as one desires to have a unit for rays of light or heat. It
does not seem to me improbable that further research will supply
the means of establishing a standard of this kind. In the mean
time, for the enlargement of the utility of the idea in relation to
the magnetic force, and to indicate its conditions graphically,
lines may be employed as representing these units in any given
case. I have so employed them in former series of these Re-
searches (2807. 2821. 2831. 2874. &c.), where the direction of
the line of force is shown at once, and the relative amount of
force, or of lines of force in a given space, indicated by their
concentration or separation, i. e. by their number in that space.
Such a use of unit lines involves, I believe, no error either in
the direction of the polarity or in the amount of force indicated
at any given spot included in the diagrams.
3123. The currents produced in wires, when they cross lines
of magnetic force, are so feeble in intensity (though abundant
enough in quantity, as many results show), that a fine wire
galvanometer must of necessity offer great obstruction to their
passage. Therefore, before entering upon further experimental
350
On lines of magnetic force. [SERIES XXVIII.
Fig. 13.
inquiries, I had another galvanometer constructed, in which the
needles belonging to that made by Rhumkorff were employed,
but the coil was replaced by a single convolution of very stout
wire. The wire was of copper, 0.2 of an inch in diameter. It
passed horizontally under the lower needle, then, as nearly as
might be, between that and the upper needle, over the upper, and
then again between that and the lower needle, fig. 13, and was
afterwards attached to the stand, and
continued for 19 or 20 feet outside of
the glass cover. Such a wire had
abundant conducting power; and
though it passed but once round each
needle, gave a deflection many times
greater than that belonging to the for-
mer galvanometer. Thus when the
ends of the nineteen feet of wire were
soldered together, so as to form one
loop or circuit, the passage of the wire once
between the poles of a horseshoe magnet (3124.),
caused a deflection, or rather swing of the
needle of above 90°. I have had a more per-
fect instrument, of the same kind, constructed,
in which the conducting coil was cut out of
plates of copper, so as to form a square band
0.2 of an inch in thickness, which passed twice
round the vibration plane of each needle, as
represented, fig. 14. The length of metal

Fig. 14.

around the needles was 24 inches, and the galvanometer was
very sensitive, but the experiments to be described were made
chiefly with the former instrument.
Fig. 15.
3124. It was necessary, first to ascertain the effect of certain
circumstances upon this simple galvanometer, as to their modi-
fication of its indications. The magnet to be used was a com-
pound horseshoe instrument, weigh-
ing 16 lbs., and able to support 40 lbs.
by the keeper or submagnet. It is
some years since it was magnetized,
and it is therefore, probably, in a
nearly constant state as to power.
The poles have the form delineated,
fig. 15. Their distance apart is 1.375 inch, and the distance
OCT. 1851.] Thick wire galvanometer-precautions.
351
downwards, from their summit to the bottom or equator of the
magnet, is 8.5 inches. The galvanometer stood in the prolonga-
tion of the magnetic axis, i. e. the line from pole to pole, and
whether it were 6 or only 3 feet distant, was hardly at all affected
in the time of its vibration, being adjusted so nearly astatic as
to require about ten seconds to swing to the right or to the left.
3125. On passing the wire across the magnetic field, as just
described (3123.), but with different velocities, effects different
in degree were obtained at the galvanometer, for the reasons
formerly given (3104. 3106.). The quickest velocity gave the
greatest result, equal at times to 140°, whilst a very slow motion
gave only 30° or 40°. Still with moderately quick velocities the
effects were nearly alike, and by operating with the same velo-
city, and taking the average of several observations, a very
uniform result could be obtained.
3126. On cutting the wire across, and then putting the ends
together in various ways, it was found that great care was requi-
site in making contact, in this or in similar cases. Thus, to
press the ends lightly together was not sufficient; they re-
quired to be well and recently cleaned and pressed closely into
contact. Junctions effected by soldering or dipping into cups
of mercury were still better, when made with care, and were
employed at the galvanometer and elsewhere as often as possible.
3127. To ascertain generally the obstruction caused by the
interposition of thin wires, 28 inches of copper wire, 0·045 of an
inch in diameter, was introduced into the circuit at a part away
from the magnet, with excellent junctions. The oscillation or
swing, which before was 140° or more, was now reduced to 40°.
On taking out the wire and replacing it by another, also of copper,
but only 19.5 inches in length, and 0·0135 in diameter, the de-
flection was reduced to 7° or 8°.
3128. For a rough comparison of the power of this magnet
and the former bar magnets (3085.), by the present galvanometer,
the thick wire was bent into a loop (3086.), and the two bar
magnets, with like ends together, passed quickly through it up
to the equatorial part; the deflection was about 30°. Such a
passage intersected nearly all the lines of force of the bar mag-
nets. A similar motion of the magnets close to, but outside of,
the loop, produced no effect at the galvanometer.
3129. In respect of the alteration of the lines of force, either
352
On lines of magnetic force. [SERIES XXVIII.
in position or in total amount, by bringing the poles of the
horseshoe magnet (3124.) much nearer together, the following
experiments were made. The distance between the poles is
1.375 inch; by placing a cube of soft iron, 0·8 of an inch in the
side, within this space, it was diminished to 0.575, and thus, vir-
tually, the distance apart much lessened, and, as was afterwards
shown experimentally (3130.), the external power of the magnet
concentrated there. Then, whilst the cube was in place, the
thick wire of 0·2 of an inch in diameter, was arranged so as to
pass across the magnetic axis or place of strongest action, and
fixed; after which the iron cube was alternately removed and
again restored, and the effects observed. Feeble electric currents
were produced at these times; but whether the cube was put
into its place from below, or above or the sides, the current pro-
duced was always in the same direction; and when it was re-
moved the current produced was in the reverse direction. If
the cube was carried up to, by, and away from, the magnetic
axis in one motion, then there was no effect at the galvanometer.
On the other hand, when the wire was carried across the mag-
netic field as described (3123.), so as to intersect all the lines of
force in one moment, and sum up their power at the galvano-
meter, then there was no difference in the result, whether the
iron cube was in its place or not; showing, as far as this appa-
ratus could indicate, that the sum of power in the section of all
the lines of force external to the magnet, was the same under
both circumstances, though the distribution of it was different.
3130. The very action produced by the cube, when in and
out of place (3129.), upon the forces which affected the stationary
wire, was a proof of the difference of distribution at different
times.
3131. A block of bismuth, employed in place of the iron cube,
had no sensible effect upon the wire whether it were still or
moving.
3132. This galvanometer was first employed for a repetition
of all the former experiments with the bar magnets (3091. &c.).
The results were absolutely the same, except that the amount of
the deviation produced, when deviation was a result, was larger
than in the former cases.
3133. For the comparison of different thicknesses of the same
OCT. 1851.] Moving wires-different thicknesses.
Ост.
353
metal, I took copper wires in lengths of 10·5 inches, and different
diameters, and bending them into loops of a form and size such
as would admit them to pass with facility over a pole of the
horseshoe magnet, soldered them to the ends of two conducting
rods, made of copper wire 0·2 of an inch in diameter and 35
inches in length each, which were fixed on opposite sides of a
narrow slip of wood. The whole arrangement is seen in fig. 16;
Fig. 16.

C
the terminations a b dip into the mercurial cups of the galvano-
meter, the parts at c are brought so close together as to touch,
except for the intervention of a piece of card, and thus the parts
from c to a b are thrown out of action, except as mere conductors,
whilst the loop, being made to descend over one magnetic pole,
intersects very nearly the whole of the magnetic curves, and
always the same proportion.
3134. The former magnet was too powerful for comparative
experiments, therefore a smaller one was employed, consisting
of five plates, weighing 8 lbs., and able to carry 21 lbs. easily at
the keeper. The poles were 1·2 inch apart and an inch thick
each, in the direction of the magnetic axis. If less magnetic
power were required, an adjustment was easily made, by apply-
ing the keeper to the side upon both limbs, the magnetic com-
munication being effected either nearer to the poles, or nearer
to the equator or bend, as less or more power was required.
The descent of the loop between the poles is then best regulated
by causing the conductor wires to bear ultimately against a
stopping-block.
3135. The effect of a quick and a slow motion was found to
be the same as before (3104. 3105.). Such velocities as the hand
could impart were very effectual, and gave results of very con-
siderable uniformity when quick motions were employed.
3136. Three different loops were compared together, consisting
of copper wire, the diameters of which were 0.2, 0·1 and 0.05 of
an inch, or as 4, 2 and 1; their sectional areas or masses there-
fore were as 16, 4 and 1. Ten or twelve observations were made
with each loop; the results were near together, and the average
2 A
VOL. III.
354
[SERIES XXVIII.
Lines of magnetic force.
for each loop, being the extent of the swing declination on one
side from zero, is as follows:
Copper wire of
th of an inch in thickness
10
th of an inch in thickness
th of an inch in thickness.
16.00
44.40
57.37
Copper wire of
Copper wire of
Now though the thicker wires produced the largest effect, the
results were evidently not at all in proportion to the masses of
the wires; the smaller having greatly the advantage in that
respect. On the other hand, when four of the smaller wires
were placed side by side, so as to form one loop equal in mass
to the second loop, it gave the same result as that loop, being of
the same power.
3137. The disproportion of the difference of these three wires
is evidently a consequence of the relative difference of the mere
conducting part of the circuit. To compare accurately the
effect of the lines of force on wires of different diameters moving
across them, these diameters should continue to, and through
the galvanometer (205.), otherwise the thin wire current has an
advantage given to it in the conducting part, which the thick
wire current has not. Hence the reason why a thin wire galva-
nometer, such as that before described (3086.), gives results
which are alike, for thick or thin wire loops, or for fasciculi of
few or many wires. To enlarge the comparison, I soldered on
to two pairs of conductors, the dimensions of those described
(3133.), two cylinders of copper, each 5.5 inches long, but one
was only 0.2 of an inch thick and the other 07, or twelve times
the mass of the first, fig. 17. They were then passed in suc-
Fig. 17.

cession between the poles of the magnet, and gave results very
nearly alike. If there was any difference, the effect was highest
with the smallest cylinder; and this may very well be; for as the
magnetic field was not equal in force, but most intense in the
magnetic axis, so it is evident, that whilst one part of the large
cylinder, in passing across, was at the axis, other parts were in
places of less intense force and action, and so a return current
1
OCT. 1851.]
355
Moving wires-different diameters.
may have existed in them, which could not occur to the same
extent in a cylinder little more than a fourth of the diameter of
the former, and which, at the same time, had an outlet for the
currents equal to its own diameter, through the conducting wires.
A similar relation of mass occurs in the case where the body of
the magnet itself in revolving, does no more than a small radial
wire within it (3118.).
3138. The influence of this lateral conduction (3137.), in cases
of magneto-electric conduction, must be well understood; other-
wise, in the application of the principles to investigation, errors
will frequently creep in. Their effect may be shown in the
following instances:—a loop of four wires, 0·048 of an inch in
diameter (3136.), was passed over the pole of the magnet, and
produced a certain result of deflection or swing; when the wires
were separated two and two, so as to be half or three-quarters
of an inch apart, and when, therefore, in moving across the mag-
netic field, one pair went before the others, the effect was less,
for the reason already given in the case of the copper cylinder
(3137.). When three wires were allowed to go by together, but
one taken aside a couple of inches, the effect fell very much; and
when that fourth one was cut across to prevent the return current
in it, the effect of the three rose at the galvanometer very greatly,
almost equalling the effect of the four when together.
3139. A loop was constructed of seventy-six equal fine copper
wires, each 10.5 inches long and 0.0125 of an inch in diameter,
and its effect observed when more and more of the wires were
cut away.
As it is the comparison of the smaller numbers of
wires, one with the other, that is of most value, I will give the
averages of each number for several observations, in the reverse
order in which they were obtained; and I introduce the results
with larger numbers of wires only for the general purpose of
showing how the effect passes into that with the cylinder of copper
(3137.), the galvanometer conductors always being of the same
length and thickness.
1 wire produced an average swing of
2 wires produced an average swing of .
3 wires produced an average swing of
4 wires produced an average swing of.
5 wires produced an average swing of
8.3
15.3
21.8
27.9
34.4
2A2
356
[SERIES XXVIII.
Lines of magnetic force.
6 wires produced an average swing of
8 wires produced an average swing of
12 wires produced an average swing of
16 wires produced an average swing of
26 wires produced an average swing of.
36 almost swung the needle round.
46 stronger than the last.
56 swung the needle quite round.
66 a little stronger.
37.8
50.1
65.1
80.5
118.0
76 stronger: swung the needle freely round the circle.
Each time that the needle passed 180°, it was returned, that the
torsion force might remain the same for every case.
3140. When the loop of four equal wires (3136.) was employed,
so arranged that, in respect of the part which passed between
the poles, they should be close together in one plane, it made no
difference in the result, whether that plane was perpendicular to
the magnetic axis or parallel to it; i. e. whether the wires in
moving, formed a band which moved edgeways or flat ways; the
results were the same as with the four wires close together, so
as to represent, as far as they could, a round or square wire.
3141. From all these results it may be concluded, that the
current or amount of electricity evolved in the wire moving
amongst the lines of force, is not, simply, as the space occupied
by its breadth correspondent to the direction of the line of force,
which has relation to the polarity of the power, nor by that
width or dimension of it which includes the number or amount
of the lines of force, and which, corresponding to the direction
of the motion, has relation to the equatorial condition of the lines;
but is jointly as the compound ratio of the two, or as the mass
of the moving wire. The power acts just as well on the interior
portions of the wire as on the exterior or superficial portions,
and a central particle, surrounded on all sides by copper, is just
in the same relation to the force as those which, being superficial,
have air next them on one side.
3142. By immersing the poles of the magnet in different
media, and then making comparative experiments with the same
copper wire loop (3145.), it was found that the amount of the
induced current was the same in air, water, alcohol, and oil of tur-
pentine. The experiments in air were repeated between those
Ост. 1851.]
357
Moving wires-variation of substance.
with the liquids, so as to give a very consistent and safe result
as to the equality of action in all the cases.
3143. The effect of variation of substance was the next subject
which seemed to me important to bring under investigation,
because it has a direct relation to the amount of force exerted,
or ready to be exerted, within solid bodies, at any distance from
the magnet, in situations and under circumstances where it was
absolutely impossible to apply the vibrations of a magnetic needle,
or any other form of the effects of attractive and repulsive forces.
The interior of such bodies as iron, copper, bismuth, mercury,
&c., including the most paramagnetic and the most diamagnetic,
seemed, in this way, open to experimental investigation, both
as to the amount of lines of force traversing them under various
circumstances, and also as to the direction of the lines or their
polarity.
3144. In an early series of these Researches', experiments
bearing upon this subject are described (205-213.). Wires of
different metals were moved across the lines of force of a magnet,
and the result arrived at was, that the currents induced in these
different bodies were proportional to their electro-conduction
power (202. 213.).
3145. The thick wire galvanometer (3123.), with its good and
short conducting communications, promised however better re-
sults, and therefore loops like those already described of copper
wire (3133.), were prepared with wires of different metals, all of the
same diameter, namely, 0·04 of an inch, being only th of the
substance of the conducting and galvanometer wire. The metels
were copper, silver, iron, tin, lead, platinum, zinc. Under these
circumstances the substance concerned in the excitement of the
current is made to vary, whilst the conducting part of the system
is very good and remains the same. The results with these
loops were as follows, being the average of from six to ten ex-
periments for each loop:-
Copper
63.0
Silver.
61.9
Zinc
31.5
Tin
19.1
Iron .
Platinum
Lead..
18.0
16.9
12.1
¹ Philosophical Transactions, 1832, pp. 179–182.
358
[SERIES XXVIII.
Lines of magnetic force.
3146. In order to dismiss, as much as possible, the obstruction
caused by bad conducting power, and bring out any difference
that might exist between paramagnetic and diamagnetic metals,
three metals were selected, namely, tin, iron and lead in wires, as
before, of 0.04 of an inch diameter; but the length was restricted
to 3 inches, instead of extending to 10.5 inches, and the rest of
the loop was made up of the conducting copper wire of 0.2 in
diameter, as in fig. 18 Of course, the effect of the whole loop
Fig. 18

α
is a mixed effect, being partly due to the power represented by
the lines intersected by the thick copper portion, and partly by
those intersected by the three inches of special wire passing
between the poles. But as the great amount of force is concen-
trated within a space not more than an inch and a half or
2 inches in extent (as is seen on carrying any of the loops across
the magnetic axis), and as even that could be made still more
concentrated by using the iron cube (3129.), and so bringing the
poles virtually nearer to each other, it was hoped that the chief
effect would be there, and so any peculiar difference existing
between iron on the one hand and tin and lead on the other, be
rendered manifest, especially as the resistance to conduction was
greatly diminished by shortening the wires from 10.5 to 3 inches.
3147. The many experiments made with each metal were
very close together. The average of the results for the three
metals was as follows:-
Tin
Iron
Lead
37.1
34.8
25.4
The proportions, and therefore the results, are almost identical
with those obtained before (3145.).
3148. When lead and copper, arranged at the bar magnets
(3084. 3085.), had been compared in former experiments with
each other by the fine wire galvanometer, the results for both
had been the same. But then the two wires used were short,
and far thicker than the wires of the galvanometer or of the
conducting circuit, and were therefore limited in the production
Ост. 1851.]
359
Moving wires-variation of substance.
of their peculiar action, by those circumstances of mass already
described (3137.). To show that that was the case, I now, with
the thick wire galvanometer, employed two equal loops of
copper and iron wire, 02 of an inch in thickness, fig. 16
(3133.), passing them equably over the pole of the small horse-
shoe magnet, reduced by the keeper (3134.). The results were
very consistent, and the mean of them was, for
Copper.
Iron.
41.7
33.7
3149. Here, therefore, the difference between copper and iron
is not so great as that of 1 to 1.24; whilst when the conductors,
not concerned in the excitement, were very good, and able,
comparatively, to carry on to the galvanometer nearly all the
effect of the excitement, it was as great as 1 to 3′5, the dif-
ference being in the latter case above tenfold what it is in the
former.
3150. To raise the effect dependent upon the mass in relation
to that of the conducting wires to a still higher degree, I had a
cylinder of iron, 5.5 inches in length and 0·7 of an inch in
diameter, soldered on to the ends of conducting wires, so as to
be in all respect like that of copper before described (3137.).
In this case the iron not only rose up to the copper in effect,
but even surpassed it; the results being for copper 35°66, and
for iron 38°.32. Thus, under these circumstances of mass, the
difference between iron and copper disappears. The apparent
inferiority of copper is probably due to the lateral discharge,
which before reduced the effect of a cylinder below that of a
thick wire (3137.). The iron being a worse conductor in itself,
and having equally good conductors in the prolongation of the
circuit as when it was employed as wire, would, I think, have
proportionately less lateral discharge in it than the copper.
3151. For a comparison, both as regards the particular sub-
stance and the mass, I attached a similar cylinder of bismuth to
conductors. Its effect, with the same magnet and force, was
23°; a very high proportion in relation to the copper, and no
doubt due to its mass. If it could have been compared as a
wire, only 0.04 in diameter (3145.), it would probably have ap-
peared almost indifferent (3127.)'.
¹ When bismuth is soldered into the circuit, it requires to be left a long
360
Lines of magnetic force. [SERIES XXVIII.
3152. So the current of electricity excited in different sub-
stances, moving across lines of magnetic force, appears to be
directly as the conducting power of the substance. It appears
to have no particular reference to the magnetic character of the
body, for iron comes between tin and platinum, presenting no
other distinction than that due to conducting power, and differ-
ing far less from them, than they do from other metals not
magnetic.
3153. The amount of lines of force (and of the force repre-
sented by them) appears, therefore, to be equal for equal spaces
occupied and traversed by tin, iron, and platina under the cir-
cumstances; for the difference in result is in no proportion to the
ordinary magnetic difference, and only as the conducting power.
This agrees with the conclusion before arrived at, that, for air,
water, bismuth, oxygen, nitrogen, or a vacuum, the lines of force
are the same in amount, except as they are more or less concen-
trated in the substance across which they pass (2807.), according
as it is more or less competent to conduct (2797.), or transmit
the magnetic force.
3154. Such a conclusion as that just arrived at, brings on the
question of what is magnetic polarity, and how is it to be defined?
For my own part, I should understand the term to mean, the
opposite and antithetical actions which are manifested at the
opposite ends, or the opposite sides, of a limited (or unlimited)
portion of a line of force (2835.). The line of dip of the earth,
or a part of it, may again be referred to as the natural case; and
a free needle above or below the part, or a wire moving across it
(3076. 3079.), will give the direction of the polarity. If we refer
to an entirely different and artificial source as the electro-mag-
netic helix, the same meaning and description will apply.
3155. If the term polarity have any meaning, which has re-
ference to experimental facts and not to hypotheses only, beyond
that included in the above description, I am not aware that it
time before it is used for experiments, and should then be covered up, and
the loop handled with great care; otherwise thermo-currents are produced.
For an hour or two after soldering it generates electrical currents, which
appear at the galvanometer very irregularly, being probably due to internal
molecular changes, which occur from time to time until the whole has ac-
quired a permanent state of equilibrium.
OCT. 1851.]
361
Magnetic polarity.
has ever been distinctly and clearly expressed. It may be so,
for I dare not venture to say that I recollect all I have read, or
even all the conclusions I myself have at different times come to.
But if it neither have, nor should have, any other meaning, then
the question arises, is it correctly exhibited or indicated in every
case by attractions and repulsions, i. e. by such like mutual ac-
tions of particular bodies on each other under the magnetic influ-
ence? A weak solution of protosulphate of iron, if surrounded
by water, will, in the magnetic field, point axially; if in a stronger
solution than itself, it will point equatorially (2357. 2366. 2422.)
The same is true with stronger cases. We cannot doubt it would
be true even up to iron, nickel, and cobalt, if we could render
these bodies fluid in turn without altering their paramagnetic
power, or if we had the command of magnets and of paramag-
netic and diamagnetic media, stronger or weaker at pleasure.
But in the case of the solutions, we cannot suppose that the
weaker has one polarity in the stronger solution and another in
the water. The lines of force across the magnetic field have the
same general polarity in all the cases, and would be shown ex-
perimentally to have it, by the moving wire (3076.), though not
by the attractions and repulsions.
3156. Here, therefore, we have a difference in the two modes
of experimental indication; not merely as to the method, but as
to the nature of the results, and the very principles which are
concerned in their production. Hence the value I think of the
moving wire as an investigator; for it leads us into inquiries
which touch upon the very nature of the magnetic force. There
is no doubt that the needle gives true experimental indications;
but it is not so sure that we always interpret them correctly.
To assume that pointing is always the direct effect of attractive
and repulsive forces acting in couples (as in the cases in ques-
tion, or as in bismuth crystals), is to shut out ideas, in relation
to magnetism, which are already applied in the theories of the
nature of light and electricity; and the shutting out of such
ideas may
be an obstruction to the advancement of truth and a
defence of wrong assumptions and error.
3157. What is the idea of polarity in a field of equal force?
(whether it be occupied by air or by a mass of soft iron?). A
magnetic needle, or an oblong piece of iron, would not show it
in the air or elsewhere, except by disturbing the equal arrange-
362
Lines of magnetic force. [SERIES XXVIII.
ment of the force and rendering it unequal; for on that the
pointing of the needle or the iron, or the motions of either
towards the walls of the magnetic field, if limited (2828.), would
depend. A crystal of bismuth in showing this polarity by posi-
tion (2464. 2839.), does it without much altering the distribu-
tion of the force, and the alteration which does take place is in
the contrary direction to that effected by iron (2807.), for it
expands the lines of force. It seems readily possible that a
magnecrystal might exist, which, when in its stable position,
should neither cause the convergence nor divergence of the
lines of force within it. It need only be neutral in relation to
space or any surrounding medium in that direction, and dia-
magnetic in its relation in the transverse direction, and the con-
ditions would be fulfilled.
3158. But though an ordinary magnetic needle cannot show
polarity in a field of equal force¹, having no reference to it, and
in fact ignoring such a condition of things, a moving wire makes
it manifest instantly, and also shows the full amount of magnetic
power to which such polarity belongs; and this it does without
disturbing the distribution of the power, as far as we comprehend
or understand distribution, when thinking of magnetic needles.
At least such at present appears to me to be the case, from the
consideration of the action of thin and thick wires (3141.) and
wires of different substances (3153.).
Fig. 19.
3159. As an experimentalist, I feel bound to let experiment
guide me into any train of thought which it may justify; being
satisfied that experiment, like analysis, must lead to strict truth
if rightly interpreted; and be-
lieving also, that it is in its
nature far more suggestive of
new trains of thought and
new conditions of natura
power. In order to extend
its indications, and vary the
form in which the principle of
the moving wire may be ap-
plied, I had an apparatus con-
structed, fig. 19, consisting of
a wooden axis, one extremity
¹ One could easily imagine hypothetically a needle that should do so.

Ост. 1851.]
363
Magnetic polarity.
of which was terminated by a copper screw, intended to recieve
and carry one or more discs of metal that might be screwed on
to it. This end projected so far beyond the support, that such
discs could be partly introduced between the poles of a horse-
shoe magnet, so as when revolving, to move across the lines of
force at their most intense place of action; and, whilst the mag-
net and the apparatus continued fixed, to revolve continuously
across the same lines of force. One of the galvanometer wires
was pointed, and so held as to bear into and against the surface
of a cup-shaped cavity at the end of the axial screw; and the
other was applied by the hand, or so fixed as to bear by a
rounded part against the rim of the disc, at that point which
was furthest within the poles of the magnet.
3160. Discs of metal were prepared for this apparatus, each
2.5 inches in diameter, and of different thicknesses and material.
When a disc of copper was fixed on the axis, and adjusted in
association with the large horseshoe magnet (3159.), as described
above, three, or even two revolutions of it, would deflect the
needle of the thick wire galvanometer through a swing of 30°.
In his apparatus, the most effectual part of the portion of the
disc which is at any moment passing across the magnetic axis,
is that which is near the circumference; for it has the greatest
velocity, consequently moves through more space, and that in a
part where the lines of force are most concentrated,
3161. The contact at the end of the axle should always be
carefully watched and made good. The degree of pressure on
the edge of the disc should not be too slight; otherwise the
contact, under the circumstances of the motion, is not sufficient
to carry forward the same constant proportion of current
generated. Neither should it be made at the angles of the disc
edge; if a grating or cutting friction occur, an electric current is
genrated by it. With a smooth hard friction of copper wire
against the copper disc there is very little evolution of current.
When the copper wire presses against the edge of an iron disc
there is far more. In either case, however, the effect may be
eliminated or compensated; for, in whichever direction the disc
is revolved without the magnet, the deviation of the needle, if any
be produced, remains the same; whereas, when the magnet is in
place, the deviations produced by it are in the reversed direction
for reversed revolutions. Hence, if an equal number of revolu-
364
Lines of magnetic force. [SERIES XXVIII.
tions be made in the two directions, and the unequal deflections
in opposite directions be noted, the half of their sum will give
nearly the amount of deflection which would have occurred if no
current had been exerted by friction at the edge, i. e. provided
the deflections have not been through large arcs. These effects
of friction are no doubt objections to the principle in this form;
still the results are, as it appears to me, valuable in relation to
copper and iron, and are as follows.
3162. A copper disc, 0.05 of an inch in thickness, gave a
swing deflection for two revolutions, which, being the avarage of
several experiments =20°.8. A second copper disc, of 01 of
an inch in thickness, gave an average deflection of 27°.8. A
third copper disc, of 0.2 in thickness, gave a deflection of 26°·5.
Here, therefore, not only has the thickness (with these conditions
of contact) been attained for the maximum effect, but even sur-
passed (3137.). Then an iron disc of 0.05 in thickness, was
placed on the axle, and gave, as its mean result, a deflection of
15°-4. Another iron disc of four times the thickness (or 0·2)
gave a deflection only of 14°. So here also, as before, the thick-
ness of maximum effect had been surpassed.
3163. The two discs of copper and iron of 0.2 in thickness
each, which had produced separately the respective deviations
of 26°.5 and 14°, were then both fixed on the axle, being
separated from mutual contact in respect of their mass, by a disc
of paper, though both were of course in contact at the centre of
motion with the copper axle, by means of which the electric
communication was perfected. In arranging their place between
the poles of the magnet, the iron was placed at mid-distance,
and therefore the copper a little on one side. When the copper
disc was brought into the circuit, it, by two revolutions, gave an
average deviation of 2304; and when the iron disc was in the
circuit, the deviation produced by it was 11°.91. Here, there-
fore, the proportions were nearly the same, when the two discs
were subject at the same moment to the magnetic power, as
when they were examined separately. Both have fallen a little,
but not in any manner which seems to indicate that the iron has
had any peculiar influence in altering or affecting the lines of
force passing across the magnetic field. The effect which has
taken place, appears to be one due to the action of the collateral
mass of conducting matter.
OCT. 1851.]
365
Magnetic polarity.
3164. If the direction of the electric current induced by the
magnetic force in the moving metal be taken as the true indica-
tion of polarity, and, I think, it cannot be denied that it repre-
sents that character of the force, which the term polarity s
intended to express, and is unchangeably associated with that
character; then these results show that the polarity of the lines
of force within the iron is the same with that within the copper,
when both are submitted in like manner to the magnetic force.
In association with the former and new results with bismuth
(2431. 3151. 3168.), and numerous other phænomena, the same
conclusion may be drawn as to the lines of force within that sub-
stance, for the effects are the same with regard to the production
of a current in it; and so further evidence is added to that which
I have given, tending to show that bismuth is not polarized in the
reverse direction as iron or a magnet (2429. 2640.). By reference
to the phænomena presented by the relative actions of paramag-
netic and diamagnetic substances, the same conclusions may be
drawn with respect to all bodies and to space itself (2787. &c.).
3165. That the iron disc affects the disposition of the lines of
force, is no doubt true, and the extent to which this is done is
easily seen, by fixing a small magnetic needle, about 0·1 or 0·05
of an inch in length, across the middle of a piece of stretched
thread as an axis, and then bringing it into the magnetic field
and near the edges of the stationary disc. The lines of force will
be seen (3071. 3076.) gathering in upon the iron at and near its
edge, but only for a very little distance from it in any direction:
the effect is that which I have considered proper to a paramag-
netic body (2807.). Elsewhere, the lines of force go with the
same direction across the magnetic field where the iron is, as
where it is not; and it is to me a proyed fact, proved by the
numerous results given, that a section of the lines of force
taken across the magnetic field through the air, close to the
iron, is exactly equal in amount of force to a section taken
across parallel to and through the iron disc (3163.). All iron
under induction must have just as much force, i. e. lines of
force in its internal parts, as is equivalent to the lines which
fall on to, and are continued through and out of it; and the
same is true, as it appears to me, of any other paramagnetic
or diamagnetic substance whatever. The same is true for the
magnet itself; for a section through the magnet has been shown
.
"
366
[SERIES XXVIII.
Lines of magnetic force.
to be exactly equal to a section anywhere through the outer
lines of force (3121.), and these sections may be taken at the
surface of the magnet, where they may be considered as either
in the air or in the magnet indifferently; and therefore alike in
size, shape, power, polarity, and every other point.
3166. I have used the phrase conduction polarity on a former
occasion (2818. 2835.), but so limited, that it could lead to no
mistake of my meaning, either then or now. It requires no
words to show how it is included in the higher and general
expression of the direction or polarity of the lines of force.
3167. Some other results with the disc apparatus (3159.)
were obtained, which it may be useful to describe here. Tin
was formed into a disc of 0·1 in thickness, and 2.5 inches in
diameter. The effect of the friction of the copper conductor
at its edge, was a feeble current, the reverse of that produced
in the cases of copper and iron (3161.); but the current pro-
duced by the revolution, and dependent on the polarity of the
lines of force, was the same as before. It produced a swing
deflection of 14°.9 for two revolutions of the disc.
3168. A disc of bismuth produced far too strong a current by
friction against the copper conductor, to allow of any useful result
in its simple state. A ring of copper foil was therefore formed,
and being placed tightly on the bismuth disc, was wedged up
by plates of clean copper foil, so as to produce a clean hard
contact; imperfect, no doubt, but as general as could be made
under the circumstances. When this disc was rotated in the
one direction, it gave a deflection in the same direction as if
a copper or iron disc had been used; when rotated the other
way, the deflection was little or nothing. This difference is
due to the united influence of the rotation effect and the friction
effect in the one case, and their opposition in the other; but the
results show that the lines of force are in the same direction
through bismuth, when between the magnetic poles, as they
are through copper and iron. The induced current is small,
both because of the bad conducting power of the bismuth and
the imperfect contact at the edge. When the same copper
rim was placed on the copper disc, it reduced the deflection of
the needle from 26°5 to 9°.34.
.
OCT. 1851.]
367
Moving discs-considerations.
3169. In illustration of the effect produced by those parts
of the disc, which, not being in the place of greatest action, are
conducting back those currents formed by the radial parts in
the place of maximum effect, I had a wooden disc constructed,
0.2 in thickness and 2.5 inches in diameter, the centre of which
was copper, for the purpose of attachment and electrical con-
nection, and the outer edge a ring of copper not more than th
of an inch in thickness. The two were connected by a single
copper wire radius, in thickness 0·056 of an inch, which, as the
disc revolved, was of course carried across and through the
magnetic field. It gave a deflection of 14°. The copper disc
of 0.05 thickness, gave only an average of 28°. Now, though
the matter of the copper ring round the wood will cause part of
the current, yet the chief portion must be due to the copper
radius, which, at the effectual part near the edge (3160.), is not
more than the 14th part of the full copper disc; and this indi-
cates how much of the electricity put in motion there by the
magnetic force must be returned back in short circuits in the
other parts of the disc.
3170. The disc apparatus shows well the dependence of the
induced current upon the intersection of the lines of force (3082.
3113.). If the disc be so arranged as to stand edgeways to the
magnetic poles, and in the plane of the magnetic axis, so that
it shall be parallel to the lines of force which pass by and through
it, then no revolution of it, with the most powerful magnet,
produces the slightest signs of a current at the galvanometer.
3171. The relation of the induced current to the electro-con-
ducting power of the substance, amongst the metals (3152.),
leads to the presumption that with other bodies, as water, wax,
glass, &c., it is absent, only in consequence of the great defi-
ciency of conducting power. I thought that processes analo-
gous to those employed with the metals, might in such non-
conductors as shell-lac, sulphur, &c., yield some results of static
electricity (181. 192.); and have made many experiments with
this view in the intense magnetic field, but without any distinct
result.
3172. All the results described are those obtained with moving
metals. But mere motion would not generate a relation, which
368
[SERIES XXVIII.
Lines of magnetic force.
had not a foundation in the existence of some previous state;
and therefore the quiescent metals must be in some relation to
the active centre of force, and that not necessarily dependent on
their paramagnetic or diamagnetic condition, because a metal
at zero in that respect, would have an electric current generated
in it as well as the others. The relation is not as the attractions
or repulsions of the metals, and therefore not magnetic in the
common sense of the word; but according to some other function
of the power. Iron, copper, and bismuth are very different in
the former sense, but when moving across the lines of force,
give the same general result, modified only by electro-con-
ducting power.
3173. If such a condition be hereafter verified by experiment
and the idea of an electrotonic state (60. 242. 1114. 1661. 1729.)
be revived and established, then, such bodies as water, oil,
resin, &c., will probably be included in the same state; for the
non-conducting condition, which prevents the formation of a
current in them, does not militate against the existence of that
condition which is prior to the effect of motion. A piece of
copper, which cannot have the current, because it is not in a
circuit (3087.), and a piece of lac, which cannot, because it is a
non-conductor of electricity, may have peculiar but analogous
states when moving across a field of magnetic power.
3174. On bringing this paper to a close, I cannot refrain
from again expressing my conviction of the truthfulness of the
representation, which the idea of lines of force affords in regard
to magnetic action. All the points which are experimentally
established with regard to that action, i. e. all that is not hypo-
thetical, appear to be well and truly represented by it. What-
ever idea we employ to represent the power, ought ultimately
to include electric forces, for the two are so related that one
expression ought to serve for both. In this respect, the idea
of lines of force appears to me to have advantages over the
method of representing magnetic forces by centres of action.
In a straight wire, for instance, carrying an electric current, it
is apparently impossible to represent the magnetic forces by
centres of action, whereas the lines of force simply and truly
represent them. The study of these lines have, at different
times, been greatly influential in leading me to various results,
which I think prove their utility as well as fertility. Thus, the
Ост. 1851.]
369
Value of the moving wire.
law of magneto-electric induction (114.); the earth's inductive
action (149. 161. 171.); the relation of magnetism and light
(2146. and note); diamagnetic action and its law (2243.), and
magnecrystallic action (2454.), are cases of this kind: and a
similar influence of them, over my mind, will be seen in the
further instances of the polarity of diamagnetic bodies (2640.);
the relation of magnetic curves and the evolved electric currents
(243.); the explication of Arago's phænomenon (81.), and the
distinction between that and ordinary magnetism (342. 245.);
the relation of electric and magnetic forces (1709.); the views
regarding magnetic conduction (2797.), and atmospheric mag-
netism (2847.). I have been so accustomed, indeed, to employ
them, and especially in my last Researches, that I may, unwit-
tingly, have become prejudiced in their favour, and ceased to be
a clear-sighted judge. Still, I have always endeavoured to make
experiment the test and controller of theory and opinion; but
neither by that nor by close cross examination in principle, have
I been made aware of any error involved in their use.
3175. Whilst writing this paper I perceive, that, in the late
Series of these Researches, Nos. XXV. XXVI. XXVII., I have
sometimes used the term lines of force so vaguely, as to leave
the reader doubtful whether I intended it as a merely repre-
sentative idea of the forces, or as the description of the path
along which the power was continuously exerted. What I have
said in the beginning of this paper (3075.) will render that
matter clear. I have as yet found no reason to wish any part
of those papers altered, except these doubtful expressions: but
that will be rectified if it be understood, that, wherever the ex-
pression line of force is taken simply to represent the disposition
of the forces, it shall have the fullness of that meaning; but that
wherever it may seem to represent the idea of the physical mode
of transmission of the force, it expresses in that respect the
opinion to which I incline at present. The opinion may be
erroneous, and yet all that relates or refers to the disposition of
the force will remain the same.
3176. The value of the moving wire or conductor, as an exa-
miner of the magnetic forces, appears to me very great, because
it touches the physics of the subject in a manner altogether dif-
ferent to the magnetic needle. It not only gives its indications
upon a different principle and in a different manner, but in the
VOL. III.
2 B
370
[SERIES XXVIII.
Lines of magnetic force.
mutual action of it and the source of power, it affects the power
differently. The wire when quiescent does not sensibly disturb
the arrangement of the force in the magnetic field; the needle
when present does. When the wire is moving it does not sensibly
disturb the forces external to it, unless perhaps in large masses,
as in the discs (3163.), or when time is concerned (1730.), i. e. it
does not disturb the disposition of the whole force, or the arrange-
ment of the lines of force; a field of equal magnetic power is
still equal to anything but the moving wire, whilst the wire
moves across or through it. The moving wire also indicates
quantity of force, independent of tension (2870.); it shows that
the quantity within a magnet and that outside is the same, though
the tension be very different. In addition to these advantageous
points, the principle is available within magnets, and paramag-
netic and diamagnetic bodies, so as to have an application beyond
that of the needle, and thus give experimental evidence, of a
nature not otherwise attainable.
Royal Institution,
October 9, 1851.
371
TWENTY-NINTH SERIES ¹.
§ 35. On the employment of the Induced Magneto-electric
Current as a test and measure of Magnetic Forces.
Received December 31, 1851,-Read March 25 and April 1, 1852.
3177. THE proposition which I have made to use the induced
magneto-electric current as an experimental indication of the
presence, direction and amount of magnetic forces (3074.), makes
it requisite that I should also clearly demonstrate the principles
and develope the practice necessary for such a purpose: and
especially that I should prove that the amount of current in-
duced is precisely proportionate to the amount of lines of mag-
netic force intersected by the moving wire, in which the electric
current is generated and appears (3082. 3109.). The proof
already given is, I think, sufficient for those who may repeat the
experiments; but in order to accumulate evidence, as is indeed
but proper in the first announcement of such a proposition, I pro-
ceeded to experiment with the magnetic power of the earth,
which presents us with a field of action, not rapidly varying in
force with the distance, as in the case of small magnets, but one
which for a given place may be considered as uniform in power
and direction; for if a room be cleared of all common magnets,
then the terrestrial lines of magnetic force which pass through
it, have one common direction, being that of the dip, as indi-
cated by a free needle or other means, and are in every part in
equal proportion or quantity, i. e. have equal power. Now the
force being the same everywhere, the proportion of it to the
current evolved in the moving wire is then perhaps more simply
and directly determined, than in the case where, a small magnet
being employed, the force rapidly changes in amount with the
distance.
¹ Philosophical Transactions, 1852, p. 137.
2 B 2
372
[SERIES XXIX.
Lines of magnetic force.
Ti. Galvanometer.
3178. For such experimental results as I now propose to give,
I must refer to the galvanometer employed and the precautions
requisite for its proper use. The instrument has been already
described in principle (3123.), and a figure of the conductor
which surrounds the needles, given. This conductor may be
considered as a square copper bar, 0-2 of an inch in thickness,
which passes twice round the plane of vibration of each of the
needles forming the astatic combination, and then is continued
outwards and terminates in two descending portions, which are
intended to dip into cups of mercury. As both the needles are
within the convolutions of this bar, an indicating bristle or fine
wire of copper is fixed parallel to, and above them upon the
same axis, and this, in travelling over the usual graduated circle,
shows the place and the extent of vibration or swing of the
needles below. The suspension is by cocoon silk, and in other
respects the instrument is like a good ordinary galvanometer.
Fig. 1.
3179. It is highly important that the bar of copper about the
needles should be perfectly clean. The vertical zero plane
should, according to the construction, be midway between the
two vertical coils of the bar, fig. 1; instead of which the
needle at first pointed to the one side or the
other, being evidently attracted by the upright
portions of the bar. I at first feared that the
copper was magnetic, but on cleaning the
surface carefully with fine sand-paper, I was
able to remove this effect, due no doubt to
iron communicated by handling or the use of
tools, and the needle then stood truly in a
plane equidistant from the two coils, when
that plane corresponded with the magnetic
meridian.
3180. The connexions for this galvanometer (3123. 3133.)
were all of copper rod or wire 0.2 of an inch in diameter; but
even with wires of this thickness the extent of the conductors
should not be made more than is necessary; for the increase
from 6 to 8, 10 or 12 feet in length, makes a considerable dif-
ference at the galvanometer, when electric currents, low in in-
tensity, are to be measured. It is most beautiful to observe in

DEC. 1851.]
373
Thick wire galvanometer.
such cases the application of Ohm's law of currents to the effects
produced. When the connexions were extended to a distance,
straight lengths of wire with dropping ends were provided, and
these by dipping into cups of mercury completed the connexion
and circuit. The cups consisted of cavities turned in flat pieces
of wood. The ends of the connecting rods and of the galvano-
meter bar were first tinned, and then amalgamated; after which
their contact with the mercury was both ready and certain.
Even where connexion had to be made by contact of the solid
substances, I found it very convenient and certain to tin and
amalgamate the ends of the conductors, wiping off the excess
of mercury. The surfaces thus prepared are always ready for
a good and perfect contact.
3181. When the needle has taken up its position under the
earth's influence, and the copper coil is adjusted to it, the needle
ought to stand at true zero, and appears so to do. When that is
really the case, equal forces applied in succession on opposite
sides of the needle (by two contrary currents through the coil
for instance) ought to deflect the needle equally on both sides,
and they do so. But sometimes, when the needle appears to
stand at zero, it may not be truly in the magnetic meridian;
for a little torsion in the suspension thread, even though it be
only 10° or 15° (for an indifferent needle), and quite insensible
to the eye looking at the magnetic needle, does deflect it, and
then the force which opposes the swing of the needle, and
which stops and returns the needle towards zero (being due
both to the torsion and the earth's force), is not equal on the
two sides, and the consequence is, that the extent of swing in
the two directions is not equal for equal powers, but is greater
on one side than the other.
3182. I have not yet seen a galvanometer which has an ad-
justment for the torsion of the suspending filament. Also, there
may be other causes, as the presence about a room, in its walls
and other places, of unknown masses of iron, which may render the
forces on opposite sides of the instrument zero unequal in a slight
degree; for these reasons it is better to make double observations.
All the phænomena we have to deal with, present effects in two
contrary directions. If a loop pass over the pole of a magnet
(3133.), it produces a swing in one direction; if it be taken
away, the swing is in the other direction; if the rectangles and
374
[SERIES XXIX.
Lines of magnetic force.
rings to be described (3192.) be rotated one way, they produce
one current; if the contrary way, the other and contrary current
is produced. I have therefore, always, in measuring the power of
a pole or the effect of a revolving intersecting wire, made many
observations in both directions, either alternately or irregularly;
have then ascertained the average of those on the one side, and
also on the other (which have differed in different cases from th
tooth part); and have then taken the mean of these averages
as the expression of the power of the induced electric current, or
of the magnetic forces inducing it.
1
50
3183. Care must be taken as to the position of the instrument
and apparatus connected with it, in relation to a fire or sources
of different temperatures, that parts which can generate thermo-
currents may not become warmed or cooled in different degrees.
The instrument is exceedingly sensible to thermo-electric cur-
rents; the accidental falling of a sun-beam upon one of two
connecting mercury cups for a few moments disturbed the indi-
cations and rendered them useless for some time.
3184. In order to ascertain practically, i. e. experimentally,
the comparative value of degrees in different parts of the scale
or graduation of this instrument and so to render it a measurer,
the following trials were made. A loop like that before de-
scribed (3133.), fig. 2, was connected with the galvanometer by
Fig. 2.

с
communications which removed the loop 9 feet from the instru-
ment, and it was then fixed. A compound bar-magnet con-
sisting of two plates, each 12 inches long, 1 inch broad, and
0.5 in thickness, was selected of such strength as to lift a bunch
of clean iron filings, averaging 45 grains at either extremity.
Blocks were arranged at the loop, so that this magnet, held in a
vertical position, could have one end passed downwards through
the loop until the latter coincided with the equator of the mag-
net (3191.); after which it could be quickly removed and the
same operation be repeated at pleasure. When the magnet was
thus moved, the loop being unconnected (at one of the mercury
cups) with the galvanometer, there was no sensible change of
DEC. 1851.]
375
Galvanometer indications.
place in the needles; the direct influence of the magnet at this
distance of 9 feet being too small for such an effect.
3185. It must be well understood, that, in all the observations
made with this instrument, the swing is observed and counted
as the effect produced, nnless otherwise expressed. A constant
current in an instrument will give a constant and continued
deflection, but such is not the case here. The currents observed
are for short periods, and they give, as it were, a blow or push
to the needle, the effect of which, in swinging the needle, con-
tinues to increase the extent of the deflection long after the cur-
rent is over. Nevertheless the extent of the swing is dependent
on the electricity which passed in that brief current; and, as
the experiments seem to indicate, is simply proportional to it,
whether the electricity pass in a longer or shorter time (3104.),
and notwithstanding the comparative variability of the current
in strength during the time of its continuance.
3186. The compound bar being introduced once into the loop
and left there, the swing at the galvanometer was observed and
found to be 16°; the galvanometer needle was then brought to
zero, and the bar removed, which gave a reverse current and
swing, and this also was 16°. Many alternations, as before
described, gave 16° as the mean result, i. e. the result of one
intersection of the lines of force of this magnet (3102.). In
order to comprehend the manner in which the effect of two or
more intersections of these lines of force were added together,
it should be remembered that a swing of the needle from right
to left occupied some time (13 seconds); so that one is able to
introduce the magnet into the loop, then break the electric cir-
cuit by raising one end of the communicating wire out of the
mercury, remove the magnet, which by this motion does nothing,
restore the mercury contact, and reintroduce the magnet into
the loop, before a tenth part of the time has passed, during
which the needles, urged by the first impulse, would swing.
In this way two impulses could be added together, and their
joint effect on the needle observed; and, indeed, by practice, three
and even four impulses could be given within the needful time,
i. e. within one-half or two-thirds of the time of the full swing;
but of course the latter impulses would have less power upon
the needles because these would be more or less oblique to the
376
[SERIES XXIX.
Lines of magnetic force.
current in the copper coil at the time when the impulses were
given. There can be no doubt, that, as regarded the currents
induced in the loop by the magnet, they would be equal on every
introduction of the same magnet.
3187. Proceeding in this way I obtained results for one,
two, three, and even four introductions with the same magnet.
One introduction.
Two introductions
Three introductions
Four introductions
15
31.25
46.87
58.50
Here the approximation to 1, 2, 3, 4, cannot escape observation';
and I may remark, that, whilst observing the place attained at
the end of a swing which is retained only for an instant, some
degree of error must creep in; and that that error must be
greatest, in the first number, where it falls altogether upon the
unit of comparison, than in the other observations, where only
one-half or one-third of it is added to a half or a third of the
whole result. Thus, if we halve the arc for two introductions
of the pole, it gives 15°.625; if we take the third of that for three
introductions, it gives 15°·61 ;-numbers which are almost iden-
tical, so that if the first number was increased by only 0°.6, the
proportion would be as 1, 2, and 3. The reason why the fourth,
which is 14° 625, is less, may perhaps be referred to the cause
already assigned, namely, the declination distance of the needle
from the coil when that impulse was given (3186.).
3188. In order to avoid in some degree this case, and to com-
pare the degrees at the beginning of the scale, which are most
important for the comparison of future experiments with one
¹ See note to (3189.)
= sin°7'30 =130526
15
sin
•130526
2
31.25
sin
= sin 15·625= sin 15 37.5=269200
2
269200
2
=·134600
46.87
sin
= sin 23·435= sin 23 26·1·3976818
2
3976818
3
=1328606
58.50
4886212
sin
= sin 29.25 = sin 27 15 =·4886212
=1221553
2
4
DEC. 1851.]
377
Galvanometer indications.
another, I took only one of the bars of the compound magnet
employed above (3184.). The results were as follows:-
One introduction
Two introductions
Three introductions
Four introductions.
15.75
23.87
31.66
which numbers are very closely as 1, 2, 3 and 4. If we divide
as before, we have 8°, 7°.87, 7°.95, 7°.91; so that if only 0.09
be substracted from the first observation, or 8°, it leaves that
simple result¹.
3189. Hence it appears, that in this mode of applying and
measuring the magnetic powers, the number of degrees of swing
deflection are for small arcs nearly proportional to the magnetic
force which has been brought into action on the moving wire².
3190. I have found the needles very constant in their strength
for days and weeks together. By care, the constancy of their
state for a day is easily secured, and that is all that is required
in comparative experiments. Those which I have in use weigh
1 sin
8
sin 4
='0697565
*0697565
2
15.75
sin
sin 7.875= sin 7 52·5·1370123
2
1370123
2
='0685061
23.87
2068019
sin
=
sin 11.935 sin 11 56·1='2068019
='0689340
2
3
31.66
sin
= sin 15·83 = sin 15 49·8='2727840
2
2727840
4
:'0681960
2 Mr. Christie has recalled my attention to a paper in the Philosophical
Transactions, 1833, p. 95, in which he has investigated, at p. 111, &c., the
effect of what may be called magneto-electric impulses in deflecting the mag-
netic needle. He found that the velocity of the projection of the needle, which
is a measure of the force acting upon it at the instant of its moving, will be
proportional to the sine of half the arc of swing. My statement, therefore,
would as a general expression be erroneous; but for small arcs the results as
given by it are not far from the truth. The error does not interfere with the
general reasoning and conclusions of the paper; and as the numbers are the
results of experiments, which, though made with a first and therefore rough
apparatus, were still made with some care, and are expressed simply as de-
flections, I prefer their appearance as they are rather than in an altered state.
Mr. Christie has been so kind as to give me the true expression of force for
many of the cases, and I have inserted the results as foot-notes where the
cases occur.-Jan. 26, 1852,
378
Lines of terrestrial magnetic force. [SERIES XXIX.
with their axis and indicating wire 9 grains; and when out of
the copper coil vibrate to and fro once in 26 secouds.
3191. With this instrument thus examined, I repeated most
of the experiments with loops formerly described (3133. &c.)
with the same results as before. It was also ascertained that
the equator of a regular bar-magnet was the place at which the
oop should be arrested, to produce the maximum action; and
that if it came short of, or passed beyond that place, the final
result was less. Employing a magnet 12 inches long, when the
loop passed.
2.3 inches over the pole the deflection was
4.1 inches over the pole the deflection was
5.1 inches over the pole the deflection was
6·1 inches over the pole the deflection was
8.0 inches over the pole the deflection was
9.0 inches over the pole the deflection was
Tii. Revolving Rectangles and Rings¹.
e
Fig. 3.
5.91
7.50
7.74
8.16
7.75
6.50
3192. The form of moving wire which I have adopted for
experiments with the magnetic forces of the earth (3177.), is
either that of a rectangle or a ring. If a wire rectangle (fig. 3)
be placed in a plane, perpendicular to the
dip and then turned once round the axis
a b, the two parts c d and e f will twice in-
tersect the lines of magnetic force within
the area ce df. In the first 180° of revolu-
tion the contrary direction in which the two
parts c d and e f intersect those lines, will
cause them to conspire in producing one current, tending to
run round the rectangle (161.) in a given direction; in the fol-
lowing 180° of revolution they will combine in their effect to
produce a contrary current; so that if the first current is from
a
C
B---
d
¹ A friend has pointed out to me that in July 1832, Nobili made experi-
ments with rotating rings or spirals subject to the earth's magnetic influence;
they were subsequent to and consequent upon my own experiments upon
swinging wires (171. 148.) and revolving globes (160.) of January 1832; but
he extended the considerations to the thickness of the wire, the diameter of
the spirals and the number of the spirals dependent upon the length of the wire.
The results (tabulated) will be found in vol. i. page 244, &c. of the Florence
edition of his Mémoires.—March 1, 1852.
DEC. 1851.]
379
Revolving rectangle apparatus.
d by ce and f to d again, the second will be from d by fe and
c to d. If the rectangle, instead of being closed, be open at b,
and the ends there produced be connected with a commutator,
which changes sides when the rectangle comes into the plane
perpendicular to the dip, i. e. at every half revolution, then these
successive currents can be gathered up and sent on to the gal-
vanometer to be measured. The parts ce and dƒ of the rect-
angle may be looked upon simply as conductors; for as they do
not in their motion intersect any of the lines of force, so they do
not tend to produce any current.
3193. The apparatus which carries these rectangles, and is
also the commutator for changing the induced currents, consists
of two uprights, fixed on a wooden stand, and carrying above a
wooden horizontal axle, one end of which is furnished with a
handle, whilst the other projects, and is shaped as in fig. 4. It
may there be seen, that two semicylindrical plates of copper a b
are fixed on the axle, forming a cylinder round it, except that
they do not touch each other at their edges, which therefore
leave two lines of separation on opposite sides of the axle. Two
strong copper rods, 0.2 of an inch in diameter, are fixed to
the lower part of the upright c, terminating there in sockets
with screws for the purpose
of receiving the ends of the
rods proceeding from the gal-
vanometer cups (3180.): in
the other direction the rods
rise up parallel to each other,
and being perfectly straight,
press strongly against the
curved plates of the commu-
tator on opposite sides; the
a
Fig. 4

consequence is, that, whenever in the rotation of the axle, the
lines of separation between the commutator plates arrive at
and pass the horizontal plane, their contact with these bearing
rods is changed, and consequently the direction of the current
proceeding from these plates to the rods, and so on to the gal-
vanometer, is changed also. The other or outer ends of the
commutator plates are tinned, for the purpose of being connected
by soldering to the ends of any rectangle or ring which is to be
subjected to experiment.
380
Lines of terrestrial magnetic force. [SERIES XXIX.
Fig. 5.
3194. The rectangle itself is tied on to a slight wooden cross
(fig. 5), which has a socket on one arm that slides on to and
over the part of the wooden axle projecting
beyond the commutator plates, so that it shall
revolve with the axle. A small copper rod
forms a continuation of that part of the frame
which occupies the place of axle, and the end
of this rod enters into a hole in a separate
upright, serving to support and steady the
rectangle and its frame. The frames are of two or three sizes,
so as to receive rectangles of 12 inches in the side, or even
larger, up to 36 inches square. The rectangle is adjusted in its
place, so that it shall be in the horizontal plane when the divi-
sion between the commutator plates is in the same plane, and
then its extremities are soldered to the two commutator plates,
one to each. It is now evident, that when dealing with the
lines of force of the earth, or any other lines, the axle has only
to be turned until the upright copper rods touch on each side at
the separation of the commutator plates, and then the instrument
adjusted in position, so that the plane of the ring or rectangle is
perpendicular to the direction of the lines of force which are to
be examined, and then any revolution of the commutator and
intersecting wire will produce the maximum current which such
wire and such magnetic force can produce. The lines of ter-
restrial magnetic force are inclined at an angle of 69° to the
horizontal plane. As, however, only comparative results were
required, the instrument was, in all the ensuing experiments,
placed in the horizontal plane, with the axis of rotation perpen-
dicular to the plane of the magnetic meridian; under which cir-
cumstances no cause of error or variation was introduced into the
results. As no extra magnet was employed, the commutator was
placed within 3 feet of the galvanometer, so that two pieces of
copper wire 3 feet long and 0.2 of an inch in thickness, sufficed to
complete the communication. One end of each of these dipped
into the galvanometer mercury cups, the other ends were tinned,
amalgamated, introduced into the sockets of the commutator
rods (3193.), and secured by the pinching screw (fig. 4).
3195. When a given length of wire is to be disposed of in the
form best suited to produce the maximum effect, then the cir-
cumstances to be considered are contrary for the case of a loop

DEC. 1851.1
381
Revolving rectangles-time.
to be employed with a small magnet (39. 3184.), and a rect-
angle or other formed loop to be employed with the lines of
terrestrial force. In the case of the small magnet, all the lines
of force belonging to it are inclosed by the loop; and if the wire
is so long that it can be formed into a loop of two or more con-
volutions, and yet pass over the pole, then twice or many times
the electricity will be evolved that a single loop can produce (36.).
In the case of the earth's force, the contrary result is true; for
as in circles, squares, similar rectangles, &c., the areas inclosed
are as the squares of the periphery, and the lines of force inter-
sected are as the areas, it is much better to arrange a given
wire in one simple circuit than in two or more convolutions.
Twelve feet of wire in one square intersects in one revolution the
lines of force passing through an area of nine square feet, whilst
if arranged in a triple circuit, about a square of one foot area, it
will only intersect the lines due to that area; and it is thrice as
advantageous to intersect the lines within nine square feet once,
as it is to intersect those of one square foot three times.
3196. A square was prepared, containing 4 feet in length of
copper wire 0.05 of an inch in diameter; it inclosed one square
foot of area, and was mounted on the commutator and connected
in the manner already described (3194.). Six revolutions of it
produced a swing deflection of 14° or 15°, and twelve quick re-
volutions were possible within the required time (3104.). The
results of quick and slow revolutions were first compared. Six
slow revolutions gave as the average of several experiments 15°.5
swing. Six moderate revolutions gave also an average of 15°5;
six quick revolutions gave an average of 15°66. At another
time twelve moderate revolutions gave an average of 280.75, and
twelve quick revolutions gave an average of 31°.33 swing. As
before explained (3186.), the probable reason why the quick
revolutions gave a larger result than the moderate or slow revo-
lutions is, that in slow time the later revolutions are performed
at a period when the needle is so far from parallel with the cop-
per coil of the galvanometer, that the impulses due to them are
less effectually exerted. Hence a small or moderate number of
revolutions and a quick motion is best. The difference in the
extreme case is less than might have been expected, and shows
that there is no practical objection in this respect to the method
proposed of experimenting with the lines of magnetic force.
382
Lines of terrestrial magnetic force. [SERIES XXIX.
3197. In order to obtain for the present an expression of the
power of the earth's magnetic force by this rectangle, observa-
tions were made on both sides of zero, as already recommended
(3182.). Nine moderately quick direct revolutions (i. e. as the
hands of the clock) gave as the average of many experiments
23°.87, and nine reverse revolutions gave 23°37; the mean of
these is 23° 62 for the nine revolutions of the rectangle, and
therefore 2°.624 per revolution. Now the six quick revolutions
(3196.) gave 15°-66, which is 2°.61 per revolution, and the
twelve quick revolutions gave 31°.33, which is also 2°.61 per
revolution; and these results of 2°-624, 2°.61, and 2°.61, are
very much in accordance, and give great confidence in this
method of investigating magnetic forces'.
3198. A rectangle was prepared of the same length (4 feet) of
the same wire, but the sides were respectively 8 and 16 inches
(fig. 6), so that when revolving the in-
tersecting parts should be only 8 inches Fig. 6.
in length instead of 12 The area of the
rectangle was necessarily 128 square
inches instead of 144. This rectangle
showed the same difference of quick and
Fig. 7.
slow rotations as before (3196.). When nine direct revolutions
were made, the result was 20°-87 swing. Nine reverse revolu-
tions gave an average of 20° 25 swing: the mean is 20°.56, or
2°.284 per revolution. A third rectangle was prepared of the
same length and kind of wire, the sides of which were respectively
8 and 16 inches long (fig. 7), but now so revolved that the in-
tersecting parts were 16 inches, or twice as long as before; the
area of the rectangle remained the same, i. e. 128 inches. The
like effect of slow and quick revolutions appeared as in the former
cases (3196. 3198.). Nine direct revolutions gave as the average
effect 20°.75; and nine reverse revolutions produced 21°.375;
the mean is 21°.06, or 2°.34 per revolution.
15.66
1 sin-
sin 7.83 sin 7 49.8·1362343
1362343
'0227057
2
6
23.62
sin
-sin11.81 = sin11 48.6=2047069
2
2047069
9
•0227474
31.33
sin- =sin15.665=sin15 40 =2700403
2
2700403
12
-=·0225034
DEC. 1851.]
383
Revolving rectangles-effect of form.
3199. Now 2°.34 is so near to 20.284, that they may in the
present state of the investigation be considered the same. The
little difference that is evident, was, I suspect, occasioned by
centrifugal power throwing out the middle of the longer inter-
secting parts during the revolution. The coincidence of the
numbers shows, that the variation in the arrangement of the
rectangle and in the length of the parts of the wires intersecting
the lines of magnetic force, have had no influence in altering the
result, which, being dependent alone on the number of lines of
force intersected, is the same for both; for the area of the
rectangles is the same. This is still further shown by comparing
the results with those obtained with the square. The area in
that case was 144 square inches, and the effect per revolution
2º.61. With the long rectangles the area is 128 square inches,
and the mean of the two results is 2°.312 per revolution. Now
144 square inches is to 128 square inches as 2061 is to
2º.32; a result so near to 2°.312 that it may be here considered
as the same; proving that the electric current induced is
directly as the lines of magnetic force intersected by the moving
wire¹.
3200. It may also be perceived that no difference is produced
when the lines of force are chiefly disposed in the direction of
the motion of the wire, or else, chiefly in the direction of the
length of the wire; i. e. no alterations are occasioned by varia-
tions in the velocity of the motion, or of the length of the wire
provided the amount of lines of magnetic force intersected re-
mains the same.
3201. Having a square on the frame 12 inches in the side but
consisting of copper wire 0·1 of an inch in thickness, I obtained
the average result of many observations for one, two, three, four
and five revolutions of the wire.
1
¹ Oblong rectangles of 128 square inches area give a mean of 20°.81 (3198.).
The rectangle of 144 square inches gave a mean of 23°.62 (3197.).
20.81
sin
sin 10-405=sin 10 24:3-1806049
2
sin
23.62
2
sin 11.81 sin 11 48.6=2047069
•1806049
8
= '0225756
128
144 9
8
•1806049 x9=1.6254441
•2047069×8=1.6376552
Or thus:
•2047069
*0227452
9
384
Lines of terrestrial magnetic force. [SERIES XXIX.
OY
equal to 7
7
One revolution gave
per revolution.
Two revolutions gave 13.875 equal to 6·937 per revolution.
Three revolutions gave 21.075 equal to 7.025 per revolution.
Four revolutions gave 28 637 equal to 7·159 per revolution.
Five revolutions gave 37.637 equal to 7.527 per revolution.
These results are exceedingly close upon each other, especially
for the first 30°, and confirm several of the conclusions before
drawn (3189. 3199.) as to the indications of the instrument, the
amount of the curves, &c.¹
3202. At another time I compared the effect of equable revo-
lutions with other revolutions very irregular in their rates, the
motion being sometimes even backwards and continually differ-
ing in degree by fits and starts, yet always so that within the
proper time a certain number of revolutions should have been
completed. The rectangle was of wire 0.2 of an inch thick; the
mean of many experiments, which were closely alike in their
results, gave for two smooth, equable revolutions, 17°5, and
also for two irregular uncertain revolutions the same amount of
170.5.
2
3203. The relation of the current produced to the mass of the
wire was then examined; a relation which has been investigated
on a former occasion by loops and small magnets (3133.). For
the present purpose two other equal squares were prepared, each
a foot in the side, but the copper wire of which they consisted
was respectively 0.1 and 0.2 of an inch in diameter; so that
Differences.
sin=
= sin 3.30
='0610485
*0610485
⚫0597381
13.875
sin
sin 6.9375 = sin & 56.25=1207866
2
•1207866
2
='0603933
⚫0620924
21.075
sin
sin 10·5375 = sin 10 32·25=•1828790
2
⚫0644329
28.637
sin
sin 14.3185: sin 14 19.11=2473119
2
•1828790
3
•2473119
4
= '0609596
•0618279
0752595
37.637
sin
2
sin 18-8185 = sin 18 49.11=·3225714
•3225714
5
0645142
2 See a corresponding investigation by Christie. Philosophical Transac-
tions, 1833, p. 120.
DEC. 1851.] Moving rectangles-mass of the wire.
385
with the former rectangle they formed a series of three, having
the same size, shape and area, but the masses of the moving
wire increasing in the proportion of one, four and sixteen.
When the rectangle of 0·1 wire was employed, six direct revolu-
tions gave an average result of 41°-75, and six to the left gave
46°.25; the mean of the two is 44°, and this divided by six
gives 70.33 as the deflection per revolution. Again, three direct
revolutions gave 20° 12, and three reverse revolutions 23°1; the
mean being 21°61, and the deflection per revolution 7.20.
This is very close to the former result with six revolutions, namely
70.33, and is a large increase upon the effect of the rectangle of
wire 0.05 in diameter, namely 2°-61; nevertheless, it is not as
4:1; nor could such a result be expected, inasmuch as the mass
of the chief conductor remained the same (3137.). When the
results are compared with those made with like wires in the
form of loops, they are found to be exceedingly close; in that
case the results were as 16° to 44°•4 (3136.), which would accord
with a ratio in the present case of 2°61 to 7°26; and it is as
2º·61 to 7°-242, almost identical.
3204. The average of the direct and reverse revolutions is
seen above to differ considerably, i. e. up to 4° and 5° in the
higher case. This does not indicate any error in principle, but
results simply from the circumstance, that when the needles
were quiescent in the galvanometer, they stood a little on one
side of zero (3182.). I did not wish to adjust the instrument
at the time, as I was watching for spontaneous alterations of the
zero place, and prefer giving the numbers as they came out in
the investigation, to any pen-and-ink correction of the notes.
3205. The third square of 0.2 wire gave such large swings,
that I employed only a small number of revolutions. Three
direct revolutions gave an average of 25°58; three reverse re-
volutions gave 28°.5; the mean is 27°04, and the amount per
revolution 9°.01. Again, two direct revolutions gave 17°.5;
two reverse revolutions gave 18°; the mean is 170.75, and the
amount per revolution 8°.87; the mean of the two final results
is 8°.94, and is again an increase on the effect produced by the
preceding rectangle of wire, only half the diameter of the present.
This thickness of wire was also employed formerly as a loop
(3136.); and if we compare the results then obtained with the
present results, it is remarkable how near they approach to each
2 c
VOL. III.
386
Lines of terrestrial magnetic force. [SERIES XXIX.
other; a circumstance which leads to great confidence in the
principles and practice of both forms of examination. When
wires having masses in the proportion of 1, 4 and 16 were em-
ployed as loops, the currents indicated by the galvanometer
were as 1.00, 2-77, and 3.58; now that they are employed as
rectangles subject to the earth's magnetic power, they are as
1.00, 2.78, and 3.45¹.
3206. I formed a square, 12 inches in the side, of four convo-
lutions of copper wire 0.05 of an inch in diameter; the single
wire which formed it was consequently 16 feet long. Such a
rectangle will, in revolving, intersect the same number of lines
of magnetic force as the former rectangle made with wire 0·1 in
diameter (3203.): there will also be the same mass of wire in-
tersecting the lines, but, as a conductor, the first wire has in
respect of diameter only one-fourth the conducting power of the
second; and then, to increase the obstruction, it is four times as
long. Six direct revolutions gave an average result of 20°·6,
and six reverse revolutions 19°.7; the mean is 20°15, and the
proportion per revolution 3°.36. With the other rectangle
having equal area and mass, but a single wire (3203.), the result
per revolution was 7°.26; being above, though near upon twice
as much as in the present case. Hence for such an excellent
conducting galvanometer as that described (3123. 3178.), the
moving wire had better be as one single thick wire rather than
as many convolutions of a thin one. If it be, under all varia-
tions of circumstances, the same wire for the same area, then, of
course, two or more convolutions are better than one.
1 sin
27.04
2
sin 13°.52 = sin 13° 31'2 = ·2337848
•2337848
2
0779283. The square 12 inches side, of wire 0·05 in diameter, gave for six
1
revolutions (3196. 3197.) 0227057 as sin A for one revolution. A like
2
square of wire 0·10 in diameter gave for five revolutions (3021.)
•3225714
2
06451428 as sin A for one revolution. A like square of wire 0·20 in diameter
gave '0779283 as in A for one revolution.
1
2
⚫06451428
=2·841.
0227057
⚫0779283
0227057-
=3.432.
DEC. 1851.]
387
Revolving rectangles-thin and thick wire.
3207. It was to be expected, however, that the thin wire rect-
angle would produce a current of more intensity than that in the
thick wire, though less in quantity; and to prove this point ex-
perimentally, I connected the two rectangles in succession with
Rhumkorff's galvanometer (3086.), having wire only 1-135th of
an inch in diameter. That of the single thick wire now gave
only 1°.66 of swing for twelve revolutions of the rectangle, or
0°.138 per revolution; whilst the other four convolutions of
thin wire gave for twelve revolutions 7°.33, or 0°.61 per revolu-
tion. Now the needles of the two instruments were not very
different in weight and other circumstances, so that without
pretending to an accurate comparison, we may still perceive an
immense falling-off in both cases, due to the obstruction of the
fine wire in the Rhumkorff's galvanometer; for the thick wire it
is from 7.26 to 0°138, and for the thin wire from 3°36 to
0°610. Still the thin wire rectangle has lost far less propor-
tionately in power than the other; and by this galvanometer is
above four times greater in effect than the rectangle of thicker
wire. Of the thick wire effect less than a fiftieth passes the fine
wire galvanometer, all the rest is stopped; of the fine wire effect
more than ten times this proportion, or between a fourth and a
fifth (because of the higher intensity of the current), surmounts
the obstruction presented by the instrument. The quantity of
electricity which really passes through the fine wire galvanometer
is of course far less than in the proportion indicated above. The
thick wire coil makes at the utmost four convolutions about the
needles, whereas in the fine wire coil there are probably four
hundred or more; so that the electricity which really travels
forward as a current, is probably not a hundredth part of that
which would be required to give an equal deflection in the thick
wire galvanometer. Such a circumstance does not disturb the
considerations with respect to the relative intensity of the
magneto-electric currents from the two rectangles, which have
been stated above.
3208. A large square was now constructed of copper wire 0°.2
of an inch in diameter. The square was 36 inches in the side,
and therefore consisted of 12 feet of wire, and inclosed an area of
9 square feet; it was attached to the commutator by expedients,
which though sufficient for the present, were not accurate in the
adjustments. It produced a fine effect upon the thick wire
2c2
388
Lines of terrestrial magnetic force. [SERIES XXIX.
galvanometer (3178.); for one revolution caused a swing de-
flection of 80° or more; and when its rotation was continuous the
needles were permanently deflected 40° or 50°. It was very in-
teresting to see how, when this rectangle commenced its motion
from the horizontal plane, the current increased in its intensity
and then diminished again, the needles showing, that whilst the
first 10° or 20° of revolution were being passed, there was very
little power exerted on them; but that when it was towards, or
near the 90°, the power was great; the wires then intersecting the
lines of force nearly at right angles, and therefore, with an equal
velocity, crossing the greatest number in a given time. It was
also very interesting, by the same indications, to see the two chief
impulses (3192.) given in one revolution of the rectangle. Being
large and massive in proportion to the former wires, more time
was required for a rotation than before, and the point of time or
velocity of rotation became more essential. One rotation in a
second was as much as I could well produce. A speed somewhat
less than this was easy, convenient and quick enough; it gave
for a single revolution near 80°, whilst a revolution with one-half
or one-third the velocity, or less, gave only 60°, 50°, or even
smaller amounts of deflection.
3209. Observations were now made on the measurement of
one rotation having an easy quick velocity. The average of
fifteen observations to the right, which came very near to each
other, was 78°.846; the average of seventeen similar observa-
tions to the left was 78°.382; and the mean of these results, or
78°.614, I believe to be a good first expression for this rectangle.
On measuring the distances across after this result, I found that
in one direction, i. e. across between the intersecting portions of
wire, it was rather less than 36 inches; having therefore cor-
rected this error, I repeated the observations and obtained the
result of 81°.44. The difference of 2°.83, I believe to be a true
result of the alteration and increase of the area on making it
more accurately 9 square feet; and it is to me an evidence of
the sensibility and certainty of the instrument.
3210. As the two impulses upon the needles in one revolution
(3208.) are here sensibly apart in time, and as the needle has as
evidently and necessarily left its first place before the second
impulse is impressed upon it, so, that second impulse cannot be
so effectual as the first. I therefore observed the results with
DEC. 1851.]
389
Revolving rectangles-different areas.
half a revolution, and obtained a mean of 41°37 for the effect.
This number evidently belongs to the first of the two impulses of
one revolution; and if we subtract it from 81°44, it gives 40°07
as the value of the second impulse under the changed place of
the needle. This difference of the two impulses of one revolu-
tion, namely 41°37 and 40°07, is in perfect accordance with
the results that were to be expected.
3211. The square of this same copper wire, 0·2 in thickness,
employed on a former occasion (3205.), had an area of one square
foot, so that then the lines of force affected or affecting the
moving wire, were one-ninth part of what they are in the present
case: the effect then was 8°.94 per revolution. If, in comparing
these cases, we take the ninth part of 81°44, it gives 9º·04; a
number so near the former, that we may consider the two rect-
angles as proving the same result, and at the same time the
truth of the statement, that the magneto-electric current evolved
is as the amount of lines of force intersected. A ninth part of
the result with the large rectangle (78°.614), before its area was
corrected, is 8°.734; so that the one is above and the other below
the amount of the 12-inch rectangle. As that was not very
carefully adjusted, nor indeed any of the arrangements made as
yet with extreme accuracy, I have little doubt that with accu-
rately adjusted rectangles the results would be strictly propor-
tional to the areas¹.
3212. The moving wire, in place of being formed into a rect-
angle, may be adjusted as a ring; and then the advantage is
obtained of the largest area which a given length of wire can in-
81.44
2
¹ The 9 square feet rectangle gave 81°.44 sin
sin 40·72 = sin 40°
1
43′2 = ·6523630: or taking 41°37 for the half revolution for A (3210.)
2
sin 41°.37 = sin 41° 22′26609190, which divided by nine give 073435 as
the force per square foot. The 1 square foot rectangle of like wire (3205.)
gave '07714, or '07793 as the force of one revolution; the first of which is
1
•00370 more than of the measure of the effect of the large square; the
9
1
difference being about
29
of '07714, or the whole force of one revolution.
390
Lines of terrestrial magnetic force. [SERIES XXIX.
close, and therefore for a uniform wire, the obstruction to the
induced current, as respects its conduction, is the least. Small
rings of one or several convolutions will probably be very valuable
in the examination of small and local magnets under different
circumstances: One consisting of ten spirals of copper wire
0.032 of an inch in diameter, containing 49 inches, in a ring
about 1.5 inch in diameter, gave but small results under the
earth's influence; but when brought near a horseshoe magnet
told, in its effects for every difference in distance or in position.
A single ring 4 inches in diameter, being made of a convolution
of copper wire 0.2 in thickness, was employed with the earth's
magnetic force as before; it gave as the average of six revolu-
tions many times repeated 5°.995, or 0°.999 per revolution.
For twelve revolutions it gave a mean of 12°.375 or 1°.031 per
revolution¹; the mean of the two results with such different
numbers of revolutions being 1°. Another ring, consisting of
26 convolutions of copper wire 0.04 of an inch in diameter, was
constructed and had a mean diameter of 3.6 or 3.7 inches; it
contained 300 inches in length of wire. So the masses of the
metal in the two rings are nearly the same, but the latter wire
is singly only 1-25th of the mass of the former. It gave for
twelve revolutions a mean of 6°.25, or 0°.52 per revolution.
With the earth's power and the thick wire galvanometer, it gave
therefore little more than half the result of the single thick wire
ring. We know from former considerations (3206.), that if the
300 inches had been made into one single ring, it would have
given a very high effect compared to the present.
3213. The application of the principle of the moving wire in
the form of a revolving rectangle, makes the investigation of con-
ducting power, and the results produced by difference in the
nature of the substance, or in diameter, i. e. mass, or in length,
very easy; and the obstruction offered by those parts, which
moving not across but parallel to the lines of force (3071.), have
no exciting action but perform the part of conductors merely,
might be greatly removed by making them massive. They
might be made to shift upon the axle so as to bear adjustment
5.995
= sin 2.9975 = sin 2 59-85-
1 sin
⚫0522925
2
12.375
•1077825
sin
sin 6.1875 sin 6 11.25 =·1077825
='0538912
2
2
DEC. 1851.]
391
Forces of associated magnets.
for different lengths of wires, and the commutator might in fact
be made to a large extent a general instrument.
3214. In looking forward to further applications of the prin-
ciple of the moving wire, it does not seem at all unlikely that by
increased delicacy and perfection of the instrument, by increased
velocity, by continued motion for a time in one direction and
then reversal of the revolution with the reversal of the direction
of the swing, &c., it may be applied with advantage hereafter to
the investigation of the earth's magnetic force in different lati-
tudes and places. To obtain the maximum effect, the axis of
rotation must be perpendicular to the lines of force, i. e. the dip.
It would even be possible to search for the direction of the lines
of force, or the dip, by making the axis of rotation variable about
the line of dip, adjusting it in two directions until there was no
action at the galvanometer, and then observing the position of
the axis; a double commutator would be required corresponding
to the lines of adjustment, but that is an instrument of very
simple construction.
§ 36. On the amount and general disposition of the Forces of a
Magnet when associated with other magnets.
3215. Prior to further progress in the experimental develop-
ment by a moving wire of the disposition of the lines of magnetic
force pertaining to a magnet, or of the physical nature of this
power and its possible mode of action at a distance, it became
quite essential to know what change, if any, took place in the
amount of force possessed by a perfect magnet, when subjected
to other magnets in favourable or adverse positions; and how
the forces combined together, or were disposed of, i. e. generally,
and in relation to the principle already asserted and I think
proved, that the power is in every case definite under those
different conditions. The representation of the magnetic power
by lines of force (3074.), and the employment of the moving
wire as a test of the force (3076.), will I think assist much in
this investigation.
3216. For such a purpose an ordinary magnet is a very irre-
gular and imperfect source of power. It not only, when mag-
netized to a given degree, is apt by slight circumstances to have
its magnetic power diminished or exalted, in a manner which
392
Lines of magnetic force. [SERIES XXIX.
may be considered for the time, permanent; but if placed in
adverse or favourable relations to other magnets, frequently
admits of a considerable temporary diminution or increase of its
power externally, which change disappears as soon as it is
removed from the neighbourhood of the dominant magnet.
These changes produce corresponding effects upon the moving
wire, and they render any magnet subject to them unfit for in-
vestigation in relation to definite power. Unchangeable mag-
nets are, therefore, required, and these are best obtained, as is
well known, by selecting good steel for the bars, and then
making them exceedingly hard; I therefore procured some
plates of thin steel twelve inches long and one inch broad, and
making them as hard as I could, afterwards magnetized them
very carefully and regularly, by two powerful steel bar-magnets,
shook them together in different and adverse positions for a
little while, and then examined the direction of the forces by iron
filings. Small cracks and irregularities were in this way detected
in several of them; but two which are very regular in the dis-
position of their forces were selected for further experiment, and
may be distinguished as the subjected magnets D and E.
3217. These two magnets were examined by the moving loop
precisely in the manner before described (3133.), i. e. by passing
the loop over one of the poles, observing the swing, removing it,
and again observing the swing and taking an average of many
results; the process was performed over both poles at different
times. The loop contained 7.25 inches in length of copper wire
0.1 of an inch in diameter, and was of course employed in all the
following comparative experiments; the distance of the loop and
magnets from the galvanometer was 9 feet. For one passage
over the pole either on or off, i. e. for one intersection of the
lines of force of the magnet D, the galvanometer deflection was
8°.36. For one intersection of the lines of force of the other
bar E, the deflection was 8°.78. The two bars were then placed
side by side with like poles together, and afterwards used as one
magnet; their cojoined power was 16° 3, being only 0°.84 less
than the sum of the powers of the two when estimated separately.
This indicates that the component magnets do affect, and in this
position reduce, each other somewhat; but it also shows how
small the effect is as compared with ordinary magnets (3222.).
3218. The compound magnet D E (3217.) was now subjected
DEC. 1851.] Associated magnets—various positions.
393
to the close action of another magnet, sometimes under adverse,
and at other times under favourable conditions; and was exa-
mined by the loop as to the sum of its power (not the direction)
under these circumstances. For this purpose it was fixed, and
another magnet A brought near, and at times in contact with it,
in the positions indicated by the figure 8; the loop in each case
Fig. 8.
A
S

I
N
A
2
3
1 1
I
SIN
A
N
S
being applied many times to D E, that a correct average of its
power might be procured. The dominant magnet A was much
the stronger of the two, having the power indicated by a swing
deflection of 25°.74.
3219. When the relative position of the magnets was as at 1,
then the power of D E was 16°.37; when as at 2, the power
was 16º4; when as at 3, it was 180.75; and when as at 4, it
was 170.18. All these positions are such as would tend to raise,
by induction, the power of the magnet D E, and they do raise
it above its first value, which was 16°3; but it is seen at once
how little the first and second positions elevate it; and even the
third, which presents the most favourable conditions, only in-
creases the power 2°.45, which falls again in the fourth position.
3220. Then the dominant magnet A was placed in the same
positions, but with the ends reversed, so as to exert an adverse
or depressing influence; and now the results with D E were_as
follows:
Position 1.
Position 2
Position 3
Position 4
15.37
15.68
15.37
16.06
All these are a little below the original force of D E, or 16°.3,
as they ought to be, and show how slightly this hard bar-magnet
is affected.
394
[SERIES XXIX.
Lines of magnetic force.
3221. A soft iron bar, now applied in the first, second and
third positions instead of the magnet A, raised D E to the fol-
lowing values respectively, 16°.24, 16°43, and 18°.
3222. When an ordinary bar-magnet was employed instead
of the hard magnet D E, great changes took place. Thus a
bar B, corresponding to bar A in size and general character,
was employed in the place of the hard magnet. Alone, B had a
power of 14°83, but when associated adversely with A, as in
position 3 (3218.), its power fell to 7°.87, being reduced nearly
one-half. This loss was chiefly due to a coercion internally, and
not to a permanent destruction of the state of magnet B; for
when A was removed, B rose again to 13°-06. When B was
laid for a few moments favourably on A and then removed, it
was found that the latter had been raised to a permanent exter-
nal action of 15°.25.
3223. A very hard steel bar 6 inches long, 0·5 broad and 0·1
in thickness, given to me by Dr. Scoresby, was magnetized and
then found, by the use of the loop, to have a value at my gal-
vanometer of 6°.88 (3189.). It was submitted in position 2 to a
compound bar-magnet like D E, having a power of 110.73, or
almost twice its own force, but whether in the adverse or the
favourable position, its power was not sensibly altered. When
submitted in like manner to a 12-inch bar-magnet having a force
of 40°.21, it was raised to 7°53, or lowered to 5º.87, but here
the dominant magnet had nearly six times the power of the one
affected.
3224. The variability of fresh steel magnets, both in respect
of their absolute degree of excitation or charge, and also of the
disposition of the force externally or internally, when their
degree of excitation may for the time be considered as the same,
is made very manifest by this mode of examination; and the re-
sults agree well with our former knowledge in this respect. It
is equally manifest, that hard and invariable magnets are requi-
site for a correct and close investigation of the disposition and
characters of the magnetic force. A common soft bar-magnet
may be considered as an assemblage of hard and soft parts,
disposed in a manner utterly uncertain; of which some parts
take a much higher charge then others, and change less under
the influence of external magnets; whilst, because of the pre-
sence of other parts within, acting as the keeper or submagnet,
DEC. 1851.]
395
Associated magnets.
they may seem to undergo far greater changes than they really
do. Hence the value of these hard and comparatively un-
changeable magnets which Scoresby describes.
3225. From these and such results, it appears to me, that
with perfect, unchangeable magnets, and using the term line of
force as a mere representant of the force as before defined (3071.
3072.), the following useful conclusions may be drawn.
3226. Lines of force of different magnets in favourable posi-
tions to each other coalesce.
3227. There is no increase of the total force of the lines by
this coalescence; the section between the two associated poles
gives the same sum of power as that of the section of the lines
of the invariable magnet when it is alone (3217.). Under these
circumstances there is, I think, no doubt that the external and
internal forces of the same magnet have the same relation and
are equivalent to each other, as was determined in a former part
of these Researches (3117.); and that therefore the equatorial
section, which represents the sum of forces or lines of forces
passing through the magnet, remains also unchanged (3232.).
3228. In this case the analogy with two or more voltaic bat-
teries associated end to end in one circuit is perfect. Probably
some effect, correspondent to intensity in the case of the batteries,
will be found to exist amongst the magnets.
3229. The increase of power upon a magnetic needle, or piece
of soft iron placed between two opposite, favourable poles, is
caused by concentration upon it of the lines which before were
diffused, and not by the addition of the power represented by the
lines of force of one pole to that of the lines of force of the other.
There is no more power represented by all the lines of force
than before; and a line of force is not more powerful because
it coalesces with a line of force of another magnet. In this re-
spect the analogy with the voltaic pile is also perfect.
3230. A line of magnetic force being considered as a closed
circuit (3117.), passes in its course through both the magnets,
which are for the time placed so as to act on each other favour-
ably, i. e. whose lines coincide and coalesce. Coalescence is not
the addition of one line of force to another in power, but their
union in common circuit.
3231. A line of force may pass through many magnets before
its circuit is complete; and these many magnets coincide as a
396
[SERIES XXIX.
Lines of magnetic force.
case with that of a single magnet. If a thin bar-magnet 12
inches long be examined by filings (3235.), it will be found to
present the well-known beautiful system of forces, perfectly simple
in its arrangement. If it be broken in half, without being se-
parated, and again examined, the manner in which, from the
destruction of the continuity, the transmission of the force at
the equator is interfered with, and many of the lines, which
before were within are made to appear externally there, is at
nce evident, Plate III. fig. 6. Of those lines, which thus become
external, some return back to the pole which is nearest to the
new place, at which the lines issue into the air, making their
circuit through only one of the halves of the magnet; whilst
others proceed onward by paths more or less curved into the
second half of the magnet, keeping generally the direction or
polarity which they had whilst within the magnet, and complete
their circuit through the two. Gradually separating the two
halves, and continuing to examine the course of the lines of
force, it is beautiful to observe how more and more of the lines
which issue from the two new terminations, turn back to the
original extremities of the bar, fig. 7, and how the portion which
makes a common circuit through the two halves diminishes,
until the halves are entirely removed from each other's influence,
and then become two separate and independent magnets. The
same process may be repeated until there are many magnets in
place of one.
3232. All this time the amount of lines of force is the same if
the fragments of the bar preserve their full state of magnetism;
i. e. the sum of lines of force in the equator of either of the
new magnets is equal to the sum of lines of force in the equator
of the original unbroken bar. I took a steel bar 12 inches long,
1 inch broad and 0·05 of an inch thick, made it very hard, and
magnetized it to saturation by the use of soft iron cores and a
helix; its power was 6°.9. I broke it into two pieces nearly in
the middle, and found the power of these respectively 5º.94 and
5°.89; indicating a fall not more than was to be expected con-
sidering the saturated state of the original magnet. When these
halves were placed side by side, with like poles together as a
compound magnet, they had a joint power of 11°06, which,
though it shows a mutual quelling influence, is not much below
the sum of their powers ascertained separately. All this is in
DEC. 1851.]
397
Their delineation by iron filings.
perfect harmony with the voltaic battery, where lines of dynamic
electric force are concerned. If, as is well known, we separate
a battery of 20 pair of plates into two batteries of 10 pair, or
4 batteries of 5 pair, each of the smaller batteries can supply
as much dynamic electricity as the original battery, provided no
sensible obstruction be thrown into the course of the lines, i. e.
the path of the current.
3233. When magnets are placed in an adverse position, as
neither could add power to the other in the former case, so now
each retains its own power; and the lines of magnetic force re-
present this condition accurately. Two magnets placed end
to end with like poles together are in this relation; so also are
they if placed with like poles together side by side. In the
latter case the two acting as one compound magnet, give a
system of lines of force equal to the sum of the two separately
(3232.), minus the portion which, as in imperfect magnets, is
either directed inwards by the softer parts or ceases to be excited
altogether.
§ 37. Delineation of Lines of Magnetic Force by iron filings.
3234. It would be a voluntary and unnecessary abandonment
of most valuable aid, if an experimentalist, who chooses to con-
sider magnetic power as represented by lines of magnetic force,
were to deny himself the use of iron filings. By their employ-
ment he may make many conditions of the power, even in com-
plicated cases, visible to the eye at once; may trace the varying
direction of the lines of force and determine the relative polarity;
may observe in which direction the power is increasing or dimi-
nishing; and in complex systems may determine the neutral
points or places where there is neither polarity nor power, even
when they occur in the midst of powerful magnets. By their
use probable results may be seen at once, and many a valuable
suggestion gained for future leading experiments.
3235. Nothing is simpler than to lay a magnet upon a table,
place a flat piece of paper over it, and then sprinkling iron
filings on the paper, to observe the forms they assume. Never-
theless, to obtain the best and most generally useful results, a
few particular instructions may be desirable. The table on
which the magnet is laid should be quite horizontal and steady.
398
[SERIES XXIX.
Lines of magnetic force.
Means should be taken, by the use of thin boards or laths, or
otherwise, to block up round the magnet, so that the paper
which is laid over it should be level. The paper should be
without any cockle or bend, and perfectly flat, that the filings may
be free to assume the position which the magnet tends to give
them. I have found well-made cartridge or thin drawing-paper
good for the purpose. It should not be too smooth in ordinary
cases, or the filings, when slightly agitated, move too freely to-
wards the magnet. With very weak or distant magnets I have
found silvered paper sometimes useful. The filings should be
clean, i. e. free from much dirt or oxide; the latter forms the lines
but does not give good delineations. The filings should be distri-
buted over the paper by means of a sieve more or less fine, their
quantity being partly a matter of taste. It is to be remembered,
however, that the filings disturb in some degree the conditions
of the magnetic power where they are present, and that in the
case of small magnets, as needles, a large proportion of them
should be avoided. Large and also fine filings are equally useful
in turn, when the object is to preserve the forms obtained. For
the distribution of the latter it is better to use a fine sieve with
the ordinary filings than to separate the filings first: a better
distribution on the paper is obtained. The filings being sifted
evenly on the paper, the latter should be tapped very lightly by
a small piece of wood, as a pen-holder; the taps being applied
wherever the particles are not sufficiently arranged. The taps
must be perpendicularly downwards, not obliquely, so that the
particles, whilst they have the liberty of motion, for an instant
are not driven out of their places, and the paper should be held
down firmly at one corner, so as not to shift right or left; the
lines are instantly formed, especially with fine filings.
3236. The designs thus obtained may be fixed in the following
manner, and then form very valuable records of the disposition
of the forces in any given case. By turning up two corners of
the paper on which the filings rest, they may be used as handles
to raise the paper upwards from the magnet, to be deposited on
a flat board or other plane surface. A solution of one part of
gum in three or four of water having been prepared, a coat of
this is to be applied equably by a broad camel-hair pencil, to a
piece of cartridge paper, so as to make it fairly wet, but not to
float it, and after wafting it through the air once or twice to break
DEC. 1851.]
399
Their delineation by iron filings.
the bubbles, it is to be laid carefully over the filings, then covered
with ten or twelve folds of equable soft paper, a board placed
over the paper, and a half-hundred weight on the board for
thirty or forty seconds. Or else, and for large designs it is a
better process, whilst the papers are held so that they shall not
shift on each other, the hand should be applied so as to rub
with moderate pressure over all the surface equably and in one
direction. If, after that, the paper be taken up, all the filings
will be found to adhere to it with very little injury to the forms
of the lines delineated; and when dry they are firmly fixed. If
a little solution of the red ferroprussiate of potassa and a small
proportion of tartaric acid be added to the gum-water, a yellow
tint is given to the paper, which is not unpleasant; but besides
that, prussian blue is formed under every particle of iron; and
then when the filings are purposely or otherwise displaced, the
design still remains recorded. When the designs are to be pre-
served in blue only, the gum may be dispensed with and the
red ferroprussiate solution only be used.
3237. It must be well understood that these forms give no
indication by their appearance of the relative strength of the
magnetic force at different places, inasmuch as the appearance
of the lines depends greatly upon the quantity of filings and the
amount of tapping; but the direction and forms of the lines are
well given, and these indicate, in a considerable degree, the di-
rection in which the forces increase and diminish.
3238. Plate III. fig. 1, shows the forms assumed about a bar-
magnet. On using a little electro-magnet and varying the strength
of the current passed through it, I could not find that a variation
in the strength of the magnet produced any alteration in the
forms of the lines of force external to it. Fig. 2 shows the lines
over a pole, and fig. 3 those between contrary poles. The latter
accord with the magnetic curves, as determined and described by
Dr. Roget and others, with the assumption of the poles as centres
of force. The difference between them and those belonging to
a continuous magnet, shown in fig. 1, is evident. Figs 4, 5 show
the lines produced by short magnets. In the latter case the
magnet was a steel disc about one inch in diameter and 0·05
in thickness. Fig. 6 shows the result when a bar-magnet is
broken in half, but not separated. Fig. 7 shows the development
400
[SERIES XXIX.
Lines of magnetic force.
of the lines externally at the two ends as the halves are more
and more separated (3231.). Figs. 8, 9 and 10 present the re-
sults, with the two halves or new magnets in different positions.
Figs. 11, 12, 13 and 14 show the results with disc magnets.
Fig. 15 shows the condition of a system of magnetic force when
it is inclosed by a larger one, and is contrary to it. Fig 16
shows the coalescence of the lines of force (3226.) when the
magnets are so placed that the polarities are in accordance.
3239. Fig. 17 exhibits the lines of force round a vertical wire
carrying a current of electricty. Whether the wire was thick
or thin appeared to make no difference as to the intensity of the
forces, the current remaining the same. Fig. 18 represents the
lines round two like currents when within mutual influence.
Fig. 19 shows the result when a third current is introduced in
the contrary direction. Fig. 20 presents the transition to a helix
of three convolutions. Fig. 21 indicates the direction of the
lines within and outside the end of a cylindrical helix, on a plane
through its axis. Fig 22 presents the effect when a very small
soft iron core is within the helix.
3240. Figs. 23 and 24 give an experimental illustration of the
principles which I have adopted in relation to atmospheric mag-
netism and the general cause of the daily variations, &c. (2864.
2917.). A hemisphere of pure nickel presented to me by Dr. Percy,
was supported with its flat face uppermost, and a large ring ar-
ranged round it to carry paper, which, resting both on the ring
and the nickel, could then have iron filingssprinkled and arranged
in form on it. The end of a bar-magnet in the same horizontal
plane was adjusted about 2 inches from the nickel, and thus the
forms of the lines of force associated with this pole could be de-
termined over the place of the nickel hemisphere, under different
circumstances, or even when it was removed. When the nickel
was away, the forms of the lines of force were as in fig. 23;
when the nickel was there, they were as in fig. 24. The appli-
cation of a spirit-lamp to the nickel when in its place, raised its
temperature to such a degree (above 600° Fahr.) that it lost its
ordinary magnetic condition; and then the forms of the lines of
force, as shown by filings, were the same as if the nickel was
away. Removing the lamp, I was able to obtain the disposition
of filings on successive pieces of paper, and as many as four
DEC. 1851.]
401
Effect of temperature on nickel.
results, like fig. 23, could be procured before the temperature
had sunk so much as to cause the production of lines of force
corresponding to fig. 24.
3241. These are exactly the same results with nickel as those
I have assumed for the oxygen of the atmosphere. The change
in the forms of the lines about the cooling nickel in this experi-
ment are the same changes as those I have figured in the type
globe of cooling air (2865. 2874.). Both nickel and oxygen are
paramagnetic bodies, and change in the same direction by heating
and cooling; and as the period of change with oxygen extends
through degrees above and below common temperature (2861),
so inflections of the lines of force passing through the atmo-
sphere, correspondent to those of the heating and cooling nickel,
must take place to some extent. It is seen in the nickel results,
that lines of force entirely outside of it do not for that reason
continue an undeviating course, but are curved to and fro in
consequence of the disposition of other lines within the nickel; a
result, which, without reference to either one view or another of
the physical action of the magnetic force, must be as true in the
oxygen case as in the nickel case, because of the definite character
of the magnetic force, whether represented by centres of action
or by lines of power.
3242. Whether the amount of the deflection in the case of the
atmosphere corresponds with the facts registered by observers,
is a question which cannot be answered, I suppose, until we
know the effect of very low temperatures upon the magnetic force
of the atmosphere. In the nickel experiment the deflection is
in places 30° or 40°; in nature the effect to be accounted for is
not more than 13 or 14 minutes.
Royal Institution,
December 20, 1851.
2 D
VOL. III.
402
On the Lines of Magnetic Force¹.
THAT beautiful system of power which is made manifest in
the magnet, and which appears to be chiefly developed in the
two extremities, thence called ordinarily the magnetic poles, is
usually rendered evident to us in the case of a particular magnet
by the attractive or repulsive effect of these parts on the corre-
sponding parts of another magnet; and these actions have been
employed, both to indicate the direction in which the magnetic
force is exerted and also the amount of the force at different
distances. Thus, if the attraction be referred to, it may be ob-
served either upon another magnet or upon a piece of soft iron;
and the law which results, for effects beyond a certain distance,
is, that the force is inversely as the square of the distance.
When the distances of the acting bodies from each other is
small, then this law does not hold, either for the surface of the
magnets or for any given point within them.
It is proposed to employ a new method, founded upon
a property of the magnetic forces different from that pro-
ducing attraction or repulsion, for the purpose of ascertaining
the direction, intensity, and amount of these forces,-not to the
displacement of the former method, but to be used in con-
junction with it; and which may be highly influential in the
further development of the nature of this power, inasmuch as
the principle of action, though different, is not less magnetic
than attraction and repulsion, not less strict, and the results not
less definite.
The term line of magnetic force is intended to express simply
the direction of the force in any given place, and not any phy-
sical idea or notion of the manner in which the force may be
there exerted; as by actions at a distance, or pulsations, or
waves or a current, or what not. A line of magnetic force may
be defined to be that line which is described by a very small
magnetic needle, when it is so moved in either direction corre-
spondent to its length, that the needle is constantly a tangent to
the line of motion; or, it is that line along which, if a trans-
verse wire be moved in either direction, there is no tendency
1
¹ Royal Institution Proceedings, 23rd January, 1852.
JAN. 1852.]
403
Lines of magnetic force.
to the formation of an electric current in the wire, whilst if
moved in any other direction there is such a tendency. The
direction of these lines about and between ordinary magnets is
easily represented in a general manner by the well-known use of
iron filings.
The proposed method of recognizing and taking account of
these lines of force, is to collect and measure the electricity set
into motion in the moving transverse wire; a process entirely
different in its nature and action to that founded on the use of
a magnetic needle. That it may be advantageously employed,
excellent conductors are required; and therefore those pro-
ceeding from the moving wire to the galvanometer were of
copper 0-2 of an inch in thickness, and as short as was con-
venient. The galvanometer, also, instead of including many
hundred convolutions of a long fine wire, consisted only of about
48 or 50 inches of such wire as that described above, disposed
in two double coils about the astatic needle: and that used in
the careful research contained only 20 inches in length of a
copper bar 0.2 of an inch square. These galvanometers showed
effects 30, 40 or 50 times greater than those constructed with
fine wire; so abuundant is the quantity of electricity produced
by the intersections of the lines of magnetic force, though very
low in intensity.
The lines of force already described will, if observed by iron
filings or a magnetic needle or otherwise, be found to start off
from one end of a bar-magnet, and after describing curves of
different magnitudes through the surrounding space, to return to
and set on at the other end of the magnet; and these forces
being regular, it is evident that if a ring, a little larger than the
magnet, be carried from a distance towards the magnet and over
one end until it has arrived at the equatorial part, it will have
intersected once all the external lines of force of that magnet.
Such rings were soldered on to fitly shaped conductors connected
with the galvanometer, and the deflections of the needle observed
for one, two, or more such motions or intersections of the lines
of force: it has been found that when every precaution was taken,
and the results at the galvanometer carefully observed, the effect
there was sensibly proportionate for small or moderate arcs to
the number of times the loop or ring had passed over the pole.
In this way, not only could the definite actions of the inter-
2 D 2
404
[JAN. 1852.
Lines of magnetic force.
secting wire be observed and established, but also one magnet
could be compared to another: wires of different thickness and
of different substances could be compared; and the sections also
described by the wire in its journey could be varied. When the
wire was the same in length, diameter, and substance, no matter
what its course was across the lines of force, whether direct or
oblique, near to or far from the poles of the magnet, the result
was the same.
A compound bar-magnet was so fitted up that it could revolve
on its axis, and a broad circular copper ring was fixed on it at
the middle distance or equator, so as to give a cylindrical exterior
at that place. A copper wire being made fast to this ring
within, then proceeded to the middle of the magnet, and after-
wards along its axis and out at one end. A second wire
touched, by a spring contact, the outside of the copper ring, and
was then continued outwards six inches, after which it rose and
finally turned over the upper pole towards the first wire, and
was attached to a cylinder insulated from but moving round it.
This cylinder and the wire passing through it were connected
with the galvanometer so that the circuit was complete; but that
circuit had its course down the middle of the magnet, then out-
wards at the equator, and back again on the outside, and whilst
always perfect, allowed the magnet to be rotated without the ex-
ternal part of the circuit, or the latter without the magnet, or
both together. When the magnet and external wire were re-
volved together, as one arrangement fixed in its parts, there was
no effect at the galvanometer, however long the rotation was
continued. When the magnet with the internal wire made four
revolutions, as the hand of a watch, the outer conductor being
still, the galvanometer needle was deflected 35° or 40° in one
direction: when the magnet was still, and the outer wire made
four revolutions as the hands of a watch, the galvanometer
needle was deflected as much as before in the contrary direction :
and in the more careful experiments the amount of deflection for
four revolutions was precisely the same, whatever the course of
the external wire, either close to or far off from the pole of the
magnet. Thus it was shown, that when the magnet and the
wire revolved in the same direction, contrary currents of elec-
tricity, exactly equal to each other, tended to be produced; that
those outside resulted from the intersection by the outer wire of
JAN. 1852.1
405
Lines of magnetic force.
the lines of magnetic force external to the magnet; that whereve
this intersection was made the result was the same; and that
there were corresponding lines of force within the magnet,
exactly equal in force or amount to those without, but in the
contrary direction. That in fact every line of magnetic force is a
closed curve, which in some part of its course passes through the
magnet to which it belongs. The vicinity of other magnets to
this magnet made no difference in the effect, provided they were
not moved during the experiments; and in this manner the non-
interference of such magnets with that under investigation was
fully established.
In the foregoing cases the lines of force, belonging as they did
to small systems, rapidly varied in intensity according to their
distance from the magnet, by what may be called their divergence.
The earth, on the contrary, presents us, within the limits of one
experiment at any one time, a field of equal force. The dipping
needle indicates the direction or polarity of this force; and if we
work in a plane perpendicular to the dip, then the number or
amount of the lines of force experimented with will be in pro-
portion to the area which our apparatus may include. Wires
were therefore formed into parallelograms, inclosing areas of
various extent, as one square foot, or nine square feet, or any
other proportion, and being fixed upon axes equidistant from
two of the sides could have these axes adjusted perpendicular to
the line of dip and could then be revolved. A commutator was
employed, and associated both with the galvanometer and the
parallelograms, so that the upper part of the revolving wire
always sent the current induced in it in the same direction.
Here it was found that rotation in one direction gave one electric
current; that rotation in the reverse direction gave the contrary
current; that the effect at the galvanometer was proportionate to
the number of rotations with the same rectangle; that with
different sized rectangles of the same wire the effect was propor-
tionate to the area of the rectangle, i. e. the number of curves
intersected, &c.
All these and other results are more fully stated and proved in
papers sent to the Royal Society'. The general conclusions
are, that the magnetic lines of force may be easily recognized and
taken account of by the moving wire, both as to direction and
¹ See page 328, &c.
406
[JAN. 1852.
Lines of magnetic force.
intensity, within metals, iron or magnets, as well as in the space
around; and that the wire sums up the action of many lines in
one result:—that the lines of forces well represent the nature,
condition, direction, and amount of the magnetic forces:-that
the effect is directly as the number of lines of force intersected,
whether the intersection be direct or oblique :-that in a field of
equal force, it is directly as the velocity; or as the length of the
moving wire; or as the mass of the wire:-that the external
power of an unchangeable magnet is definite yet illimitable in
extent; and that any section of all the lines of force is equal to
any other section :-that the lines of force within the magnet are
equal to those without; and also that they are continuous with
those without, the lines of force being closed curves.
407
On the Physical Character of the Lines of Magnetic Force¹.
NOTE.-The following paper contains so much of a speculative
and hypothetical nature, that I have thought it more fitted for
the pages of the Philosophical Magazine than those of the Phi-
losophical Transactions. Still it is so connected with, and de-
pendent upon former researches, that I have continued the
system and series of paragraph numbers from them to it. I
beg, therefore, to inform the reader, that those in the body of
the text refer chiefly to papers already published, or ordered for
publication, in the Philosophical Transactions; and that they
are not quite essential to him in the reading of the present paper,
unless he is led to a serious consideration of its contents.
paper, as is evident, follows Series xxviii. and xxix., now printing
in the Philosophical Transactions, and depends much for its ex-
perimental support upon the more strict results and conclusions
contained in them.
The
3243. I have recently been engaged in describing and defining
the lines of magnetic force (3070.), i. e. those lines which are
indicated in a general manner by the disposition of iron filings
or small magnetic needles, around or between magnets; and I
have shown, I hope satisfactorily, how these lines may be taken
as exact representants of the magnetic power, both as to disposi-
tion and amount; also how they may be recognized by a moving
wire in a manner altogether different in principle from the in-
dications given by a magnetic needle, and in numerous cases
with great and peculiar advantages. The definition then given
had no reference to the physical nature of the force at the place
of action, and will apply with equal accuracy whatever that may
be; and this being very thoroughly understood, I am now about
to leave the strict line of reasoning for a time, and enter upon a
few speculations respecting the physical character of the lines of
force, and the manner in which they may be supposed to be con-
tinued through space. We are obliged to enter into such
speculations with regard to numerous natural powers, and, in-
¹ Philosophical Magazine for June 1852.
408
[JUNE 1852
Physical lines of force :-
deed, that of gravity is the only instance where they are appa-
rently shut out.
3244. It is not to be supposed for a moment that speculations
of this kind are useless, or necessarily hurtful, in natural philo-
sophy. They should ever be held as doubtful, and liable to
error and to change; but they are wonderful aids in the hands
of the experimentalist and mathematician. For not only are they
useful in rendering the vague idea more clear for the time, giving
it something like a definite shape, that it may be submitted to
experiment and calculation; but they lead on, by deduction and
correction, to the discovery of new phænomena, and so cause an
increase and advance of real physical truth, which, unlike the
hypothesis that led to it, becomes fundamental knowledge not
subject to change. Who is not aware of the remarkable pro-
gress in the development of the nature of light and radiation in
modern times, and the extent to which that progress has been
aided by the hypotheses both of emission and undulation? Such
considerations form my excuse for entering now and then upon
speculations; but though I value them highly when cautiously
advanced, I consider it as an essential character of a sound mind
to hold them in doubt; scarcely giving them the character of
opinions, but esteeming them merely as probabilities and possi-
bilities, and making a very broad distinction between them and
the facts and laws of nature.
3245. In the numerous cases of force acting at a distance, the
philosopher has gradually learned that it is by no means sufficient
to rest satisfied with the mere fact, and has therefore directed his
attention to the manner in which the force is transmitted across
the intervening space; and even when he can learn nothing sure
of the manner, he is still able to make clear distinctions in
different cases, by what may be called the affections of the lines
of power; and thus, by these and other means, to make di-
stinctions in the nature of the lines of force of different kinds
of power as compared with each other, and therefore be-
tween the powers to which they belong. In the action of
gravity, for instance, the line of force is a straight line as far as
we can test it by the resultant phænomena. It cannot be de-
flected, or even affected, in its course. Neither is the action in
one line at all influenced, either in direction or amount, by a like
action in another line; i. e. one particle gravitating toward
JUNE 1852.]
409
gravity—radiant forces.
another particle has exactly the same amount of force in the
same direction, whether it gravitates to the one alone or towards
myriads of other like particles, exerting in the latter case upon
each one of them a force equal to that which it can exert upon
the single one when alone: the results of course can combine,
but the direction and amount of force between any two given
particles remain unchanged. So gravity presents us with the
simplest case of attraction; and appearing to have no relation to
any physical process by which the power of the particles is carried
on between them, seems to be a pure case of attraction or action
at a distance, and offers therefore the simplest type of the cases
which may be like it in that respect. My object is to consider
how far magnetism is such an action at a distance; or how far
it may partake of the nature of other powers, the lines of which
depend, for the communication of force, upon intermediate phy-
sical agencies (3075.).
3246. There is one question in relation to gravity, which, if
we could ascertain or touch it, would greatly enlighten us. It
is, whether gravitation requires time. If it did, it would show un-
deniably that a physical agency existed in the course of the line
of force. It seems equally impossible to prove or disprove this
point; since there is no capability of suspending, changing, or
annihilating the power (gravity), or annihilating the matter in
which the power resides.
3247. When we turn to radiation phænomena, then we obtain
the highest proof, that though nothing ponderable passes, yet
the lines of force have a physical existence independent, in a
manner, of the body radiating, or of the body receiving the rays.
They may be turned aside in their course, and then deviate from
a straight into a bent or a curved line. They may be affected
in their nature so as to be turned on their axis, or else to have
different properties impressed on different sides. Their sum of
power is limited; so that if the force, as it issues from its source,
is directed on to or determined upon a given set of particles, or
in a given direction, it cannot be in any degree directed upon
other particles, or into another direction, without being propor-
tionately removed from the first. The lines have no dependence
upon a second or reacting body, as in gravitation; and they
require time for their propagation. In all these things they are
in marked contrast with the lines of gravitating force.
3248. When we turn to the electric force, we are presented
410
[JUNE 1852.
Physical lines of force :-
with a very remarkable general condition intermediate between
the conditions of the two former cases. The power (and its
lines) here requires the presence of two or more acting particles
or masses, as in the case of gravity; and cannot exist with one
only, as in the case of light. But though two particles are re-
quisite, they must be in an antithetical condition in respect of
each other, and not, as in the case of gravity, alike in relation to
the force. The power is now dual; there it was simple. Re-
quiring two or more particles like gravity, it is unlike gravity in
that the power is limited. One electro-particle cannot affect a
second, third and fourth, as much as it does the first; to act
upon the latter its power must be proportionately removed from
the former, and this limitation appears to exist as a necessity
in the dual character of the force; for the two states, or places,
or directions of force must be equal to each other.
3249. With the electric force we have both the static and
dynamic state. I use these words merely as names, without
pretending to have a clear notion of the physical condition which
they seem meaningly to imply. Whether there are two fluids or
one, or any fluid of electricity, or such a thing as may be rightly
called a current, I do not know; still there are well-established
electric conditions and effects which the words static, dynamic,
and current are generally employed to express; and with this
reservation they express them as well as any other. The lines
of force of the static condition of electricity are present in all
cases of induction. They terminate at the surfaces of the con-
ductors under induction, or at the particles of non-conductors,
which, being electrified, are in that condition. They are subject
to inflection in their course (1215. 1230.), and may be compressed
or rarefied by bodies of different inductive capacities (1252.
1277.); but they are in those cases affected by the intervening
matter; and it is not certain how the line of electric force would
exist in relation to a perfect vacuum, i. e. whether it would be a
straight line, as that of gravity is assumed to be, or curved in
such a manner as to show something like physical existence
separate from the mere distant actions of the surfaces or par-
ticles bounding or terminating the induction. No condition of
quality or polarity has as yet been discovered in the line of static
electric force; nor has any relation of time been established in
respect of it.
3250. The lines of force of dynamic electricity are either
JUNE 1852.]
411
of electricity-distinctions.
limited in their extent, as in the lowering by discharge, or
otherwise of the inductive condition of static electricity; or
endless and continuous, as closed curves in the case of a voltaic
circuit. Being definite in their amount for a given source, they
can still be expanded, contracted, and deflected almost to any
extent, according to the nature and size of the media through
which they pass, and to which they have a direct relation. It is
probable that matter is always essentially present; but the hypo-
thetical æther may perhaps be admitted here as well as elsewhere.
No condition of quality or polarity has as yet been recognised in
them. In respect of time, it has been found, in the case of a
Leyden discharge, that time is necessary even with the best con-
ductors; indeed there is reason to think it is as necessary there
as in the cases dependent on bad conducting media, as, for in-
stance, in the lightning flash.
3251. Three great distinctions at least may be taken among
these cases of the exertion of force at a distance; that of gravita-
tion, where propagation of the force by physical lines through the
intermediate space is not supposed to exist; that of radiation,
where the propagation does exist, and where the propagating line
or ray, once produced, has existence independent either of its
source, or termination; and that of electricity, where the propa-
gating process has intermediate existence, like a ray, but at the
same time depends upon both extremities of the line of force, or
upon conditions (as in the connected voltaic pile) equivalent to
such extremities. Magnetic action at a distance has to be com-
pared with these. It may be unlike any of them; for who shall
say we are aware of all the physical methods or forms under
which force is communicated? It has been assumed, however,
by some, to be a pure case of force at a distance, and so like that
of gravity; whilst others have considered it as better represented
by the idea of streams of power. The question at present
appears to be, whether the lines of magnetic force have or have
not a physical existence; and if they have, whether such phy-
sical existence has a static or dynamic form (3075. 3156. 3172.
3173.).
3252. The lines of magnetic force have not as yet been
affected in their qualities, i. e. nothing analogous to the polariza-
tion of a ray of light or heat has been impressed on them. A
relation between them and the rays of light when polarized has
412
:—
Physical lines of magnetic force :- [JUNE 1852.
been discovered (2146.) '; but it is not of such a nature as to
give proof as yet, either that the lines of magnetic force have a
separate existence, or that they have not; though I think the
facts are in favour of the former supposition. The investigation
is an open one, and very important.
3253. No relation of time to the lines of magnetic force has
as yet been discovered. That iron requires time for its mag-
netization is well know. Plücker says the same is the case for
bismuth, but I have not been able to obtain the effect showing
this result. If that were the case, then mere space with its
æther ought to have a similar relation, for it comes between bis-
muth and iron (2787.); and such a result would go far to show
that the lines of magnetic force have a separate physical existence.
At present such results as we have cannot be accepted as in any
degree proving the point of time; though if that point were
proved, they would most probably come under it. It may be as
well to state, that in the case also of the moving wire or con-
ductor (125. 3076.), time is required 2. There seems no hope
of touching the investigation by any method like those we are
able to apply to a ray of light, or to the current of the Leyden
discharge; but the mere statement of the problem may help
towards its solution.
3254. If an action in curved lines or directions could be proved
to exist in the case of the lines of magnetic force, it would also
prove their physical existence external to the magnet on which
they might depend; just as the same proof applies in the case
of static electric induction. But the simple disposition of the
lines, as they are shown by iron particles, cannot as yet be
brought in proof of such a curvature, because they may be de-
pendent upon the presence of these particles and their mutual
action on each other and the magnets; and it is possible that
attractions and repulsions in right lines might produce the same
arrangement. The results therefore obtained by the moving
wire (3076. 3176.) *, are more likely to supply data fitted to elu-
cidate this point, when they are extended, and the true magnetic
relation of the moving wire to the space which it occupies is
fully ascertained.
4
1 Philosophical Transactions, 1846, p. 1.
2 Experimental Researches, 8vo edition, vol. ii. pp. 191, 195.
3 Philosophical Transactions, 1838, p. 16.
4 Ibid. 1852.
JUNE 1852.] their definite character and amount.
413
3255. The amount of the lines of magnetic force, or the force
which they represent, is clearly limited, and therefore quite un-
like the force of gravity in that respect (3245); and this is true,
even though the force of a magnet in free space must be con-
ceived of as extending to incalculable distances. This limitation
in amount of force appears to be intimately dependent upon the
dual nature of the power, and is accompanied by a displacement
or removability of it from one object to another, utterly unlike
anything which occurs in gravitation. The lines of force abut-
ting on one end or pole of a magnet may be changed in their
direction almost at pleasure (3238.), though the original seats of
their further parts may otherwise remain the same. For, by
bringing fresh terminals of power into presence, a new disposi-
tion of the force upon them may be occasioned; but though
these may be made, either in part or entirely, to receive the
external power, and thus alter its direction, no change in the
amount of the force is thus produced. And this is the case in
strict experiments, whether the new bodies introduced are soft
iron or magnets (3218. 3223.). In this respect, therefore, the
lines of magnetic force and of electric force agree. Results of
this kind are well shown in some recent experiments on the
effect of iron, when passing by a copper wire in the magnetic
field of a horseshoe magnet (2129. 3130.), and also by the action
of iron and magnets on each other (3218. 3223.).
3256. It is evident, I think, that the experimental data are
as yet insufficient for a full comparison of the various lines of
power. They do not enable us to conclude, with much assu-
rance, whether the magnetic lines of force are analogous to those
of gravitation, or direct actions at a distance; or whether, having
a physical existence, they are more like in their nature to those
of electric induction or the electric current. I incline at present
to the latter view more than to the former, and will proceed to
the further and future elucidation of the subject.
3257. I think I have understood that the mathematical ex-
pression of the laws of magnetic action at a distance is the same
as that of the laws of static electric actions; and it has been
Philosophical Transactions, 1852,
1
414
Physical lines of magnetic force. [JUNE 1852.
assumed at times that the supposition of north and south mag-
netisms, spread over the poles or respective ends of a magnet,
would account for all its external actions on other magnets or
bodies. In either the static or dynamic view, or in any other
view like them, the exertion of the magnetic forces outwards, at
the poles or ends of the magnet, must be an essential condition.
Then, with a given bar-magnet, can these forces exist without a
mutual relation of the two, or else a relation to contrary mag-.
netic forces of equal amount originating in other sources?
I
do not believe they can; because, as I have shown in recent
researches, the sum of the lines of force is equal for any sec-
tion across them taken anywhere externally between the poles
(3109.). Besides that, there are many other experimental facts
which show the relation and connexion of the forces at one pole
to those at the other; and there is also the analogy with static
electrical induction, where the one electricity cannot exist without
relation to, equality with, and dependence on the other. Every
dual power appears subject to this law as a law of necessity. If
the opposite magnetic forces could be independent of each other,
then it is evident that a charge with one magnetism only is pos-
sible; but such a possibility is negatived by every known expe-
riment and fact.
3258. But supposing this necessary relation, which constitutes
polarity, to exist, then how is it sustained or permitted in the
case of an independent bar-magnet situated in free space? It
appears to me, that the outer forces at the poles can only have
relation to each other by curved lines of force through the sur-
rounding space; and I cannot conceive curved lines of force
without the conditions of a physical existence in that interme-
diate space. If they exist, it is not by a succession of particles,
as in the case of static electric induction (1215. 1231.), but by
the condition of space free from such material particles. A
magnet placed in the middle of the best vacuum we can pro-
duce, and whether that vacuum be formed in a space previously
occupied by paramagnetic or diamagnetic bodies, acts as well
upon a needle as if it were surrounded by air, water or glass;
¹ The manner in which a large powerful magnet deranges, overpowers,
and even inverts the magnetism of a smaller magnet, when it is brought
near it in different directions without touching it, presents a number of such
cases.
JUNE 1852.]
415
Duality of the magnetic force.
and therefore these lines exist in such a vacuum as well as
where there is matter.
3259. It may perhaps be said that there is no proof of any
outer lines of force, in the case of a magnet, except when the
objects employed experimentally to show these lines, as a mag-
netic needle, soft iron, a moving wire, or a crystal of bismuth,
are present; that these bodies, in fact, cause and develope the
lines; just as in the case of gravity no idea of a line of gravita-
ting force, in respect of a particle of matter by itself, can be
formed the idea exists only when a second particle is con-
cerned. We are dealing, however, with a dual power; and we
know that we cannot call into action, by magnetic induction
upon soft iron or by electric currents, or otherwise, one mag-
netism without the other. Supposing, therefore, a bar of soft
iron, or another bar-magnet, when brought end on and near to
the first magnet, did by that approach develope the external
force, the power which then only would become external should
produce a corresponding external force of the contrary kind at
the opposite extremity, or should not. If the first case occurs,
it should be accompanied by the development of lines of force
equivalent to it within the magnet. But I think we know, now,
that in a very hard and perfect magnet there is no change of
this kind (3223.). The outer and the inner lines of force remain
the same in amount, whether the secondary magnet or the soft
iron is present or away. It is the disposition only of the outer
lines that is changed; their sum, and therefore the existence,
remains the same. If the second case occurs, then the magnet,
if broken in half under induction, should present in its fragments
case of absolute magnetic charge, or charge with one magnetism
only (3257. 3261.).
3260. Or if it be imagined for a moment, that the two polari-
ties of the bar-magnet are in relation to each other, but that
whilst there is no external object to be acted upon they are
related to each other through the magnet itself (an idea very
difficult to conceive after the experimental demonstration of the
course of the lines as closed curves (3117.3230.)), still it would
follow, that upon the forces being determined externally, a
change in the sum of force both within and without the magnet
should be caused. We can now, however, take cognizance of
both these portions of force: and it appears that, with a good
416
Physical lines of magnetic force. [JUNE 1852.
magnet, whether alone or under the influence of soft iron or
other magnets of fourfold strength, the sum of forces without
(3223.), and therefore also within (3117. 3121.) the magnet
remains the same.
3261. If the northness and southness be considered so far in-
dependent of each other as to be compared to two fluids diffused
over the two ends of the magnet (like the two electricities over a
polarised conductor), then breaking the magnet in half ought to
leave the two parts, one absolutely or differentially north in
character, and the other south. Each should not be both north
and south in equality of proportion, considering only the external
force. But this never happens. If it be said that the new frac-
ture renders manifest, externally, two new poles, opposite in
kind but equal in force (which is the fact), because of the neces-
sity of the case, then the same necessity exists also for the depen-
dence and relation of the original poles of the original magnet,
no matter what or where the first source of the power may be.
But in that case the curved lines of force between the poles of
the original magnet follow as a consequence; and the curvature
of these lines appears to me to indicate their physical existence.
3262. If the magnetic poles in a bar-magnet be supposed to
exert some kind of power internally, backward, as if they were
centres of force, both within and without the magnet, by which
they are able, upon the breaking of the magnet, to develope the
contrary poles and their force, then that power cannot be the
identical portion which is at the same time exerted externally ;
and if not the same, then when the magnet is broken, the two
halves ought to have a degree of north or south charge. They
ought not to be determinate magnets having equipotential poles.
But they are so; and we may break a hard magnet in half whilst
opposed to another powerful magnet which ought most to disturb
the forces, and yet the broken halves are perfect magnets, equi-
valent in their polarities, just as if, when they were made by
breaking, the dominant magnet was away. The power at the
old poles is neither increased nor diminished, but remains in
amount and in polar direction unchanged.
3263. Falling back, therefore, upon the case of a hard, well-
made and well-charged straight bar-magnet, subject only to its
own powers, it appears to me that we must either deny the joint
external relation of the poles, and consider them as having no
JUNE 1852.]
417
Relation between the poles of a magnet.
mutual tendency towards or action upon each other, or else
admit that there is such an action exerted in or transmitted on
through curved lines. To deny such an action, would be to set
up a distinction between the action of the north end of a bar
upon its south end, and its action upon the south end of other
magnets, which, in the face of all the old experiments, and the
new ones made with the moving wire (3076.), it appears to me
impossible to admit. To acknowledge the action in curved lines,
seems to me to imply at once that the lines have a physical exist-
ence. It may be a vibration of the hypothetical æther, or a
state or tension of that æther equivalent to either a dynamic or
a static condition; or it may be some other state, which though
difficult to conceive, may be equally distinct from the supposed
non-existence of the line of gravitating force, and the indepen-
dent and separate existence of the line of radiant force (325).
Still the existence of the state does not appear to me to be mere
assumption or hypothesis, but to follow in some degree as a
consequence of the known condition of the force concerned, and
the facts dependent on it.
3264. I have not referred in the foregoing considerations to
the view I have recently supported by experimental evidence,
that the lines of force, considered simply as representants of the
magnetic power (3117.), are closed curves, passing in one part
of their course through the magnet, and in the other part through
the space around it. These lines are identical in their nature,
qualities and amount, both within the magnet and without. If
to these lines, as formerly defined (3071.), we add the idea of
physical existence, and then reconsider such of the cases which
have just been mentioned as come under the new idea, it will be
seen at once that the probability of curved external lines of force,
and therefore of the physical existence of the lines, is as great,
and even far greater, than before. For now no back action in
the magnet could be supposed; and the external relation and
dependence of the polarities (3257. 3263.) would, if it were pos-
sible, be even more necessary than before. Such a view would
tend to give, but not necessarily, a dynamic form to the idea of
magnetic force; and its close relation to dynamic electricity is
well known (3265.) This I will proceed to examine; but before
¹ See Euler's views of the disposition of the magnetic force; also of the
magnetic fluid, or æther and its streams. Letters, vol. ii. letters 62, 63.
VOL. III.
2 E
418
Physical lines of magnetic force. [JUNE 1852.
doing so, will again look for a moment at static electric induc-
tion, as a case of the dual powers in mutual dependence by
curved lines of force, but with these lines terminated, and not
existing as closed circuits. An electric conductor polarized by
induction, or an insulated, unconnected, rectilineal, voltaic bat-
tery presents such a case, and resembles a magnet in the dispo-
sition of the external lines of force. But the sustaining action
(as regards the induction) being dependent upon the necessary
relation of the opposite dual conditions of the force, is external
to the conductor, or the battery; and in such a case, if the con-
ductor or battery be separated in the middle, no charge appears
there, nor any origin of new lines of inductive force. This is,
no doubt, a consequence of the fact, that the lines of static in-
ductive force are not continued internally; and, at the same time,
a cause why the two divided portions remain in opposite states
or absolutely charged. In the magnet such a division does de-
velope new external lines of force; which being equal in amount
to those dependent on the original poles, shows that the lines of
force are continuous through the body of the magnet, and with
that continuity gives the necessary reason why no absolute charge
of northness or southness is found in the two halves.
3265. The well-known relation of the electric and magnetic
forces may be thus stated. Let two rings, in planes at right
angles to each other, represent them, as in Plate IV fig. 1. If
a current of electricity be sent round the ring E in the direction
marked, then lines of magnetic force will be produced, corre-
spondent to the polarity indicated by a supposed magnetic
needle placed at NS, or in any other part of the ring M to which
such a needle may be supposed to be shifted. As these rings
represent the lines of electro-dynamic force and of magnetic
force respectively, they will serve for a standard of comparison.
I have elsewhere called the electric current, or the line of electro-
dynamic force, "an axis of power having contrary forces exactly
equal in amount in contrary directions" (517.). The line of
magnetic force may be described in precisely the same terms; and
these two axes of power, considered as right lines, are perpendi-
cular to each other; with this additional condition, which deter-
mines their mutual direction, that they are separated by a right
line perpendicular to both. The meaning of the words above,
when applied to the electric current, is precise, and does not
JUNE 1852.] Relation between the magnetic and electric axes. 419
imply that the forces are contrary because they are in reverse
directions, but are contrary in nature; the turning one round,
end for end, would not at all make it resemble the other; a con-
sideration which may have influence with those who admit elec-
tric fluids, and endeavour to decide whether there are one or
two electricities.
1
3266. When these two axes of power are compared, they have
some remarkable correspondences, especially in relation to their
position at right angles to each other. As a physical fact, Am-
père¹ and Davy2 have shown, that an electric current tends to
elongate itself; and, so far, that may be considered as marking
a character of the electric axis of power. When a free magnetic
needle near the end of a bar-magnet first points and then tends
to approach it, I see in the action a character of the contrary
kind in the magnetic axis of power; for the lines of magnetic
force, which, according to my recent researches, are common to
the magnet and the needle (3230.), are shortened, first by the
motion of the needle when it points, and again by the action
which causes the needle to approach the magnet. I think I
may say, that all the other actions of a magnet upon magnets,
or soft iron, or other paramagnetic and diamagnetic bodies, are
in harmony with the same effect and conclusions.
3267. Again :-like electric currents, or lines of force, or
axes of power, when placed side by side, attract each other.
This is well known and well seen, when wires carrying such cur-
rents are placed parallel to each other. But like magnetic axes
of power or lines of force repel each other: the parallel case to
that of the electric currents is given, by placing two magnetic
needles side by side with like poles in the same direction; and
by the use of iron filings, numerous pictorial representations
(3234.) of the same general result may be obtained.
3268. Now these effects are not merely contrasts continued
through two or more different relations, but they are contrasts
which coincide when the position of the two axes of power at
right angles to each other are considered (1659. 3265.). The
tendency to elongate in the electric current, and the tendency to
lateral separation of the magnetic lines of force which surround
that current, are both tendencies in the same direction, though
they seem like contrasts, when the two axes are considered out
¹ Ann. de Chim. 1822, vol. xxi. p. 47. 2 Phil. Trans. 1823, p. 153.
2 E 2
420
[JUNE 1852.
Physical lines of magnetic force.
of their relation of mutual position; and this, with other consi-
derations to be immediately referred to, probably points to the
intimate physical relation, and it may be, to the oneness of con-
dition of that which is apparently two powers or forms of power,
electric and magnetic. In that case many other relations, of
which the following are some forms, will merge in the same result.
Thus, unlike magnetic lines, when end on, repel each other, as
when similar poles are face to face; and unlike electric currents,
if placed in the same relation, stop each other; or if raised in
intensity, when thus made static, repel each other. Like electric
currents or lines of force, when end on to each other, coalesce;
like magnetic lines of force similarly placed do so too (3266.
3295.). Like electric currents, end to end, do not add their
sums; but whilst there is no change in quantity, the intensity
is increased. Like magnetic lines of force, similarly placed do
not increase each other, for the power then also remains the
same (3218.): perhaps some effect correspondent to the gain of
intensity in the former case may be produced, but there is none
as yet distinctly recognised. Like electric currents, side by side,
add the quantities together; a case supplied either by uniting
several batteries by their like ends, or comparing a large plate
battery with a small one. Like magnetic lines of force do the
same (3232.).
3269. The mutual relation of the magnetic lines of force and
the electric axis of power has been known ever since the time of
Ersted and Ampère. This, with such considerations as I have
endeavoured to advance, enables us to form a guess or judge-
ment, with a certain degree of probability, respecting the nature
of the lines of magnetic force. I incline to the opinion that they
have a physical existence correspondent to that of their analogue,
the electric lines; and having that notion, am further carried on
to consider whether they have a probable dynamic condition, ana-
logous to that of the electric axis to which they are so closely
and, perhaps, inevitably related, in which case the idea of mag-
netic currents would arise; or whether they consist in a state of
tension (of the æther?) round the electric axis, and may there-
fore be considered as static in their nature. Again and again.
the idea of an electro-tonic state (60. 1114. 1661. 1729. 1733.)
has been forced on my mind; such a state would coincide and
become identified with that which would then constitute the
JUNE 1852.] Indications given by moving conductors.
421
physical lines of magnetic force. Another consideration tends
in the same direction. I formerly remarked that the magnetic
equivalent to static electricity was not known; for if the unde-
veloped state of electric force correspond to the like undeveloped
condition of magnetic force, and if the electric current or axis
of electric power correspond to the lines of magnetic force or
axis of magnetic power, then there is no known magnetic condi-
tion which corresponds to the static state of the electric power
(1734.). Now assuming that the physical lines of magnetic force
are currents, it is very unlikely that such a link should be na-
turally absent; more unlikely, I think, than that the magnetic
condition should depend upon a state of tension; the more espe-
cially as under the latter supposition, the lines of magnetic power
would have a physical existence as positively as in the former
case, and the curved condition of the lines, which seems to me
such a necessary admission, according to the natural facts, would
become a possibility.
3270. The considerations which arise during the contempla-
tion of the phænomena and laws that are made manifest in the
mutual action of magnets, currents of electricity, and moving
conductors (3084. &c.), are, I think, altogether in favour of the
physical existence of the lines of magnetic force. When only a
single magnet is employed in such cases, and the use of iron or
paramagnetic bodies is dismissed, then there is no effect of at-
traction or repulsion or any ordinary magnetic result produced.
The phænomena may all very fairly be looked upon as purely
electrical, for they are such in character; and if they coincide
with magnetic actions (which is no doubt the case), it is pro-
bably because the two actions are one. But being considered
as electrical actions, they convey a different idea of the condition
of the field where they occur, to that involved in the thought of
magnetic action at a distance. When a copper wire is placed in
the neighbourhood of a bar-magnet, it does not, as far as we are
aware (by the evidence of a magnetic needle or other means),
disturb in the least degree the disposition of the magnetic forces,
either in itself or in surrounding space. When it is moved across
the lines of force, a current of electricity is developed in it, or
tends to be developed; and I have every reason to believe, that
if we could employ a perfect conductor, and obtain a perfcct
result, it would be the full equivalent to the force, electric or
422
Physical lines of magnetic force. [JUNE 1852.
magnetic, which is exerted in the place occupied by the con-
ductor. But, as I have elsewhere observed (3172.), this cur-
rent, having its full and equivalent relation to the magnetic
force, can hardly be conceived of as having its entire foundation
in the mere fact of motion. The motion of an external body,
otherwise physically indifferent, and having no relation to the
magnet, could not beget a physical relation such as that which
the moving wire presents. There must, I think, be a previous
state, a state of tension or a static state, as regards the wire,
which, when motion is superadded, produces the dynamic state or
current of electricity. This state is sufficient to constitute and
give a physical existence to the lines of magnetic force, and permit
the occurrence of curvature or its equivalent external relation of
poles, and also the various other conditions, which I conceive are
incompatible with mere action at a distance, and which yet do
exist amongst magnetic phænomena.
3271. All the phænomena of the moving wire seem to me to
show the physical existence of an atmosphere of power about a
magnet, which, as the power is antithetical, and marked in its
direction by the lines of magnetic force, may be considered as
disposed in sphondyloids, determined by the lines or rather shells
of force¹. As the wire intersects the lines within a given sphon-
dyloid external to the magnet, a current of electricity is gene-
rated, and that current is definite and the same for any or every
intersection of the given sphondyloid. At the same time, whether
the wire be quiescent or in motion, it does not cause derange-
ment, or expansion, or contraction of the lines of force; the state
¹ The lines of magnetic force have been already defined (3071.). They
have also been traced, as I think, and shown to be closed curves passing in
one part of the course through the magnet to which they belong, and in the
other part through space (3117.). If, in the case of a straight bar-magnet,
any one of these lines, E, be considered as revolving round the axis of the
magnet, it will describe a surface; and as the line itself is a closed curve, the
surface will form a tube round the axis and inclose a solid form. Another
line of force, F, will produce a similar result. The sphondyloid body may be
either that contained by the surface of revolution of E, or that contained be-
tween the two surfaces of E and F, and which, for the sake of brevity, I have
(by the advice of a kind friend) called simply the sphondyloid. The parts of
the solid described, which are within and without the magnet, are in power
equivalent to each other. When it is needful to speak of them separately,
they are easily distinguished as the inner and outer sphondyloids; the surface
of the magnet being then part of the bounding surface.
JUNE 1852.] The magnet as a source of power.
423
of the power in the neighbouring or other parts of the sphondy-
loid remaining sensibly the same (3176.).
I
3272. The old experiment of a wire when carrying an electric
current ¹ moving round a magnetic pole, or of a current being
produced in the same wire when it is carried per force round the
same pole (114.), shows the electrical dependence of the magnet
and the wire, both when the current is employed from the first,
and when it is generated by the motion. It coincides in principle
with the results already quoted, and it includes, experimentally,
all currents of electricity, whatever the medium in which they
occur, even up to that due to the discharge of the Leyden jar
or that between the electrodes of the voltaic battery. I think
it also indicates the state of magnetic or electric tension in the
surrounding space, not only when that space is occupied by metal
or a wire, but also by air and other bodies; for whatever be the
state in one case, it is probably general and therefore common
to all (3173.).
3273. I will now venture for a time to assume the physical
existence of the external lines of magnetic force, for the purpose
of considering how the idea will accord with the general phæno-
mena of magnetism. The magnet is evidently the sustaining
power, and in respect of its internal condition or that of its par-
ticles, there is no idea put forth to represent it which at all ap-
proaches in probability and beauty to that of Ampère (1659.).
Its analogy with the helix is wonderful; nevertheless there is,
as yet, a striking experimental distinction between them; for
whereas an unchangeable magnet can never raise up a piece of
soft iron to a state more than equal to its own, as measured by
the moving wire (3219.), a helix carrying a current can develope
in an iron core magnetic lines of force, of a hundred or more
times as much power as that possessed by itself, when measured
by the same means. In every point of view, therefore, the mag-
net deserves the utmost exertions of the philosopher for the
development of its nature, both as a magnet and also as a source
of electricity, that we may become acquainted with the great law
under which the apparent anomaly may disappear, and by which
all these various phænomena presented to us shall become one.
3274. The physical lines of force, in passing out of the mag-
net into space, present a great variety of conditions as to form
Experimental Researches, 8vo edition, vol. ii. p. 127.
1
424
[JUNE 1852.
Physical lines of magnetic force.
(3238.). At times their refraction is very sudden, leaving the
magnet at right, or obtuse, or acute angles, as in the case of a
hard well-charged bar-magnet, fig. 2; in other cases the change
of form of the line in passing from the magnet into space is more
gradual, as in the circular plate or globe-magnet, figs. 3, 4, 5.
Here the form of the magnet as the source of the lines has much
to do with the result; but I think the condition and relation of
the surrounding medium has an essential and evident influence,
in a manner I will endeavour to point out presently. Again,
this refraction of the lines is affected by the relative difference
of the nature of the magnet and the medium or space around it;
as the difference is greater, and therefore the transition is more
sudden, so the line of force is more instantaneously bent. In
the case of the earth, both the nature of its substance and also
its form, tend to make the refractions of the line of force at its
surface very gradual; and accordingly the line of dip does not
sensibly vary under ordinary circumstances, at the same place,
whether it be observed upon the surface or above or below it.
3275. Though the physical lines of force of a magnet may,
and must be considered as extending to infinite distance around
it as long as the magnet is absolutely alone (3110.), yet they may
be condensed and compressed into a very small local space, by
the influence of other systems of magnetic power. This is indi-
cated by fig. 6. I have no doubt, after the experimental results
given in Series XXVIII. respecting definite magnetic action
(3109.), that the sphondyloid representing the total power, which
in the experiment that supplied the figure had a sectional area
of not two square inches in surface, would have equal power
upon the moving wire, with that infinite sphondyloid which would
exist if the small magnet were in free space.
3276. The magnet, with its surrounding sphondyloid of power,
may be considered as analogous in its condition to a voltaic bat-
tery immersed in water or any other electrolyte; or to a gym-
notus (1773. 1784.) or torpedo, at the moment when these crea-
tures, at their own will, fill the surrounding fluid with lines of
electric force. I think the analogy with the voltaic battery so
placed, is closer than with any case of static electric induction,
because in the former instance the physical lines of electric force
may be traced both through the battery and its surrounding
medium, for they form continuous curves like those I have ima-
JUNE 1852.] Analogy between the magnet and a V. battery. 425
gined within and without the magnet. The direction of these
lines of electric force may be traced, experimentally, many ways.
A magnetic needle freely suspended in the fluid will show them
in and near to the battery, by standing at right angles to the
course of the lines. Two wires from a galvanometer will show
them; for if the line joining the two ends in the fluid be at right
angles to the lines of electric force (or the currents), there will
be no action at the galvanometer; but if oblique or parallel to
these lines, there will be deflection. A plate, or wire, or ball of
metal in the fluid will show the direction, provided any electro-
lytic action can go on against it, as when a little acetate of lead
is present in the medium, for then the electrolysis will be a
maximum in the direction of the current or line of force, and
nothing at all in the direction at right angles to it. The same
ball will disturb and inflect the lines of electric force in the sur-
rounding fluid, just as I have considered the case to be with
paramagnetic bodies amongst magnetic lines of force (2806.
2821. 2874.). No one I think will doubt that as long as the
battery is in the fluid, and has its extremities in communication
by the fluid, lines of electric force having a physical existence
occur in every part of it, and the fluid surrounding it.
3277. I conceive that when a magnet is in free space, there is
such a medium (magnetically speaking) around it. That a va-
cuum has its own magnetic relations of attraction and repulsion
is manifest from former experimental results (2787.); and these
place the vacuum in relation to material bodies, not at either
extremity of the list, but in the midst of them, as, for instance,
between gold and platina (2399.), having other bodies on either
side of it. What that surrounding magnetic medium, deprived
of all material substance, may be, I cannot tell, perhaps the
æther. I incline to consider this outer medium as essential
to the magnet; that it is that which relates the external polari-
ties to each other by curved lines of power; and that these must
be so related as a matter of necessity. Just as in the case of the
battery above, there is no line of force, either in or out of the
battery, if this relation be cut off by removing or intercepting
the conducting medium;-or in that of static electric induction,
which is impossible until this related state be allowed (1169.)¹;-
¹ Philosophical Magazine, March 1843; or Experimental Researches, 8vo,
vol. ii. p. 279.
426
Physical lines of magnetic force. [JUNE 1852.
so I conceive, that without this external mutually related
condition of the poles, or a related condition of them to other
poles sustained and rendered possible in like manner, a magnet
could not exist; an absolute northness or southness, or an
unrelated northness or southness, being as impossible as an
absolute or an unrelated state of positive or negative electricity
(1178.).
3278. In this view of a magnet, the medium or space around
it is as essential as the magnet itself, being a part of the true and
complete magnetic system. There are numerous experimental
results which show us that the relation of the lines to the surround-
ing space can be varied by occupying it with different substances;
just as the relation of a ray of light to the space through which
it passes can be varied by the presence of different bodies made
to occupy that space, or as the lines of electric force are affected
by the media through which either induction or conduction takes
place. This variation in regard to the magnetic power may be
considered as depending upon the aptitude which the surround-
ing space has to effect the mutual relation of the two external
polarities, or to carry onwards the physical line of force; and I
have on a former occasion in some degree considered it and its
consequences, using the phrase magnetic conduction to represent
the physical effect (2797.) produced by the presence either of
paramagnetic or diamagnetic bodies.
3279. When, for instance, a piece of cold iron (3129.) or
nickel (3240.) is introduced into the magnetic field, previously
occupied by air or being even mere space, there is a concentration
of lines of force on to it, and more power is transmitted through
the space thus occupied than if the paramagnetic body were not
there. The lines of force therefore converge on to or diverge
from it, giving what I have called conduction polarity (2818.);
and this is the whole effect produced as regards the amount of
the power; for not the slightest addition to, or diminution of,
that external to the magnet is made (3218. 3223.). A new dis-
position of the force arises; for some passes now where it did
not pass before, being removed from places where it was previ-
ously transmitted. Supposing that the magnet was inclosed in
a surrounding solid mass of iron, then the effect of its superior
conducting power would be to cause a great contraction inwards
of the sphere of external action, and of the various sphondyloids,
JUNE 1852.] Needle indications not always the same. 427
which we may suppose to be identified in different parts of it.
A magnetic needle, if it could be introduced into the iron me-
dium, would indicate extreme diminution, if not apparent anni-
hilation, of the external power of this magnet; but the moving
wire would show that it was there present to its full extent
(3152. 3162.) in a very concentrated condition, just as it shows
it in the very body of a magnet (3116.); and the power within
the magnet, it being a hard and perfect one, would remain the
same.
3280. The reason why a magnetic needle would fail as a cor-
rect indicator of the amount of power present in a given space
is, that when perfect, it, because of the necessary condition of
hardness, cannot carry on through its mass more lines of force
than it can excite (3223.). But because of the coalescence of like
lines of force end on (3226.), such a needle, when surrounded by
a bad magnetic conductor, determines on to itself many of the
lines which would otherwise pass elsewhere, has a high magnetic
polarity, and is affected in proportion; every experiment, as far
as I can perceive, tending to show that the attractions and repul-
sions are merely consequences of the tendency which the lines of
physical magnetic force have to shorten themselves (3266.). So
when the magnetic needle is surrounded by a medium gradually
increasing in conducting power, it seems to show less and less
force in its neighbourhood, though in reality the force is increasing
there more and more. We can easily conceive a very hard and
feebly charged magnetic needle surrounded by a medium, as soft
iron, better than itself in conducting power, i. e. carrying on by
conduction more lines of force than the needle could determine
or carry on by its state of charge (3298.). In that case I con
ceive it would, if free to move, point feebly in the iron, because
of the coalescence of the lines of force, but would be repelled
bodily from the chief magnet, in analogy with the action on a
diamagnetic body. As I have before stated, the principle of the
moving wire can be applied successfully in those cases where that
of the magnetic needle fails (3155.).
.
•
3281. If other paramagnetic bodies than iron be considered
in their relation to the surrounding space, then their effects may
be assumed as proportionate to the conducting power. If the
surrounding medium were hard steel, the contraction of the
sphondyloid of power would be much less than with iron; and
428
[JUNE 1852.
Physical lines of magnetic force.
the effects, in respect of the magnetic needle, would occur in a
limited degree. If a solution of protosulphate of iron were used,
the effect would occur in a very much less degree. If a solution
were prepared and adjusted so as to have no paramagnetic or
diamagnetic relation (2422.), it would be the same to the lines
of force as free space. If a diamagnetic body were employed, as
water, glass, bismuth or phosphorus, the extent of action of the
sphondyloids would expand (3279.); and a magnetic needle
would appear to increase in intensity of action, though placed
in a region having a smaller amount of magnetic force passing
across it than before (3155.). Whether in any of these cases,
even in that of iron, the body acting as a conductor has a state
induced upon its particles for the time like that of a magnet in
the corresponding state, is a question which I put upon a former
occasion (2833.); but I leave its full investigatian and decision
for a future time.
3282. The circumstances dependent upon the shape and size
of magnets appear to accord singularly well with the view I am
putting forth of the action of the surrounding medium. If there
be a function in that medinm equivalent to conduction, involving
differences of conduction in different cases, that of necessity im-
plies also reaction or resistance. The differences could not exist
without. The analogous case is presented to us in every part
by the electric force. When, therefore, a magnet, in place of
being a bar, is made into a horseshoe fcrm, we see at once that
the lines of force and the sphondyloids are greatly distorted or
removed from their former regularity; that a line of maximum
force from pole to pole grows up as the horseshoe form is more
completely given; that the power gathers in, or accumulates
about this line, just because the badly conducting medium, i. e.
the space or air between the poles, is shortened. A bent voltaic
battery in its surrounding medium (3276.), or a gymnotus curved
at the moment of its peculiar action (1785.), present exactly the
like results.
3283. The manner in which the keeper or sub-magnet, when
in place, reduces the power of the magnet in the space or air
around, is evident. It is the substitution of an excellent con-
ductor for a poor one; far more of the power of the magnet is
transmitted through it than through the same space before, and
JUNE 1852.]
429
Size and shape of magnets.
less, therefore, in other places. If a horseshoe magnet be charged
to saturation with its keeper on, and its power be then ascer-
tained, removing the keeper will cause the power to fall. This
will be (according to the hypothesis) because the iron keeper
could, by its conduction, sustain higher external conditions of
the magnetic force, and therefore the magnet could take up and
sustain a higher condition of charge. The case passes into that
of a steel ring magnet, which being magnetized, shows no ex-
ternal signs of power, because the lines of force of one part are
continued on by every other part of the ring; and yet when
broken exhibit strong polarity and external action, because then
the lines, which, being determined at a given point, were before
carried on through the continuous magnet, have now to be car-
ried on and continued through the surrounding space.
3284. These results, again, pass into the fact, easily verified
partially, that if soft iron surround a magnet, being in contact
with its poles, that magnet may receive a much higher charge
than it can take, being surrounded with a lower paramagnetic
substance, as air; also another fact, that when masses of soft
iron are at the ends of a magnet, the latter can receive and keep
a higher charge than without them; for these masses carry on
the physical lines of force, and deliver them to a body of sur-
rounding space; which is either widened, and therefore increased
in the direction across the lines of force, or shortened in that
direction parallel to them, or both; and both are circumstances
which facilitate the conduction from pole to pole, and the relation
of the external lines to the lines of force within the magnet. In
the same way the armature of a natural loadstone is useful. All
these effects and expedients accord with the view, that the space
or medium external to the magnet is as important to its exist-
ence as the body of the magnet itself.
3285. Magnets, whether large or small, may be surpersaturated,
and then they fall in power when left to themselves; quickly at
first if strongly supersaturated, and more slowly afterwards. This,
upon the hypothesis, would be accounted for by considering the
surrounding medium as unable, by its feeble magneto-conducting
power, to sustain the higher state of charge. If the conducting
power were increased sufficiently, then the magnet would not be
supersaturated, and its power would not fall. Thus, if a magnet
were surrounded by iron, it might easily be made to assume and
430
[JUNE 1852.
Physical lines of magnetic force.
retain a state of charge, which, if the iron were suddenly replaced
by air, would instantly fall. Indeed, magnets can only be su-
persaturated by placing them for the time under the dominion
of other sources of magnetic power, or of other more favourable
surrounding media than that in which they manifest themselves
as supersaturated.
3286. The well-known result, that small bar-magnets are far
stronger in proportion to their size than larger similar magnets,
harmonizes and sustains that view of the action of the external
medium which has now been given. A sewing-needle can be
magnetized far more strongly than a bar twelve inches long and
an inch in diameter; and the reason under the view taken is,
that the excited system in the magnet (correspondent to the vol-
taic battery in the analogy quoted (3276.)) is better sustained
by the necessary conjoint action of the surrounding medium in
the case of the small magnet. For as the imperfect magneto-
conducting power of that medium (or the consequent state of
tension into which it is thrown) acts back upon the magnet
(3282.), so the smaller the sum of exciting force in the centre
of the magnetic sphondyloids, the better able will the surround-
ing medium be to do its part in sustaining the resultant of force.
It is very manifest, that if the twelve-inch bar be conceived of as
subdivided into sewing-needles, and these be separated from each
other, the whole amount of exciting force acts upon, and is car-
ried onwards in closed magnetic curves, by a very much larger
amount of external surrounding medium than when they are all
accumulated in the single bar.
.
3287. The results which have been observed in the relation
of length and thickness of a bar-magnet, harmonize with the view
of the office of the external medium now urged. If we take a
small, well-proportioned, saturated magnet, as a sewing-needle ;
alone, it has, as just stated, such relation to the surrounding
space as to have its high condition sustained; if we place a
second like magnetic needle by the side of the first, the surround-
ing space of the two is scarcely enlarged, it is not at all improved
in conducting character, and yet it has to sustain double the in-
ternal exciting magnetic force exerted when there was one needle
only (3232.); this must react back upon the magnets, and cause
a reduction of their power. The addition of a third needle repeats
the effect; and if we conceive that successive needles are added
JUNE 1852.]
431
Size and shape of magnets.
until the bundle is an inch thick, we have a result which will
illustrate the effect of a thickness too large, and disproportionate
to the length.
3288. On the other hand, if we assume two such needles
similarly placed in a right line at a distance from each other,
each has its surrounding system of curves occupying a certain
amount of space; if brought together by unlike poles, they form
a magnet of double the length; the external lines of force
coalesce (3226.), those at the faces of contact nearly disappear;
those which proceed from the extreme poles coalesce externally,
and form one large outer system of force, the lines of which have
a greater length than the corresponding lines of either of the
two original needles. Still, by the supposition that the magnets
are perfectly hard and invariable, the exciting force within re-
mains, or tends to remain the same (3227.) in quantity, there
is nothing to increase it. The increase in length, therefore, of
the external circuit, which acts as a resisting medium upon the
internal action, will tend to diminish the force of the whole
system. Such would be the case if a voltaic battery surrounded
by distilled water, as the analogous illustration (3276.), could
be elongated in the water, and so its poles be removed further
apart; and though in the case of magnets previously charged,
some effect equivalent to intensity of excitement may be pro-
duced by conjoining several together end on, yet the diminished
sustentation of power externally appears to follow as a conse-
quence of the increased distance of the extreme poles, or external,
mutually dependent parts. Static electric induction also supplies
a correspondent and illustrative case.
3289. The usual case in which the influence of length and
thickness becomes evident, is not, however, always or often that
of the juxtaposition of magnets already as highly charged as they
can be, but rather that of a bar about to be charged. If two
bars, alike in steel, hardness, &c., one an inch long and the tenth
of an inch in diameter, and the other of the same length but
five-tenths of an inch in diameter, be magnetized to supersatu-
ration, the latter, though it contains twenty-five times the steel
of the former, will not retain twenty-five times the power, for
the reason already given (3287.); the surrounding medium not
being able to sustain external lines of force to that amount. But
if a third bar, two inches long and also five-tenths in diameter,
432
[JUNE 1852.
Physical lines of magnetic force.
be magnetized at the same time, it can receive much more power
than the second one. A natural reason for this presents itself
by the hypothesis; for the limitation of power in the two cases
is not in the magnets themselves, but in the external medium.
The shorter magnet has contact and connexion with that medium
by a certain amount of surface; and just what power the medium
outside that surface can support, the magnet will retain. Make
the magnet as long again, and there is far more contact and rela-
tion with the surrounding medium than before; and therefore
the power which the magnet can retain is greater. If there were
such limited points of resulting action in the magnet as is often
understood by the word poles, then such a result could hardly
be the case, on my view of the physical actions. But such poles
do not exist. Every part of the surface of the magnet, so to
say, is pouring forth externally lines of magnetic force, as may
be seen in figs. 2, 3, 4, 5 (3274.). The larger the magnet, to a
certain extent, and the larger the amount of external conducting
medium in contact with it, the more freely is this transmission
made. If the second magnet, being an inch long, be conceived
to be charged to its full amount, and then, whilst in free space,
could have half an inch of iron added to its length at each end,
we see and know that many of the lines of force originally issuing
from that part of its surface still left in contact with the air at
the equatorial part, would now move internally towards the ends,
and issue at a part of the soft iron surface; indicating the
manner in which the tension would be relieved by this better
conducting medium at the ends, aud by increased surface of
contact with the surrounding bad conductor of air or space.
The thick, short magnet could evidently excite and carry on
physical lines of magnetic power far more numerous than those
which the space about it can receive and convey from pole to
pole; and the increase in the length of the magnet may go on
advantageousely, until the increasing sum of power, sustainable
by the increasing medium in the circuit, is equal to that which
the magnet can sustain or transmit internally; for all the lines
of power, wherever they issue from the magnet, have to pass
through its equator; and in this way the equator or thickness
of the magnet becomes related to its length. So the advan-
tageous increase in length of the bar is limited by the increasing
resistance within, aud especially at the equator of the bar; and
JUNE 1852.]
433
Size and shape of magnets.
the increase in breadth, by the increasing resistance (for in-
creasing powers) of the external surrounding medium (3287.).
3290. It is very interesting to observe the results obtained
when an attempt is made to magnetize, regularly, a thin steel
wire, about 15 or 20 inches in length, and 0·05 of an inch in
diameter. It can hardly be effected by bars; and when the wire
is afterwards examined by filings (3234.), it is found to have
irregular and consecutive poles, which vary as the magnetization
is repeated with the same wire, as if they broke out suddenly by
a rupture of something like unstable equilibrium; the effects
apparently being chiefly referable to the cause now assigned.
Again, when a magnet is made out of a thin, hard, steel plate,
whose length is ten or twelve times its width, it is well known
how the lines of force issue from it in greatest abundance at the
extreme angles, and then at the edges; and how a spot on the
face gives exit to a much smaller number of lines than a like spot
on the edge, at the same distance from the magnetic equator.
Iron filings show such results readily, and so also do the vibra-
tions of a magnetic needle, and likewise the revolutions of a wire
ring (3212.). Now this state of the plate-magnet is precisely
that which would be expected from the hypotheses of the neces-
sary and dependent state of the magnet on the medium sur-
rounding it.
3291. The mutual dependence of a magnet and the external
medium, assumed in the view now put forth, bears upon, and
may probably explain, numerous observations of the apparently
superficial character of the magnetism of iron and magnets in
different cases. If a hard steel bar be magnetized by touch of
other magnets, both the vicinity of the superficial parts of the
bar to the exciting magnet in the first instance, and afterwards
to the surrounding sustaining medium, will tend to cause the
magnetism to be superficial in the bar. If a small magnet or
a horseshoe bar be surrounded by a thick shell of iron as its ex-
ternal medium, the inner surface of the iron, or that nearest to the
magnet, with its neighbouring parts, will convey on more power
than the parts further away. If a thick iron core be placed in a
helix carrying a feeble or moderate electric current, it is the part
of the core nearest to the helix which becomes most highly
charged. Probably many other like results may appear, or be
hereafter devised, and may greatly help to assist the discus-
2 F
VOL. III.
434
Physical lines of magnetic force. [JUNE 1852.
sion of the question of physical lines of force now under con-
sideration.
3292. When, in place of considering the medium external to
a magnet as homogeneous or equal in magnetic power, we make
it variable in different parts, then the effects in it appear to me
still to be in perfect accordance with the notion of physical lines
of magnetic force, which, being present externally, are definite in
direction and amount. The series of substances at our command
which affect the surrounding space in this respect, do not present
a great choice of successive steps; but having iron, nickel and
cobalt, very high as paramagnetic bodies, we then possess hard
steel, as very far beneath them; next, perhaps, oxides of iron,
and so on by solutions of the magnetic metals to oxygen, water,
glass, bismuth and phosphorus, in the diamagnetic direction.
Taking the magnetic force of the earth as supplying the source
of power, and placing a globe of iron or nickel in the air, we see
by the pointing of a small magnetic needle (or in another case,
by the use of iron filings (3240.)), the deflected course of the
lines of force as they enter into and pass out of the sphere, con-
sequent upon the conducting power of the paramagnetic body.
These have been described in their forms in another place (3238.).
If we take a large bar-magnet, and place a piece of soft iron,
about half the width of the magnet, and three or four times as
long as it is wide, end on to, and about its own width from one
pole, and covering that with paper, then observe the forms of
the lines of force by iron filings; it will be seen how beautifully
those issuing from the magnet converge, by fine inflections, on
to the iron, entering by a comparatively small surface, and how
they pass out in far more diffuse streams by a much larger sur-
face at the further part of the bar, fig. 7. If we take several
pieces of iron, cubes for instance, then the lines of force which
are altogether outside of them, may be seen undergoing success-
ive undulations in contrary directions, fig. 8. Yet in all these
cases of the globe, bar and cubes, I, at least, am satisfied that a
section across the same lines of force in any part of their course,
however or whichever way deflected, would yield the same amount
of effect (3109. 3218.); at the same time this effect of deflection
is not only consistent with, but absolutely suggests the idea of a
physical line of force.
3293. Then the manner in which the power disappears in such
JUNE 1852.]
435
Media surrounding a magnet.
cases to an ordinary magnetic needle is perfectly consistent. A
little needle held by the side of the soft bar described above
(3292.), indicates much less magnetic power than if the iron
were away. If held in a hole made in the iron, it is almost in-
different to the magnet; yet what power remains shows that
the lines through the air in the hole are in the same general di-
rection as those through the neighbouring iron. These effects
are perfectly well known, no doubt; and my object is only to
show that they are consistent with, and support the idea of ex-
ternal media having magnetic conducting power. But these
apparent destructions of power, and even far more anomalous
cases (2868. 3155.), are fully accounted for by the hypothesis ;
and the force absolutely unaffected in amount is found, experi-
mentally, by the moving wire. I have had occasion before to
refer to the modification of the magnetic force (in relation to the
magnetic needle), where, its absolute quantity being the same,
it passes across better or worse conductors, and I have tempo-
rarily used the words quantity and intensity (2866. 2868. 2870.).
I would, however, rather not attempt to limit or define these or
such like terms now, however much they may be wanted, but
wait until what is at present little more than suggestion, may
have been canvassed, and if true in itself, may have received
assurance from the opinions or testimony of others.
.
3294. The association of magnet with magnet, and all the
effects then produced (3218.), are in harmony, as far as I can
perceive, with the idea of a physical line of magnetic force. If
the magnets are all free to move, they set to each other, and then
tend to approach; the great result being, that the lines from all
the sources tend to coalesce, to pass through the best conductors,
and to contract in length. When there are several magnets in
presence and in restrained conditions, the lines of force, which
they present by filings, are most varied and beautiful (3238.);
but all are easily read and understood by the principles I have
set forth. As the power is definite in amount, its removability
from place to place, according to the changing disposition of
the magnets, or the introduction of better or worse conductors
into the surrounding media, becomes a perfectly simple result.
3295. As magnets may be looked upon as the habitations of
bundles of lines of force, they probably show us the tendencies
of the physical lines of force where they occur in the space
2 F 2
436
Physical lines of magnetic force. [JUNE 1852.
around; just as electric currents, when conducted by solid wires,
or when passing, as the Leyden or the voltaic spark, through
air or a vacuum, are alike in their essential relations. In that
case, the repulsion of magnets when placed side by side, indi-
cates the lateral tendency of separation of lines of magnetic force
(3267.). The effect, however, must be considered in relation to
the simultaneous gathering up of the terrestrial lines of force in
the surrounding space upon each magnet, and also the tendency
of each magnet to secure its own independent external medium.
The effect coincides with, and passes into that of the lateral re-
pulsion of balls of iron in a previously equal magnetic field (2814.);
which again, by a consideration of the action in two directions,
i. e. parallel to and across the magnetic axis, links the phæno-
mena of separation with those of attraction.
3296. When speaking of magnets, in illustration of the ques-
tion under consideration, I mean magnets perfect in their kind,
i. e. such as are very hard and hold their charge, so that there
shall be neither internal reaction of discharge or development
(3224.), nor any external change, except what may depend upon
such absolute and permanent loss of exciting power as is conse-
quent upon an over-ruling change of the external relations.
Heterogeneous magnets which might allow of irregular varia-
tions of power, are out of present consideration.
3297. With regard to the great point under consideration, it
is simply, whether the lines of magnetic force have a physical
existence or not? Such a point may be investigated, perhaps
even satisfactorily, without our being able to go into the further
questions of how they account for magnetic attraction and repul-
sion, or even by what condition of space, æther or matter, these
lines consist. If the extremities of a straight bar-magnet, or if
the polarities of a circular plate of steel (3274.), are in magnetic
relation to each other externally (3257.), then I think the exist-
ence of curved lines of magnetic force must be conceded (3258.
2633.); and if that be granted, then I think that the physical
nature of the lines must be granted also. If the external rela-
tion of the poles or polarity is denied, then, as it appears to me,
the internal relation must be denied also; and with it a vast
number of old and new facts (3070. &c.) will be left without
1 See for a case of curved lines the inclosed and compressed system of
forces belonging to the central circular magnet, fig. 6 (3275.).
JUNE 1852.] Magnetic attraction and repulsion.
4.37
either theory, hypothesis, or even a vague supposition to explain
them.
3298. Perhaps both magnetic attraction and repulsion, in all
forms and cases, resolve themselves into the differential action
(2757.) of the magnets and substances which occupy space, and
modify its magnetic power. A magnet first originates lines of
magnetic force; and then, if present with another magnet, offers in
one position a very free conduction of the new lines, like a para-
magnetic body; or if restrained in the contrary position, resists
their passage, and resembles a highly diamagnetic substance. So,
then, a source of magnetic lines being present, and also magnets or
other bodies affecting and varying the conducting power of space,
those bodies which can convey onwards the most force, may tend,
by differential actions, with the others present, to take up the
position in which they can do so the most freely, whether it is
by pointing or by approximation; the best conductor passing to
the place of strongest action (2757.), whilst the worst retreats
from it, and so the effects both of attraction and repulsion be
produced. The tendency of the lines of magnetic force to shorten
(3266. 3280.) would be consistent with such a notion. The
result would occur whether the physical lines of force were sup-
posed to consist in a dynamic or a static state (3269.).
3299. Having applied the term line of magnetic force to an
abstract idea, which I believe represents accurately the nature,
condition, direction, and comparative amount of the magnetic
forces, without reference to any physical condition of the force,
I have now applied the term physical line of force to include the
further idea of their physical nature. The first set of lines I
affirm upon the evidence of strict experiment (3071. &c.). The
second set of lines I advocate, chiefly with a view of stating the
question of their existence; and though I should not have raised
the argument unless I had thought it both important, and likely
to be answered ultimately in the affirmative, I still hold the
opinion with some hesitation, with as much, indeed, as accom-
panies any conclusion I endeavour to draw respecting points in
the very depths of science, as for instance, regarding one, two
or no electric fluids; or the real nature of a ray of light, or the
nature of attraction, even that of gravity itself, or the general
nature of matter.
Royal Institution, March 6, 1852.
439
On the Physical Lines of Magnetic Force.
[Royal Institution Proceedings, June 11, 1852.]
ON a former occasion' certain lines about a bar-magnet were
described and defined (being those which are depicted to the eye
by the use of iron filings sprinkled in the neighbourhood of
the magnet), and were recommended as expressing accurately
the nature, condition, direction, and amount of the force in any
given region either within or outside of the bar. At that time
the lines were considered in the abstract. Without departing
from or unsettling anything then said, the inquiry is now entered
upon of the possible and probable physical existence of such lines.
Those who wish to reconsider the different points belonging to
these parts of magnetic science may refer to two papers in the
first part of the Phil. Trans. for 18522 for data concerning the
representative lines of force, and to a paper in the Phil. Mag.
4th Series, 1852, vol. iii. p. 401, for the argument respecting the
physical lines of force 3.
.
Many powers act manifestly at a distance; their physical
nature is incomprehensible to us; still we may learn much that
is real and positive about them, and amongst other things some-
thing of the condition of the space between the body acting and
that acted upon, or between the two mutually acting bodies.
Such powers are presented to us by the phænomena of gravity,
light, clectricity, magnetism, &c. These when examined will be
found to present remarkable differences in relation to their
respective lines of forces; and at the same time that they esta-
blish the existence of real physical lines in some cases, will facili-
tate the consideration of the question as applied especially to
magnetism.
When two bodies, a, b, gravitate towards each other, the line
in which they act is a straight line, for such is the line which
either would follow if free to move. The attractive force is not
altered, either in direction or amount, if a third body is made to
act by gravitation or otherwise upon either or both of the two
first. A balanced cylinder of brass gravitates to the earth with
a weight exactly the same, whether it is left like a pendulum
freely to hang towards it, or whether it is drawn aside by other
¹ See page 402.
2 See page 328.
³ See page 407.
JUNE 1852.]
439
Physical lines of force-light.
attraction or by tension, whatever the amount of the latter may
be. A new gravitating force may be exerted upon a, but that
does not in the least affect the amount of power which it exerts
towards b. We have no evidence that time enters in any way
into the exercise of this power, whatever the distance between
the acting bodies, as that from the sun to the earth, or from star
to star. We can hardly conceive of this force in one particle
by itself; it is when two or more are present that we comprehend
it: yet in gaining this idea we perceive no difference in the
character of the power in the different particles; all of the same
kind are equal, mutual, and alike. In the case of gravitation, no
effect which sustains the idea of an independent or physical line
of force is presented to us; and as far as we at present know, the
line of gravitation is merely an ideal line representing the direc-
tion in which the power is exerted.
Take the Sun in relation to another force which it exerts upon
the earth, namely its illuminating or warming power. In this
case rays (which are lines of force) pass across the intermediate
space; but then we may affect these lines by different media
applied to them in their course. We may alter their direction
either by reflection or refraction; we may make them pursue
curved or angular courses. We may cut them off at their origin
and then search for and find them before they have attained
their object. They have a relation to time, and occupy 8 minutes
in coming from the sun to the earth: so that they may exist
independently either of their source or their final home, and
have in fact a clear distinct physical existence. They are in
extreme contrast with the lines of gravitating power in this
respect; as they are also in respect of their condition at their
terminations. The two bodies terminating a line of gravitating
force are alike in their actions in every respect, and so the line
joining them has like relations in both directions. The two
bodies at the terminals of a ray are utterly unlike in action; one
is a source, the other a destroyer of the line; and the line itself
has the relation of a stream flowing in one direction. In these
two cases of gravity and radiation, the difference between an
abstract and a physical line of force is immediately manifest.
Turning to the case of Static Electricity we find here attrac-
tions (and other actions) at a distance as in the former cases;
but when we come to compare the attraction with that of gravity,
440
Physical lines of electric force;- [JUNE 1852.
very striking distinctions are presented which immediately affect
the question of a physical line of force. In the first place, when
we examine the bodies bounding or terminating the lines of
attraction, we find them as before, mutually and equally con-
cerned in the action; but they are not alike: on the contrary,
though each is endued with a force which speaking generally is
of the like nature, still they are in such contrast that their actions
on a third body in a state like either of them are precisely the
reverse of each other,-what the one attracts the other repels;
and the force makes itself evident as one of those manifestations
of power endued with a dual and antithetical condition. Now
with all such dual powers, attraction cannot occur unless the
two conditions of force are present and in face of each other
through the lines of force. Another essential limitation is that
these two conditions must be exactly equal in amount, not merely
to produce the effects of attraction, but in every other case; for
it is impossible so to arrange things that there shall be present
or be evolved more electric power of the one kind than of the
other. Another limitation is that they must be in physical rela-
tion to each other; and that when a positive and a negative
electrified surface are thus associated, we cannot cut off this
relation except by transferring the forces of these surfaces to
equal amounts of the contrary forces provided elsewhere. An-
other limitation is that the power is definite in amount.
If a
ball a be charged with 10 of positive electricity, it may be made
to act with that amount of power on another ball b charged with
10 of negative electricity; but if 5 of its power be taken up by
a third ball c charged with negative electricity, then it can only
act with 5 of power on ball a, and that ball must find or evolve
5 of positive power elsewhere: this is quite unlike what occurs
with gravity, a power that presents us with nothing dual in
its character. Finally, the electric force acts in curved lines.
If a ball be electrified positively and insulated in the air, and a
round metallic plate be placed about 12 or 15 inches off, facing
it and uninsulated, the latter will be found, by the necessity
mentioned above, in a negative condition; but it is not negative
only on the side facing the ball, but on the other or outer face
also, as may be shown by a carrier applied there, or by a strip
of gold or silver leaf hung against that outer face. Now the
power affecting this face does not pass through the uninsulated
JUNE 1852.] of static and dynamic electricity.
441
plate, for the thinnest gold leaf is able to stop the inductive
action, but round the edges of the face, and therefore acts in
curved lines. All these points indicate the existence of physical
lines of electric force :-the absolutely essential relation of
positive and negative surfaces to each other, and their depen-
dence on each other contrasted with the known mobility of the
forces, admit of no other conclusion. The action also in curved
lines must depend upon a physical line of force. And there is
a third important character of the force leading to the same
result, namely its affection by media having different specific
inductive capacities.
When we pass to Dynamic Electricity the evidence of physical
lines of force is far more patent. A voltaic battery having its
extremities connected by a conducting medium, has what has
been expressively called a current of force running round the
circuit, but this current is an axis of power having equal and
contrary forces in opposite directions. It consists of lines of
force which are compressed or expanded according to the trans-
verse action of the conductor, which changes in direction with
the form of the conductor, which are found in every part of the
conductor, and can be taken out from any place by channels
properly appointed for the purpose; and nobody doubts that
they are physical lines of force.
Finally as regards a Magnet, which is the object of the present
discourse. A magnet presents a system of forces perfect in itself,
and able, therefore, to exist by its own mutual relations. It has
the dual and antithetic character belonging to both static and
dynamic electricity; and this is made manifest by what are
called its polarities, i. e. by the opposite powers of like kind
found at and towards its extremities. These powers are found
to be absolutely equal to each other; one cannot be changed in
any degree as to amount without an equal change of the other;
and this is true when the opposite polarities of a magnet are not
related to each other, but to the polarities of other magnets.
The polarities, or the northness and southness of a magnet are
not only related to each other, through or within the magnet
itself, but they are also related externally to opposite polaritics
(in the manner of static electric induction), or they cannot exist ;
and this external relation involves and necessitates an exactly
equal amount of the new opposite polarities to which those of
442
Physical lines of magnetic force. [JUNE 1852.
the magnet are related. So that if the force of a magnet a is
related to that of another magnet b, it cannot act on a third
magnet c without being taken off from b, to an amount propor-
tional to its action on c. The lines of magnetic force are shown
by the moving wire to exist both within and outside of the
magnet; also they are shown to be closed curves passing in one
part of their course through the magnet; and the amount of those
within the magnet at its equator is exactly equal in force to the
amount in any section including the whole of those on the out-
side. The lines of force outside a magnet can be affected in
their direction by the use of various media placed in their course.
A magnet can in no way be procured having only one magnetism,
or even the smallest excess of northness or southness one over
the other. When the polarities of a magnet are not related
externally to the forces of other magnets, then they are related
to each other: i. e. the northness and southness of an isolated
magnet are exterally dependent on and sustained by each other.
Now all these facts, and many more, point to the existence of
physical lines of force external to the magnets as well as within.
They exist in curved as well as in straight lines; for if we con-
ceive of an isolated straight bar-magnet, or more especially of a
round disc of steel magnetized regularly, so that its magnetic
axis shall be in one diameter, it is evident that the polarities
must be related to each other externally by curved lines of force;
for no straight line can at the same time touch two points having
northness and southness. Curved lines of force can, as I think,
only consist with physical lines of force.
The phænomena exhibited by the moving wire confirm the
same conclusion. As the wire moves across the lines of force, a
current of electricity passes or tends to pass through it, there
being no such current before the wire is moved. The wire when
quiescent has no such current, and when it moves it need not
pass into places where the magnetic force is greater or less. It
may travel in such a course that if a magnetic needle were carried
through the same course it would be entirely unaffected mag-
netically, i. e. it would be a matter of absolute indifference to the
needle whether it were moving or still. Matters may be so
arranged that the wire when still shall have the same diamagnetic
force as the medium surrounding the magnet, and so in no way
cause disturbance of the lines of force passing through both ;
JUNE 1852.]
443
Medium in which they exist.
and yet when the wire moves, a current of electricity shall be
generated in it. The mere fact of motion cannot have produced
this current: there must have been a state or condition around
the magnet and sustained by it, within the range of which the
wire was placed; and this state shows the physical constitution
of the lines of magnetic force.
What this state is, or upon what it depends, cannot as yet be
declared. It may depend upon the æther, as a ray of light does,
and an association has already been shown between light and
magnetism. It may depend upon a state of tension, or a state of
vibration, or perhaps some other state analogous to the electric
current, to which the magnetic forces are so intimately related.
Whether it of necessity requires matter for its sustentation will
depend upon what is understood by the term matter. If that is
to be confined to ponderable or gravitating substances, then
matter is not essential to the physical lines of magnetic force any
more than to a ray of light or heat; but if in the assumption of
an æther we admit it to be a species of matter, then the lines of
force may depend upon some function of it. Experimentally
mere space is magnetic; but then the idea of such mere space
must include that of the æther, when one is talking on that belief;
or if hereafter any other conception of the state or condition of
space rise up, it must be admitted into the view of that, which
just now in relation to experiment is called mere space.
On
the other hand it is, I think, an ascertained fact, that ponderable
matter is not essential to the existence of physical lines of mag-
netic force.
444
2
On the Magnetic Relations and Characters of the Metals'
In two former communications to the Philosophical Magazine *
respecting the magnetic characters of metals generally and the
temperatures at which they respectively lost or gained the
powers of magnetic induction, I said that iron and nickel were
the only metals which had this power, and that I could not find
it in pure cobalt. In this I was in error; cobalt has this pro-
perty in common with iron and nickel, as others have said. I
have sought for the piece of cobalt on which I experimented
and believed to be pure, but cannot find it, and am now unable
to ascertain the cause of my error, though not too late to
correct it.
By favour of Dr. Percy and Mr. Askin I have recently ex-
perimented with two fine pieces of pure cobalt prepared by the
latter, both being well-fused and perfectly clean masses. This
metal becomes strongly magnetic by induction, either of a mag-
net or an electro-current, and can easily be made to lift more
than its own weight. Like soft iron and nickel, it does not
retain its magnetism when the inducing influence is removed.
It was to me a point of great interest to ascertain whether,
and at what temperature, cobalt would lose this power and be-
come as the unmagnetic metals. To my surprise I found this
to be very high, not merely much higher than with nickel, but
far above that required for iron or steel, and nearly approaching
the temperature of melted copper. That for iron is a moderate
red heat, and that for nickel the temperature of boiling oil only.
As the temperature rises, the magnetic force of the cobalt con-
tinues, apparently undiminished, to a certain degree of heat, and
then suddenly ceases; and it comes on as suddenly in descending
from still higher tempetatures.
The oxide of cobalt procured by burning the metal cobalt on
charcoal by a jet of oxygen was obtained as a fused globule and
was not magnetic.
The oxide of nickel being heated and cooled is not magnetic,
but whilst heating care must be taken that it is not reduced. If
heated in the flame of a spirit-lamp, especially at the lower part,
¹ Philosophical Magazine, July 1845.
2
1836, vol. viii. p. 177, and 1839, vol. xiv. p. 161; or Exp. Res. vol. ii. pp.
217, 223.
JUNE 1845.] Magnetic relations of cooled metals.
445
it will often appear to be not magnetic, and then as the tempera-
ture falls will become magnetic; but this is caused by the reduc-
tion of a little of the oxide at the edges or elsewhere in the mass
to the metallic state, and its exhibition of the properties of the
metal at temperatures above and below the magnetic point.
Manganese.—A piece of manganese prepared by Mr. Thompson
and considered pure was put into my hands. It contained a
trace of iron; it was very slightly magnetic, and probably only
in consequence of the little iron present. Before a jet of oxygen
or charcoal, it burnt with sparkles somewhat in the manner of
iron, and produced an oxide which could be obtained either as a
porous white mass or as a dense compact brown mass, trans-
lucent in small slices; but in neither state was the oxide mag-
netic.
I then cooled' manganese, chromium, and many other metals
and bodies to the lowests temperature which I could obtain by a
mixture of æther and solid carbonic acid placed in vacuo², the
temperature being then not higher than 156° F. below 0°, but
not one of them assumed the magnetic state. The following is
a list of the substances:-
Platinum.
Gold.
Speculum metal.
Plumbago.
Gas-retort carbon.
Kish.
Silver.
Palladium.
Copper.
Orpiment.
Tin.
Realgar.
Lead.
Sulphuret of antimony.
Cadmium.
Zinc.
Rhodium.
Manganese.
Chromium.
Titanium.
bismuth.
copper.
iron.
lead.
silver.
tin.
Iridium and Osmium.
Antimony.
Arsenic.
Bismuth.
Fusible metal.
Carbonate of iron (native).
Prussian blue.
Crystallized sulphate of iron.
Calomel.
Chloride of silver.
¹ Philosophical Magazine, 1839, vol. xiv. p. 162; or Exp. Res. vol. ii.
Philosophical Transactions, 1845, pp. 157, 158.
p.
224.
446
Magnetic relations of cooled metals. [JUNE 1845.
Chloride of lead.
Protoxide of arsenic.
antimony.
lead.
Oxide of bismuth.
tin (native).
manganese (native).
Thus it appears that only iron, nickel and cobalt are mag-
netic, or can be made magnetic amongst metals after the manner
of iron; but the addition of cobalt, and still more, the very high
temperature required to take away this property from it, in-
creases the probability' that all the metals form a common class
in respect of this property; and that it is only a difference of
temperature which distinguishes these three from the rest, just
as it also in a similar respect distinguishes them from each other.
In connexion with the effect of heat it may be remarked (and
perhaps has been remarked already), that, assuming an elevated
temperature for the internal parts of the earth, then it is evident
that at a very moderate distance from the surface, as compared
with the earth's diameter, the substances composing the earth
must be destitute of such magnetic power as is possessed by a
magnet; and, at a distance somewhat greater, none of them can
retain even that power which soft iron has of becoming magnetic
by induction. In such case, whether the earth be considered as
magnetic of itself, like a loadstone, or rendered magnetic by in-
duction under the influence of external magnetic masses, as the
sun for instance; still it can only be in its crust that the magnetic
power could be developed. Assuming with Ampère, that the
magnetism of the earth is due to electric currents circulating
around it parallel to the equator, then of course the above ob-
servations regarding the effects of heat would not apply.
1
Royal Institution,
June 7, 1845.
¹ Philosophical Magazine, 1836, vol. viii. p. 177; or Exp. Res. ii. 217.
447
Thoughts on Ray-vibrations¹.
To Richard Phillips, Esq.
DEAR SIR,
Ar your request I will endeavour to convey to you a notion of
that which I ventured to say at the close of the last Friday-
evening Meeting, incidental to the account I gave of Wheat-
stone's electro-magnetic chronoscope; but from first to last un-
derstand that I merely threw out as matter for speculation, the
vague impressions of my mind, for I gave nothing as the result
of sufficient consideration, or as the settled conviction, or even
probable conclusion at which I had arrived.
The point intended to be set forth for consideration of the
hearers was, whether it was not possible that the vibrations
which in a certain theory are assumed to account for radiation
and radiant phænomena may not occur in the lines of force
which connect particles, and consequently masses of matter
together; a notion which as far as it is admitted, will dispense
with the æther, which, in another view, is supposed to be the
medium in which these vibrations take place.
You are aware of the speculation 2 which I some time since
uttered respecting that view of the nature of matter which con-
siders its ultimate atoms as centres of force, and not as so many
little bodies surrounded by forces, the bodies being considered
in the abstract as independent of the forces and capable of
existing without them. In the latter view, these little particles
have a definite form and a certain limited size; in the former
view such is not the case, for that which represents size may be
considered as extending to any distance to which the lines of
force of the particle extend: the particle indeed is supposed to
exist only by these forces, and where they are it is. The con-
sideration of matter under this view gradually led me to look at
the lines of force as being perhaps the seat of the vibrations of
radiant phænomena.
Another consideration bearing conjointly on the hypothetical
view both of matter and radiation, arises from the comparison
1 Philosophical Magazine, S. 3, vol. xxviii. No. 188, May 1846.
2 Philosophical Magazine, 1844, vol. xxiv. p. 136; or Exp. Res. ii. 284.
448
[MAY 1846.
Thoughts on ray-vibrations.
of the velocities with which the radiant action and certain powers
of matter are transmitted. The velocity of light through space
is about 190,000 miles in a second; the velocity of electricity is,
by the experiments of Wheatstone, shown to be as great as this,
if not greater: the light is supposed to be transmitted by vibra-
tions through an æther which is, so to speak, destitute of gravi-
tation, but infinite in elasticity; the electricity is transmitted
through a small metallic wire, and is often viewed as transmitted
by vibrations also. That the electric transference depends on
the forces or powers of the matter of the wire can hardly be
doubted, when we consider the different conductibility of the
various metallic and other bodies; the means of affecting it by
heat or cold; the way in which conducting bodies by combina-
tion enter into the constitution of non-conducting substances,
and the contrary; and the actual existence of one elementary
body, carbon, both in the conducting and non-conducting state.
The power of electric conduction (being a transmission of force
equal in velocity to that of light) appears to be tied up in and
dependent upon the properties of the matter, and is, as it were,
existent in them.
I suppose we may compare together the matter of the æther
and ordinary matter (as, for instance, the copper of the wire
through which the electricity is conducted), and consider them
as alike in their essential constitution; i. e. either as both com-
posed of little nuclei, considered in the abstract as matter, and
of force or power associated with these nuclei, or else both con-
sisting of mere centres of force, according to Boscovich's theory
and the view put forth in my speculation; for there is no reason
to assume that the nuclei are more requisite in the one case
than in the other. It is true that the copper gravitates and the
æther does not, and that therefore the copper is ponderable and
the æther is not; but that cannot indicate the presence of nuclei
in the copper more than in the æther, for of all the powers of
matter gravitation is the one in which the force extends to the
greatest possible distance from the supposed nucleus, being in-
finite in relation to the size of the latter, and reducing that
nucleus to a mere centre of force. The smallest atom of matter
on the carth acts directly on the smallest atom of matter in
the sun, though they are 95,000,000 of miles apart; further,
atoms which, to our knowledge, are at least nineteen times that
MAY 1846.]
449
Thoughts on ray-vibrations.
distance, and indeed, in cometary masses, far more, are in a
similar way tied together by the lines of force extending from
and belonging to each. What is there in the condition of the
particles of the supposed æther, if there be even only one such
particle between us and the sun, that can in subtility and extent
compare to this?
Let us not be confused by the ponderability and gravitation
of heavy matter, as if they proved the presence of the abstract
nuclei; these are due not to the nuclei, but to the force super-
added to them, if the nuclei exist at all; and, if the æther parti-
cles be without this force, which according to the assumption is
the case, then they are more material, in the abstract sense, than
the matter of this our globe; for matter, according to the as-
sumption, being made up of nuclei and force, the æther parti-
cles have in this respect proportionately more of the nucleus and
less of the force.
On the other hand, the infinite elasticity assumed as belong-
ing to the particles of the æther, is as striking and positive a
force of it as gravity is of ponderable particles, and produces in
its way effects as great; in witness whereof we have all the
varieties of radiant agency as exhibited in luminous, calorific,
and actinic phænomena.
Perhaps I am in error in thinking the idea generally formed
of the æther is that its nuclei arc almost infinitely small, and
that such force as it has, namely its elasticity, is almost infinitely
intense. But if such be the received notion, what then is left in
the æther but force or centres of force? As gravitation and
solidity do not belong to it, perhaps many may admit this con-
clusion; but what are gravitation and solidity? certainly not the
weight and contact of the abstract nuclei. The one is the con-
sequence of an attractive force, which can act at distances as
great as the mind of man can estimate or conceive; and the
other is the consequence of a repulsive force, which forbids for
ever the contact or touch of any two nuclei; so that these
powers or properties should not in any degree lead those per-
sons who conceive of the æther as a thing consisting of force
only, to think any otherwise of ponderable matter, except that it
has more and other forces associated with it than the æther has.
In experimental philosophy we can, by the phænomena pre-
sented, recognize various kinds of lines of force; thus there are
2 &
VOL. III.
450
[MAY 1846.
Thoughts on ray-vibrations.
the lines of gravitating force, those of electro-static induction,
those of magnetic action, and others partaking of a dynamic
character might be perhaps included. The lines of electric aud
magnetic action are by many considered as exerted through space
like the lines of gravitating force. For my own part, I incline
to believe that when there are intervening particles of matter
(being themselves only centres of force), they take part in carry-
ing on the force through the line, but that when there are none,
the line proceeds through space¹. Whatever the view adopted
respecting them may be, we can, at all events, affect these lines
of force in a manner which may be conceived as partaking of the
nature of a shake or lateral vibration. For suppose two bodies,
A B, distant from each other and under mutual action, and
therefore connected by lines of force, and let us fix our attention
upon one resultant of force, having an invariable direction as re-
gards space; if one of the bodies move in the least degree right
or left, or if its power be shifted for a moment within the mass
(neither of these cases being difficult to realise if A and B be
either electric or magnetic bodies), then an effect equivalent to a
lateral disturbance will take place in the resultant upon which
we are fixing our attention; for, either it will increase in force
whilst the neighbouring resultants are diminishing, or it will fall
in force as they are increasing.
It may be asked, what lines of force are there in nature which
are fitted to convey such an action and supply for the vibrating
theory the place of the æther? I do not pretend so answer this
question with any confidence; all I can say is, that I do not per-
ceive in any part of space, whether (to use the common phrase)
vacant or filled with matter, anything but forces and the lines in
which they are exerted. The lines of weight or gravitating
force are, certainly, extensive enough to answer in this respect
any demand made upon them by radiant phænomena; and so,
probably, are the lines of magnetic force: and then who can
forget that Mossotti has shown that gravitation, aggregation,
electric force, and electro-chemical action may all have one
common connection or origin; and so, in their actions at a
distance, may have in common that infinite scope which some
of these actions are known to possess?
1
Experimental Researches in Electricity, pars. 1161, 1613, 1663, 1770,
1729, 1735, 2443.
.
MAY 1846.]
451
Thoughts on ray-vibrations.
The view which I am so bold as to put forth considers, there-
fore, radiation as a high species of vibration in the lines of force
which are known to connect particles and also masses of matter
together. It endeavours to dismiss the æther, but not the
vibration. The kind of vibration which, I believe, can alone
account for the wonderful, varied, and beautiful phænomena of
polarization, is not the same as that which occurs on the surface
of disturbed water, or the waves of sound in gases or liquids,
for the vibrations in these cases are direct, or to and from the
centre of action, whereas the former are lateral. It seems to me,
that the resultant of two or more lines of force is in an apt con-
dition for that action which may be considered as equivalent to
a lateral vibration; whereas a uniform medium, like the æther,
does not appear apt, or more apt than air or water.
The occurrence of a change at one end of a line of force easily
suggests a consequent change at the other. The propagation of
light, and therefore probably of all radiant action, occupies time;
and, that a vibration of the line of force should account for the
phænomena of radiation, it is necessary that such vibration
should occupy time also. I am not aware whether there are any
data by which it has been, or could be ascertained whether such
a power as gravitation acts without occupying time, or whether
lines of force being already in existence, such a lateral dis-
turbance of them at one end as I have suggested above, would
require time, or must of necessity be felt instantly at the other
end.
As to that condition of the lines of force which represents the
assumed high elasticity of the æther, it cannot in this respect be
deficient: the question here seems rather to be, whether the lines
are sluggish enough in their action to render them equivalent to
the æther in respect of the time known experimentally to be oc-
cupied in the transmission of radiant force.
The æther is assumed as pervading all bodies as well as space :
in the view now set forth, it is the forces of the atomic centres
which pervade (and make) all bodies, and also penetrate all space.
As regards space, the difference is, that the æther presents suc-
cessive parts or centres of action, and the present supposition
only lines of action; as regards matter, the difference is, that the
æther lies between the particles and so carries on the vibrations,
whilst as respects the supposition, it is by the lines of force be-
2 & 2
452
[MAY 1816.
Thoughts on ray-vibrations.
tween the centres of the particles that the vibration is continued.
As to the difference in intensity of action within matter under
the two views, I suppose it will be very difficult to draw any con-
clusion, for when we take the simplest state of common matter
and that which most nearly causes it to approximate to the con-
dition of the æther, namely the state of rare gas, how soon do we
find in its elasticity and the mutual repulsion of its particles, a
departure from the law, that the action is inversely as the square
of the distance!
And now, my dear Phillips, I must conclude. I do not think
I should have allowed these notions to have escaped from me,
had I not been led unawares, and without previous consideration,
by the circumstances of the evening on which I had to appear
suddenly and occupy the place of another. Now that I have
put them on paper, I feel that I ought to have kept them much
longer for study, consideration, and, perhaps, final rejection ; and
it is only because they are sure to go abroad in one way or
another, in consequence of their utterance on that evening, that
I give them a shape, if shape it may be called, in this reply to
your inquiry. One thing is certain, that any hypothetical view
of radiation which is likely to be received or retained as satis-
factory, must not much longer comprehend alone certain phæ-
nomena of light, but must include those of heat and of actinic
influence also, and even the conjoined phænomena of sensible
heat and chemical power produced by them. In this respect, a
view, which is in some degree founded upon the ordinary forces
of matter, may perhaps find a little consideration amongst the
other views that will probably arise. I think it likely that I
have made many mistakes in the preceding pages, for even to
myself, my ideas on this point appear only as the shadow of a
speculation, or as one of those impressions on the mind which
are allowable for a time as guides to thought and research. He
who labours in experimental inquiries knows how numerous
these are, and how often their apparent fitness and beauty
vanish before the progress and development of real natural
truth.
Royal Institution,
April 15, 1846.
I am, my dear Phillips,
Ever truly yours,
M. FARADAY.
453
On the Magnetic Affection of Light, and on the Distinction
between the Ferromagnetic and Diamagnetic Conditions of
Matter¹.
WHEN a ray of polarized light and lines of magnetic force pass
simultaneously and parallel to each other through a transparent
solid or liquid medium not possessing forces of double refraction,
the ray is rotated according to a simple law of action, which I
have expressed in the last part of the Philosophical Transactions
(2160. 2161.). When such a ray passes through certain speci-
mens of rock-crystal, oil of turpentine, &c., it is also rotated ac-
cording to a natural law well-known, without any reference to
magnetic force. A very striking distinction exists between these
two cases of rotation, though they at first appear to be the same;
for the former rotation is dependent in its direction upon the lines
of magnetic force, and not upon the position of the observer or the
course of the ray of light, whereas the latter is dependent upon
the position of the observer or the course of the ray.
Upon consideration it appeared that the peculiar character of
the magnetic rotation might be made available in exalting the
final effect of the magnetic force upon the ray, and also in
demonstrating many important points in a more marked man-
ner and higher degree than had yet been possible; and upon
referring the idea to experiment, it was found to be true. The
following pages contain some of the results.
A parallelopiped of heavy glass 07 of an inch square and
2.5 inches long, had the two ends polished and silvered. The
silvering was then removed from a space about 0·1 of an inch
wide along one of the edges of one end, and also from a corre-
sponding space on the other end, except that the parts cleared
were on the contrary side of the parallelopiped; so that each
end was furnished with a good plane reflector, but these over-
lapped each other (fig. 2). In consequence of this arrangement,
a ray of light could be transmitted diagonally across the length
of the piece of glass; or the ray, after entering at one end,
could be reflected two or more times within the glass and then
allowed to pass out.
¹ Phil. Mag. Sept. and Oct. 1846.
2 1846, part i. pp. 4, 5. [Phil. Mag. vol. xxviii. pp. 298, 299.]
454
[SEPT. 1846.
Magnetic affection of light.
A similar piece of heavy glass was silvered at the two ends
and one side of the prism; and the silvering was then removed
at the ends for the space of 01 of an inch from those edges
which were the furthest from the silvered side (fig. 1). A ray
of light passing in at the unsilvered part of one end with a
certain degree of obliquity, could be reflected at the other end,
then at the side, and again at the first
end, passing thus three times along the
glass and finally out at the second end.
At other inclinations the ray would pass
five, seven, nine, eleven, or a greater
number of times along the glass before
Fig. 1.

it issued forth on its course through the air to the eye of the
observer.
Either of these pieces of glass could produce the desired
result of repeated reflexions within, but the first form was found
most convenient in use. When a strong light was employed, it
was not difficult to follow the series of images produced by
successive reflexion up to the ninth or tenth image, these cor-
responding of course to a transit of the ray seventeen or nineteen
times along the substance of the glass. A little change of posi-
tion of the silvered glass between the Nichol's prisms used as
the polarizing and analyzing apparatus, was sufficient to bring
any one of these images into view, the glass being at the same
time under the full influence of the electro-magnet, or the helix,
employed to generate lines of magnetic force. A further advan-
tage is gained if the ends of the piece of glass are not quite
parallel to each other, the sides proceeding from the edges where
the ray enters and issues forth being in a very slight degree
different in length. This arrangement causes the series of re-
flected images to open out if seen at one end and to close up if
seen at the other, and thus the observation of a particular image
or the simultaneous comparison of two or more images, is
favoured.
On considering the effect of this ar-
rangement, it is evident that if ABCD
represent a trough of solution of
sugar, or any other body having the
ordinary rotating influence over a po-
larized ray, then a ray sent in at D
Fig. 2.

B
7
CA
с
E
SEPT. 1846.]
455
Repeated reflexions.
and passing out at A would be rotated to a certain amount.
But if, instead of proceeding onwards at A, it were reflected by
the surface AF to E, and were there observed, it would be
found to have received no rotation, for the effect produced in
going from D to A would be exactly compensated by its return
from A to E. Or if the reflexions were made more numerous
and recurred at E F and C, so that the ray should traverse the
body five times, still the amount of rotation equal only to that
which its passage once along the substance could effect would
be finally produced.
Such would not be the case if ABCD were a diamagnetic,
rotating the ray by means of magnetic force; for then, which-
ever way the ray was passing, it would still be rotated in the
same direction in relation to the lines of force. So if observed
issuing forth at A, it would have an amount of rotation (which
we may call right handed) equal to what one transit across the
diamagnetic could produce; if observed at E, it would have an
amount of left-handed rotation double the amount of the first
or unit quantity; if observed at F, it would have three times
the first amount of right-handed rotation; if observed at C, four
times the amount of left-handed rotation; and at B would
possess five times the original amount of right-handed rotation.
This was confirmed by the result of an experiment. The great
magnet described in the Philosophical Transactions' (2247.) was
employed, and the parallelopiped of glass (fig. 2) submitted to
its powers; the direct ray, or that producing the firs image of
the luminous object, acquired a right-handed rotatio equal to
12°.
Moving the glass a little the second image was brought
into view, or that produced by the ray which had traversed the
glass three times, and its rotation was 36°. The third image
was then observed, and the rotation of the ray producing it was
60°, as nearly as my rough apparatus could measure angular
quantities. The same general results were obtained with the
second piece of glass described.
The experiment proves in a very striking manner, that which-
ever way the ray of light is passing through the interposed body,
the direction of its rotation depends essentially and alone upon
the direction of the lines of magnetic force.
It also proves and makes manifest in a manner not to be mis-
¹ 1846, p. 22. Phil. Mag. vol. xxviii. p.
456
[SEPT. 1846.
Magnetic affection of light.
taken, the difference in this respect between the magnetic rotation
of the ray, and that produced by quartz, sugar, oil of turpentine,
and such bodies.
Either by independent or by conjoint observations of the
different images, it proves that the effect is proportionate to the
length of ray submitted to the magnetic force (2163.); for the
unit length and multiples of the unit length may be observed at
once, the intensity of the magnetic force and other circumstances
remaining unchanged.
It permits the attainment of a far greater degree of accuracy
in the measurement of the amount of rotation of a given ray, or
in the estimation of the comparative degrees of rotation of the
different coloured rays.
The form of the arrangement makes a short piece of any
given diamagnetic, as a crystal, &c., sufficient for an experi-
ment, which would not suffice if the ray were passed but once
through it.
It allows of the concentration of the magnetic force by an
approximation of the poles, when a magnet is used, so as to
exalt the effect; or to render a weak magnet equivalent to a
stronger one, so that even good ordinary magnets may now be
made available. Or if a helix be used, a much shorter and
weaker one than that which before was necessary, may now be
employed.
Having ascertained the great advantage which this form of
apparatus possessed for the examination of many substances
which would give no sensible results by the process I formerly
described, I proceeded to apply it to the cases of air and some
doubly refracting bodies (2237.). For this purpose I made the
faces of the magnetic poles reflectors, by applying to each a
polished plate of steel; and as the poles were moveable, their
reflecting surfaces could be placed at any distance and in any
position required, the substance experimented on being between
them.
Air.-I could obtain no signs of action upon the ray when
air was between the magnetic poles, even with the fourth, fifth,
and sixth images.
Rock-crystal. The cubes of this substance formerly described
(2178.) were submitted to examination; but I could detect no
trace of action on the ray of light when passing through them,
SEPT. 1846.]
457
Repeated reflexions.
although they were 0.75 of an inch in the side, and the ray was
observed after passing seven, and even nine times across them.
The cubes were examined in all directions.
Iceland Spar.-A cube of this substance (2179.) was examined
in the same manner, but I obtained no effect.
Heavy glass presented the expected phænomena easily and
well.
Failing to procure any positive result in these trials, either
with air or with doubly refracting crystals, I silvered the latter
in the manner that had been employed for the heavy glass, that
the magnetic poles might be brought as close as possible; still
no evidence of any magnetic action on the ray could be observed.
A natural six-sided prism of rock-crystal, 2·3 inches in length,
was polished and silvered at the ends: no magnetic effect upon
the light could be observed with this crystal with either the
first, second, or third image.
M. E. Becquerel thinks that he has observed an effect
produced in doubly refracting crystalline bodies; and it is
probable that his apparatus is far more delicate for the ob-
servance of optical changes than mine. In that case, if com-
bined with the method founded on repeated transits of the ray,
it perhaps would produce very distinct results; but the latter
process alone has not as yet given any evidence of the action
sought after.
Certain indications led me to look with interest for any
possible effect which the crossing of the reflected rays might
produce in the arrangement of reflectors and glass represented
in fig. 1; but I could find no difference of action between it
and the other arrangement, fig. 2, in which no such crossing
occurred.
Near the close of last year I sent to the Royal Society two
papers On the Magnetic Condition of all matter¹ (2243. 2343.),
in which I believe that I proved the existence of a magnetic ac-
tion new to our knowledge; antithetical in its nature to the
magnetism manifested by iron in any of its forms or conditions,
strong or weak, or to that magnetism which iron could, in any
quantity, or under any circumstances produce. Further, that
1 Philosophical Transactions, 1846, p: 21, or Phil. Mag. vol. xxviii. 1846.
458
[SEPT. 1846.
Diamagnetic condition of matter.
all bodies not magnetic as iron, were magnetic according to this
new mode of action; and that as attraction by the magnet marked
the magnetic condition of iron, however small its quantity, or
whatever its state might be, so repulsion was the distinctive
characteristic of all those bodies which were naturally fitted to
acquire the new state, and develope this new form of power.
M. Becquerel has sent a note to the Academy of Sciences',
in which he states certain results of his own much anterior to
mine, due to ordinary magnetic action, and in which the po-
sition of the substances was across the magnetic axis. I need
not quote the whole, but will select the following words at the
end:-"From these facts it results that the magnetic effects
produced in steel or in soft iron by the influence of a magnet,
differ from those which occur in all bodies, in this; that in the
first the distribution of magnetism is always in the direction of
the length, whilst in tritoxide of iron, wood, gumlac, &c., it
occurs generally in a transverse direction, especially when they
are formed into needles. This difference of effect is due to the
circumstance, that the magnetism being very weak in these bodies,
we may neglect the reaction of the particles of the bodies on
themselves." These words, and the time of their publication
(January (1846) sufficiently show that M. Becquerel does not
admit the new form or condition of magnetic action, which I
supposed I had previously demonstrated.
M. E. Becquerel, in a communication to the Academy of the
date of June 18462, after confirming the action on light which
I had announced, touches the question of magnetic action on
all bodies; and at this late period is still of the same opinion
as his father. I need quote only a few brief lines here and there
to show this state of his mind. After speaking of Coulomb's
results, and of his father's in 1827, he says, "These experi-
ments have been made nearly twenty years, and nevertheless
M. Faraday has announced anew the phænomenon of trans-
verse direction, has made of the bodies which place them-
selves thus a new class of substances, and has named them
diamagnetic substances. . . . I ask myself how, under
these circumstances, one can push the spirit of classification
thus far, when one may give to the same substance all the va-
2 Ibid. 1846, p. 595.
¹ Comptes Rendus, 1846, p. 147.
SEPT. 1846.]
459
Diamagnetic condition of matter.
rious positions of longitudinal, transverse, or oblique. In fact,
place the two extremities of two strong magnets opposite each
other, at 0.08 or 0.12 of an inch apart, and at about 0.04 from
their surface, suspend by means of coccoon silk, a small needle
of wood or of copper, about 0.04 in diameter and 1.9 or 2·3
inches long, it will place itself transversely. If the needle be
cut in two and again divided, &c., we shall end by having a
fragment, which will place itself in the line of the poles. It
is simply a phænomenon of the resultant forces; for we may
give to one and the same substance these different positions,
according to its form, by modifying the distance of the poles."
Then, speaking of the small quantity of iron which he found
in certain specimens, and of his former statement, that these
substances behaved as a mixture of inert matter and magnetic
particles, or as ferruginous mixtures, he says, "all these con-
clusions still subsist at this day in all their generality."
These conclusions from two profound philosophers, so well
able in every respect to judge any question arising on such a
subject as magnetism, made me anxious on two accounts; for
first, I thought it possible I might really be in error respect-
ing the broad and general principle of magnetic action, which
I supposed I had discovered; and next, that if right on that
point, I must have been sadly deficient in describing my re-
sults not to have conveyed a better impression to the minds of
those so competent to receive and understand. I therefore,
for my own sake, entered into an examination of this point;
for though I am nearly indifferent to the fate of any specula-
tive or hypothetical view I may venture to send forth, I am
far from being so as regards the correctness of any announce-
ment I may make of a law of action or a new fact; and having
carefully experimented on one or two of the cases of transverse
position assumed by certain bodies magnetic, as iron, I now
give the general result.
محرم
*.
Some good uniform peroxide of iron (being one of the sub-
stances which M. Becquerel experimented with) was prepared
and introduced regularly into a thin glass tube, 0.25 of an inch
in diameter and 1·4 inch long; it was then suspended by a long
filament of cocoon silk, and could be brought into any position
relative to one of the poles of a strong electro-magnet, which
could be made to assume various forms by the use of terminal
460
[SEPT. 1846.
Diamagnetic condition of matter.
pieces of iron. As peroxide of iron can occasionally receive and
retain a feeble magnetic state, it is necessary the experimenter
should be aware of the possibility, and guard against its effect
in producing irregular results.
The pole of the magnet was in the first place a cone, of
which the base was 1.5 inch in diameter, its axis being in a
horizontal line. The cylinder of peroxide of iron was advanced
towards the cone with its centre of suspension in a line with
the axis. When within the influence of the magnet, and trans-
verse to the axial line, it retained that position; but this was a
position of unstable equilibrium; for if the cylinder became
oblique to the axial line on either side, then the end nearest
to the cone approached towards it, being attracted, and at last
went up to and remained against it. But whether directly
across the axial line, and so in the position of unstable equi-
librium, or in any other position, the centre of gravity of the
whole was always attracted; an effect easily appreciated with
an electro-magnet by interrupting and renewing the exciting
current.
As a contrast with diamagnetic bodies, I will state, that if
a similar cylinder of phosphorus, bismuth, or heavy glass be
placed in precisely the same circumstances, then the transverse
position is a position of stable equilibrium : if the cylinder be
moved from it, it returns by vibrations into it; and during the
whole time the centre of gravity of the mass is repelled.
A square end was now given to the pole of the magnet, the
face opposed to the cylinder of peroxide being 1.75 inch wide
and of an equal height. The axial line is that which passed
horizontally from the middle of this face, and took its course
through the centre of gravity of the cylinder, which was also its
centre of rotation. When the cylinder was at any distance
less than 0.3 of an inch from the face of the pole, it stood parallel
to the face, and therefore transverse to the axial line being
moved out of this position, it resumed it, so that the position
was one of stable equilibrium. At distances a little greater this
became a position of unstable equilibrium, and two positions of
stable equilibrium were found equally inclined on the opposite side
of the transverse position, becoming more and more oblique to
it as the distance was increased. Both the transverse positions
and the oblique positions were easily referable to the concentra-
SEPT. 1846.]
461
Diamagnetic condition of matter.
tion of the lines of magnetic force at the edges of the square
end of the magnet. Effects due to the same cause have already
been pointed out (2298. 2299. 2384.)¹.
In every position of the cylinder of peroxide before this mag-
netic pole, the peroxide, as a mass, was attracted.
By using another termination of iron, the end of the pole
opposite the peroxide was enlarged in its horizontal dimensions
to 2.5 inches. All the former phænomena recurred; but the
distance between the face of the pole and the tube of peroxide
could be increased to one inch or more, before the tube began
to assume the oblique positions.
A third termination presented a face having 3.5 inches of
horizontal extension: the phænomena were here precisely the
same, but the distance could be increased to 1·75 inch before the
cylinder ceased to be parallel to the face, and began to acquire
an oblique position.
Fig. 3.
For the complete comprehension of this and other effects due
to the form of the face of the pole, and the concentration of the
lines of magnetic force passing through the air
near the edges, I will indicate the positions
assumed by the cylinder of peroxide, when its
centre of suspension was preserved at a con-
stant distance from the face of the pole, but
was carried into different positions on one side
or the other of the axial line. These are re-
presented in the figure; by which it will be
seen, that as the peroxide was carried to one
side or the other of the axial line it became in-
clined to that line, in a manner and to a degree
easily comprehensible by those who consider
the concentration of magnetic force at the edges
of the face. The same was the case with the
former face of 2.5 inches. Either end of the
cylinder of peroxide might be the end nearest to the face of the
pole; but the centre of gravity of the cylinder was in every case
attracted by the magnet.
Other cylinders of peroxide of iron of different diameters and
lengths were employed; and when they were smaller in length
¹ Philosophical Transactions, 1846, pp. 32, 48.

1
462
[SEPT. 1846.
Diamagnetic condition of matter.
than the opposed faces of the magnetic poles, the results were
precisely the same.
A cylinder of paper, magnetic through the presence of iron,
was used and produced the same results.
Having been led to think that the disintegration of the per-
oxide of iron had considerable influence over these phænomena,
by obstructing and preventing the communication of magnetic
induction from particle to particle, and was far more influential
than the mere weakness of magnetic force, I took some sub-
stances, even more weak in magnetic power than the peroxide,
and formed them into cylinders. The substances were solution
of proto-sulphate of iron, muriate of cobalt and muriate of nickel,
which were introduced into thin glass tubes 0.25 of an inch in
diameter and 14 inch long. These, when suspended before the
poles with their centres of suspension in the axial line, did not
act as the peroxide of iron or the paper. They could indeed be
kept in a position parallel to the face of the pole, but this was
a position of unstable equilibrium; and when the least removed
out of that position, the end nearest the magnet continued to
approach until it came in contact, and then the whole remained
unchanged. The action was precisely like that of a piece of iron,
but very inferior in energy.
A saturated solution of proto-sulphate of iron was diluted
with five times its volume of water, and still showed precisely
the same phænomena as the stronger solution: yet its magnetic
power was very far inferior to the magnetic force of the peroxide
of iron, as was fully manifested by the degree of the attraction
of the centre of gravity of the two portions of the substances.
When the peroxide was under experiment, the suspension-thread
was drawn twice or even three times further from the perpen-
dicular than when the solution was used.
If a piece of iron wire be substituted for the cylinder of per-
oxide or the magnetic solutions, it will not remain parallel to
the face of the pole, or oblique and not touching it; for one end
will always go up to the face of the pole; or if it be very short,
and then by loading, or otherwise be prevented from coming in
contact with the pole, one end will point towards the part of
the pole face nearest to it. In this respect it is as the magnetic
solution, and not as the peroxide: however weak the magnetic
SEPT. 1846.] Diamagnetic condition of matter.
463
pole may be, if it have power to affect the iron wire at all, it will
produce the same effect. Further, if the iron wire be rendered
perfectly free from magnetism, by making it red hot, either end
may be made that which is nearest to the face of the pole.
.
A piece of hæmatite, separated, not by an iron tool but by an
agate, or otherwise in a careful manner, pointed in the manner
of iron, though of course not with the same power, i. e. it did
not take up a stable position either parallel to the face of the
magnet or inclined, but not touching it; for one end or the other
always went up to and remained in contact with the metal of the
pole. The hæmatite, being powdered and put into a small tube,
acted in the same way as when whole.
A piece of bottle-glass tube, which was magnetic from the
iron it contained, acted as the hæmatite, either when whole or
powdered up and put into a flint-glass tube: it therefore was
unlike the peroxide of iron.
Pure peroxide of manganese appeared to take a place between
these bodies and the peroxide of iron. Generally speaking, the
end nearest to the flat face of the pole went up to it and remained
there; but when one end was opposite the edge of the face and
the other end nearly opposite the middle, at the time the magnet
was made active, the latter end, though nearer than the former,
would recede, and the former end come up and remain in contact.
If the latter end was still nearer, it would approach from the
first; and, there was no place of stable equilibrium for the tube
in which it remained parallel to the face, or nearly so, with neither
end touching it.
A piece of thick platinum wire acted as the hæmatite or green
glass, and not as the peroxide in Becquerel's experiment. Spongy
platina pressed into a tube acted as the peroxide of manganese,
giving like it in certain situations, the beginnings of an action
like that of the peroxide of iron.
The centre of gravity of all these bodies was attracted by the
magnet, whatever part of the face they were placed in juxtapo-
sition with. In no case was anything like a repulsion shown.
Now I do not see how any difficulty can arise in referring all
these results of position to the ordinary action of magnets upon
matter ordinarily magnetic, as iron is. All depends upon the
shape and size of the poles, and upon the state of unity or dis-
integration, more or less complete, of the magnetic matter; for
464
Diamagnetic condition of matter. [SEPT. 1846.
matter which is much weaker in magnetic power than peroxide
of iron, as the solution of nickel, or dilute solution of iron, or
the metal platina, does not act as the peroxide, but as metallic
iron. Still, in every case, the phænomena are phænomena of
attraction; for not only is the centre of gravity of the whole
mass attracted, but the parts of the cylinder of peroxide of iron,
as well as of the other magnetic substances, are in those positions
which the resultants of attractive force would necessarily give
them. This is precisely the reverse of what takes place with
diamagnetic bodies, for there the centre of gravity of the whole
mass is repelled; and whatever form the mass may have, its parts
take those positions which are most consistent with the direction
and degree of the repulsive force.
All ambiguity and doubt may be removed in such cases as the
above by the use of a single pole, either conical, wedge-shaped
or round. It is true, that if a wire of iron, two or three inches
long, be placed with its middle part near the apex of a conical or
wedge-shaped pole, it will stand at right angles across the axis of
the cone or wedge, vibrating like a balance-beam; and also that
if a cylinder of bismuth, phosphorus or heavy glass be placed in
the same position, it will take a similar position. But no mag-
netician who looks at the effect can for a moment confound the
phænomena; for he will see at once that the iron as a mass is
attracted, and the diamagnetic is, as a mass, repelled: and then,
if for this observation of the latter phænomena he will take small
spheres of iron, peroxide of iron, or solution of muriate of iron
on the one hand, and of bismuth or phosphorus, copper or wood
on the other, he will have the phænomena in the simplest state,
and the fundamental fact will be before him; for the magnetics
will be attracted, the diamagnetics will be repelled.
I cannot find any case of transverse position which does not
enter into one or other of the two kinds referred to above; that
is to say, which is not either a magnetic or a diamagnetic result.
Even as regards the effect of ordinary magnetism in peroxide of
iron and such like bodies, I see no reason to accept the statement
of M. Becquerel, that the distribution of magnetism tends to take
place especially in a transverse direction. It appears to me that
the destruction of the continuity of the mass in these cases, com-
bined with the degree of magnetic force in the substance, prevents
the transmission of the force by induction or conduction from
SEPT. 1846.] Natural zero-magnetic-electric.
465
particle to particle, to the same extent as when the continuity
exists, and so consecutive poles at short distances and in different
directions are produced; and hence the reason why the solution
of iron or nickel, or the metal platina, does not behave as the
peroxide of iron, though weaker in magnetic force, but acts as
metallic iron.
If it had not been for the remarkable relation of a vacuum,
and with it of those attenuated forms of matter, air, gases and
vapours, which I have for this very reason amongst others in-
sisted on in the Experimental Researches (2432. &c.), it might
have become questionable whether those bodies which I have
called diamagnetics, were not acted upon strictly in the same
manner as magnetic bodies; and the result, whether of attraction
or repulsion, a consequence of a difference of degree only between
the body observed and the medium surrounding it (2438. &c.).
But I cannot help looking upon a vacuum as presenting a zero
point in the phænomena of attraction and repulsion; and as
magnetic bodies are attracted, and diamagnetic bodies repelled
(2406. 2436.) by a magnet, when surrounded by and in relation
to it, so I believe that these two conditions represent two anti-
thetical forms of magnetic force. This is the conclusion I have
set forth in my original papers, and notwithstanding my very
great respect for the judgment of MM. Becquerel, it is that
which by the facts I am encouraged still to maintain¹.
¹ I take the liberty in this note to refer to a similar point in the philosophy
of static electricity. I have often been asked for the proof of an absolute
natural zero between positive and negative electricity; and in reference to
M. Peltier's views, that the earth is negative to the space around it, which in
its turn is positive, have been told that if all parts of a portion of its plane
surface were equally negative, we on that surface could not tell that it was
not in a zero state. But such is not the case. A surface which is truly negative
may appear, in comparison, to be positive to one still more highly negative;
or a negative surface may seem to be in a zero state in relation to two other
surfaces, one of which is more negative and the other less so, or even posi-
tive; but if referred to a true standard its real state is shown at once, and this
standard is given by the inside of any metallic vessel, from which, by its shape
or depth, external influence is excluded. Such a vessel always presents the
same normal condition within, whatever charge its external surface may have;
and by comparing the surface of the earth with the inside of such a vessel,
which is easily done by the use of carriers, such as Coulomb employed, any
one may tell for himself whether that surface is in a negative or a zero state.
VOL. III,
2 H
466
[SEPT. 1846.
Magnetic affection of light-time.
When heavy glass is submitted to the action of a powerful
electro-magnet, the maximum degree of rotation of the ray is
not obtained at once, but requires a sensible interval of time
(Experimental Researches, 2170.); this I have attributed to the
gradual rising in intensity of the force of the magnet, and the
corresponding rising of the effect of that force in the glass. M.
E. Becquerel does not agree with me in the above explanation,
but thinks it is due to this; that the particles of the diamagnetic
itself require time to assume their new state. That they may
require time is, I think, very probable. I do not know any
state the acquiring of which does not need time. This time
is however most probably exceedingly small in the instance of
diamagnetic bodies; and that the phænomena referred to by me
are not due to such a cause, is, I think, shown by two consider-
ations. The first is, that the electro-magnet is well known by
other kinds of proof, as the induction of currents, &c., to require
time to develope its maximum force due to a given electric cur-
rent. I have shown that the rotation of the ray must increase
during the time the magnet is thus rising; and I found that
the power to induce currents exists simultaneously with the
increasing rotation. The next consideration is, that when the
diamagnetic is submitted, not to the action of an electro-magnet,
but of a helix, the rotation does not increase in the same gradual
manner as before, but is instantly at a maximum (Experimental
Researches, 2195.): hence my reasons for adhering to the ex-
planation I gave in the papers themselves last year.
But on subjects so new as these, differences of opinion must
inevitably arise upon many points; and it is better for the inqui-
ries themselves that it should be so, for the facts in consequence
receive a more close investigation. I therefore leave many
points of difference between myself and others unnoticed for
the present; believing that new and connected facts will rapidly
accumulate, and that time, with his powerful aid, will in a very
few years give both facts and opinions their right places.
Royal Institution,
August 11, 1846.
467
On the Diamagnetic conditions of Flame and Gases¹.
MY DEAR SIR,
To Richard Taylor, Esq.
I LATELY received a paper from Professor Zantedeschi, pub-
lished by him, and containing an account of the discovery, by
P. Bancalari, of the magnetism (diamagnetism) of flame, and of
the further experiments of Zantedeschi, by which he confirms
the result, and shows that flame is repelled from the axial line
joining two magnetic poles. I send you the paper that you
may, if you estimate its importance as highly as I do, reprint
it in the Philosophical Magazine; and I send also with it these
further experimental confirmations and extensions of my own.
As M. Zantedeschi has published his results, I have felt myself
at liberty to work on the subject, which of course interested
me very closely. Probably what I may describe will only come
in confirmation of that which has been done already in Italy
or elsewhere; and if so, I hope to stand excused; for a second
witness to an important fact is by no means superfluous, and
may in the present case help to induce others to enter actively
into the new line of investigation presented by diamagnetic
bodies generally.
I soon verified the chief result of the diamagnetic affection of
flame, and scarcely know how I could have failed to observe the
effect years ago.
As I suppose I have obtained much more
striking evidence than that referred to in Zantedeschi's paper, I
will describe the shape and arrangement of the essential parts of
my apparatus. The electro-magnet used was the powerful one
described in the Experimental Researches (2247.). The two
terminal pieces of iron forming the virtual magnetic poles were
each 1.7 inch square and 6 inches long; but the ends were
shaped to a form approaching that of a cone, of which the sides
have an angle of about 100°, and the axis of which is horizontal
and in the upper surface of the pieces of iron. The apex of each
end was rounded; nearly a tenth of an inch of the cone being in
this way removed. When these terminations are brought near
¹ Philosophical Magazine, S. 3, vol. xxxi. No. 210, December 1847.
2 H 2
468
[DEC. 1847.
Diamagnetic condition of flame.
to each other, they give a powerful effect in the magnetic field,
and the axial line of magnetic force is of course horizontal, and
on a level nearly with the upper surface of the bars. I have
found this form exceedingly advantageous in a great variety of
experiments.
When the flame of a wax taper was held near the axial line,
but on one side or the other, about one-third of the flame rising
above the level of the upper surface of the poles, as soon as the
magnetic force was on, the flame was affected; and receded from
the axial line, moving equatorially, until it took an inclined
position, as if a gentle wind was causing its deflection from the
upright position; an effect which ceased the instant the mag-
netism was removed.
The effect was not instantaneous, but rose gradually to a
maximum. It ceased very quickly when the magnetism was
removed. The progressive increase is due to the gradual pro-
duction of currents in the air about the magnetic field, which
tend to be, and are, formed on the assumption of the magnetic
conditions, in the presence of the flame.
When the flame was placed so as to rise truly across the mag-
netic axis, the effect of the magnetism was to compress the flame
between the points of the poles, making it recede in the direction
of the axial line from the poles towards the middle transverse
plane, and also to shorten the top of the flame. At the same
time the top and sides of the compressed part burnt more vividly,
because of two streams of air which set in from the poles on
each side directly against the flame, and then passed out with
it in the equatorial direction. But there was at the same time
a repulsion or recession of the parts of the flame from the axial
line; for those portions which were below did not ascend so
quickly as before, and in ascending they also passed off in an
inclined and equatorial direction.
On raising the flame a little more, the effect of the magnetic
force was to increase the intensity of the results just described,
and the flame actually became of a fish-tail shape, disposed across
the magnetic axis.
If the flame was raised until about two-thirds of it were above
the level of the axial line, and the poles approached so near to
each other (about 0·3 of an inch) that they began to cool and
compress the part of the flame at the axial line, yet without in-
DEC. 1847.]
P. Bancalari-M. Zantedeschi.
469
terfering with its rising freely between them; then, on rendering
the magnet active, the flame became more and more compressed
and shortened; and as the effects proceeded to a maximum, the
top at last descended, and the flame no more rose between the
magnetic poles, but spread out right and left on each side of the
axial line, producing a double flame between two long tongues.
This flame was very bright along the upper extended forked
edge, being there invigorated by a current of air which descended
from between the poles on to the flame at this part, and in fact.
drove it away in the equatorial direction.
When the magnet was thrown out of action, the flame resumed
its ordinary upright form between the poles, at once; being de-
pressed and redivided again by the renewal of the magnetic
action.
When a small flame, only about one-third of an inch high, was
placed between the poles, the magnetic force instantly flattened
it into an equatorial disc.
If a ball of cotton about the size of a nut be bound up by
wire, soaked in æther and inflamed, it will give a flame six or
seven inches high. This large flame rises freely and naturally
between the poles; but as soon as the magnet is rendered active,
it divides and passes off in two flames, the one on one side, and
the other on the other side of the axial line.
Such therefore is the general and very striking effect which
may be produced on a flame by magnetic action, the important
discovery of which we owe to P. Bancalari.
I verified the results obtained by M. Zantedeschi with dif-
ferent flames, and found that those produced by alcohol, æther,
coal-gas, hydrogen, sulphur, phosphorus, and camphor were
all affected in the same manner, though not apparently with
equal strength. The brightest flames appeared to be most
affected.
The chief results may be shown in a manner in some respects
still more striking and instructive than those obtained with
flame, by using a smoking taper. A taper made of wax,
coloured green by verdigris, if suffered to burn upright for a
minute and then blown out, will usually leave a wick with a
spark of fire on the top. The subdued combustion will however
still go on, even for an hour or more, sending up a thin dense
stream of smoke, which, in a quiet atmosphere, will rise verti-
470
Diamagnetic condition of flame. [DEC. 1847.
cally for six or eight inches; and in a moving atmosphere will
show every change of its motion, both as to direction and inten-
sity. When the taper is held beneath the poles, so that the
stream of smoke passes a little on one side of the axial line, the
stream is scarcely affected by the power of the magnet, the taper
being three or four inches below the poles; but if the taper be
raised, so that the coal is not more than an inch below the axial
line, the stream of smoke is much more affected, being bent
outwards; and if it be brought still higher, there is a point at
which the smoke leaves the taper-wick even in a horizontal di-
rection, to go equatorially. If the taper be held so that the
smoke-stream passes through the axial line, and then the di-
stances be varied as before, there is little or no sensible effect
when the wick is four inches below: but being raised, as soon
as the warm part of the stream is between the poles, it tends to
divide; and when the ignited wick is about an inch below the
axial line, the smoke rises vertically in one column until about
two-thirds of that distance is passed over, and then it divides,
going right and left, leaving the space between the poles clear.
As the taper is slowly raised, the division of the smoke descends,
taking place lower down, until it occurs upon the wick, at the
distance of 0·4 or 0·5 of an inch below the axial line. If the
taper be raised still more, the magnetic effect is so great, as not
only to divide the stream, but to make it descend on each side
of the ignited wick, producing a form resembling that of the
letter W; and at the same time the top of the burning wick is
greatly brightened by the stream of air that is impelled down-
wards upon it. In these experiments the magnetic poles should
be about 0.25 of an inch apart.
A burning piece of amadou, or the end of a splinter of wood,
produced the same effect.
By means of a like small spark and stream of smoke, I have
even rendered evident the power of an ordinary magnet. The
magnet was a good one, and the poles were close to each other
and conical in form.
Before leaving this description of the general phænomenon
and proceeding to a consideration of the principles of magnetic
action concerned in it, I may say that a single pole of the mag-
net produces similar effects upon flame and smoke, but that they
are much less striking and observable.
DEC. 1847.]
471
Effect of heat-the currents.
Though the effect be so manifest in a flame, it is not, at first
sight, evident what is the chief cause or causes of the result.
The heat of the flame is the most apparent and probable con-
dition; but there are other circumstances which may be equally
or more influential. Chemical action is going on at the time :-
solid matter, which is known to be diamagnetic, exists in several
of the flames used:-and a great difference exists between the
matter of the flame and the surrounding air. Now any or all
of these circumstances of temperature, chemical action, solidity
of part of the matter, and differential composition in respect to
the surrounding air, may concur in producing or influencing the
result.
I placed the wires of an electrometer, and also of a galvano-
meter, in various parts of the affected flame, but could not pro-
cure any indications of the evolution of electricity by any action
on the instruments.
I examined the neighbourhood of the axial line as to the
existence of any current in the air when there was no flame or
heat there, using the visible fumes produced when little pellets
of paper dipped in strong solutions of ammonia and muriatic
acid were held near each other; and though I found that a
stream of such smoke was feebly affected by the magnetic
power, yet I was satisfied there was no current or motion in
the common air, as such, between the poles. The smoke itself
was feebly diamagnetic; due, I believe, to the solid particles
in it.
But when flame or a glowing taper is used, strong currents
are, under favourable circumstances, produced in the air. If
the flame be between the poles, these currents take their course
along the surface of the poles, which they leave at the opposite
faces connected by the axial line, and passing parallel to the
axial line, impinge on the opposite sides of the flame; and
feeding the flame, they make part of it, and proceed out equa-
torially. If the flame be driven asunder by the force of these
currents and retreat, the currents follow it; and so, when the
flame is forked, the air which is between the poles forms a cur-
rent which sets from the poles downwards and sideways towards
the flame. I do not mean that the air in every case travels
along the surface of the poles or along the axial lines, or even
from between the poles; for in the case of the glowing taper,
472
[DEC. 1847.
Diamagnetic condition of flame.
held half an inch or so beneath the axial line, it is the cool air
which is next nearest to the taper, and (generally) between the
taper and the axial line, that falls with most force upon it. In
fact the movements of the parts of the air and flame are due to a
differential action. We shall see presently that the air is dia-
magnetic as well as flame or hot smoke; i. e. that both tend,
according to the general law which I have expressed in the Ex-
perimental Researches (2267. &c.), to move from stronger to
weaker places of magnetic force, but that hot air and flame are
more so than cold or cooler air: so, when flame and air, or air
at different temperatures, exist at the same time within a space
under the influence of magnetic forces, differing in intensity of
action, the hotter particles will tend to pass from stronger to
weaker places of action, to be replaced by the colder particles;
the former therefore will have the effect of being repelled; and
the currents that are set up are produced by this action, com-
bined with the mechanical force or current possessed by the
flame in its ordinary relation to the atmosphere.
It will be evident to you that I have considered flame only as
a particular case of a general law. It is a most important and
beautiful one, and it has given us the discovery of diamagnetism
in gaseous bodies: but it is a complicated one, as I shall now
proceed to show, by analysing some of its conditions and sepa-
rating their effects.
For the purpose of examining the effect of heat alone in con-
ducing to the diamagnetic condition of flame, a small helix of
fine platina wire was attached to two stronger wires of copper,
so that the helix could be placed in any given position as re-
garded the magnetic poles, and at the same time be ignited at
pleasure by a voltaic battery. In this manner it was substituted
for the burning taper, and gave a beautiful highly heated current
of air, unchanged in its chemical condition. When the helix
was placed directly under the axial line, the hot air rose up be-
tween the poles freely, being rendered evident above by a ther-
mometer, or by burning the finger, or even scorching paper;
but as soon as the magnet was rendered active, the hot air
divided into a double stream, and was found ascending on the
two sides of the axial line; but a descending current was
formed between the poles, flowing downwards towards the helix
and the hot air, which rose and passed off sideways from it.
DEC. 1847.]
473
Effect of heat on air.
It is therefore perfectly manifest that hot air is diamagnetic
in relation to, or more diamagnetic than, cold air; and, from
this fact I concluded, that, by colling the air below the natural
temperature, I should cause it to approach the magnetic axis, or
appear to be magnetic in relation to ordinary air. I had a little
apparatus made, in which a vertical tube delivering air was
passed through a vessel containing a frigorific mixture; the
latter being so clothed with flannel that the external air should
Lot be cooled, and so invade the whole of the magnetic field.
The central current of cold air was directed downwards a little
on one side of the axial line, and falling into a tube containing a
delicate air-thermometer, there showed its effect. On rendering
the magnet active, this effect however ceased, and the thermo-
meter rose; but on bringing the latter under the axial line it
again fell, showing that the cold current of air had been drawn
inwards or attracted towards the axial line, i. e. had been ren-
dered magnetic in relation to air at common temperatures, or
less diamagnetic than it. The lower temperature was 0° F.
The effect was but small; still it was distinct.
The effect of heat upon air, in so greatly increasing its dia-
magnetic condition, is very remarkable. It is not, I think, at
all probable that the mere effect of expanding the air is the
cause of the change in its condition, because one would be led
to expect that a certain bulk of expanded air would be less sen-
sible in its diamagnetic effects than an equal bulk of denser air;
just as one would anticipate that a vacuum would present no
magnetic or diamagnetic effects whatever, but be at the zero
point between the two classes of bodies (Experimental Re-
searches, 2423. 2424.). It is certainly true, that if the air were a
body belonging to the magnetic class, then its expansion, being
equivalent to dilution, would make it seem diamagnetic in rela-
tion to ordinary air (Experimental Researches, 2367. 2438.);
but that, I think, is not likely to be the case, as will be seen
by the results described further on in reference to oxygen and
nitrogen.
If the power conferred by heat is a direct consequence, and
proportionate to the temperature, then it gives a very remark-
able character to gases and vapours, which, as we shall see
hereafter, possess it in common. In my former experiments
(Experimental Researches, 2359. 2397.) I heated various dia-
474
[DEC. 1847.
Diamagnetic condition of gases.
magnetic bodies, but could not perceive that their degree of
magnetic force was at all increased or affected by the tempera-
ture given to them. I have again submitted small cylinders of
copper and silver to the action of a single pole, at common
temperatures and at a red heat, with the same result. If there
was any effect of increased temperature, it was that of a very
slight increase in the diamagnetic force, but I am not sure of
the result. At present, therefore, the gaseous and vaporous
bodies seem to be strikingly distinguished by the powerful effect
which heat has in increasing their diamagnetic condition.
As all the experiments, whether on flame, smoke, or air,
seemed to show that air had a distinct magnetic relation, which,
though highly affected by temperature, still belonged to it at
all temperatures; so it was a probable conclusion that other
gaseous or vaporous bodies would be diamagnetic or magnetic,
and that they would differ from each other even at common or
equal temperatures. I proceeded therefore to examine them,
delivering streams of each into the air, in the first instance, by
fit apparatus and arrangements, and examining the course taken
by these streams in passing across the magnetic field, the mag-
netic force being either induced or not at the time.
In delivering the various streams, I sometimes introduced the
gases into a globe with a mouth and also a tubular spout, and
then poured the gas out of the spout, upwards or downwards,
according as it was lighter or heavier than air. At other times,
as with muriatic acid or ammonia, I delivered the streams from
the mouth of the retort. But as it is very important not to
deluge the magnetic field with a quantity of invisible gas, I de-
vised the following arrangement, which answered well for all the
gases not soluble in water. A Woulf's bottle was chosen
having three apertures at the top, a, b and c; a wide tube was
fixed into aperture a, descending within the bottle to the
bottom, and being open above and below; by this any water
could be poured into the bottle and employed to displace the
gas previously within it. Aperture b was closed by a stopper.
Aperture c had an external tube, with a stop-cock fixed in it to
conduct the gas to any place desired. To expel the gas and
send it forward, a cistern of water was placed above the bottle,
and its cock so plugged by a splinter of wood, that when full
open it delivered only twelve cubic inches of fluid in a minute.
DEC. 1847.]
475
Currents of gas at the poles.
This stream of water being directed into aperture a, and the
cock of tube c open, twelve cubic inches of any gas within the
Woulf's bottle was delivered in a minute of time; and this I
found an excellent proportion for our magnet and apparatus.
With respect to the delivery of this gas at the magnetic poles,
a piece of glass tube bent into this shape Jwas held by a
clamp on the stage of the magnet, so that it could easily be
slipped backward and forward, or to one side, and so its vertical
part be placed anywhere below the axial line. The aperture at
this end was about the one-eighth of an inch internal diameter.
In the horizontal part near the angle was placed a piece of
bibulous paper, moistened with strong solution of muriatic acid
(when necessary). The horizontal part of the tube was con-
nected and disconnected in a moment, when necessary, with the
tube c of the gas-bottle, by a short piece of vulcanized rubber
tube. If the gas to be employed as a stream were heavier than
the surrounding medium, then the glass tube, instead of having
the form delineated above, was so bent as to deliver its stream
downwards and over the axial line. In this manner currents of
different gases could be delivered, perfectly steady and under
perfect command.
The next point was to detect and trace the course of these
streams. A little ammonia vapour, delivered near the magnetic
field, did this in some degree, but was not satisfactory; for, in
the first place, the little cloud of muriate of ammonia particles
formed, is itself diamagnetic; and further, the tranquil condi-
tion of the air in the magnetic field was then too much dis-
turbed.
Catch-tubes were therefore arranged, consisting of
tubes of thin glass about the size and length of a finger, open
at both ends, and fixed upon little stands so that they could be
adjusted either over or under the magnetic poles at pleasure.
When they were over the poles, I generally had three at once;
one over the axial line and one at each side. When they were
under the poles, the lower end was turned up a little for the
purpose of facilitating observation there.
The gas delivered at the poles, as already described, con-
tained a little muriatic acid (obtained from the solution in the
paper), but not enough to render it visible. To make it mani-
fest up which catch-tube it passed, a little piece of bibulous
paper, folded and bound round and suspended by a copper wire,
476
Magnetic condition of air-nitrogen. [DEC. 1847.
was dipped in the solution of ammonia and hung in each of the
tubes. It was then evident at once, by the visible fume formed
at the top of one of the tubes, whether the gas delivered below
passed up the one or the other tube, and which: and yet the
gas was perfectly clear and transparent as it passed by the place
of magnetic action.
In addition to these arrangements, I built up a sheltering
chamber about the magnetic poles and field, to preserve the air
undisturbed. This was about six inches long by four inches in
width and height, and was easily made of thin plates of mica,
which were put together or taken down in a moment. The
chamber was frequently left more or less open at the top or
bottom for the escape of gases, or the place of the catch-tubes.
Its advantages were very great.
Air.-In the first place air was sent in under these arrange-
ments, the stream being directed by the axial line. It made
itself visible in the catch-tube above by the smoke produced; but
whether the magnet was active or not, its course was the same;
showing that, so far, the apparatus worked well, and did not of
itself cause any erroneous indications.
Nitrogen. This gas was sent from below upwards, and passed
directly by the axial line into the catch-tube above; but when
the magnet was made active, the stream was affected, and though
not stopped in the middle catch-tube, part appeared in the side
tubes. The jet was then arranged a little on one side of the
axial line, so that, without the magnetic action, it still ascended
and went up the middle catch-tube: then, when the magnetic
action was brought on, it was clearly affected, and a great por-
tion of it was sent to the side catch-tube. The nitrogen was,
in fact, manifestly diamagnetic in relation to common air, when
both were at the same temperature; but as four-fifths of the at-
mosphere consists of nitrogen, it seemed very evident, from the
result, that nitrogen and oxygen must be very different from
each other in their magnetic relations.
Oxygen.-A stream of oxygen was sent down through air
between the poles. When there was no magnetic action it
descended vertically, and when the magnetic action was on it
appeared to do the same; at all events it did not pass off equa-
torially. But as there was reason, from the above experiments
with nitrogen, to expect that oxygen would appear, not diamag-
DEC. 1847.] Oxygen-hydrogen-carbonic acid, &c.
477
netic but magnetic in air; so the place of the stream was
changed and made to be on one side of the axial line. In this
case it fell perfectly well at first into a catch-tube placed be-
neath; but as soon as the magnet was rendered active, the
stream was deflected, being drawn towards the axial line, and
fell into another catch-tube placed there to receive it. So oxy-
gen appears to be magnetic in common air. Whether it be
really so, or only less diamagnetic than air (a mixture of oxygen
and nitrogen), we shall be better able to consider hereafter.
Hydrogen. This gas proved to be clearly and even strongly
diamagnetic; but notwithstanding the powerful ascensive force
which its stream has in the atmosphere, because of its small
specific gravity, still it was well deflected and sent equatorially.
Considering the lightness of the gas, one might have expected
that it would have been drawn towards the axial line, as a
stream of rarefied air (if it could exist) would be. Its diamag-
netic state, therefore, shows in a striking point of view, that
gases, like solids, have peculiar and distinctive degrees of dia-
magnetic force.
Carbonic acid.—This gas made a beautiful experiment. The
stream was delivered downwards a little on one side of the axial
line; a catch-tube was placed a little further out, so that the
stream should fall clear of it as long as there was no activity in
the magnet.
But on rendering the magnet efficient, the stream
left its vertical direction, passed equatorially, and fell into the
catch-tube; and by looking horizontally, could be seen flowing
out at its lower extremity like water, and falling away through
the air. Again, the magnet was thrown out of action, and a
glass with lime-water placed beneath the lower end of the catch-
tube; no carbonic acid appeared there, though the fluid in the
glass was continually stirred; but the instant the magnet was
excited, the carbonic acid appeared in the catch-tube, fell into
the glass and made the lime-water turbid. This gas therefore is
diamagnetic in air.
Carbonic oxide.-This gas was carefully freed from carbonic
acid before it was used. It was employed as a descending
stream, and was apparently very diamagnetic: but it is to be
remarked, that a substance which is so nearly the specific gra-
vity of atmospheric air is easily dispersed right and left in it,
and therefore that the facility of dispersion is not a correct
478
Magnetic condition of various gases. [DEC. 1847.
indication of the diamagnetic force. By introducing a little
ammonia into the mica chamber, it was, however, easily seen
that carbonic oxide was driven away equatorially with consider-
able power; and I judge from the appearance, that it is more
diamagnetic than carbonic acid.
Nitrous oxide.-This gas was moderately, but clearly, dia-
magnetic in air. Much interest belongs to this and the other
compounds of nitrogen and oxygen, both because they contain
the same elements as air, and because of the relations of nitrogen
and oxygen separately.
Nitric oxide.-I tried this gas both as an up and down cur-
rent, but could not determine its magnetic condition. What
with the action of the oxygen of the air, the change of the
nature of the substances, and the heat produced, there was so
much incidental disturbance and so little effect due to magnetic
influence, that I could not be sure of the result. On the whole
it was very slightly diamagnetic; but so little, that the effect
might be due to the smoke particles which served to render it
visible.
Nitrous acid gas.-Difficult to observe, but I believe it is
slightly magnetic in relation to air.
Olefiant gas was diamagnetic, and well so. The little differ-
ence in specific gravity of this gas and air, even creates a diffi-
culty in following the course of the olefiant gas, unless it be
watched for on every side.
Coal-gas.―The coal-gas of London is lighter than air, being
only about two-thirds in weight of the latter. It is very well
diamagnetic, and gives exceedingly good and distinct results.
Sulphurous acid gas is diamagnetic in air. It was generated
in a small tube containing liquid sulphurous acid; this being
connected, in place of the gas bottle, with the delivery-tube and
mouthpiece by the vulcanized rubber tube. The presence or
absence of the gas in the catch-tube was well shown by ammo-
nia, and still better by litmus paper.
Muriatic acid.-The retort in which it was generated was
connected, as just described, with the delivery-tube. The gas
was very decidedly diamagnetic in air.
Hydriodic acid was also diamagnetic in air. When there
was an abundant stream of gas, its entrance into and passage
through the side catch-tube, on rendering the magnet active,
DEC. 1847.]
479
Ammonia-iodine and bromine vapour.
was very striking.
When there was less gas, the stream was
dispersed equatorially in all directions, and less entered the
tube.
Fluo-silicon.-Diamagnetic in air.
Ammonia.-This gas was evolved from materials in a retort,
and tested in the catch-tube above by muriatic acid in the
paper. It was well diamagnetic, corresponding in this respect
with the character of its elements. It could also be
It could also be very well
indicated by reddened litmus paper held over the tubes.
Chlorine was sent from the Woulf's bottle apparatus, and
proved to be decidedly diamagnetic in air. Either ammonia by
its fumes, or litmus paper by its becoming bleached, served to
indicate the entrance of the chlorine into the side catch-tube
every time the magnet was rendered active.
Iodine.-A piece of glass tube was so shaped at its lower ex-
tremity as to form a chamber for the reception of iodine, which
chamber had a prolonged mouth directed downwards so as to
deliver the vapour formed within. On putting a little iodine
into the chamber, then heating it, and especially the mouth
part, by a spirit-lamp, and afterwards inclining the apparatus,
abundance of the vapour of iodine was generated as the sub-
stance flowed on to the hotter parts, and passed in a good stream
from the mouth downwards. This purple stream was diamag-
netic in air, and could be seen flowing right and left from the
axial line, when not too dense. If very dense and heavy, its
gravity was such as to make it break through the axial line,
notwithstanding the action of the magnet; still it was manifest
that iodine is diamagnetic to air.
Bromine.-A little bromine was put into the horizontal part
of the delivery-tube, and then air passed over it by the apparatus
already described. So much bromine rose into vapour as to
make the air of a yellow colour, and caused it to fall well in a
stream by the axial line. A little ammonia delivered near the
magnetic field showed that this stream was diamagnetic, and
hence it may fairly be presumed that the pure vapour of bromine
would be diamagnetic also.
Cyanogen.-Strongly diamagnetic in air.
Taking air as the standard of comparison, it is very striking
to observe, that much as gases appear to differ one from another
in the degree of their diamagnetic condition, there are very few
480
Magnetic condition of air and gases. Dec. 1847
that are not more diamagnetic than it; and when the investiga-
tion is carried forward into the relation of the two chief consti-
tuents of air, oxygen and nitrogen, it is still more striking to
observe the very low condition of oxygen, which, in fact, is the
cause of the comparatively low condition of air. Of all the
vapours and gases yet tried, oxygen seems to be that which has
the least diamagnetic force. It is as yet a question where it
stands; for it may be as low as a vacuum, or may even pass to
the magnetic side of it, and experiment does not as yet give an
answer to the question. I believe it to be diamagnetic; and
this belief is strengthened by the action of heat upon it, to be
described hereafter; but it is exceedingly low in the scale, and
far below chlorine, iodine, and such like bodies.
All the compounds of oxygen and nitrogen seem to show the
influence of the presence of the oxygen. Nitrous acid seems to
be less diamagnetic than air. Nitric oxide mingled with nitrous
acid and warm, is about as air. Nitrous oxide is clearly dia-
magnetic in air, though it contains more oxygen: but it also
contains more nitrogen than air, and is also denser than it, so
that there is more matter present; still I think the results are
in favour of the idea that oxygen is diamagnetic. By referring
to the relation of carbonic oxide to carbonic acid, described
further on, it will be seen that the addition of oxygen seems to
make a body less diamagnetic. But the truth may be, not that
oxygen is really magnetic, but that a compound body possesses
a specific diamagnetic force, which is not the sum of the forces
of its particles.
.
It is very difficult to form more than a mere guess at the re-
lative degree of diamagnetic force possessed by different gaseous
bodies when they are examined only in air, because of the many
circumstances which tend to confuse the results. First, there
is the invisibility of the gas which deprives us of the power of
adjusting by sight so as to obtain the best effect: then, there is
the difference of gravity; for if a gas ascend or descend in a
rapid stream, it may seem less deflected than another flowing
more slowly, though it be more diamagnetic; and as to gases
nearly of the specific gravity of air, whether more or less dia-
magnetic, they are almost entirely dispersed in different direc-
tions, so that little only enters the catch-tube. Another
modifying circumstance is the distance of the aperture deliver-
DEC. 1817.]
481
Different gases in carbonic acid.
ing gas from the axial line, which, to obtain the maximum
effect, ought to vary with the gravity of the gases and their dia-
magnetic force. Again, it is important that the magnetic field
be not filled with the gas to be examined, and that generally
speaking only a moderate stream be employed; which however
must depend again upon the specific gravity.
The only correct way therefore of comparing two gases to-
gether is to experiment with them one in the other. For the
experiments made with gases, in gases or in air, are differential,
and similar in their nature with those made on a former occasion
with solutions (Experimental Researches, 2362. &c.); I there-
fore changed the surrounding medium in a few experiments,
substituting other gases for air; and first selected carbonic acid
as a body easy to experiment with, and one that would, pro-
bably, be more powerfully than some other of the gases, dia-
magnetic (I speak as to the appearances or relative results only)
in air.
I constructed a kind of tray or box, by folding up a
doubled sheet of waxed paper; thus making a vessel 13 inches
long, 5 inches wide, and 5 inches high. This was placed on
the ends of the great magnet, and the terminal pieces of iron
before described, placed in it. The box was covered over
loosely by plates of mica, and formed a long square chamber in
which were contained the magnetic poles and field. All the
former arrangements in respect of the magnetic field, the
delivery-tube, the catch-tubes, &c., were then made; and lastly,
the box was filled with carbonic acid by a tube, which entered it
at one corner; and was, from time to time, supplied with a fresh
portion of gas, as the previous contents became diluted with
gases or air. Everything answered perfectly, and the following
results were easily obtained.
Air passed axially, being less diamagnetic than carbonic acid
gas.
Oxygen passed to the magnetic axis, as was to be expected.
Nitrogen went equatorially, being therefore diamagnetic, even
in carbonic acid.
Hydrogen, coal-gas, olefiant gas, muriatic acid and ammonia
passed equatorially in carbonic acid, and were fairly diamagnetic
in relation to it.
Carbonic oxide was very fairly diamagnetic in carbonic acid
VOL. III.
2 I
482
Magnetic condition of air and gases. [DEC. 1847.
gas. Here the effect of oxygen seems to be very well illustrated.
Equal volumes of carbonic oxide and carbonic acid contain equal
quantities of carbon; but the former contains only half as much
oxygen as the latter. Yet it is more diamagnetic than the latter;
so that, though an additional volume and quantity of oxygen,
equal to that in the carbonic oxide, is in the carbonic acid added
and compressed into it, it does not add to, but actually takes
from, the diamagnetic force.
Nitrous oxide appears to be slightly diamagnetic in relation to
carbonic acid; but nitric oxide gas was in the contrary relation
and passed towards the axial line.
Hence it seems that carbonic acid, though more diamagnetic
than air, is not far removed from it in that respect; and this
position it probably holds because of the quantity of oxygen in
it. The apparent place of nitrous oxide close to it appears, in a
great measure, to depend on the same circumstance of oxygen
entering largely into its composition. Still it is manifest that
the action is not directly as the oxygen, for then common air
would be more diamagnetic than either of them. It seems
rather that the forces are modified, as in the cases also of iron
and oxygen, and that each compound body has its peculiar but
constant intensity of action.
In order to make similar experiments in light gases, the two
terminal pieces of the magnet were raised, so that they might be
covered by a French glass shade, which, with its stand, made a
very good chamber about them. The pipe to supply and
change the gaseous medium, and also that for bringing the gas
under trial as a stream into the magnetic field, passed through
holes made in the bottom of the stand. The different gases to
be compared with those employed as media, were, except in the
cases of ammonia and chlorine, mingled with a trace of muriatic
acid, as before described. The gaseous media used were two,
coal-gas and hydrogen. Whilst using coal-gas, I observed the
direction of the currents of the other gases in it by bringing a
little piece of paper, at the end of a wire and dipped in am-
monia solution, near the stream. In the case of the hydrogen,
I diffused a little ammonia through the whole of the gas in the
first instance.
Air passed towards the axial line in coal-gas, but was not
much affected.
DEC. 1847.]
483
Different gases in hydrogen.
Oxygen had the appearance of being strongly magnetic in
coal-gas, passing with great impetuosity to the magnetic axis,
and clinging about it; and if much muriate of ammonia fume
were purposely formed at the time, it was carried by the oxygen
to the magnetic field with such force as to hide the ends of the
magnetic poles. If then the magnetic action were suspended
for a moment, this cloud descended by its gravity; but being
quite below the poles, if the magnet were again rendered active,
the oxygen cloud immediately started up and took its former
place. The attraction of iron filings to a magnetic pole is not
more striking than the appearance presented by the oxygen
under these circumstances.
Nitrogen.-Clearly diamagnetic in coal-gas.
Olefiant, carbonic oxide, and carbonic acid gases were all
slightly, but more or less diamagnetic in the coal-gas.
On substituting hydrogen as the surrounding medium in
place of coal-gas, more care was taken in the experiments.
Each gas experimented upon was tried in it twice at least;
first in the hydrogen of a previous experiment, and then in a
new atmosphere of hydrogen.
Air.-Air passes axially in hydrogen when there is very little
smoke in it: when there is much smoke in the stream the latter
is either indifferent or tends to pass equatorially. I believe that
air and hydrogen cannot be far from each other.
Nitrogen is strikingly diamagnetic in hydrogen.
Oxygen is as strikingly magnetic in relation to hydrogen. It
presented the appearances already described as occurring in coal-
gas; but as the jet delivered the descending stream of oxygen a
little on one side of the axial line, its centrifugal power, in rela-
tion to the axial line, was so balanced by the centripetal power
produced by the magnetic action, that the stream at first revolved
in a regular ring round the axial line, and produced a cloud
that continued to spin round it as long as the magnetic force was
continued, but fell down to the bottom of the chamber when that
force was removed.
Nitrous oxide.-This gas was clearly diamagnetic in the hy-
drogen, and gave rise to a very beautiful result in consequence
of its following the oxygen; for at the beginning of the experi-
ment, the little oxygen contained in the conducting tube passed
axially; but the instant that was expelled, and the nitrous oxide
212
484
Magnetic condition of air and gases. [Dec. 1847.
issued forth, the stream changed its direction, and passed off
diamagnetically in the most striking manner.
Nitric oxide. This gas passed axially in hydrogen, and there-
fore is magnetic in relation to it.
Ammonia.-Diamagnetic in hydrogen.
Carbonic oxide, carbonic acid, and olefiant gases were diamag-
netic in hydrogen; the last most so, and the carbonic acid ap-
parently the least.
Chlorine was slightly diamagnetic in hydrogen. It was
clearly so; but the cloudy particles might conduce much to
the small effect produced.
Muriatic acid gas.—I think it was a little diamagnetic in the
hydrogen.
Notwithstanding the many disturbing causes which interfere
with first and hasty experiments of this kind, and produce re-
sults which occasionally cross and contradict each other, still
there are some very striking considerations which arise in com-
paring the gases with each other at the same temperature.
Foremost amongst these is the place of oxygen; for of all the
gaseous bodies yet tried it is the least diamagnetic, and seems in
this respect to stand far apart from the rest of them. The con-
dition of nitrogen, as being highly diamagnetic, is also important.
The place of hydrogen, as being less diamagnetic than nitrogen,
and of chlorine, which, instead of approaching to oxygen, is
above hydrogen, and also of iodine, which is probably far above
chlorine, are marked circumstances.
Air of course owes its place to the proportion and the indivi-
dual diamagnetic character of the oxygen and nitrogen in it.
The great difference existing between these two bodics in re-
spect of magnetic relation, and the striking effect presented by
oxygen in coal-gas and hydrogen, bodies not far removed from
nitrogen in diamagnetic force, made me think it might not be
impossible to separate air into its two chief constituents by
magnetic force alone. I made an experiment for this purpose,
but did not succeed; but I am not convinced that it cannot be
done. For since we can actually distinguish certain gases, and
especially these two by their magnetic properties, it does not
seem impossible that sufficient power might cause their sepa-
ration from a state of mixture.
In the course of these experiments I subjected several of the
DEC. 1847.]
485
Different gases heated-oxygen.
gases to heat, to ascertain whether they generally underwent the
same exaltation of their diamagnetic power which occured with
common air (2854.). For this purpose a helix of platina wire was
placed in the mouth of the delivering tube, which itself was placed
below the magnetic axis between the poles. The helix could be
raised to any temperature by a little voltaic battery, and any gas
could be sent through it and upwards across the magnetic field
by means of the Woulf's bottle apparatus already described. It
was easy to ascertain whether the gas went directly up between
the poles, or, when the magnet was active, left that direction and
formed two equatorial side-streams, either by the sensation on
the finger, or by a thermoscope formed of a spiral compound
lamina of platinum and silver placed in a tube above. In every
case the hot gas was diamagnetic in the air, and I think far more
so than if the gas had been at common temperatures. The
gases tried were as follows: oxygen, nitrogen, hydrogen, nitrous
oxide, carbonic acid, muriatic acid, ammonia, coal-gas, ole-
fiant gas.
But as in these experiments the surrounding air would, of
necessity, mingle with the gas first heated, and so form, in fact,
a part of the heated stream, I arranged the platinum helix so
that I could heat it in a given gas, and thus compare the same
gas at different temperatures with itself.
ปี
A stream of hot oxygen in cold oxygen was powerfully dia-
magnetic. The effect and its degree may be judged of by the
following circumstances. When the platinum helix below the
axial line was ignited, the effect of heat on the indicating com-
pound spiral, placed in a tube over the axial line, was such as
to cause its lower extremity to pass through one and a half re-
volutions, or 540°: when the magnetic force was rendered active,
the spiral returned through all these degrees to its first position,
as if the ignited helix below had been lowered to the common
temperature or taken away; and yet in respect of it, nothing
had been changed. On rendering the magnet inactive, the cur-
rent of hot oxygen instantly resumed its perpendicular course
and affected the thermoscope as before.
On experimenting with carbonic acid, it was found that hot
carbonic acid was diamagnetic to cold carbonic acid; and the
effects were apparently as great in amount as in oxygen.
On making the same arrangement in hydrogen, I failed to
486
[DEC. 1847.
Magnetic condition of air and gases.
obtain any result regarding the relation of the hot and cold gas,
for this reason :-that I could not, in any case, either with or
without the magnetic action, obtain any signs of heat on the
thermoscopic spiral above, even when the platinum helix, not
more than an inch below it, was nearly white hot. This effect
is, I think, greatly dependent upon the rapidity with which hy-
drogen is heated and cooled in comparison with other gases, and
also upon the vicinity of the cold masses of iron forming the
magnetic poles, between which the hot gas has to pass in its way
upwards; and it is most probably connected with the fact ob-
served by Mr. Grove of the difficulty of igniting a platinum wire
in hydrogen.
When the igniting helix was placed in coal-gas, it was found
that the hot gas was diamagnetic to that which was cold; as
in all the other cases. Here, again, an effect like that which
was observed in hydrogen occurred; for when there was no mag-
netic action, the ascending stream of hot coal-gas could cause
the thermoscopic spiral to revolve through only 280° or 300°,
in place of above 540°; through which it could pass when the
surrounding gas was oxygen, air, or carbonic acid; and that even
when the helix was at a higher temperature in the coal-gas than
in any of these gases.
The proof is clear then that oxygen, carbonic acid, and coal-
gas, are more diamagnetic hot than cold. The same is the case
with air; and as air consists of four-fifths nitrogen and only one-
fifth oxygen, and yet shows an effect of this kind as strongly
as oxygen, it is manifest that nitrogen also has the same relation
when hot and cold.
Of the other gases also I have no doubt; though to be quite
certain, they ought to be tried in atmospheres of their own sub-
stance (2854), or else in gases more diamagnetic at common tem-
peratures than they. The olefiant and coal-gases in air easily bore
the elevation of the helix to a full red heat, without inflaming
when out of the exit-tube: the hydrogen required that the helix
should be at a lower temperature. Muriatic acid and ammonia
showed the division of the one stream into two, very beautifully,
on holding blue and red litmus paper above.
There is another mode of observing the diamagnetic condition
of flame, and experimenting with the various gases, which is
sometimes useful, and should always be understood, lest it inad-
DEC. 1847.]
487
Pierced poles-flames.
vertently might lead to confusion. I have a pair of terminal
magnetic poles which are pierced in a horizontal direction, that
a ray of light may pass through them. The opposed faces of
these vertical poles are not, as in the former case, the rounded
ends of cones; but, though rounded at the edges, may be con-
sidered as flat over an extent of surface an inch in diameter. The
pierced passages are in the form of cones, the truncation of
which in this flat surface is rather more than half an inch in dia-
meter. When these poles were in their place, and from 0·3
to 0.4 of an inch apart, a taper flame, burning freely between
them, was for a few moments unaffected by throwing the mag-
net into action; but then it suddenly changed its form, and ex-
tending itself axially, threw off two horizontal tongues, which
entered the passages in the poles; and thus it continued as long
as the magnetism continued, and no part of it passed equa-
torially.
On using a large flame made with the cotton ball and æther,
two arms could be thrown off from the flame by the force of the
magnetism, which passed in an equatorial direction, as before;
and other two parts entered the passages in the magnetic poles,
and actually issued out occasionally at their further extremities.
When the poles were about 0·25 of an inch apart, and the
smoking taper was placed in the middle between them level with
the centres of the passages, the effect was very good; for the
smoke passed axially and issued out at the further ends of the
pole passages.
Coal-gas delivered in the same place also passed axially, i. e.
into the pole passages and parallel to the line joining them.
A little consideration easily leads to the true cause of these
effects, and shows that they are not inconsistent with the former
results. The law of all these actions is, that if a particle, placed
amongst other particles, be more diamagnetic (or less magnetic)
than they, and free to move, it will go from strong to weaker
places of magnetic action; also, that particles less diamagnetic
will go from weaker to stronger places of action. Now with the
poles just described, the line or lines of maximum force are not
coincident with the axis of the holes pierced in the poles, but lie
in a circle having a diameter, probably, a little larger than the
diameter of the holes; and the lines within that circle will be of
lesser power, diminishing in force towards the centre. A hot
488
Magnetic condition of air and gases. [DEC. 1847
particle therefore within that circle will be driven inwards, and
being urged by successive portions of matter driven also inwards,
will find its way out at the other ends of the passages, and there-
fore seem to go in an axial direction; whilst a hot particle outside
of that circle of lines of maximum force will be driven outwards,
and so, with others, will form the two tongues of flame which
pass off in the equatorial direction. By bringing the glowing
taper to different parts, the circle of lines of maximum magnetic
intensity can be very beautifully traced; and by placing the taper
inside or outside of that circle, the smoke could be made to pass
axially or equatorially at pleasure.
I arranged an apparatus on this principle for trying the gases,
but did not find it better than, or so good as, the one I have
described.
Such are the results I have obtained in verifying and extending
the discovery made by P. Bancalari. I would have pursued
them much further, but my present state of health will not per-
mit it; I therefore send them to you with, probably, many imper-
fections. It is now almost proved that many gaseous bodies are
diamagnetic in their relations, and probably all will be found to
be so. I say almost proved; for it is not, as yet, proved in fact.
That many, and most, gaseous bodies are subject to magnetic
force is proved; but the zero is not yet distinguished. Now,
until it is distinguished, we cannot tell which gaseous bodies will
rank as diamagnetic and which as magnetic; and also, whether
there may not be some standing at zero. There is evidently no
natural impossibility to some gases or vapours being magnetic,
or that some should be neither magnetic nor diamagnetic. It is
the province of experiment to decide such points; and the affirm-
ative or negative may not be asserted before such proof is given,
though it may, very philosophically, be believed.
For myself I have always believed that the zero was repre-
sented by a vacuum, and that no body really stood with it. But
though I have only guarded myself from asserting more than
I knew, Zantedeschi (and I think also De la Rive), with some
others, seem to think that I have asserted the gases are not sub-
ject to magnetic action; whereas I only wished to say that I
could not find that they were, and perhaps were not: I will
therefore quote a few of my words from the Experimental Re-
searches. Speaking of the preparation of a liquid medium at
DEC. 1847.1
489
True zero-gases and light.
zero, I say, "Thus a fluid medium was obtained, which practi-
cally, as far as I could perceive, had every magnetic character
and effect of a gas, and even of a vacuum, &c."-Experimental
Researches, 2423. Again, at (2433.) I say, "At one time I looked
to air and gases as the bodies which, allowing attenuation of
their substance without addition, would permit of the obser-
vation of corresponding variations in their magnetic proper-
ties, but now all such power by rarefaction appears to be taken
away." And further down at (2435.), "Whether the negative
results obtained by the use of gases and vapours depend upon
the smaller quantity of matter in a given volume, or whether
they are the direct consequences of the altered physical condition
of the substance, is a point of very great importance to the
theory of magnetism. I have imagined in elucidation of the
subject an experiment, &c., but expect to find great diffi-
culty in carrying it into execution, &c." Happily P. Bancalari's
discovery has now settled this matter for us in a most satisfac-
tory manner. But where the true zero is, or that every body is
more or less removed from it on one side or the other, is not, as
yet, experimentally shown or proved.
I cannot conclude this letter without expressing a hope that
since gases are shown to be magnetically affected, they will also
shortly be found, when under magnetic influence, to have the
power of affecting light (Experimental Researches, 2186. 2212.).
Neither can I refrain from signalizing the very remarkable
and direct relation between the forces of heat and magnetism
which is presented in the experiments on flame, and heated air
and gases. I did not find on a former occasion (Experimental
Researches, 2397.) that solid diamagnetic bodies were sensibly
affected by heat, but shall repeat the experiments and make more
extensive ones, if the Italian philosophers have not already done
In reference to the effect upon the diamagnetic gases, it
may be observed, that, speaking generally, it is in the same di-
rection as that of heat upon iron, nickel and cobalt; i. e. heat
tends in the two sets of cases, either to the diminution of mag-
netic force, or the increase of diamagnetic force; but the results
are too few to allow of any general conclusion as yet.
So.
As air at different temperatures has different diamagnetic re-
lations, and as the atmosphere is at different temperatures in the
upper and lower strata, such conditions may have some general
490
[DEC. 1847.
Zantedeschi on the
influence and effect upon its final motion and action, subject as
it is continually to the magnetic influence of the earth.
I have for the sake of brevity frequently spoken in this letter
of bodies as being magnetic or diamagnetic in relation one to
another, but I trust that in all the cases no mistake of my
meaning could arise from such use of the terms, or any vague
notion arise respecting the clear distinction between the two
classes, especially as my view of the true zero has been given
only a page or two back.
I am, my dear Sir,
Yours, &c.,
Richard Taylor, Esq.,
Ed. Phil. Mag., &c. &c.
M. FARADAY.
On the Motions presented by Flame when under the Electro-
magnetic Influence. By Prof. ZANTEDESCHI.
THE most eminent philosophers have at all times maintained
the universality of the magnetism of bodies¹; and in our days
Faraday is the only one who has placed the expansible fluids at
the zero of the scale of action among magnetic and diamagnetic
bodies. On the 21st of September 1847, at the Physical Section
of the Ninth Italian Scientific Congress in Venice, Padre Ban-
calari, Professor of Physics in the Royal University of Genoa,
read a memoir on the universality of magnetism; and the argu-
ment was considered by philosophers to be of such importance,
that a desire arose to verify chiefly the action of magnetism on
expansible fluids. It was announced by the Reporter Belli at
the sitting of the 27th of September, that it had been proved in
the presence of various philosophers that, on the interposition
of a flame between the two poles of an electro-magnet, it was re-
pulsed at the instant the electric current was closed, to return to
the first position the instant it was broken. This discovery re-
ceived well-merited applause in the sitting of the 28th of Sep-
tember, from the General Secretary and the Secretary of the
Section of Physics. A wish was expressed by some to witness
the experiment of Bancalari; and a Daniell's apparatus having
been got ready, of ten elements eighteen centimeters each in di-
mension, I endeavoured to repeat the experiment in the Cabinet
¹ Raccolta Fisico-Chimica Italiana, t. iii. Dei corpi magnetici e diamagnetici.
DEC. 1847.]
magnetic condition of flame.
491
of Physics of the Royal Imperial Lyceum of Venice; but I did
not chance to see the asserted phænomenon. My temporary
magnet had the power of sustaining above 48 kilogrms. weight;
but as my principle is, that a negative argument never destroys
a positive one, I for my further information requested the ma-
chinist Cobres to give me the particulars of the apparatus; Belli
not having treated of these in his report, and they having
escaped Prof. Zambra, the Secretary of the Section. I knew that
the two pieces of soft iron, which constituted the interrupted
anchor, were perforated in the axial direction. I suspected that
the repulsion of the flame was not the immediate effect of the
magnetism, but of two currents of air issuing from the apertures
of the perforated keeper generated by a vorticose movement
produced by the magnetism, as the celebrated Faraday had ob-
served in liquids'; and I was confirmed in this suspicion by the
negative experiment which I had instituted in Venice with solid
pieces. On arriving in Turin, I communicated my doubts to
the well-known mechanicians Jest, father and son, who to their
professional ability unite a rare courtesy. They soon furnished
me in their laboratory with a Bunsen's apparatus, and constructed
terminal pieces of soft iron forming the interrupted anchor, both
solid and pierced, of a parallelopipedon and cylindric form, as I
pointed out to them; and I have repeated the experiments in
their company: the temporary magnet, made in the shape of a
horseshoe, was formed of a cylinder of soft iron of the length of
Om.335 and the diameter of Om·015; and its electro-magnetic spiral
was formed of a copper wire.33m long, and of a diameter of a milli-
meter and a third; the internal distance of the poles was Om-027;
the two solid parallelopipedon contacts, forming the interrupted
anchor, were Om-04 long; and of the sides Om-011 and Om-006: and
the hollow terminal pieces were 0m-035 long; and of the side
Om-009. They were placed at a distance from one another of four
to five millimeters, the magnet being kept in a vertical position
with the poles turned upwards. In front of the interval of the
separation of the contact pieces was placed the flame of a small
candle, or of a little oil or alcohol lamp, so that it surmounted with
its top by nearly a fourth the thickness of the contacts. The
electric circuit was closed by copper wires, and the metallic unions
I
Raccolta, cited above, t. ii. Relazione dell' influenza delle forze elettriche
e magnetiche sulla luce ed il calorico.
492
[DEC. 1847.
Zantedeschi on the
were maintained both at the magnetic poles and at those of the
pile by clamps one of the wires therefore was divided into two
equal parts, and the ends being dipped into a tumbler of mercury,
allowed the closing and opening of the circuit at pleasure.
I have constantly observed repulsion in the act of closing the
circle, which lasted the whole time that the magnetism was kept
up; and, when in the act of opening the circle, I saw the flame
return to its primitive position. Well satisfied with having in
this manner confirmed this important fact which reflects honour
on its discoverer, I applied myself to the study of the phæno-
menon, and I found-
I. That this happens with contacts of both solid and hollow
soft iron; whereupon I abandoned my suspicion that the move-
ment of the flame was attributable to currents of air; I convinced
myself that it was an immediate action of the magnetism upon
the flame, a fact of the greatest importance to science.
II. That the repulsion, when it is quite distinct and the flame
quite pure, and terminated in a well-shaped top, is accompanied
by depression: repulsion and depression are simultaneously ob-
served at the closing of the circle; the return of the flame and
rising of the same, at the opening of the circle.
III. That, ceteris paribus, the greatest effect takes place when
the flame is touching the convex of the magnetic curves indicated
by iron filings.
IV. That the action is null, or almost null, when the flame is
placed in the centre of the interval which separates the two con-
tacts.
V. That in the manifestation of the effects stated above, it is
not necessary for the contacts to be entirely separated: they may
be placed at an angle and touch at two corners: the flame placed
within the base of this triangle, generally manifests the two
phænomena indicated.
VI. That there is a certain mass of the contacts (or keeper
pieces) which is the most efficacious: beyond a limit, which can
be shown by experiment, increase of the mass causes a diminution
of the effect; from this I found the cause of my negative re-
sults, which I obtained in Venice in the first experiments that I
made.
VII. That the movements of the flame increase with the number
of the pairs (of battery plates). With one pair the effect was
DEC. 1847.]
493
magnetic condition of flame.
not perceptible to me: with two pairs the movements began to
show themselves; with three pairs they became distinct, and in-
creased with the increase of the number of pairs up to ten, which
was the greatest that I employed in this experiment. The pairs
were of the known ordinary size.
On the repetition of the phænomena as above stated, the pre-
caution was taken to cover the apparatus with a bell, which was
open above and supported by two discs below, which left a free
access to the air, by which to support the combustion: in this
manner all agitation and danger of disturbance under the cir-
cumstances were avoided.
I must not forget, in concluding this article, to state that the
celebrated Prof. Gazzaniga, starting from his numerous experi-
ments, which demonstrate the influence of magnetism upon the
same aëriform fluids, in a manner therefore different from that
of Bancalari, was induced to consider the sun and all the other
celestial bodies are so many enormous magnets; by which he
established that attraction is merely an effect of the magnetism of
the great celestial masses placed at an enormous distance,—an
idea which reappeared in 1846 in Prussia, and in 1847 in France,
as we see from the Comptes Rendus of the Royal Academy of
Sciences at Paris. The mystery that attraction operates at a
distance without intermedia would be removed in this case, and
the phænomena of attraction would enter again into the class of
those of common dynamics.
Dalla Gazz. Piem.,
Oct. 12, 1847, No. 242.
¹ Messrs. Jest prepared for me last evening an electro-magnet of a circular
form interrupted by a prismatic section having an interval of two millimeters;
and I had, without need of contact pieces, the phænomena distinct with a
single element. The most conspicuous movements here appeared in the greater
proximity of the flame to the section.
The complete apparatus, of a circular form, furnished with a glass bell with
its accessories, is sold in Turin by Messrs. Jest, at the price of thirty francs,
not including the electro-motor.
494
On the Use of Gutta Percha in Electrical Insulation'.
MY DEAR PHILLIPS.
I HAVE lately found gutta percha very useful in electrical ex-
periments; and therefore, that others may take advantage of its
properties if they have occasion or are so inclined, give you this
notice for insertion in the Philosophical Magazine. Its use de-
pends upon the high insulating power which it possesses under
ordinary conditions, and the manner in which it keeps this power
in states of the atmosphere which make the surface of glass a
good conductor. All gutta percha is not however equally good
as it comes from the manufacturer's hands; but it does not seem
difficult to bring it into the best state: I will describe the
qualities of a proper specimen, and refer to the differences after-
wards. A good piece of gutta perch will insulate as well as an
equal piece of shell-lac, whether it be in the form of sheet, or
rod, or filament; but being tough and flexible when cold, as
well as soft when hot, it will serve better than shell-lac in many
cases where the brittleness of the latter is an inconvenience.
Thus it makes very good handles for carriers of electricity in
experiments on induction, not being liable to fracture in the
form of thin band or string it makes an excellent insulating
suspender: a piece of it in sheet makes a most convenient insu-
lating basis for anything placed on it. It forms excellent insu-
lating plugs for the stems of gold-leafed electrometers when they
pass through sheltering tubes, and larger plugs supply good
insulating feet for extemporary electrical arrangements: cylinders
of it half an inch or more in diameter have great stiffness, and
form excellent insulating pillars. In these and in many other
ways its power as an insulator may be useful.
:
Because of its good insulation it is also an excellent substance
for the excitement of negative electricity. It is hardly possible
to take one of the soles sold by the shoemakers out of paper or
into the hand, without exciting, it to such a degree as to open
the leaves of an electrometer one or more inches; or if it be
unelectrified, the slightest passage over the hand or face, the
clothes, or almost any other substance gives it an electric state.
Some of the gutta percha is sold in very thin sheets, resembling
¹ Philosophical Magazine, March 1848, xxxii. 165.
FEB. 1848.]
495
Insulating power of gutta percha.
in general appearance oiled silk; and if a strip of this be drawn
through the fingers, it is so electric as to adhere to the hand or
attract pieces of paper. The appearance is such as to suggest
the making a thicker sheet of the substance into a plate electrical
machine for the production of negative electricity.
Then as to inductive action through the substance, a sheet of
it is soon converted into an excellent electrophorus; or it may
be coated and used in place of a Leyden jar; or in any of the
many other forms of apparatus dependent on inductive action.
I have said that all gutta percha is not in this good electrical
condition. With respect to that which is not so (and which has
constituted about one-half of that which, being obtained at the
shops, has passed through my hands), it has either discharged
an electrometer as a piece of paper or wood would do, or it
has made it collapse greatly by touching, yet has on its removal
been followed by a full opening of the leaves again: the latter
effect I have been able to trace and refer to a conducting portion
within the mass covered by a thin external non-conducting coat.
When a piece which insulates well is cut, the surface exposed
has a resinous lustre and a compact character that is very di-
stinctive; whilst that which conducts has not the same degree of
lustre, appears less translucent, and has more the aspect of a
turbid solution solidified. I believe both moist steam-heat and
water-baths are used in its preparation for commerce; and the
difference of specimens depends probably upon the manner in
which these are applied, and followed by the after process of
rolling between hot cylinders. However, if a portion of that
which conducts be warmed in a current of hot air, as over the
glass of a low gas flame, and be stretched, doubled up, and
kneaded for some time between the fingers, as if with the inten-
tion of dissipating the moisture within, it becomes as good an
insulator as the best.
•
:
I have soaked a good piece in water for an hour; and on
taking it out, wiping it, and exposing it to the air for a minute
or two, found it insulate as well as ever. Another piece was
soaked for four days and then wiped and tried at first it was
found lowered in insulating power; but after twelve hours' ex-
posure to air under common circumstances it was as good as
ever. I have not found that a week's exposure in a warm air
cupboard of a piece that did not insulate made it much better;
496
[FEB. 1848.
Insulating power of gutta percha.
a film on the outside became non-conducting; but if two fresh
surfaces were exposed by cutting, and these were brought into
contact with the electrometer and the finger, the inside por-
tion was still found to conduct.
If the gutta percha in either the good or the bad condition
(as to electrical service) be submitted to a gradually increasing
temperature, at about 350° or 380°, it gives off a considerable
proportion of water; being then cooled, the substance which
remains has the general properties of gutta percha, and insulates
well. The original gum is probably complicated, being a mix-
ture of several things; and whether the water has existed in the
substance as a hydrate, or is the result of a deeper change of one
part or another of the gum, I am not prepared to say. All I
desire in this note is to make known its use in the arrangement
of extemporary or permanent electrical apparatus for the advan-
tage of working philosophers, both juvenile and adult.
I am, dear Phillips,
Yours,
Royal Institution,
Feb. 9, 1848.
M. FARADAY.
497
Observations on the Magnetic Force'.
INASMUCH as the general considerations to be brought forward
have respect to those great forces of the globe, exerted by it, both
as a mass and through its particles, namely magnetism and
gravitation, it is necessary briefly to recall certain relations
and differences of the two which have been insisted upon on
former occasions. Both can act at a distance, and doubtless
at any distance; but whilst gravitation may be considered as
simple and unpolar in its relations, magnetism is dual and
polar. Hence one gravitating particle or system cannot be con-
ceived to act by gravitation, as a particle or system, on itself;
whereas a magnetic particle or system, because of the dual nature
of its force, can have such a self-relation. Again, either polarity
of the magnetic force can act either by attraction or repulsion;
and not merely so, but the joint or dual action of a magnet can
act also either by attraction or repulsion, as in the case of para-
magnetic and diamagnetic bodies: the action of gravity is always
that of attraction. As a further consequence of the difference
in character of the powers, little or no doubt was entertained
regarding the existence of physical lines of force² in the cases
of dual powers, as electricity and magnetism; but in respect of
gravitation the conclusion did not seem so sure. In reference to
the growing magnetic relations of the sun and the earth, it is
well to keep in mind Arago's idea, of the relative magnitude of
the two; for, supposing that the centres of the two globes
were made to coincide, the sun's body would not only extend
as far as the moon, but nearly as far again, its bulk being about
seven times that of a globe which should be girdled by the
moon's orbit.
For the more careful study of the magnetic power, a torsion
balance has been constructed of a particular kind. The torsion
wire was of hard drawn platinum, 24 inches in length, and of
such diameter that 28.5 inches weighed one grain. It was
1 Proceedings of the Royal Institution, Jan. 21, 1853.
2 Proceedings of the Royal Institution, June 11, 1852, p. 216 (see p. 438);
also Phil. Mag. 4th Series, 1852, iii. p. 401 (see p. 407).
VOL. III.
2 K
498
Magnetic Force-Logeman's magnet. [JAN. 1853.
attached as usual to a torsion head and index.
The horizontal
beam was a small glass tube terminated at the object end by a
glass hook. The objects to be submitted to the magnetic force
were either cylinders of glass with a filament drawn out from each,
so as to make a long stiff hook for suspension from the beam; or
cylindrical bulbs of glass, of like shape, but larger size, formed out
of glass tube; or other matters. The fine tubular extremities of
the bulbs being opened, the way through was free from end to end;
the bulbs could then be filled with any fluid or gas, sealed, and be
re-submitted many times in succession to the magnetic force. The
scurce of power employed was at first a large electro-magnet; but
afterwards, in order to be certain of a constant power, and for the
advantage of allowing any length of time for the observations,
the great magnet, constructed by M. Logeman upon the prin-
ciples developed by Dr. Elias (and which, weighing above
100 lbs., could support 430 lbs. according to the report of the
Great Exhibition Jury), was purchased by the Royal Institution
and used in the inquiries. The magnet was so arranged that
the axis of power was 5 inches below the level of the glass
beam, the interval being traversed by the suspension filament
or hook, spoken of above. The form and position of the termi-
nation of soft iron are shown in plan by the diagram upon a
scale of, and also the place of the object. All this part is

ου
931/
enclosed in the box which belongs to and carries the torsion-
balance, which box is governed by six screws fixed upon the
magnet table; and as both the box and the table have lines and
scales marked upon them, it is easy to adjust the former on the
latter so that the beam shall be over and parallel to the line a, e,
with the point of suspension over c; or, by moving the whole
box parallel to itself towards m, to give the point of suspension
any other distance from the angle c. As already said, the objects
were constructed with a suspension filament of such length as to
make them coincide in height with the angle in the magnetic
field. When suspended on the beam, they were counterpoised
JAN. 1853.]
499
Torsion-balance.
by a ring or rings of lead on the further arm of the beam. These
when required were moved along the beam until the latter was hori-
zontal; and that state was ascertained by a double arm support,
which sustained the beam when out of use, brought it into a
steady state when moving, and delivered it into a condition of
freedom when required. The motion of the box to the right or
left, so as to place the object in the middle of the magnetic angle,
was given by two of the screws before spoken of; the motion to
the given distance from c, by the other four.
Supposing the distance from c towards m to be adjusted to
0.6 of an inch, when the beam was loaded above, and no object
before the magnet (the beam having been of course previously
adjusted to its normal position and the torsion index placed at
zero), it then remained to determine the return of the beam to
its place when the object had been suspended on it and repelled:
this was done in the following manner. A small plane reflector
is fixed on the beam, near its middle part, under the point of
suspension; a small telescope associated with a divided scale is
placed about 6 feet from the reflector, and in such a position
that when the beam is in its right place, a given degree in the
scale coincides with the fine wire in the telescope. Of course
the scale appears to pass by the wire as the beam itself moves,
and with a double angular velocity, because of the reflexion. As
it is easy to read to the fiftieth and even to the hundredth of
an inch in this way, and as each degree occupies apparently
2.4 inches with the radius of 6 feet, so an angular motion, or
difference of 24th of a degree could be observed; and as the
radius of the arm of the beam carrying the object was 6 inches,
such a quantity there would be less than 20th of an inch ; i. e.
the return of the beam to its first or normal position by the
torsion force put on to counteract the repulsion, could be ascer-
tained to within that amount. When an object was put on the
adjusted beam, if diamagnetic, it was repelled; and then, as the
observer sat at the telescope, he, by means of a long handle,
a wheel and pinion, put on torsion until the place of the beam
was restored; and afterwards the amount of torsion read off on
the graduated scale became the measure in degrees of the repul-
sive force exerted. At the time of real obscrvations, the magnet,
balance, and telescope were all fixed in a basement room, upon
a stone floor. But it is unnecessary to describe here the numerous
00
2 K 2
500
[JAN. 1853.
Magnetic force-relation of media.
precautions required in relation to the time of an observation,
the set of the suspension wire by a high torsion, the possible
electricity of the object or beam by touch, the effect of feeble
currents of air within the box, the shape of the object, the pre-
caution against capillary action when fluids were employed as
media, and other circumstances; or the use of certain stops, and
the mode of procedure in the cases of paramagnetic action;—
the object being at present to present only an intelligent view of
the principles of action.
When a body is submitted to the power of a magnet, it is
affected, as to the result, not merely by the magnet, but also by
the medium surrounding it; and even if that medium be changed
for a vacuum, the vacuum and the body still are in like relation
to each other. In fact the result is always differential; any
change in the medium changes the action on the object, and
there are abundance of substances which when surrounded by
air are repelled, and when by water, are attracted, upon the
approach of a magnet. When a certain small glass cylinder
weighing only 66 grains was submitted on the torsion-balance
to the Logeman magnet surrounded by air, at the distance of
0·5 of an inch from the axial line, it required 15° of torsion to
overcome the repulsive force and restore the object to its place.
When a vessel of water was put into the magnetic field, and the
experiment repeated, the cylinder being now in the water was
attracted, and 54°.5 of torsion were required to overcome this at-
traction at the given distance of 0.5. If the vessel had contained
a fluid exactly equal in diamagnetic power to the cylinder of glass,
neither attaction nor repulsion would have been exerted on the
latter, and therefore the torsion would have been 0°. Hence
the three bodies, air, glass (the especial specimen), and water,
have their relative force measured in relation to each other by
the three experimental numbers 15°, 0°, and 54°5. If other
fluids are taken, as oil, æther, &c., and employed as the media
surrounding the same glass cylinder, then the degrees of torsion
obtained with each of them respectively, show its place in the
magnetic series. It is the principle of the hydrometer or of
Archimedes in respect of gravity applied in the case of the mag-
netic forces. If a different cylinder be:employed of another size
or substance, or at a different distance, the torsion numbers will
be different, and the zero (given by the cylinder) also different;
JAN. 1853.]
501
Scale of magnetic forcc-zero.
but the media (with an exception to be made hereafter) will have
the same relation to each other as in the former case. Therefore
to bring all the experimental results into one common relation,
a Centigrade scale has been adopted bounded by air and water
at common temperatures, or 60° F. For this purpose every
separate series of results made under exactly the same circum-
stances included air and water; and then all the results of one
series were multiplied by such a number as would convert the
difference between air and water into 100°: in this way the three
results given above become 21°·6, 0°, and 78°4. By such a
process the magnetic intervals between the bodies are obtained on
the Centigrade scale, but the true zero is not as yet determined.
Either water, or air, or the glass, may be assumed as the zero,
the intervals not being in any way dependent upon that point,
but the results will then vary in expression thus :-
Air
Glass
21.6
Water. 100
21.6
0
78.4
100
78.4
0
all above the zero being paramagnetic, and all below diamagnetic,
in relation to it. I have adopted a vacuum as the zero in the
table of results to be given hereafter.
In this manner it is evident that, upon principle, any solid,
whatever its size, shape, or quality, may be included in the list,
by its subjection to a magnet in air and in water, or in fluids
already related to these: also that any fluids may be included,
by the use of the same immersed solid body for them, air and
water; and also that by using the same vessel, as for instance
the same glass bulb, and filling it successively with various
gases and fluids, including always air and water in each series,
these included bodies may then have their results reduced and
be entered upon the list. The following is a table of some sub-
stances estimated on the Centigrade scale, and though there are
many points both of theory and practice yet to be wrought out,
as regards the use of the torsion balance described, so that the
results can only as yet be recorded as approximations, even now,
the average of three or four careful experiments gives an ex-
pression for any particular substance under the same conditions.
of distance, power, &c. near upon and often within a degree
of the place assigned to it. The powers are expressed for a
$
502
Magnetic relation of certain bodies. [Jan. 1853.
distance of 0.6 of an inch from the magnetic axis of the magnet as
arranged and described, and of course, for equal volumes of the
bodies mentioned. The extreme decimal places must not be
taken as correct, except as regards the record of the experi-
ments: they are the results of calculation. Hydrogen, nitro-
gen, and perhaps some other of the bodies near zero, may
ultimately turn out to be as a vacuum; it is evident that a very
little oxygen would produce a difference, such as that which
appears in nitrogen gas. The first solution of copper mentioned
was colourless, and the second the same solution oxidized by
simple agitation in a bottle with air, the copper, ammonia, and
water being in both the same.
о
Prot-ammo. of copper
134.23
Camphor.
82.59
Per-ammo. of copper
119.83
Camphine
82.96
Oxygen.
17.5
Linseed oil
85.56
Air
3.4
Olive oil.
85.6
Olefiant gas
0.6
Wax
86.73
Nitrogen
0.3
Nitric acid
87.96
Vacuum
0.0
Water
96.6
Carbonic acid gas
0.0
Solution of ammonia
98.5
Hydrogen.
0.1
Bisulphide of carbon
99.64
Ammonia gas
0.5
Sat. sol. nitre
100.08
Cyanogen
0.9
Sulphuric acid.
104.47
A glass
18.2
Sulphur
118
Pure zinc.
74.6
Chloride of arsenic
121.73
Æther
75.3
Fused borate of lead.
136-6
Alcohol, absolute
78.7
Phosphorus
Oil of lemons
80
Bismuth.
1967.6
•
Plücker in his very valuable paper' has dealt with bodies
which are amongst the highly paramagnetic substances, and his
estimate of power is made for equal weights.
One great object in the construction of an instrument delicate
as that described, was the investigation of certain points in the
philosophy of magnetism; and amongst them especially that of
the right application of the law of the inverse square of the di-
stance as the universal law of magnetic action. Ordinary mag-
netic action may be divided into two kinds, that between
1 Taylor's Scientific Memoirs, vol. v. pp. 713, 730.
JAN. 1853.] Law of the inverse square of the distance.
503
magnets permanently magnetized and unchangeable in their
condition, and that between bodies of which one is a permanent
unchangeable magnet, and the other, having no magnetic state
of its own, receives and retains its state only whilst in subjection
to the first. The former kind of action appears in the most rigid
and pure cases to be subject to that law; but it would be pre-
mature to assume beforehand, and without abundant sufficient
evidence, that the same law applies in the second set of cases
also; for a hasty assumption might be in opposition to the truth
of nature, and therefore injurious to the progress of science, by
the creation of a preconceived conclusion. We know not whe-
ther such bodies as oxygen, copper, water, bismuth, &c., owe
their respective paramagnetic and diamagnetic relation to a
greater or less facility of conduction in regard to the lines of
magnetic force, or to something like a polarity of their particles
or masses, or to some as yet unsuspected state; and there is
little hope of our developing the true condition, and therfore
the cause of magnetic action, if we assume beforehand the un-
proved law of action and reject the experiments that already
bear upon it;-for Plücker has distinctly stated as the fact, that
diamagnetic force increases more rapidly than magnetic force,
when the power of the dominant magnet is increased; and such
a fact is contrary to the law above enunciated. The following
are further results in relation to this point.
When a body is submitted to the great unchanging Logeman
magnet in air and in water, and the results are reduced to the
Centigrade scale, the relation of the three substances remains the
same for the same distance, but not for different distances.
Thus, when a given cylinder of flint glass was submitted to the
magnet surrounded by air and by water, at the distance of 0.3
of an inch, as already described, it proved to be diamagnetic in
relation to both; and when the results were corrected to the
Centigrade scale, and water made zero, it was 9°1 below, or on
the diamagnetic side of water. At the distance 0.4 of an inch it
was 10°.6 below water: at the distance of 0.7 it was 12°1 below
water. When a more diamagnetic body, as heavy glass, was
employed, the same result in a higher degree was obtained; for
at the distance of 0.3 it was 37°.8 below water, and at that of
0.8 it was 48°.6 beneath it. Bismuth presented a still more
striking case, though, as the volume of the substance was
504
JAN. 1853.
Magnetic force :-
necessarily small, equal confidence cannot be placed in the exacti-
tude of the numbers. The results are given below for the three
substances, air being always 100° and water 0°; the first column
of figures for each substance contains the distance¹ in tenths of
an inch from the axial line of the magnetic field, and the second,
the place in Centigrade magnetic degrees below water.
Heavy Glass.
Flint-Glass.
Bismuth.
O
0.3
9.1
0.3
37.8
0·6 — 1871
0.4
10.6
0.4
38.6
1.0 2734
0.5 — 11·1
0.6
40.0
1.5 - 3626
0.6 — 11.2
0.8
48.6
0·7 — 12·1
1.0 — 51.5
1.2 65.6
The result here is, that the greater the distance of the diamag-
netic body from the magnet, the more diamagnetic is it in re-
lation to water, taking the interval between water and air as the
standard: and it would further appear, if an opinion may
be
formed from so few experiments, that the more diamagnetic the
body compared to air and water, the greater does this difference
become. At first it was thought possible that the results might
be due to some previous state induced upon the body, by its
having been nearer to or further from the magnet; but it was
found that whether the progress of the experiments was from
small to large distances, or the reverse; or whether, at any given
distance, the object was previous to the measurement held close
up to the magnet or brought from a distance, the results were
the same; no evidence of a temporary induced state could in
any of these ways be found.
It does not follow from the experiments, if they should be
sustained by future researches, that it is the glass or the bismuth
¹ A given change of distance necessarily implies change in degree of force,
and change in the forms of the lines of force; but it does not imply always
the same amount of change. The forces are not the same at the same di-
stance of 0·4 of an inch in opposite directions from the axial line towards m and
n in the figure, page 498, nor at any other equal moderate distance; and though
by increase and diminution of distance the change is in the same direction, it
is not in the same proportion. By fitly arranged terminations, it may be made
to alter with extreme rapidity in one direction, and with extreme slowness or
not at all in another.
JAN. 1853.]
505
its variation by distance.
only that changes in relation to the other two bodies. It may
be the oxygen of the air that alters, or the water, or more pro-
bably all these bodies; for if the result be a true and natural
result in these cases, it is probably common to all substances.
The great point is, that the three bodies concerned, air, water,
and the subject of the experiment, alter in the degree of their
magnetic relations to each other;-at different given distances
from the magnet the ratio of their magnetic power does not,
according to the experiments, remain the same; and if that re-
sult be confirmed, then it cannot be included by a law of action
which is inversely as the square of the distance. A hydrometer
floating in a fluid and subject to the gravity of the earth alone,
would (other things being the same) stand at the same point,
whether at the surface of the earth, or removed many diameters
of the earth from it, because the action of gravity is inversely as
the square of the distance; but if we suppose the substance of
the hydrometer and the fluid to differ magnetically, as water and
bismuth do, and the earth to act as a magnet instead of by
gravity, then the hydrometer would, according to the experi-
ments, stand at a different point for different distances, and if so
could not be subject to the former law.
The cause of this variation in the ratio of the substances one
to another, if it be finally proved, has still to be searched out.
It may depend in some manner upon the forms of the lines of
magnetic force, which are different at different distances; or not
upon the forms of the lines, but the amount of power at the dif-
ferent distances; or not upon the mere amount, but on the cir-
cumstance that in every case the body submitted to experiment
has lines of different degrees of force passing through different
parts of it (for however different the magnetic or diamagnetic
conditions of a body and the fluid surrounding it, they would
not move at all in relation to each other in a field of equal
force); but whatever be the cause, it will be a concomitant of
magnetic actions; and therefore ought to be included in the re-
sults of any law by which it is supposed that these actions are
governed.
It has not yet been noticed that these general results appear
to be in direct opposition to those of Plucker, who finds that
diamagnetic power increases more rapidly than magnetic power
with increase of force. But such a circumstance, if both con-
506
Magnetic force of different substances. [JAN. 1853.
clusions be accordant with facts, only shows that we have yet a
great deal to learn about the physical nature of this force; and
we must not shut our eyes to the first feeble glimpses of these
things, because they are inconsistent on both sides with our
assumed laws of action; but rather seize them, as hoping that
they will give us the key to the truth of nature. Bodies when
subject to the power of the magnet appear to acquire a new
physical state, which varies with the distance or the power of
the magnet. Each body may have its own rate of increase and
decrease; and that may be such as to connect the extreme effect
of Plücker, amongst paramagnetic bodies on the one hand, and
the extreme effects amongst diamagnetic bodies now described,
on the other; and when we understand all this rightly, we may
see the apparent contradiction become harmony, though it may
not conform to the law of the inverse square of the distance as
we now try to apply it.
Plücker has already said, because of his observations regarding
paramagnetic and diamagnetic force, that no correct list of mag-
netic substances can be given. The same consequence follows,
though in a different direction, from what has now been stated,
and hence the reservation before made (p. 501). Still the former
table is given as an approximation, and it may be useful for a
time. Before leaving this first account of recent experimental
researches, it may be as well to state that they are felt to be im-
perfect and may perhaps even be overturned; but that, as such
a result is not greatly anticipated, it was thought well to present
them to the Members of the Royal institution and the scientific
world, if peradventure they might excite criticism and experi-
mental examination, and so aid in advancing the cause of physical
science.
On a former occasion¹ the existence of physical lines of force
in relation to magnetism and electricity was inferred from the
dual nature of these powers, and the necessity in all cases and at
all times of a relation and dependence between the polarities of
the magnet, or the positive and negative electrical surfaces.
With respect to gravity a more hesitating opinion was expressed,
because of the difficulty of observing facts having any relation
to time, and because two gravitating particles or masses did not
seem to have any necessary dependence on each other for the
¹ See p. 438.
JAN. 1853.]
507
Physical lines of force.
existence or excitement of their mutual power'. A passage
may now be quoted from Newton which has since been dis-
covered in his works, and which, showing that he was an
unhesitating believer in physical lines of gravitating force,
must from its nature rank him amongst those who sustain the
physical nature of the lines of magnetic and electrical force: it
is as follows, in words written to Bentley 2: "That gravity should
be innate, inherent and essential to matter, so that one body may
act upon another at a distance through a vacuum, without the
mediation of anything else, by and through which their action
and force may be conveyed from one to another, is to me so
great an absurdity, that I believe no man who has in philosophi-
cal matters a competent faculty of thinking, can ever fall into
it. Gravity must be caused by an agent acting constantly ac-
cording to certain laws; but whether this agent be material or
immaterial, I have left to the consideration of my readers."
¹ Philosophical Magazine, 4th Series, 1852, vol. iii. p. 403 (3246.).
2 Newton's Works, Horsley's edition, 4to, 1783, vol. iv. p. 438, or the
Third Letter to Bentley.
508
On Electric Induction—Associated cases of current and
static effects¹.
CERTAIN phænomena that have presented themselves in the
course of the extraordinary expansion which the works of the
E ectric Telegraph Company have undergone, appeared to me
to offer remarkable illustrations of some fundamental principles
of electricity, and strong confirmation of the truthfulness of the
view which I put forth sixteen years ago, respecting the mu-
tually dependent nature of induction, conduction, and insulation
(Exp. Res., 1318. &c.). I am deeply indebted to the Company
to the Gutta Percha works, and to Mr. Latimer Clarke, for
the facts; and also for the opportunity both of seeing and
showing them well.
Copper wire is perfectly covered with gutta percha at the
Company's works, the metal and the covering being in every
part regular and concentric. The covered wire is usually made
into half-mile lengths, the necessary junctions being effected by
twisting or binding, and ultimately, soldering; after which the
place is covered with fine gutta percha, in such a manner as to
make the coating as perfect there as elsewhere: the perfection
of the whole operation is finally tried in the following striking
manner, by Mr. Statham, the manager of the works. The half-
mile coils are suspended from the sides of barges floating in a
canal, so that the coils are immersed in the water, whilst the two
ends of each coil rise into the air: as many as 200 coils are thus
immersed at once, and when their ends are connected in series,
one great length of 100 miles of submerged wire is produced,
the two extremities of which can be brought into a room for ex-
periment. An insulated voltaic battery of many pairs of zinc
and copper, with dilute sulphuric acid, has one end connected
with the earth, and the other, through a galvanometer, with
either end of the submerged wire. Passing by the first effect,
and continuing the contact, it is evident that the battery current
can take advantage of the whole accumulated conduction or de-
fective insulation in the 100 miles of gutta percha on the wire,
and that whatever portion of electricity passes through to the
¹ Proceedings of the Royal Institution, Jan. 20, 1854.
JAN. 1854.]
509
Charge of subaqueous telegraph wires.
water will be shown by the galvanometer. Now the battery is
made one of intensity, in order to raise the character of the
proof, and the galvanometer employed is of considerable deli-
cacy; yet so high is the insulation that the deflection is not
more than 5º. As another test of the perfect state of the wire,
when the two ends of the battery are connected with the two
ends of the wire, there is a powerful current of electricity shown
by a much coarser instrument; but when any one junction in
the course of the 100 miles is separated, the current is stopped,
and the leak or deficiency of insulation rendered as small as be-
fore. The perfection and condition of the wire may be judged
of by these facts.
32
16
The 100 miles, by means of which I saw the phænomena,
were thus good as to insulation. The copper wire was th of an
inch in diameter :-the covered wire was; some was a little
less, being in diameter :—the gutta percha on the metal may
therefore be considered as 0·1 of an inch in thickness. 100
miles of like covered wire in coils were heaped up on the floor
of a dry warehouse and connected in one series, for comparison
with that under water.
Consider now an insulated battery of 360 pairs of plates (4×3
inches) having one extremity to the earth; the water wire with
both its insulated ends in the room, and a good earth-discharge
wire ready for the requisite communications :—when the free
battery end was placed in contact with the water wire and then
removed, and, afterwards, a person touching the earth-discharge
touched also the wire, he received a powerful shock. The shock
was rather that of a voltaic than of a Leyden battery: it occu-
pied time, and by quick tapping touches could be divided into
numerous small shocks: I obtained as many as forty sensible
shocks from one charge of the wire. If time were allowed to
intervene between the charge and discharge of the wire, the
shock was less; but it was sensible after 2, 3, or 4 minutes, or
even a longer period.
When, after the wire had been in contact with the battery, it
was placed in contact with a Statham's fuse, it ignited the fuse
(or even six fuses in succession) vividly:-it could ignite the fuse
3 or 4 seconds after separation from the battery. When, having
been in contact with the battery, it was separated and placed in
contact with a galvanometer, it affected the instrument very
powerfully it acted on it, though less powerfully, after the lapse
510
[JAN. 1854.
Subaqueous telegraph wires :-
of 4 or 5 minutes, and even affected it sensibly 20 or 30
minutes after it had been separated from the battery. When
the insulated galvanometer was permanently attached to the end
of the water wire, and the battery pole was brought in contact
with the free end of the instrument, it was most instructive to
see the great rush of electricity into the wire; yet after that was
over, though the contact was continued, the deflection was not
more than 50, so high was the insulation. Then separating the
battery from the galvanometer, and touching the latter with the
earth wire, it was just as striking to see the electricity rush out
of the wire, holding for a time the magnet of the instrument in
the reverse direction to that due to the ingress or charge.
5º,
These effects were produced equally well with either pole of the
battery or with either end of the wire; and whether the electric
condition was conferred and withdrawn at the same end, or at the
opposite ends of the 100 miles, made no difference in the results.
An intensity battery was required, for reasons which will be very
evident in the sequel. That employed was able to decompose
only a very small quantity of water in a given time. A Grove's
battery of eight or ten pair of plates, which would have far sur-
passed it in this respect, would have had scarcely a sensible power
in affecting the wire.
When the 100 miles of wire in the air were experimented with
in like manner, not the slightest signs of any of these effects were
produced. There is reason, from principle, to believe that an
infinitesimal result is obtainable, but as compared to the water
wire the action was nothing. Yet the wire was equally well and
better insulated, and as regarded a constant current, it was an
equally good conductor. This point was ascertained, by attach-
ing the end of the water wire to one galvanometer, and the end
of the air wire to another like instrument; the two other ends of
the wires were fastened together, and to the earth contact; the
two free galvanometer ends were fastened together, and to the
free pole of the battery; in this manner the current was di-
vided between the air and water wires, but the galvanometers
were affected to precisely the same amount. To make the
result more certain, these instruments were changed one for the
other, but the deviations were still alike: so that the two wires
conducted with equal facility.
The cause of the first results is, upon consideration, evident
enough. In consequence of the perfection of the workmanship
JAN. 1854.]
511
their charge— wires in air.
a Leyden arrangement is produced upon a large scale; the cop-
per wire becomes charged statically with that electricity which
the pole of the battery connected with it can supply¹; it acts by
induction through the gutta percha (without which induction it
could not itself become charged, Exp. Res. 1177.), producing
the opposite state on the surface of the water touching the gutta
percha, which forms the outer coating of this curious arrange-
ment. The gutta percha across which the induction occurs, is
only 0.1 of an inch thick, and the extent of the coating is enor-
mous. The surface of the copper wire is nearly 8300 square
feet, and the surface of the outer coating of water is four times
that amount, or 33,000 square feet. Hence the striking charac-
ter of the results. The intensity of the static charge acquired is
only equal to the intensity at the pole of the battery whence it
is derived; but its quantity is enormous, because of the immense
extent of the Leyden arrangement; and hence when the wire is
separated from the battery and the charge employed, it has all
the powers of a considerable voltaic current, and gives results
which the best ordinary electric machines and Leyden arrange-
ments cannot as yet approach.
That the air wire produces none of these effects is simply
because there is no outer coating correspondent to the water, or
only one so far removed as to allow of no sensible induction, and
therefore the inner wire cannot become charged. In the air wire
of the warehouse, the floor, walls, and ceiling of the place con-
stituted the outer coating, and this was at a considerable distance;
and in any case could only affect the outside portions of the coils
of wire. I understand that 100 miles of wire stretched in a line
through the air, so as to have its whole extent opposed to earth,
is equally inefficient in showing the effects, and there it must be
the distance of the inductric and inducteous surfaces (1483.),
combined with the lower specific inductive capacity of air, as
compared with gutta percha, which causes the negative result.
The phænomena altogether offer a beautiful case of the identity
of static and dynamic electricity. The whole power of a consi-
derable battery may in this way be worked off in separate por-
tions, and measured out in units of static force, and yet be em-
ployed afterwards for any or every purpose of voltaic electricity.
I now proceed to further consequence of associated static and
¹ Davy, Elements of Chemical Philosophy, p. 154.
512
[JAN. 1854
Subterraneous telegraph wires:-
dynamic effects. Wires covered with gutta percha, and then en-
closed in tubes of lead or of iron, or buried in the earth or sunk
in the sea, exhibit the same phænomena as those described; the
like static inductive action being in all these cases permitted by
the conditions. Such subterraneous wires exist between London
and Manchester, and when they are all connected together so as
to make one series, offer above 1500 miles; which, as the dupli-
cations return to London, can be observed by one experimenter
at intervals of about 400 miles, by the introduction of galvano-
meters at these returns. This wire, or the half, or fourth of it,
presented all the phænomena already described; the only dif-
ference was that as the insulation was not so perfect, the charged
condition fell more rapidly. Consider 750 miles of the wire in
one length, a galvanometer a being at the beginning of the wire,
a second galvanometer b in the middle, and a third c at the end:
-these three galvanometers being in the room with the experi-
menter, and the third c perfectly connected with the earth. On
bringing the pole of the battery into contact with the wire through
the galvanometer a, that instrument was instantly affected; after
a sensible time b was affected, and after a still longer time c:
when the whole 1500 miles were included, it required two seconds
for the electric stream to reach the last instrument. Again;
all the instruments being deflected (of course not equally because
of the electric leakage along the line), if the battery were cut off
at a, that instrument instantly fell to zero; but b did not fall
until a little while after; and c only after a still longer interval;--
a current flowing on to the end of the wire whilst there was none
flowing in at the beginning. Again; by a short touch of the
battery pole against a, it could be deflected and could fall back
into its neutral condition, before the electric power had reached b;
which in its turn would be for an instant affected, and then left
neutral before the power had reached c; a wave of force having
been sent into the wire which gradually travelled along it, and
made itself evident at successive intervals of time, in different
parts of the wire. It was even possible, by adjusted touches of
the battery, to have two simultaneous waves in the wire, follow-
ing each other, so that at the same moment that c was affected
by the first wave, a or b was affected by the second; and there
is no doubt that by the multiplication of instruments and close
attention, four or five waves might be obtained at once.
JAN. 1854.]
513
retardation of the current in them.
{
If after making and breaking battery contact a, a be imme-
diately connected with the earth, then additional interesting
effects occur.
Part of the electricity which is in the wire will
return, and passing through a will deflect it in the reverse di-
rection; so that currents will flow out of both extremities of the
wire in opposite directions, whilst no current is going into it
from any source. Or if a be quickly put to the battery and then
to the earth, it will show a current first entering into the wire,
and then returning out of the wire at the same place; no sensible
part of it ever travelling on to b or c.
When an air wire of equal extent is experimented with in like
manner, no such effects as these are perceived: or if, guided by
principle, the arrangements are such as to be searching, they are
perceived only in a very slight degree, and disappear in compa-
rison with the former gross results. The effect at the end of
the very long air wire (or c) is in the smallest degree behind the
effect at galvanometer a; and the accumulation of a charge in the
wire is not sensible.
All these results as to time, &c. evidently depend upon
the
same condition as that which produced the former effect of static
charge, namely lateral induction; and are necessary consequences
of the principles of conduction, insulation, and induction, three
terms which in their meaning are inseparable from each other
(Exp. Res. 1320. 1326'. 1338. 1561. &c.). If we put a plate of
shell-lac upon a gold-leaf electrometer and a charged carrier (an
insulated metal ball of two or three inches diameter) upon it, the
électrometer is diverged; removing the carrier, this divergence
¹ 1326. All these considerations impress my mind strongly with the con-
viction, that insulation and ordinary conduction cannot be properly separated
when we are examining into their nature; that is, into the general law or laws
under which their phænomena are produced. They appear to me to consist in
an action of contiguous particles, dependent on the forces developed in electrical
excitement; these forces bring the particles into a state of tension or polarity,
which constitutes both induction and insulation; and being in this state the con-
tiguous particles have a power or capability of communicating these forces,
one to the other, by which they are lowered and discharge occurs. Every body
appears to discharge (444.987); but the possession of this capability in a greater
or smaller degree in different bodies, makes them better or worse conductors,
worse or better insulators: and both induction and conduction appear to be the
same in their principle and action (1320.), except that in the latter, an effect
common to both is raised to the higher degree, whereas in the former it occurs,
in the best cases, in only an almost insensible quantity.
VOL. III.
2 L
514 Electric induction and conduction connected. [JAN. 1854.
instantly falls; this is insulation and induction: if we replace the
shell-lac by metal, the carrier causes the leaves to diverge as be-
fore, but when removed, though after the shortest possible con-
tact, the electroscope is left diverged; this is conduction. If we
employ a plate of spermaceti instead of the metal, and repeat the
experiment, we find the divergence partly falls and partly remains,
because the spermaceti insulates and also conducts, doing both
imperfectly; but the shell-lac also conducts, as is shown if
time be allowed; and the metal also obstructs conduction, and
therefore insulates, as is shown by simple arrangements. For if
a copper wire, 74 feet in length and 12th of an inch in diameter,
be insulated in the air, having its end m a
metal ball; its end e connected with the
earth, and the parts near m and e brought
within half an inch of each other, as at s;
then an ordinary Leyden jar being charged
sufficiently, its outside connected with e and
its inside with m, will give a charge to the
wire, which instead of travelling wholly
through it, though it be so excellent a con-
ductor, will pass in large proportion through
the air at s, as a bright spark; for with such
a length of wire, the resistance in it is accu-
mulated until it becomes as much, or perhaps
even more, than that of the air, for electricity
of such high intensity.

73
m
Admitting that such and similar experiments show that con-
duction through a wire is preceded by the act of induction (1338.),
then all the phænomena presented by the submerged or subter-
ranean wires are explained; and in their explanation confirm, as
I think, the principles given. After Mr. Wheatstone had, in
1834, measured the velocity of a wave of electricity through a
copper wire, and given it as 288,000 miles in a second, I said,
in 1838, upon the strength of these principles (1333.), “that the
velocity of discharge through the same wire may be greatly
varied, by attending to the circumstances which cause variations
of discharge through spermaceti or sulphur. Thus, for instance,
it must vary with the tension or intensity of the first urging
force, which tension is charge and induction. So if the two
ends of the wire in Professor Wheatstone's experiment were im-
JAN. 1854.] Varying velocity of electricity in wires.
515
mediately connected with two large insulated metallic surfaces
exposed to the air, so that the primary act of induction, after
making the contact for discharge, might be in part removed from
the internal portion of the wire at the first instant, and disposed
for the moment on its surface jointly with the air and surround-
ing conductors, then I venture to anticipate that the middle
spark would be more retarded than before: and if these two
plates were the inner and outer coating of a large jar, or a Leyden
battery, then the retardation of that spark would be still greater."
Now this is precisely the case of the submerged or subterraneous
wires, except that instead of carrying their surfaces towards the
inducteous coatings (1483.), the latter are brought near the
former; in both cases the induction consequent upon charge,
instead of being exerted almost entirely at the moment within
the wire, is to a very large extent determined externally; and so
the discharge or conduction being caused by a lower tension,
therefore requires a longer time. Hence the reason why, with
1500 miles of subterraneous wire, the wave was two seconds in
passing from end to end; whilst with the same length of air wire,
the time was almost inappreciable.
With these lights it is interesting to look at the measured
velocity of electricity in wires of metal, as given by different
experimenters.
1 Wheatstone in 1834, with copper wire made it
1 Walker in America with telegraph iron wire.
1 O'Mitchell, ditto
ditto
1 Fizeau and Gonnelle (copper wire)
1
Ditto
(iron wire)
Miles per second.
288,000
18,780
28,524
112,680
62,600
2,700
2 A. B. G. (copper) London and Brussels Telegraph
2 Ditto (copper) London and Edinburgh Telegraph 7,600
Here, the difference in copper is seen by the first and fifth
result to be above a hundredfold. It is further remarked in
Liebig's report of Fizeau's and Gonnelle's experiments, that the
velocity is not proportional to the conductive capacity, and is
independent of the thickness of the wire. All these circum-
stances and incompatibilities appear rapidly to vanish, as we
recognize and take into consideration the lateral induction of the
¹ Liebig and Kopp's report, 1850 (translated), p. 168.
2 Athenæum, 14th January, 1854, p. 54.
2 L 2
516
[JAN. 1854.
Subaqueous telegraph wires.
wire carrying the current. If the velocity of a brief electric dis-
charge is to be ascertained in a given length of wire, the simple
circumstances of the latter being twined round a frame in small
space, or spread through the air through a large space, or ad-
hering to walls, or lying on the ground, will make a difference
in the results, And in regard to long circuits such as those
described, their conducting power cannot be understood, whilst
no reference is made to their lateral static induction, or to the
conditions of intensity and quantity which then come into play;
especially in the case of short or intermitting currents, for then
static and dynamic are continually passing into each other.
It has already been said that the conducting power of the air
and water wires is alike for a constant current. This is in
perfect accordance with the principles and with the definite
character of the electric force, whether in the static or current or
transition state. When a voltaic current of a certain intensity
is sent into a long water wire, connected at the further extremity
with the earth, part of the force is in the first instance occupied
in raising a lateral induction round the wire, ultimately equal in
intensity at the near end to the intensity of the battery stream,
and decreasing gradually to the earth end, where it becomes
nothing. Whilst this induction is rising, that within the wire
amongst its particles is beneath what it would otherwise be; but
as soon as the first has attained its maximum state, then that in
the wire becomes proportionate to the battery intensity, and
therefore equals that in the air wire, in which the same state is
(because of the absence of lateral induction) almost instantly
attained. Then of course they discharge alike and therefore
conduct alike.
.
A striking proof of the variation of the conduction of a wire
by variation of its lateral static induction, is given in the expe-
riment proposed sixteen years ago (1333.). If, using a constant
charged jar, the interval s, page 514, be adjusted so that the spark
shall freely pass there (though it would not if a little wider),
whilst the short connecting wires n and o are insulated in the air,
the experiment may be repeated twenty times without a single
failure; but if after that, n and o be connected with the inside
and outside of an insulated Leyden jar, as described, the spark
will never pass across s, but all the charge will go round the
whole of the long wire. Why is this? The quantity of electri-
JAN. 1854.]
517
Subterraneous telegraph wires.
city is the same, the wire is the same, its resistance is the same,
and that of the air remains unaltered; but because the intensity
is lowered, through the lateral induction momentarily allowed,
it is never enough to strike across the air at s; and it is finally
altogether occupied in the wire, which in a little longer time than
before, effects the whole discharge. M. Fizeau has applied the
same expedient to the primary voltaic currents of Rhumkorff's
beautiful inducting apparatus, with great advantage. He thereby
reduces the intensity of these currents at the moment when it
would be very disadvantageous, and gives us a striking instance
of the advantage of viewing static and dynamic phænomena as
the result of the same laws.
Mr. Clarke arranged a Bains' printing telegraph with three
pens, so that it gave beautiful illustrations and records of facts
like those stated: the pens are iron wires, under which a band
of paper imbued with ferro-prussiate of potassa passes at a regu-
lar rate by clock-work; and thus regular lines of prussian blue
are produced whenever a current is transmitted, and the time of
the current is recorded. In the case to be described, the three
lines were side by side, and about 0.1 of an inch apart. The pen
m belonged to a circuit of only a few feet of wire, and a separate
battery; it told whenever the contact key was put down by the
finger; the pen n was at the earth end of the long air wire, and
the pen o at the earth end of the long subterraneous wire; and
by arrangement, the key could be made to throw the electricity
of the chief battery into either of these wires, simultaneously
with the passage of the short circuit current through pen m.
When pens m and n were in action, the m record was a regular
line of equal thickness, showing by its length the actual time
during which the electricity flowed into the wires; and the n
record was an equally regular line, parallel to, and of equal
length with the former, but the least degree behind it; thus indi-
cating that the long air wire conveyed its electric current almost
instantaneously to the further end. But when pens m and o
were in action, the o line did not begin until some time after the
m line, and it continued after the m line had ceased, i. e. after the
o battery was cut off. Furthermore, it was faint at first, grew
up to a maximum of intensity, continued at that as long as
battery contact was continued, and then gradually diminished to
nothing. Thus the record o showed that the wave of power
518
Subterraneous telegraph wires. [JAN. 1854.
took time in the water wire to reach the further extremity; by
its first faintness, it showed that power was consumed in the ex-
ertion of lateral static induction along the wire; by the attainment
of a maximum and the after equality, it showed when this induc-
tion had become proportionate to the intensity of the battery
current; by its beginning to diminish, it showed when the bat-
tery current was cut off; and its prolongation and gradual dimi-
nution showed the time of the outflow of the static electricity
laid up in the wire, and the consequent regular falling of the
induction which had been as regularly raised.
With the pens m and o the conversion of an intermitting into
a continuous current could be beautifully shown; the earth wire
by the static induction which it permitted, acting in a manner
analogous to the fly-wheel of a steam-engine, or the air-spring of
a pump. Thus when the contact key was regularly but rapidly
depressed and raised, the pen m made a series of short lines
separated by intervals of equal length. After four or more of
these had passed, then pen o, belonging to the subterraneous
wire, began to make its mark, weak at first, then rising to a
maximum, but always continuous. If the action of the contact
key was less rapid, then alternate thickening and attenuations
appeared in the o record; and if the introductions of the electric
current at the one end of the earth wire were at still longer in-
tervals, the records of action at the other end became entirely
separated from each other;-all showing most beautifully, how
the individual current or wave, once introduced into the wire,
and never ceasing to go onward in its course, could be affected
in its intensity, its time, and other circumstances, by its partial
occupation in static induction.
By other arrangements of the pens n and o, the near end of
the subterraneous wire could be connected with the earth imme-
diately after separation from the battery; and then the back flow
of the electricity, and the time and manner thereof, were beauti-
fully recorded; but I must refrain from detailing results which
have already been described in principle.
Many variations of these experiments have been made and
may be devised. Thus the ends of the insulated battery have
been attached to the ends of the long subterraneous wire, and
then the two halves of the wire have given back opposite return
currents when connected with the earth. In such a case the
JAN. 1854.]
519
Intensity and quantity.
wire is positive and negative at the two extremities, being per-
manently sustained by its length and the battery, in the same
condition which is given to the short wire for a moment by the
Leyden discharge, p. 514; or, for an extreme but like case, to a
filament of shell-lac having its extremities charged positive and
negative. Coulomb pointed out the difference of long and short
as to the insulating or conducting power of such filaments, and
the like difference occurs with long and short metal wires.
The character of the phænomena described in this report,
induces me to refer to the terms intensity and quantity as applied
to electricity; terms which I have had such frequent occasion to
employ. These terms, or equivalents for them, cannot be dis-
pensed with by those who study both the static and the dynamic
relations of electricity; every current where there is resistance,
has the static element and induction involved in it, whilst every
case of insulation has more or less of the dynamic element and
conduction; and we have seen that with the same voltaic source,
the same current in the same length of the same wire, gives a
different result as the intensity is made to vary, with variations
of the induction around the wire. The idea of intensity or the
power of overcoming resistance, is as necessary to that of elec-
tricity, either static or current, as the idea of pressure is to
steam in a boiler, or to air passing through apertures or tubes;
and we must have language competent to express these condi-
tions and these ideas. Furthermore, I have never found either
of these terms lead to any mistakes regarding electrical action,
or give rise to any false view of the character of electricity or its
unity. I cannot find other terms of equally useful significance
with these; or any which, conveying the same ideas, are not
liable to such misuse as these may be subject to. It would be
affectation, therefore, in me to search about for other words;
and besides that, the present subject has shown me more than
ever their great value and peculiar advantage in electrical lan-
guage.
The fuse referred to in page 509, is of the following nature.
Some copper wire was covered with sulphuretted gutta percha;
after some months it was found that a film of sulphuret of
copper was formed between the metal and the envelope; and
further, that when half the gutta percha was cut away in any
520
[JAN. 1854.
Statham's electric fuse for mines.
of an inch,
place, and then the copper wire removed for about
so as to remain connected only by the film of sulphuret ad-
hering to the remaining gutta percha, an intensity battery could
cause this sulphuret to enter into vivid ignition, and fire gun-
powder with the utmost ease. Gunpowder was fired with
certainty at the end of eight miles of single wire; and also
through 100 miles of covered wire immersed in the canal by the
use of this fuse.
1
521
On Subterraneons Electro-Telegraph Wires'.
To the Editors of the Philosophical Magazine and Journal.
GENTLEMEN,
A COMMUNICATION has been just brought to my notice on some
remarkable phænomena presented by subterraneous electro-tele-
graph wires observed and described by M. Werner Siemens of
Berlin, in a communication bearing date April 15, 1850. They
are the same phænomena as those shown to me by Mr. Latimer
Clarke, and used in my communication (inserted in your Maga-
zine for March 1854, p. 197) as illustrations of the truth of my an-
cient views of the nature of insulation, induction and conduction.
It is only justice that I should refer to them; and I think they
are so interesting, that you will be willing to reprint the account,
very slightly abbreviated, which I send you: the effects are pro-
duced with wires covered with gutta percha and laid in the
earth.
"A very remarkable phenomenon is constantly observed on
long, well-insulated telegraphic lines. Suppose one extremity,
B, of the wire be insulated, and the other, A, be connected with
one pole of a battery of which the other touches the earth; at
the instant of communication a brief current is observed in the
near parts of the wire in the same direction as the instantaneous
current which would exist if the extremity B were connected with
the earth; on lines of perfect insulation no trace of this current
remains. Suddenly replacing, through the action of a commu-
tator, the battery by an earth conductor, a second instantaneous
current is obtained of an intensity nearly equal to the first, but
in the inverse direction. Finally, breaking the communication
of A with the battery and also the earth, so as to insulate this
extremity, and uniting the end B at the same instant with the
ground, an instantaneous current is observed nearly equal in in-
tensity to the former, and this time in the same direction as the
first, i. e. as the continuous current of the battery. This last
experiment can only be made on a double subterranean line
having the two extremities A and B at the same station. One
might at first sight suppose these phænomena to be due to
1 From the Philosophical Magazine for June 1854.
522
[APRIL 1854.
Subterraneous telegraph wires.
secondary polarities developed on the wire, but many facts oppose
such a conclusion. 1. The phænomena are more striking as the
wire is better insulated. 2. The currents are much more brief
than those due to secondary polarities. 3. Their intensity is
proportional to the force of the battery, and independent of the
intensity of any derived current that may occur in consequence
of imperfect insulation; it follows that the intensity of the in-
stantaneous currents can greatly surpass the maximum intensity
which secondary currents in the same circuit could acquire.
4. Finally, the intensity of the instantaneous currents is propor-
tional to the length of the wire, whilst an inverse relation ought
to occur if the currents were due to secondary polarities.
"The phænomena are easily comprehended if we recall the
beautiful experiment by which Volta furnished the most striking
proof of the identity of galvanism and electricity. He showed
that on communicating one of the ends of his pile with the earth,
and the other with the interior of a non-insulated Leyden bat-
tery, the battery was charged in an instant of time to a degree
proportional to the force of the pile. At the same time an in-
stantaneous current was observed in the conductor between the
pile and the battery, which, according to Ritter, had all the pro-
perties of an ordinary current. Now it is evident that the sub-
terraneous wire with its insulating covering may be assimilated
exactly to an immense Leyden battery; the glass of the jars
represents the gutta percha; the internal coating is the surface
of the copper wire; the external surface is the moistened earth.
To form an idea of the capacity of this new kind of battery, we
have only to remember that the surface of the wire is equal to 7
square metres per kilometre. Making such a wire communicate
by one of its ends with a pile, of which the other extremity is in
contact with the earth, whilst the other extremity of the wire is
insulated, must cause the wire to take a charge, of the same cha-
racter and tension as that of the pole of the pile touched by it :
-that is what came to pass in the first of the instantaneous
currents described. In Volta's experiment, on breaking the
communication between the pole and the battery and connecting
the two coatings of the latter by a conductor, an ordinary dis-
charge was obtained:-to this discharge correspond the two in-
stantaneous currents which are observed in opposite directions
at the two extremities of the charged wire, on communicating
APRIL 1854.]
523
Subterraneous telegraph wires.
their extremities with the earth, to the exclusion of the pile. It
will be understood, also, that the first instantaneous current,
namely that which is connected with the charge of the wire,
ought to be equally produced, though of a lower intensity, even
when the other extremity of the wire is in communication with
the earth. The instantaneous current then precedes the con-
tinuous current, or, if the statement be preferred, is added to it
at the first moment. This instantaneous current has an inten-
sity much greater than that of the continuous current; doubt-
less because in the act of charging the wire, the electricity in
going to the different points of the wire passes through paths so
much the shorter as the points to be charged are nearer to the
pile." The above is from the Annales de Chimie, 1850, vol.
xxix. p. 398, &c.
I am, Gentlemen,
Royal Institution,
April 28, 1854.
Your very faithful Servant,
M. FARADAY.
524
On Magnetic Hypotheses¹.
THIS discourse, the purpose of which was to direct the attention
of the audience to the different hypothetical attempts made to
account physically for the known properties of matter in relation
to its magneto-electrical phænomena, followed on very naturally
to that of Dr. Frankland on the 2nd instant, who then gave an
account of the different views advanced by Davy, Ampère, and
Berzelius, of the manner in which electricity might be asso-
ciated with the atoms or molecules of matter, so as to account
for their electro-chemical actions, and of the logical and experi-
mental objections which stood in the way of each. Reference
was first made to Coulomb's investigations of mutual magnetic
actions; to the hypothesis advanced by him, that two magnetic
fluids, associated with the matter of magnetic bodies, would
account for all the phænomena; and to Poisson's profound
mathematical investigation of the sufficiency of the hypothesis.
Then Ersted's discovery of the relation of common magnetism
to currents of electricity was recalled to mind :—hence an
enormous enlargement of the scope of magnetic force and of
our knowledge of its actions; and hence Ampère's beautiful
investigations, and his hypothesis (also sustained by the highest
mathematical investigation),—that all magnetic phenomena are
due to currents of electricity; and that in such bodies as mag-
nets, iron, nickel, &c., the atoms or particles have naturally
currents of electricity running round them in one direction,
about what may be considered as their equatorial parts. After
Ersted's time, further experimental discoveries occurred;
currents of electricity were found competent to induce collateral
currents, and magnets proved able to produce like currents;
thus showing the identity of action of magnets and currents in
producing effects of a kind different to ordinary magnetic attrac-
tions and repulsions. Then diamagnetism was discovered, in
which actions analogous to those of ordinary magnetism oc-
curred, but with the antithesis of attraction for repulsion and
repulsion for attraction; and these were so extensive, that what-
ever bodies were not magnetic proved to be diamagnetic; and
thus all matter was brought under the dominion of that magnetic
¹ Royal Institution Proceedings, June 9th, 1854.
JUNE 1854.1
525
On magnetic hypotheses.
force, whose physical mode of action hypothesis endeavours to
account for. As the hypothesis of Ampère could not account
for diamagnetic action, some assumed that magnetic and electric
force might, in diamagnetic matter, induce currents of electricity
in the reverse direction to those in magnetic matter; or else
might induce currents where before there were none; whereas
in magnetic cases it was supposed they only constrained par-
ticle-currents to assume a particular direction, which before
were in all directions. Weber stands eminent as a profound
mathematician who has confirmed Ampère's investigations as
far as they proceeded, and who has made an addition to his hy-
pothetical views; namely, that there is electricity amongst the
particles of matter, which is not thrown into the form of a cur-
rent until the magnetic induction comes upon it, but which then
assumes the character of current, having a direction the con-
trary to that of the currents which Ampère supposed to be
always circulating round magnetic matter; and so these other
matters are rendered diamagnetic.
De la Rive, who has recently most carefully examined the
various hypotheses, and who as an experimentalist and dis-
coverer has the highest right to enter into the consideration of
these deep, searching, and difficult inquiries, after recalling the
various phænomena which show that the powers concerned be-
long to the particles of matter and not to the masses merely
(the former conferring them by association upon the latter),
then distinguishes magnetic action into four kinds or modes-
namely the ordinary, the diamagnetic, the induction of currents,
and the rotation of a ray; and points out that any acceptable
hypotheses ought to account for the four modes of action, and
it may be added, ought to agree with, if not account for, the
phænomena of electro-chemical action also. De la Rive con-
ceives that as regards these modes of action this hypothetical
result may be obtained, and both Ampère's and Weber's views
also retained in the following manner. All the atoms of matter
are supposed to be endowed with electrical currents of a like
kind, which move about them for ever, without diminution of
their force or velocity, being essentially a part of their nature.
The direction of these currents for each atom is through one
determinate diameter, which may therefore be considered as the
axis. Where they emerge from the body of the atom they
526
[JUNE 1854.
On magnetic hypotheses.
divide in all directions, and running over every part of the sur-
face converge towards the opposite end of the axis diameter, and
there re-enter the atom to run ever through the same course.
The converging and diverging points are as it were poles of
force. Where the atoms of matter are close or numerous in a
given space (and chemical considerations lead to the admission
of such cases), the hypothesis then admits that several atoms
may conjoin into a ring, so that their central or axial currents
may run one into the other, and not return as before over the
surface of each atom: these form the molecules of magnetic
matter, and represent Ampère's hypothesis of molecular cur-
rents. Where the atoms, being fewer in a given space, are
further apart, or where, being good conductors, the current runs
as freely over the surface as through the axis, then they do not
form like groups to the molecules of magnetic matter, but are
still considered subject to a species of induction by the action of
external magnets and currents; and so give rise to Weber's re-
verse currents. The induction of momentary currents and the
rotation of a ray are considered by De la Rive as in conformity
with such a supposition of the electric state of the atoms and
particles of matter.
It would seem that the great variety of these hypotheses
aud their rapid succession was rather a proof of weakness in
this department of physical knowledge than of strength, and
that the large assumptions which were made in turn for each
should ever be present to the mind. Even in the most perfect
of them, i. e. De la Rive's, these assumptions are very con-
siderable; for it is necessary to conceive of the molecules as
being flat or disc-like bodies, however numerous the atoms of
each may be; also that the atoms of one molecule do not
interfere with or break up the disposition of those of another
molecule; also that electro-chemical action may consist with
such a constituted molecule; also that the motive force of each
atom current is resident in the axis, and on the other hand
that the passage of the current over the surface offers resistance;
for unless there were a difference between the axial and the sur-
face force in one direction or the other, the atoms would have
no tendency to congregate in molecules. These remarks,
however, are not to be understood in depreciation of hypothesis,
or as objections to its right use. No discoverer could advance
JUNE 1854.]
527
On magnetic hypotheses.
without it; and such exertions as those made by De la Rive, to
bring into harmony thoughts which in their earlier forms were
adverse to each other, are of the more value, because they are
the exertions of a man who knows the value both of hypothesis
and of laws, of theory and of fact, and has given proofs of the
power of each by the productions of his own mind. Still, that
mental reservation is to be advocated which keeps hypothesis
in its right place and is ready to abandon it when it fails; and
as examples Newton may be referred to, who (as is shown by
his Letters to Bentley) had very strong convictions of the physical
nature of the lines of gravitating force, yet in what he publicly
advanced stopped short at the law of action of the force, and
thence deduced his great results ;-and also Arago, who, dis-
covering the phænomena of magnetic rotation, yet not perceiving
their physical cause, had that philosophic power of mind which
cnabled him to refrain from suggesting one.
528
On some Points of Magnetic Philosophy¹.
3300. WITHIN the last three years I have been bold enough,
though only as an experimentalist, to put forth new views of
magnetic action in papers having for titles, "On Lines of Mag-
netic Force," and "On Physical Lines of Magnetic Force³.
The first paper was simply an attempt to give, for the use of
experimentalists and others, a correct expression of the dual
nature, amount, and direction of the magnetic power both within
and outside of magnets, apart from any assumption regarding the
character of the source of the power; that the mind, in reasoning
forward towards new developments and discoveries, might be free
from the bondage and deleterious influence of assumptions of
such a nature (3075. 3243.). The second paper was a specula-
tion respecting the possible physical nature of the force, as
existing outside of the magnet as well as within it, and within
what are called magnetic bodies, and was expressly described as
being entirely hypothetical in its character (3243.).
3301. There are at present two, or rather three general hypo-
theses of the physical nature of magnetic action. First, that of
æthers, carrying with it the idea of fluxes or currents, and this
Euler has set forth in a simple manner to the unmathematical
philosopher in his Letters*;-in that hypothesis the magnetic
fluid or æther is supposed to move in streams through magnets,
and also the space and substances around them. Then there is
the hypothesis of two magnetic fluids, which being present in
all magnetic bodies, and accumulated at the poles of a magnet,
exert attractions and repulsions upon portions of both fluids at
a distance, and so cause the attractions and repulsions of the
distant bodies containing them. Lastly, there is the hypothesis
of Ampère, which assumes the existence of electrical currents
round the particles of magnets, which currents, acting at a di-
stance upon other particles having like currents, arranges them
in the masses to which they belong, and so renders such masses
¹ From the Philosophical Magazine, for February 1855.
2 Phil. Trans. 1852, p. 25.
3 Phil. Mag. 1852, June, p. 401.
4 Euler's Letters, translated, 1802, vol. i. p. 214; vol. ii. pp. 240, 242,
244.
DEC. 1854.]
529
Magnetic hypotheses.
subject to the magnetic action. Each of these ideas is varied
more or less by different philosophers, but the three distinct
expressions of them which I have just given will suffice for my
present purpose. My physico-hypothetical notion does not go
so far in assumption as the second and third of these ideas, for it
does not profess to say how the magnetic force is originated or
sustained in a magnet; it falls in rather with the first view, yet
does not assume so much. Accepting the magnet as a centre
of power surrounded by lines of force, which, as representants
of the power, are now justified by mathematical analysis (3302.),
it views these lines as physical lines of power, essential both to
the existence of the force within the magnet, and to its con-
veyance to, and exertion upon, magnetic bodies at a distance.
Those who entertain in any degree the æther notion might con-
sider these lines as currents, or progressive vibrations, or as sta-
tionary undulations, or as a state of tension. For many reasons
they should be contemplated round a wire carrying an electric
current, as well as when issuing from a magnetic pole.
3302. The attention of two very able men and eminent mathe-
maticians has fallen upon my proposition to represent the mag-
netic power by lines of magnetic force; and it is to me a source
of great gratification and much encouragement to find that they
affirm the truthfulness and generality of the method of repre-
sentation. Professor W. Thomson, in referring to a like view
of lines of force applied to static electricity (1295. 1304.), and
to Fourier's law of motion for heat, says that the lines of force
give the same mathematical results as Coulomb's theory, and by
more simple processes of analysis (if possible) than the latter¹;
and afterwards refers to the "strict foundation for an analogy on
which the conducting power of a magnetic medium for lines of force
may be spoken of." Van Rees has published a mathematical
paper on my lines of force in Dutch³, which has been transferred
into Poggendorff's Annalen, and of which I have only a very
imperfect knowledge by translated abstracts. He objects, as I
understand, to what I may call the physical part of my view as
assigning no origin for the lines, and as not presenting the higher
¹ Phil. Mag. 1854, vol. viii. p. 53.
2 Ibid. p. 56.
• Trans. Royal Acad. Sciences of Amsterdam, 1854, p. 17.
4 Poggendorff's Annalen, 1853, vol. xc. p. 415.
VOL. III.
2 M
530
[DEC. 1854.
Points of magnetic philosophy.
principle conveyed by the idea of magnetic fluids or of electric
currents he say it does not displace the old theories, or render
them superfluous; but I think I am right in believing, that, as
far as the lines are taken to be representations of the power, he
accepts them as correct representations, even to the full extent
of the hypotheses, either of magnetic fluids or electric currents.
It was always my intention to avoid substituting anything in
place of these fluids or currents, that the mind might be deli-
vered from the bondage of preconceived notions; but for those
who desire an idea to rest upon, there is the old principle of the
æthers.
3303. The encouragement I derive from this appreciation by
mathematicians of the mode of figuring to one's self the magnetic
forces by lines, emboldens me to dwell a little more upon the
further point of the true but unknown natural magnetic action.
Indeed, what we really want, is not a variety of different methods
of representing the forces, but the one true physical signification
of that which is rendered apparent to us by the phænomena, and
the laws governing them. Of the two assumptions most usually
entertained at present, magnetic fluids and electric currents, one
must be wrong, perhaps both are; and I do not perceive that the
mathematician, even though he may think that each contains a
higher principle than any I have advanced, can tell the true from
the false, or say that either is true. Neither of these views could
have led the mind to the phænomena of diamagnetism, and I
think not to the magnetic rotation of light; and I suppose that
if the question of the possibility of diamagnetic phænomena
could have been asked beforehand, a mathematician, guided by
either hypothesis, must have denied that possibility. The notion
that I have introduced complicates the matter still further, for
it is inconsistent with either of the former views, so long as they
depend exclusively upon action at a distance without inter-
mediation; and yet in the form of lines of force it represents
magnetic actions truly in all that is not hypothetical. So that
there are now three fundamental notions, and two of them at
least must be impossible, i. e. untrue.
3304. It is evident, therefore, that our physical views are very
doubtful; and I think good would result from an endeavour to
shake ourselves loose from such preconceptions as are contained
in them, that we may contemplate for a time the force as much as
DEC. 1854.]
531
Magnetic hypotheses.
possible in its purity. At present we cannot think of polarity
without feeling ourselves drawn into one or the other of the two
hypotheses of the origin of polar powers; and as mathematical
considerations cannot give a decision, we feel as if the subject
were in that same doubtful condition which hung over the con-
flicting theories of light prior to the researches of modern time;
but as there the use of Wheatstone's reflector, combined with
Arago's suggestion of a decisive experiment, and its realization
by Leon Foucault, appear to have settled that question, so we may
hope by a due exertion of judgment, united with experiment, to
obtain a resolution of the magnetic difficulty also.
3305. If we could tell the disposition of the force of a magnet,
first at the place of its origin, and next in the space around, we
should then have attained to a very important position in the
pursuit of our subject; and if we could do that, assuming little
or nothing, then we should be in the very best condition for
carrying the pursuit further. Supposing that we imagine the
magnet a sort of sun (as there is every reason to believe that the
sun is a magnet) polarized, with antithetical powers, ever filling
all space around it with its curved beams, as either the sun or a
candle fills space with luminous rays; and supposing that such
a view takes equal position with either of the two former views in
representing truly the disposition of the forces, and that mathe-
matical considerations cannot at present decide which of the
three views is either above or inferior to its co-rivals; it surely
becomes necessary that physical reasoning should be brought
to bear upon the subject as largely as possible. For if there be
such physical lines of magnetic force as correspond (in having
a real existence) to the rays of light, it does not seem so very
impossible for experiment to touch them; and it must be very
important to obtain an answer to the inquiry respecting their
existence, especially as the answer is likely enough to be in the
affirmative. I therefore purpose, without asserting anything
regarding the physical hypothesis of the magnet more strongly
than before (3299.), to call the attention of experimenters, in
a somewhat desultory manner, to the subject again, both as
respects the deficiency of the present physical views and the
possible existence of lines of physical force, concentrating the
observations I may have to make about a few points—as polarity,
duality, &c., as occasion may best serve; and I am encouraged to
2 M 2
532
[DEC. 1854.
Points of magnetic philosophy.
make this endeavour by the following considerations. 1. The
confirmation by mathematicians of the truthfulness of the ab-
stract lines of force in representing the direction and amount of
the magnetic power;-2. My own personal advantageous use of
the lines on numerous occasions (3174.) ;-3. The close analogy
of the magnetic force and the other dual powers, either in the
static or dynamic state, and especially of the magnet with the
voltaic battery or any other sustaining source of an electric cur-
rent;-4. Euler's idea of magnetic æthers or circulating fluids;
-5. The strong conviction expressed by Sir Isaac Newton, that
even gravity cannot be carried on to produce a distant effect
except by some interposed agent' fulfilling the conditions of a
physical line of force;-6. The example of the conflict and final
experimental settlement of the two theories of light.
3306. I believe that the use by me of the phrase "places of
force" has been considered by some as objectionable, inasmuch
as it would seem to anticipate the decision that there are physical
lines of force. I will endeavour so to use it, if necessary, as
not to imply the assertion. Nevertheless I may observe, that
we use such a phrase in relation to a ray of light, even in
those parts of the ray where it is not extinguished, and where
therefore we have no better knowledge of it or its existence
than in similar magnetic cases; and we also use the phrase when
speaking of gravity in respect of places where no second body to
gravitate upon is present, and where, when existing, it cannot,
according to our present views, cause the gravitating force of
the primary body, or even the determination of it, upon that
particular place.
Magnetic polarity.
3307. The meaning of this phrase is rapidly becoming more
and more uncertain. In the ordinary view, polarity does not
1 Newton says,
“That gravity should be innate, inherent, and essential to
matter, so that one body may act upon another at a distance through a
vacuum, without the mediation of anything else, by and through which their
action and force may be conveyed from one to another, is to me so great an
absurdity, that I believe no man who has in philosophical matters a com-
petent faculty of thinking can ever fall into. Gravity must be caused by an
agent acting constantly according to certain laws; but whether this agent be
material or immaterial I have left to the consideration of my readers." See
the third letter to Bentley.
DEC. 1854.]
533
Polarity-its various meanings.
necessarily touch much upon the idea of lines of physical force ;
yet in the one natural truth it must either be essential to, and
identified with it, or else absolutely incompatible with, and
opposed to it. Coulomb's view makes polarity to depend upon
the resultant in direction of the action of two separated and
distant portions of two magnetic fluids upon other like separated
portions, which are either originally separate, as in a magnet, or
are induced to separate, as in soft iron, by the action of the
dominant magnet;-it is essential to this hypothesis that the
polarity force of one name should repel polarity force of the same
name and attract that of the other name. Ampère's view of
polarity is, that there are no magnetic fluids, but that closed
currents of electricity can exist round particles of matter (or
round masses), and that the known experimental difference on
the opposite sides of these currents, shown by attraction and
repulsion of other currents, constitutes polarity. Ampère's view
is modified (chiefly by addition) in various ways by Weber, De
la Rive, Matteucci, and others. My view of polarity is founded
upon the character in direction of the force itself, whatever the
cause of that force may be, and asserts that when an electro-
conducting body moving in a constant direction near or between
bodies acting magnetically on themselves or each other, has a
current in a constant direction produced in it, the magnetic
polarity is the same; if the motion or the current be reversed, the
contrary polarity is indicated. The indication is true either
for the exterior or the interior of magnetic bodies whenever
the electric current is produced, and depends upon the unknown
but essential dual or antithetical nature of the force which we
call magnetism (3154.).
3308. The numerous meanings of the term polarity, and
various interpretations of polarity indications at present current,
show the increasing uncertainty of the idea and the word itself.
Some consider that the mere set or attraction, or even repulsion,
shown by a body when subject to a dominant magnet is sufficient
to mark polarity, and I think it is as good a test as any more
refined arrangement (2693.) when the old notion of polarity only
is under consideration. Others require that two bodies under
the power of a dominant magnet should by their actions show
a mutual relation to each other before they can be considered
as polar. Tyndall, without meaning to include any idea of the
534
[DEC. 1854.
Points of magnetic philosophy.
nature of the magnetic force, takes his type from soft iron, and
considers that any body presenting the like or the antithetical
phænomena which such iron would present under magnetic action,
is in a like or antithetical state of polarity¹. Thomson does not
view two bodies which present these antithetical positions or
phænomena as being necessarily the reverse of each other in
what may be called their polar states, but, I think, looks more
to differential action, and in that approaches towards the views
held generally by E. Becquerel and myself. Matteucci considers
that the whole mass of the polar body ought to be in dependence
by its particles as a mass of iron is, and that a solution of iron
and certain salts of iron have not poles, properly speaking, but
that at the nearest points to the dominant pole there is the con-
trary magnetism to that of the pole, surrounded by the same
magnetism as of the pole in the further part, the two ends of a
bar of such matter between two dominant poles having no rela-
tion to each others. Becquerel considers that polarity may in
certain cases occur transverse to the length, and so produce re-
sults which others explain by reverse polarity. The views of very
many parties always include the idea of the source of the polar
action, whether that be supposed to depend on the accumulation
of magnetic fluids at the chief poles of the dominant magnet, or
the action of electric currents in a determinate position around
its molecules; and such views are adhered to even when the
polarity induced is of the reverse kind, as in bismuth, &c., to that
of the inducing magnet. Others, like Weber, add to Ampère's
hypothesis an idea of electricity, loose as regards the particles,
though inseparably associated with the mass of the body under
induction. Some, I think, make the polarity not altogether de-
pendent upon the dominant magnet, but upon the neighbouring
or surrounding substances; and I propose, if the physical lines
of force should hereafter be justified, to make that which is com-
monly called polarity, in distinction from the true polarity (3307.),
dependent upon the curvature of lines of force due to the better
or worse magneto-conduction power of the substances presenting
the usual polar phænomena (2818.).
3309. The views of polar action and of magnetism itself, as
¹ Athenæum, No. 1406, p. 1203.
2 Ibid. column 3 at bottom.
3 Cours spécial sur l'induction, &c., p. 201.
DEC. 1854.]
535
Polarity of bismuth-examined.
.
formerly entertained, have been powerfully agitated by the dis-
covery of diamagnetism. I was soon driven from my first sup-
position, that the N pole of a magnet induced like or N polarity
in the near part of a piece of bismuth or phosphorus; but as
that view has been sustained by very eminent men, who tie up
with it the existence of magnetic fluids or closed electric currents
as the source of magnetic power, it claims continued exami-
nation, for it will most likely be a touchstone and developer of
real scientific truth, whichever way the arguments may prevail.
To me the idea appears to involve, if not magnetic impossibilities,
at least great contradiction and much confusion, some of which I
proceed to state, but only with the desire of elucidating the general
subject.
Fig. 1.
S
M
72
I
sn
n &
3
3310. If an ordinary magnet, M, fig. 1,
acting upon a piece of iron or other para-
magnetic matter I, renders it polar by
throwing its near end into the contrary
or S state in the manner usually under-
stood, and, acting upon a like piece of
diamagnetic matter as bismuth B, renders it also polar, but with
the near end in the same state; then B and I are for the time
two magnets, and must act back upon the magnet M; or if
they could be made able to retain their states after M is removed
(and that is the case with I), would act as magnets upon a third
piece of magnetic matter as C. When M acts upon I, it exerts
its influence, according to the received theories, upon all the
particles of the latter, bringing them into like polar position
with itself, and these, consistently with the simple assumption,
act also upon each other as particle magnets, and exalt the
polarity of the whole mass in its two extremities. In like manner
M should act upon B, polarizing the mass and all its particles;
for the particles of the diamagnetic body B, even to the smallest,
must be operated upon; and we know experimentally, that a tube
filled with powdered bismuth acts as a bar of the metal does.
But then, what is the mutual action of these bismuth particles
on each other? for though all may be supposed to have a reverse
polarity to that of M, they cannot in that case be reverse in re-
spect of each other. All must have like polarity, and the N of
one particle must be opposed to the S of the next particle in the
polarity direction. That these particles act on each other, must
536
[DEC. 1854.
Points of magnetic philosophy.
be true, and Tyndall's results on the effect of compression have
proved that by the right means, namely experiment. If they
were supposed to have no such action on each other, it would
be in contradiction to the essential nature of magnetic action,
and there would remain no reason to think that the magnet itself
could act on the particles, or the particles react on it. If they
acted on each other as the magnet is supposed to act on them,
i.e. to induce contrary poles, then the power of the magnet would
be nullified, and the more effectually the nearer the particles
were together; whereas Tyndall has shown that the bismuth
magnetic condition is exalted by such vicinity of the particles,
and hence we have a further right to conclude that they do act
on, or influence each other, to the exaltation of the state of the
mass. But if the N-ness of one particle corresponds to, and aids
in sustaining and exalting, the S-ness of the next particle, the
whole mass must have the same kind of force; so that, as a mag-
net, its polarity must have the same kind of polarity as that of
the particles themselves. For whether a particle of bismuth be
considered as acting upon a neighbouring particle or upon a
distant particle of bismuth, or whether a mass of particles be
considered as acting on the distant particle, the action in both
cases must be precisely of the same kind.
3311. But why should a polarized particle of bismuth acting
upon another particle of bismuth produce in it like polarity, and
with a particle of iron produce a contrary polarity? or why
should masses of bismuth and iron, when they act as magnets
(3310.), produce such different effects? If such were the case,
then the N pole of a paramagnetic body would induce an S pole
on the near end of an iron rod, whilst the N pole of a diamag-
netic body would produce a pole contrary to the former, i. e. an
N pole at the same end of the iron rod in the same position and
place. This would be to assume two kinds of magnetism, i. e.
two north fluids (or electric currents) and two south; and the
northness of bismuth would differ from the northness of iron as
much as pole from pole. Still more, the northness of bismuth
and the southness of iron would be found to have exactly like
qualities in all points, and to differ in nothing but name; and
the southness of bismuth and northness of iron would also
prove to be absolutely alike. What is this, in fact, but to say
they are the same? and why should we not accept the confirma-
DEC. 1854.] Two sorts of magnetism-media.
537
tion and unfailing proof that it is so, which is given to us expe-
rimentally by the moving wire? (3307. 3356.)
3312. If we employ a magnet as the originally inducing body
(3310.), and entertain the idea of magnetic fluids accumulated
at the poles, which act by their power of attracting each other,
but repelling their like, then the inconsistency of supposing that
the north fluid of a given pole can attract the north fluid of one
body and the south fluid of another, or that the north and south
fluid of the dominant magnet can attract one and the same fluid
in bismuth and in iron, &c., is very manifest. Or if we act by a
solenoid or a helix of copper wire carrying an electric current
instead of a magnet, and find that analogous effects are produced,
are we to admit at once that the electric currents in it, acting
upon the assumed electric circuits round the particles of matter,
sometimes attract them on the one side and sometimes on the
other? or if such bodies as bismuth and platinum are put into
such a helix, are we to allow that currents in opposite directions
are induced in them by one and the same inducing condition?
and that, too, when all the other phænomena, and there are
many, point to a uniformity of action as to direction with a varia-
tion only in power.
Media.
3313. Let us now consider for a time the action of different
media, and the evidence they give in respect of polarity. If a
weak solution of protosulphate of iron¹, m, be put into a selected
thin glass tube about an inch long, and one-third or one-fourth
of an inch in diameter, and sealed up hermetically (2279.),
and be then suspended horizontally between the magnetic poles
in the air, it will point axially, and behave in other respects as
iron; if, instead of air between the poles, a solution of the same
kind as m, but a little stronger, n, be substituted, the solution in
the tube will point equatorially, or as bismuth. A like solution
somewhat weaker than m, to be called l, enclosed in a similar
tube, will behave like bismuth in air but like iron in water.
Now these are precisely the actions which have been attributed
to polarity, and by which the assumed reverse polarities of para-
magnetic and diamagnetic bodies have been considered as esta-
¹ Let 7 contain 4 grains, m 8 grains, n 16 grains, and o 32 grains, of
crystallized protosulphate of iron in each cubic inch of water.
538
[DEC. 1854.
Points of magnetic philosophy.
blished; but when examined, how will ideas of polarity apply to
these cases, or they to it? The solution / points and acts like
bismuth in air and like iron in water; are we then to conclude
what are
that it has reverse polarity in these cases? and if So,
the reasons and causes for such a singular contrast in that which
must be considered as dependent upon its internal or molecular
state?
3314. In the first place, no want of magnetic continuity of
parts can have anything to do with the inversion of the phæno-
mena; for it has been shown sufficiently by former experiments¹,
that such solutions are as magnetically continuous in character
as iron itself.
Fig. 2.
3315. In the next place, I think it is impossible to say that
the medium interposed between the magnet and the suspended
cylinder of fluid can cut off, or in any way affect the direct force
of the former on the latter, so as to change the direction of its
internal polarity. Let the tube be filled with the solution m,
then if it be surrounded by the solution 7, it will point as iron;
if the stronger solution n surround it, it will point as bismuth ;
and with sufficient care a succession of these fluids may be ar-
ranged as indicated in figs. 2, 3, where the outlines between
the poles represent the forms of thin glass troughs, and the let-
ters the solution in them. In fig. 2 we see
that the action on m is the same as that on
m', and the pointing of the two portions is the
same, i. e. equatorial; neither has the action
on m been altered by the power of the poles
having to traverse n, m' and n'; and in fig. 3
we see, that, under like circumstances of the
power, m' points as bismuth and m as iron,
though they are the same solution with each
other and with the former mm' solutions. No
cutting off of power by the media could cause
these changes;—repetitions of position in the
first case, and inversions in the second. All
that could be expected from any such intercep-
tions would be perhaps diminutions of action,
but not inversions of polarity; and every con-
sideration indicates that all the portions of
¹ Phil. Mag. 1846, vol. xxix. p. 254.

m
Fig. 3.
m

m
ዝ
VEZA
DEC. 1854.] Polarity-pointing by differential action.
539
these solutions in the field at once have like polarity, i.e. like
direction of force through them, and like internal condition;
each solution in its complex arrangement being affected exactly
in the same way and degree as if it filled the whole of the mag-
netic field, although in these particular arrangements it sometimes
points like iron, and at other times like bismuth (2362. 2414.).
3316. These motions and pointings of the same or of different
solutions, contain every action and indication which is supposed
to distinguish the contrary polarities of paramagnetic and dia-
magnetic bodies from each other, and the solutions 7 and m in
air repeat exactly the phænomena presented in air by phosphorus
and platinum, which are respectively diamagnetic and paramag-
netic substances. But we know that these actions are due to
the differential result of the masses of the moving or setting
solution and of that (or the air) surrounding it. No structural
or internal polarity, having opposite directions, is necessary to
account for them (2361. 2757.). If, therefore, it is still said
that the solution m has one polarity in 7 and the reverse polarity
in n, that would be to make the polarity depend upon the mass
of m independently of its particles; for it can hardly be supposed
that the particles of m are more affected by the influence upon
them of the surrounding medium (itself under like inductive
action only, and almost insensible as a magnet), than they are
by the dominant magnet ¹. It would be also to make the polarity
of m as much, or more, dependent upon the surrounding medium
than upon the magnetitself;-and it would be, to make the masses
of m and I and even their form the determining cause of the
polarity; which would remove polarity altogether from depend-
ence upon internal molecular condition, and, I think, destroy
the last remains of the usual idea. For my own part, I cannot
conceive that when a little sphere of m in the solution 7 is
attracted upon the approach of a given magnetic pole, and re-
pelled under the action of the same pole when it is in the solu-
tion n, its particles are in the two cases polar in two opposite
I
1 If the polarity of the inner mass of solution is dependent upon that of
the outer, and cannot be affected but through it, then why is not air and
space admitted as being in effective magnetic relation to the bodies sur-
rounded by them? How else could a distant body be acted upon by a
magnet, if the inner solution of sulphate of iron is so acted on? Are we
to assume one mode of action by contiguous masses or particles in one case,
and another through distance in another case?
540
[DEC. 1854.
Points of magnetic philosophy.
directions; or that if for a north magnetic pole it is the near
side of the particles of m when in 7 that assume the south state,
it is the further side which acquires the same state when the
solution is changed for n. Nor can I think that when the
particles of m have the same polar state in both solutions, the
whole, as a mass, can have the opposite states.
3317. These differential results run on in one uninterrupted
course from the extreme of paramagnetic bodies to the extreme
of diamagnetic bodies; and there is no substance within the
series which, in association with those on each side of it, may
not be made to present in itself the appearances and action which
are considered as indicating the opposite polarities of iron and
bismuth. How then is their case, in the one or the other con-
dition, to be distinguished from the assumed polarity conditions
of bismuth or of iron ?-only, I think, by assuming other points
which beg the whole question. In the first place, it must be, or
is assumed, that no magnetic force exists in the space around a
magnet, when it is in a vacuum, it being denied that the power
either crosses or reaches a locality in that space until some ma-
terial substance, as the bismuth or iron, is there. It is assumed
that the space is in a state of magnetic darkness (3305.), an
assumption so large, considering the knowledge we have of natural
powers, and especially of dual forces, that there is none larger in
any part of magnetie or electric science, and is the very point
which of all others should be held in doubt and pursued by ex-
perimental investigation. It is as if one should say, there is no
light or form of light in the space between the sun and the earth
because that space is invisible to the eye. Newton himself durst
not make a like assumption even in the case of gravitation (3305.), ·
but most carefully guards himself and warns others against it,
and Euler¹ seems to follow him in this matter. Such an assump-
tion, however, enables the parties who make it to dismiss the
consideration of differential effects when bodies are placed in a
vacuum, and to divide the bodies into the well-known double
series of paramagnetic and diamagnetic substances. But in the
second place, even then, those who assume the reverse polarity of
diamagnetic bodies, must assume also that the state set up in
them by induction is less favourable to either the exercise or
the transmission of the magnetic force than the original unpo-
Letters, &c. translated. Letter LXVIII., or pp. 260–262.
DEC. 1854.]
541
Time results.
larized state of the bismuth; an assumption which is, I think,
contrary to the natural action and final stable condition into
which the physical forces tend to bring all bodies subject to
them. That a magnet acting on a piece of iron should so deter-
mine and dispose of the forces as to make the magnet and iron
mutually accordant in their action, I can conceive; but that it
should throw the bismuth into a state which would make it repel
the magnet, whereas if unaffected it should be so far favourable
as to be at least indifferent, is what I cannot imagine to myself.
In the third place, those who rest their ideas on magnetic fluids,
must assume that in all diamagnetic cases, and in them only, the
fundamental idea of their mutual action must not only be set
aside but inverted, so that the hypothesis would be at war with
itself; and those who assume that electric currents are the cause
of magnetic effects, would have to give up the law of their in-
ducing action (as far as we know it) in all cases of diamagnetism,
at the very same moment when, if they approached the diamag-
netic bismuth in the form of a spiral to the pole, they would
have a current produced in it according to that law.
Time.
3318. I will venture another thought or two regarding the
condition into which diamagnetic bodies are brought by the act
of magnetic induction, in connexion with the point of time. It
appears, as far as I remember, that all natural forces tend to
produce a state of rest, except in cases where vital or organic
powers are concerned; and that as in life the actions are for ever
progressive, and have respect to a future rather than a present
state (Paget), so all inorganic exertions of force tend to bring
about a stable and permanent condition, having as the result a
state of rest, i. e. a static condition of the powers.
3319. Applying this consideration to the case of bismuth in
the magnetic field, it seems to me more like the truth of nature
that the state assumed by the bismuth should be one more
favourable to the final and static exercise of the power of the
dominant magnet upon it, than that state belonging to the bis-
muth before it had suffered or undergone the induction; exactly
as in soft iron we know that before it has acquired the state
which a dominant magnet can induce upon it, it is not so favour-
able to the final static condition of the powers as it is afterwards.
542
Points of magnetic philosophy. [DEC. 1854.
Now it is very manifest, by numerous forms of experiment, that
time enters as an element into ordinary magnetic and magneto-
electric actions, and there is every reason to expect, into diamag-
netic actions also; and it is also well known that we can take
advantage of this time, and test the state of a piece of iron in
the magnetic field before it has attained its finally induced state,
and afterwards;-as, for instance, by placing it with a helix round
it in the magnetic field and quickly connecting the helix afterwards
with a galvanometer, when a current of electricity in such direc-
tion as to prove the truth of the statement will be obtained. In
other forms of experiment, and with large pieces of iron, the
time which can be so separated or snatched up during the act of
progressive induction will amount to a minute or more. Sup-
posing this could be done in any sensible degree with diamag-
netic bodies, then the following considerations present them-
selves. A globe or bar of bismuth in the magnetic field may
have its states, before and after induction, considered as sepa-
rated by a moment of time; if the induction raises up a state of
polarity the reverse of that of the magnet, then the bismuth
ought to be more favourable to the determination of magnetic
force upon it before the induction than after; whereas if, accord-
ing to my view, the polarity is not reversed, but is the same as
that of the magnet, the metal ought to be more favourable to
the determination of magnetic force upon or through it after
induction than before. Believing this to be an experiment which
would settle the question of reverse polarity, and perhaps the
existence or non-existence of physical lines of magnetic force, I
have made many attempts in various ways, and especially by
alternating motions of cylinders and balls of bismuth between
soft iron magnetic poles furnished with helices, to obtain some
results due to the time of induction, but have been as yet unable
to succeed. I cannot doubt that time is concerned; but it
seems to be so brief in period as to be inappreciable by the means
I have employed.
3320. Professor Thomson has put this matter of time and
polarity in another form. If a globe of bismuth be placed with-
out friction in the middle of the magnetic field, it will not point
or move because of its shape; but if it have reverse polarity, it
will be in a state of unstable equilibrum; and if time be an ele-
ment, then the ball, being once moved on its axis ever so little,
DEC. 1854.] Perpetual motion-dependent dualities.
543
would then have its polarity inclined to the magnetic axis, and
would go on revolving for ever, producing a perpetual motion.
I do not see how this consequence can be avoided, and therefore
cannot admit the principles on which it rests. The idea of a
perpetual motion produced by static force is philosophically illo-
gical and impossible, and so I think is the polarly opposed or
adverse static condition to which I have already referred.
3321. It is not necessary here that I should refer to the
manner in which my view of the lines of magnetic force meet
these cases, for it has been done in former papers (2797. &c.) ;
but I will call the attention of those who like to pursue the sub-
ject, to a true case of reverse polarity in the magnetic field (Ex-
perimental Researches, 3238, fig. 15), and there they will easily
see and comprehend the beginning of the rotation of Professor
Thomson's bismuth globe, and its continuance, if, as supposed,
the polar state represented in the figure could be continually
renewed.
3322. When the north pole of a magnet repels a piece of
bismuth in a vacuum, or makes a bar of it set equatorially, and
is found to produce like actions with many paramagnetic bodies
when surrounded by media a little more paramagnetic than
themselves, and with as many diamagnetic bodies when sur-
rounded by media a little less diamagnetic, it would seem more
cautious in the first instance to inquire how these latter motions
take place, and how it is that parts, which with the paramag-
netics have certainly been brought into a south condition by the
north end of the pole, recede from it; and to apply these results
in the first instance to those obtained with bismuth in a vacuum,
before we assume a total change in principle, and yet an excep-
tional change as to substances, in the general law of magnetic
polarity, without any cause assigned than, or any supporting
facts beyond, the effect in question.
Curved lines of magnetic force-dependence of the dualities.
3323. The representative idea of lines of magnetic force which
I entertain, includes in it the thought of the curvature of these
lines, not as a merely convenient notion making the idea of the
lines more manageable, but as one flowing from and suggested,
if not proved, by the phænomena themselves. It is in this point
of view that I proceed to consider it; and as the proof of the
544
[DEC. 1854.
Points of magnetic philosophy.
curvature is, in respect of principle, in the essential and neces-
sary dependence of the two qualities or parts of a dual force
upon each other (3324. &c.); and in respect of experiment, by
the numerous results supplied during the mutual actions of
magnets and magnetic bodies and the phænomena of moving
conductors (3337. &c.), I will consider each in turn.
3324. There is no known case of one form or part of a dual
power existing otherwise than with, and in dependence on, the
other, which then exists simultaneously to an equivalent, i. e. an
equal, degree. In static electricity, where supposed electric fluids
are considered as being separated from each other, they are in
equal amount (1177.), are ever related to each other (1681.),
often by curved lines of force (1215.), and the existence
of the one electricity without the other, or in the smallest
degree of excess or deficiency, is absolutely impossible (1174.).
In the voltaic battery, or in the electric current produced
in any other way, as by thermo arrangements or inductions,
the current in one part of the circuit is absolutely the same
in amount and in dual character as in another; and in the insu-
lated, unconnected voltaic battery, where the sustaining power
is internal, not the slightest development of the forces, or of
either of them, can occur until circuit is completed, or induction
allowed at the extremities; for if, when there is no circuit, the
induction be prevented, not merely no current, but no stock of
electricity at the battery poles ready to produce a current can be
evolved in the slightest degree. In like mauner I am fully per-
suaded that the northness and southness of magnetism (in what-
ever they may be supposed to consist) cannot exist alone;-nor
without exact proportion to each other;-nor without mutual de-
pendence upon each other;-but that they are subject to the
mutual relation and dependence of all dual force.
3325. Let us consider a hard invariable magnet in space,
fig. 4. If a piece of soft iron, I, be
brought towards it, the N end of the
$
Fig. 4.
N
1
magnet will cause southness in the
near end of the iron and northness in ZZZZZZZZZ
the further end, and this will continue
until the iron is removed, the south-
S n
ness and northness at the two ends or halves of the magnet
having remained all the time unchanged in their equality and
DEC. 1854.] Mutual dependence of the dualities.
545
amount (3223. 3221.). Now to say that the force emanating
from N could act on the iron, producing like and the contrary
force, and then, by removal of the iron, cease to act there or
elsewhere; and then again act on the iron if approached, or any-
thing else, and then cease to act, and so on; would in my mind
be to deny the conservation of force :-and we know that there is
no equivalent action within the magnet, to explain by any alter-
nate excitement and suppression of the dual parts, any sup-
posed appearance and disappearance of the powers at the differ-
ent times; for a helix closely applied round the middle part of
the magnet during the experiment gives no current, and by that
shows that there is no equivalent internal derangement of the
power, when the outer exercise of it may be supposed to change
between active and inert.
3326. Suppose the power of such a magnet to be due to
magnetic N and S fluids; can it be thought that the N parti-
cles can be sometimes exerting their attraction for S particles,
and sometimes not? Would not that be equivalent to the
assumption of suppression, i. e. a destruction of force ?-which
surely cannot be. Such an assumption could be surpassed only
by that which supposes that the N fluid might sometimes at-
tract S and repcl N, and at other times repel S and attract N
fluids (3311. 3312. 3317.).
4327. As to the soft iron under induction (3325.), its dual
magnetic forces do re-enter into their former mutually depend-
ent and mutually satisfying state: but suppose it to be replaced
by steel, and that the magnetisms produced in it do not recom-
bine or disappear on the removal of the dominant magnet, then
on what is their power ultimately turned, if not on each other?
(3257. 3324.). Where is the S power of the steel disposed of
when it is separated from its relation with the N power of the
magnet that evolved it? The case cannot be met except by
affirming the independent existence of the two powers (3329.);
or, admitting the suppression of force, and of either of these forces
the one without the other (3330.); or allowing the mutual de-
pendence of the two polarities of the magnet (3331.).
3328. When the N pole of a magnet (fig. 5) is acting in
free space, its force is sensible around to a certain amount
(114.); when a pice of soft iron, I, is brought near it, much of
its force gathers up upon that iron, but the whole amount of
VOL. III.
2 N
546
[DEC. 1854.
Some points of magnetic philosophy.
Fig. 5.
I
force from and about the N pole is the
same; when an S pole is brought up,
either of another magnet or of itself,
(for the effect is precisely the same),
much of the force exerted upon the
iron is removed from it, and falls
upon the S pole, but the amount of
force about the pole N remains the same; all of which can
be proved experimentally by a helix on the soft iron and loops
carried over the N pole (3218. 3223.). Indeed the way in which
the power of one pole over either iron or bismuth is affected
and diminished by the approximation on the same side of a
contrary pole, is perfectly well known, and there are hundreds
of cases in which the disposition in direction of the magnetic
power can be varied in a great variety of ways, without the
slightest change in the sum of its amount at the source, each of
which gives evidence of the antithetical and inseparable con-
dition of the two forms of force.
3329. As to independent existence of the two powers
(3327.), how is it then that they cannot be shown separately ?
-not even up to the degree which is exhibited, so to say, by
static electricity. There is nothing like a charge of northness
or a charge of southness in any one of the innumerable phæno-
mena presented by magnetism (3341.). The two are just as
closely connected as the two electricities of a voltaic battery;
whether we consider it as giving the current when properly con-
nected, or exhibiting induction at its extremities when uncon-
nected. The difficulty, indeed, is to find a fact which gives one
the least hold for consideration of the thought that the two mag-
netic forces can be separated, or considered apart from each other.
3330. As to the suppression of force (3327.), I conceive that
the creation, annihilation, or suppression of force, and still more
emphatically of one form only of a dual force, is as impossible
as the like of matter. All that is permitted under the general
laws of nature is to displace, remove, and otherwise employ it;
and these conditions are as true of the smallest suppressions of
a force, or part of a force, as of the suppression of the whole. I
may further ask, whether, as it is physically impossible to anni-
hilate or suppress force, it is not also mathematically impossible
to do so, consistently with the law of the conservation of force?
DEC. 1854.]
547
Mutual dependence of the dualities.
3331. If we say that the forces in the cases of removal
(3327.) are disposed of, sometimes in one direction and some-
times in another, but with the preservation of their full and
equivalent amount, then how are we to consider them disposed
of in the case of a cylinder or globular magnet, placed in air
or vacuo, so as to be entirely self-dependent ?-or in the case
of a magnetic sphere placed in an inverted position in the mag-
netic field, so as to be entirely surrounded and enclosed by
magnetic forces having a contrary direction to its own (3321.)
3238.) ?
3332. If we say that the dualities of such a magnet are de-
pendent on each other (which is the third case (3327.)), then
we have to consider how this can be, consistently with the
distant mutual action, either of magnetic fluids or electric
currents, acting in right lines only. Such action must then
be through the body of the magnet (3260.). If we confine our
attention to magnetic fiuids, then the direction of their forces
towards each other through the magnet when it is alone, must be
of the like nature as their direction to approached iron, in which
they are supposed to induce collections of the contrary fluids, or
towards the fluids at the contrary poles of approached equal or
superior magnets; i. e. the two poles of the magnet must be
conceived of as centres of force, sometimes exerting their power
towards each other in a given direction through the body of the
magnet, and at other times exerting them outwardly to external
poles in a direction exactly the contrary. But the currents
which are evolved by the rotation of the magnet, or of discs of
metal combined with it (3119. 3163.), show that the direction
of the force (which is its polarity) is not thus reverse in the
two halves of the case, but is the same within the, magnet as in
the prolongation of direction through and beyond the pole;
and also, that whether the magnet be alone, and therefore sup-
posed to have the polar forces exerted on each other through it,
or be in relation to outer magnets, so as to have this exertion
of force entirely removed from its interior, still it is always the
same having in both cases the same condition, direction, and
amount of power within it (3116.).
3333. If the charged and polar state of the magnet be sup-
posed to depend upon molecular electric currents, held by some
internal condition in a position of parallelism, it is impossible
2 N 2
548
Some points of magnetic philosophy. [DEC. 1854.
that these can act backwards upon each other through the mag-
net in straight lines, so as to put the northness and southness
of the pole in mutual dependence, as they are supposed to be in
relation to external poles, without the currents themselves being
displaced and turned, until the whole magnet is neutralized;
falling back into the undeveloped state, just as a piece of soft
iron falls back. When this return of state happens in soft iron
or steel in any degree, a helix round these shows the induced
currents consequent on such a change; and a loop (3133. 3217.)
shows the differenee when the iron or magnet is polar outwards
and when its state has fallen. No such effects happen with a
hard magnet, when it is alternately left to itself or put in rela-
tion to external poles of other magnets. The body of the mag-
net, and the forces passing through it, remain unchanged,
whether examined by the loop (3223.) or by its own motion,
or that of discs and wires associated with it (3116. &c.). Its
force ever remains the same in quantity and general dirrction.
3334. The case of the steel ring magnet (3283.) is well
known, and the manner in which such a magnet, showing no
external relation, developes strong poles when it is broken. The
phænomena assure us, I think, that when broken the northness
and southness then appearing, cannot, when the pieces are by
themselves, be determined upon each other backward through
the magnet; there is no sufficient reason to suppose such a
thing. And, again, the mutual destruction of highly-charged
linear magnets, such as steel needles, when many of them are
made into a thick, short bundle, shows the same thing; for if
when alone the polar powers are not external, but are deter-
mined upon each other through each individual magnet, they
are as free for a like disposal when the elementary magnets are
associated as when they are separated :-and then there remains.
no sufficient reason to expect a dominant action over each other
superior to that which each has over itself.
3335. It is not to be supposed that the change of force which
occurs when the magnet first acting externally is then made to
act internally or through itself, would be small and unnoticeable.
It should be as great as the whole amount of power which the
magnet can show under the most favourable circumstance; and
the means are abundantly sufficient, by moving wires and discs,
to make that evident in any case which might imply its passing
DEC. 1854.] Mutual dependence of the dualities.
549
through, or being removed out of, the magnet:—so that no
difficulty can occur in that respect, and there remains, therefore,
in my mind, but two suppositions; either the N polar force of
a magnet when taken off from external compensating S polar
force, is not exerted elsewhere as magnetic force at all; or else
it is externally thrown upon and associated with the S polar
force of the same magnet, and so sustained and disposed of, for
the time, in its natural, equivalent, and essential state. If con-
verted into any new form of power, what is that form? where
is it disposed of? by what effects is it recognized? what are
the proofs of its existence? To these inquiries there are no
answers. But if it be directed externally upon the opposite S
pole of the magnet, then all the consequences and foundations
of my hypotheses of magnetic force and its polarity come forth;
and, as I incline to believe, a consistent and satisfactory account
of all magnetic phænomena, short of the idea of the nature of
the magnetic force itself, is supplied.
3336. For if the dual forces of the poles of a magnet in free
space are related to, and dependent upon, each other, and yet
not through the magnet (3331.), then it must be through
the space around. Then space must have a real magnetic re-
lation to the force passing across it, just as it has to the ray of
light passing from an illuminating to an illuminated body.
Then the directions in which the two forces are exerted upon
each other, cannot be in right lines, which must, if they existed,
pass of necessity through the magnet; but in curved lines,
seeing that it is impossible that any but curved lines can hold
the poles in relation to each other through the surrounding space
(3297.)-and if they be curved lines, then I cannot imagine
them to be anything else than physical lines of force; lines fitted
to transfer the power onwards in consistency with its inevitable
dual relation, and in conformity with that direction which ought
as I think, to be properly called polarity. And it further ap-
pears to me, that if we once admit the magnetic relation of a
vacuum, then all the phænomena of paramagnetic and diamag-
netic bodies; of differential polarity and individual polarity; of
solution, needles, crystals and moving conductors, are presented
in a simple mutual relation, without any contradiction of fact or
hypothesis, and in perfect harmony with each other.
3337. I wish to avoid prolonging this paper by a repetition
550
Some points of magnetic philosophy. [DEC. 1854.
of the considerations and reasons already advanced on former
occasions, and therefore will very briefly call to mind the idea
I have put forth, that there are such lines of force in the space
around a magnet; that the mutual dependence of the dualities,
which is essential in the isolated magnet, is thus sustained; and
that bodies in this space produce paramagnetic or diamagnetic
phænomena, according as they favour or oppose the degree of
sustaining power which mere space possesses. That these bodies,
or media as they may be called, have a magnetic relation like
that of space, is easily shown by numerous experimental results ;
but as they have a further relation amongst themselves, depend-
ent upon their relative electro-conducting power,
I think a little time may be usefully employed
in considering how far the consequent results
illustrate the probable condition of space where
Fig. 6.
they are not present. Consider a magnetic pole a a a a
N, fig. 6, placed in relation to an equal mag-
netic pole S so that their powers are mutually
related and sustained, and the space between
.
them, a, a, a, occupied by a vacuum, nitrogen, or some other gas
at magnetic zero (2770. &c.) :-the force exerted by N on S, or
reciprocally, is easily taken cognizance of by spirals, &c. as
regards any change in direction or degree. Then consider the
medium a, a, a, to be all copper or all mercury, still the forces
are undisturbed or consider it part mercury or copper, and
part vacuum or glass, divided either by a line running from S
to N, or along a, a, a, or any other way, still the forces are un-
disturbed; any of these media act exactly like space, or so like
it, we can scarcely trace a difference. Then consider the metal
moving, either as a finely divided stream at a, a, a, or as a
solid globe (of copper) C, fig. 7, revolving rapidly round the line
from N to S; still it is exactly like the vacuum or
indifferent gas or glass, and there is no effect as yet
by which we might distinguish the material medium
from the mere space.
But let the stream of me-
tallic particles be converted into a continuous plate,
and then we know it becomes filled with abundant
currents of electricity; or if we apply the wires of
a galvanometer to the revolving copper globe C,
at the axial and equatorial parts, we can then cause it to
Fig. 7.
DEC. 1854.] Static and dynamic condition of media.
551
develope (by permission of currents) a new effect, and the cur-
rents are sent out most abundantly by the conductors applied.
If the copper globe C be rapidly revolved upon an axis per-
pendicular to the line S N, so strong and influential a me-
dium is it, magnetically considered, that the two poles, N and S,
if free to move, do move in the same direction as the near parts
of the globe; and are absolutely carried away from each other,
in opposition to their mutually attractive force, which tends
strongly all the while to draw them together. Now, how is it
possible to conceive that the copper or mercury could have this
power in the moving state, if it had no relation at all to the
magnetic force in the fixed state? or, that it should have like
power in the compact state, and yet have no relation to the
magnetic force in the divided and moving state? The mere
addition of motion could do nothing, unless there were a prior
static dependence of the magnet and the metal upon each other.
We know very well that the actions in the moving cases involve
the evolution, or a tendency to the evolution, of electric cur-
rents; but that knowledge is further proof that the metals are
in prior relation to the magnetic forces; and as bodies, even
down to aqueous solution, have these electric currents set up in
them under like circumstances, we have full reason to believe
that all bodies when in the magnetic field are in like static re-
lation as the copper when not moving :-and that when motion
was superadded, they would all evolve electric currents, were it
not for their bad electro-conducting powers.
3338. These effects of motion are known to be identical with
those of the moving wire (36. 55.), or those of voltaic in-
duction (6. &c.); and their intensity and power is very well
shown in the force of Elkington's magneto-electric apparatus
and Ruhmkorff's induction coil. Time is concerned in their
production, and Professor Henry has shown us, in some degree,
that when the currents are moving in helices, the magnetic action
across them is for a time cut off or deflected (1730.). These
actions are, in every case, simple; i. e. a line of force in a given
polar direction produces, or tends to produce, in a body moving
across it, whether paramagnetic, neutral, or diamagnetic (3146.
3162.), a current in the like direction; which current must, as
I conceive, be dependent upon a previous like static state. No-
thing in the slightest degree analogous to the supposed oppo-
552
Some points of magnetic philosophy. [DEC. 1854.
sitely polar states of paramagnetic and diamagnetic bodies has
ever been discovered amongst them ;-and it has never been said,
or supposed, as far as I know, that the two actions, i. e. the
magnetic and the magneto-electric, are separate in their essential
nature, or that they are not the consistent and accordant, and I
must add reciprocal, actions of one force.
If
Fig. 8.
N
As
3339. That the copper, &c. are effectual as magnetic media
when in the field, may be stated also thus :—
Let N, fig. 8, be a magnetic pole, and C a
thick disc or short cylinder of copper.
the copper revolve ever so rapidly on its
axis there will be no production of currents
in it; and the magnetic action of N on
other magnets will be the same, as if the metal were quiescent
or even away.
If N recede from C there are then currents in C,
though it be not moving; and though the effect of N upon
other magnets, as far as we know them, is unchanged; yet there
is then a slight attraction between C and the N pole. If N be
made to approach C, the reverse currents and actions occur.
N approaches or recedes more quickly or slowly, the currents
produced, and consequent temporary magnetic state, are higher.
A cylinder electro-magnet will show these effects very well.
The copper has all the time been still, no motion has been
pur-
posely given to it; it has been affected by the approximation and
recesssion of the pole, has passed from one state to another, which
states remain stationary as long as the poles are quiescent, and
it shows every character of a medium affected by the magnetic
force. By expedients the currents in the copper may be allowed
or prevented; but whether they be allowed or not, the state the
copper medium arrives at is the same. If disallowed as the
magnet approaches, but allowed as it recedes, then the current
due to the last change occurs, an effect easily shown with a
magnet and helix; and this seems to prove very distinctly that
the copper within the constant influence of the magnet has a
permanent, static, magnetic condition; and is therefore a mag-
netic medium, having lines of force passing through it. If C
be of bismuth instead of copper, the same currents in the same
direction occur, though in a far smaller degree; and, as it is
believed, only because of deficiency in its conducting power.
3340. There can be no doubt that very much is involved in
DEC. 1854.]
553
Places of weak or no action.
1
these phænomena, of the nature of which we have little or no
knowledge; and the results obtained by Matteucci will probably
lead to developments and discoveries of great importance. He
states that copper, when finely divided, presents very persisting
phænomena, proving its right to be considered as a diamagnetic
body; but that when aggregated, all, or nearly all, its diamag-
netic character disappears. Nothing is known as yet of the
manner in which the mere difference of cohesion or division
can so affect the diamagnetic character. He finds, too, that in
other respects, as in Arago's rotation, particles of matter act in
a manner not to be anticipated from what is at present known
of them as masses; and it is to be hoped and expected that
when these results are enlarged and developed, we shall be able
to form a better judgement of the true physical action of mag-
netism than at present.
or not.
Places of no magnetic action.
3341. The essential relation and dependence of the two mag-
netic dualities is manifested, I think, in a very striking manner,
by the results which occur when we attempt to isolate northness
or southness, by concentrating either of them on one space or
piece of matter, and looking for their presence by effects, either
of tension or any other kind, whether connected with polarity
A soft iron bar, an inch square, 3 or 4 inches long and
rounded at the edges, had thirty-two convolutions of covered
copper wire 0·05 of an inch in diameter put round it, so that
covering the middle part of the bar, chiefly, it could be shifted
if needful a little nearer to one end than the other; such a bar
could be rendered magnetic by an electric
current passed through the wire, and a
degree of adjustment, in the strength of
the N and S extremities, could be effected
by this motion of the iron in its helix.
Having six of these, it was easy to arrange
them with their like poles together, so as to
include a cubical space or chamber, fig. 9;
and in this space I worked by every means
at my disposal. Access to it was easily
Fig. 9.

obtained by a previous removal of a portion of the solid angles
¹ Cours spécial sur l'induction, &c., 1854, pp. 165, 269.
554
[DEC. 1854.
Some-points of magnetic philosophy.
of the ends which were to be brought together, or by withdrawing
the electro-magnets a little the one from the others, and then a
ray of light could be passed into or across it; magnetic needles
or crystals of bismuth could be suspended in it;-a ring helix
could be introduced and rotated there; and the motions of any-
thing within could be observed by the eye outside.
3342. A small magnetic needle hung in the middle of this
space, gave no indication of any magnetic power; near the open
edges and angles vibrations occurred, but they were as nothing
compared to the powerful indications given outside the chamber;
even when the needle was many inches away. A crystal of
bismuth was entirely different. A piece of soft iron hung on a
jointed copper wire within the chamber showed no trace of mag-
netic power, whether examined by the little needle or in any
other manner. Iron filings on a card across the chamber were
not affected in the middle part, but only near the partly open
angles. A ring helix of many convolutions, having its termina-
tions passing out at opposite corners, was connected with a very
sensitive galvanometer and rotated; it showed no trace of induc-
tive action. Numerous other experiments were made, but with
results altogether negative. Attempts (though desperate) were
made to ascertain if any electro-chemical conditions were induced
there, but in vain. Every kind of trial that I could think of,
not merely by tests of a polar character, but of all sorts, were
instituted, but with the same negative result.
3343. It was of course not to be expected that any polar, i. e.
any dually related polar, action could be exerted in this place;
but if the polarities can exist without mutual relation, we might
surely expect some condition, some tonic or static state, in a
chamber thus prepared and surrounded with a high intensity of
magnetic power, acting in great concentration on one particular
spot or substance. But it is not so; and the chamber offers a
space destitute of magnetic action, and free, under the circum-
stances, from magnetic influence. It is the complete analogue
of the space presented within a deep metallic vessel or globe',
when charged with electricity (1174.). There is then no elec-
tricity within, because that necessary connexion and dependence
of the electric duals, which is essential to their nature, cannot
be. In like manner, there is no appearance of magnetic force
¹ Phil. Mag., Oct. 1846, vol. xxix. p. 257, note.
DEC. 1854.]
555
Places of weak or no action.
in the cubical chamber, because the duals are not both there at
once, and one cannot be present without the other.
3344. There are many ways of examining in a more or less
perfect manner these neutral and highly instructive magnetic
places. A cavity in the end of an electro-magnetic core or a
permanent magnet will present similar phænomena, and in some
respects even more perfectly; for though a trace of power will
perhaps appear at the bottom of the cavity, the sum or amount,
as compared to the sum of power at the end of the magnet, will
show how complete the analogy between this space and the in-
terior of a metallic vessel charged with positive or negative elec-
tricity is. A cylinder of soft iron, 9 inches in length and 1·6
in diameter, had a chamber 0.9 in diameter and 1 inch in
depth formed in one extremity concentric with the cylinder;
and being placed in a powerful helix of thick copper wire, and
associated with a Grove's battery of ten pair of plates, was ready
for experiment :-a like chambered magnet can be prepared by
putting a proper iron ring against the end of any electro- or
ordinary magnet, and will show the phænomena I am about to
describe. A piece of soft iron, not more than 0·3 of an inch in
length or thickness, held at the end of a copper wire and brought
near the outer edge of the excited magnet pole, will be very
strongly attracted; but if it be applied to the bottom of the
chamber it will present no such effect, but be quite indifferent.
If applied about the sides of the chamber, it will indicate no
effect until it approaches the mouth. If the magnet be placed
horizontally, and a piece of card-board be cut, so that it can
enter the chamber and represent a horizontal section of its
cavity; and, being sprinkled over with clean iron filings, is then
put into its position and the magnet excited for a moment that
it may develope its power over the chamber and filings and give
them their indicative position; it will be found that only those
near the mouth have been driven into a new position (about the
outside angles of the pole), and that four-fifths of those upon
the surface of the card within the chamber have been left un-
affected, unmoved. If the chamber be filled with iron filings,
closed with a card, placed in a vertical position with the aperture
downward, and the magnet be then excited and the card re-
moved, the filings will fall out; as they come out they will be
caught away, and form a fine fringe round the external angles
556
[DEC. 1854.
Some points of magnetic philosophy.
of the pole, but not one will remain at the bottom of the chamber,
or even anywhere within the chamber, except near to its external
edge. Yet, if a piece of iron long enough to reach out of the
chamber, as a nail 2, 3, or 4 inches long, touch the bottom of
the chamber, it is strongly attracted and held there, and will
support a weight of several ounces, though prevented from
touching the chamber anywhere else by a card with a hole in it
placed over the mouth.
3345. If a small magnetic needle, about 0·1 of an inch long,
be brought towards this excited magnet, it is almost unmanage-
able by reason of the force exerted upon it; but, as soon as it
has entered the chamber, the power rapidly diminishes, and at
the bottom the needle is scarcely, if at all, affected.
3346. If, instead of the core and chamber described, an iron
tube of sufficient thickness of metal (as part of a gun-barrel) be
employed, then like effects occur. If the magnetic needle be
introduced, it ceases to be acted upon when about 1.5 inch
within the tube. If the tube be more or less filled with iron
filings, and then be excited and held vertical, they will all pour
out and fall away, except those which are retained at the external
edges. Yet, if a long nail or iron rod be introduced, so as to be
partly out of the cylinder, then it will be strongly attracted at the
internal point, where it touches the iron of the tube core.
Fig. 10.
N
N
N
N
3347. The realization of like effects by grouping together the
poles of ordinary magnets gives most interesting results. I have
four very hard steel magnets, each 6 inches in length, 1 inch in
breadth, and 0.4 nearly in thickness.
When the four like poles are put
together, fig. 10, they form a flat
square chamber in the same plane as
that of the magnets. If a piece of
stiff paper, the size of this chamber,
be raised on a block 0·2 of an inch
high, then sprinkled over with iron
filings, and the magnets afterwards approached regularly until
the square chamber is formed, a little tapping on the card will
then arrange the filings in lines from the sides of the square
chamber to the centre. The filings show at once the direction
of the lines of force in this median plane, and their greater
abundance at the middle of each pole than at the re-entering

DEC. 1854.]
557
Places of weak or no action.
angles; and if the filings be then removed and the indication of
the course of the lines be followed out by a small magnetic
needle, it will be found that the lines rise upwards from this plane
above, and descend from it below, and then turn back upon their
course in the free space over and beneath the arrangement
towards the S poles of the different magnets. The condition
will be understood in a moment, by considering the sphondyloids
of power belonging to each magnet (3271.), and the manner in
which they are associated when the four like poles come together.
3348. When the magnets are turned edges upwards, they
form a vertical chamber 1 inch high and
only 0.4 of an inch in width, and now
phænomena like those just described occur,
but only near the entrances to the chamber;
as the little needle proceeds into the en-
closed space, the power of the magnets be-
comes less and less, and at the middle of
the chamber scarcely a trace remains; that
place being, like the closed chamber, formed with six poles (3341.),
or like the bottom of a chamber formed in the end of a magnetic
pole, a neutral place, or place of no magnetic action.
Fig. 11.

N
N
3349. The transition by degrees, from a pointed conical pole
to an enclosed chamber, is, from the results described, very evi-
dent; and so also is their connexion with those belonging to the
numerous neutral places produced under ordinary circumstances
(3234. figs. 6, 10, 11, 15). Not the slightest difficuty or hesi-
tation occurs, when these results are read or considered by the
principle of representative lines of force; all the variation in
the strength of the magnetic force and in the direction appear
at once. But the great point is to observe how they all concur
in showing the necessity of the complete and equivalent dual
relation of the magnetic forces. When that is diminished or
interfered with in any degree, in the same proportion does the
power as a whole become dimished; until, at last, it absolutely
disappears from a given place, though energies of the strongest
kind are directing the force on to that spot, supposing that one
of the dual elements could exist in any degree without, or inde-
pendent of, the other.
3350. When formerly working with bismuth and magnets, I
described several results (2298. 2487. 2491.) due to the principle
558
Some points of magnetic philosophy. [DEC. 1854.
Fig. 12:
of neutral magnetic places, more or less developed. If a sphere
or cube of bismuth be delicately suspended by a vertical suspen-
sion or on a torsion balance, and an N pole be brought
towards it, fig. 12, the bismuth will be re-
pellled and the suspension deflected :----if a
second N' pole be brought up, as in the
figure, the bismuth will be less repelled by N
than before, will return towards it, and N' will
also seem to attract it, for on approaching
the bismuth will tend to go into the angle
formed by N and N'. If a third pole, N", be
N
N'
brought up on the opposite side, the bismuth will then seem to
be attracted by it, and by the first pole, and will, in fact, return
very nearly into the position it would have if all the magnets
were away. I thought at one time that magnetic structure, given
by the second north pole N' to the bismuth, might produce the
approximation of it to N, and if so, that this would be neutralized
by the action of a like pole N" on the opposite side, and so the
approximation of the bismuth (if due to such a cause) be pre-
vented. On the contrary, however, such a pole increased it;
and a moment's consideration, by showing that the three poles
form a chamber of diminished or no action (3341. 3347.), shows
also that such ought to be the case. All the movements of the
bismuth are the result of the tendency which it has to pass
from stronger to weaker places of magnetic action (2418.); and
in the present case they show that weakened place, which in a
higher degree would be a place of no magnetic force.
The moving conductor.
3351. I wish to make a few further remarks (3336. 3337.)
upon the value of the moving conductor, as a means of investi-
gation in magnetical science. It will be sufficient to refer to
former papers for a statement of the principles, the power,
and the certainty of its indications (3156. 3172. 3176. 3270.).
At present, I desire to apply it in a direct form of experi-
ment, to the supposed contrary polarities of iron and bismuth
(3309.).
3352. Four metallic spheres of copper, bismuth, soft iron, and
hard steel, 0.8 of an inch in diameter, have been prepared; each
has a copper axis carrying a small wooden pulley, so that when
DEC. 1854.] Moving globes of copper, bismuth, iron, steel. 559
in its supporting frame, rotation, more or less rapid, can be given
to it by the band of a multiplying wheel; each also has a thin
copper ring driven tightly on to it at the equator, which, being
grooved, serves to retain a galvanometer wire pressed against
that part during the revolution of the globe; the other wire
meanwhile being held against the copper axis. These globes, in
their frame, could be placed one by one in the magnetic field of
a powerful permanent Logeman
magnet, so as to be subject to
the magnetic force, fig. 13; and
then rotated, and the currents
of electricity induced in them
carried to galvanometers. Two
such instruments were employed,
one, a Ruhmkorff's, with fine
Fig. 13.

O
wire (2651.), the other with a thick wire of only four revolutions
(3178.). The latter was the best, but both gave good indications.
The position of all thing concerned was preserved undisturbed
during the experiments, so that it will not be necessary to do
more than to describe a standard effect, and afterwards refer
other effects to it. This standard may be taken from the current
indicated when the copper globe was in the magnetic field; and
it was such, when the upper part of the globe moved westward,
as to send the south ends of the galvanometer needles to the
west also: eight or ten revolutions of the globe would cause the
needles to pass through 80° or 90°.
3353. The soft iron sphere was placed in the magnetic field;
it was so good in character as to retain very slight traces of
magnetism when taken out again. Being revolved, it gave a
current of electricity, the same in direction as that of the
standard or copper ball. It is easy to understand, that if the
globe be moved parallel to itself, but away from the magnet, in
a line perpendicular to the magnetic axis (as into the dotted
position, 3352. fig. 13), it will pass through places of weaker
magnetic action. Under such changes of place, the induced
current was weaker or stronger, according to the distance, but
always in the same direction. Assuming that the rotating metal
supplies a true indication of the polarity or direction of the
magnetic force (3077.), the results show that the polarity
of the force which induces these currents and which is the
560
Some points of magnetic philosophy. [Dec. 1854.
magnetic force of the dominant magnet, is the same both in the
copper and in the iron. Other cases of the current from revolving
iron may be referred to in the Exp. Res. (3162.).
3354. The bismuth globe was placed in the magnetic field.
If made to revolve much, with the galvanometer wire press-
ing against the copper equator (3352.), the latter became
warm by friction, and a permanent thermo-current was pro-
duced this has been considered on a former occasion (3168.).
Its effect is easily eliminated by revolving the globe a given
number of times in opposite directions, observing the two
deflections, adding them together, and taking the half of the
sum for the amount of induced current in either one direction
or the other; for as the thermo-current is added on the one side
and subtracted on the other, such a process gives the real
amount of the induced current. When, however, the bismuth
sphere is revolved only five or ten times, the thermo-effect is so
small as to make the galvanometer deflection very little more in
one direction than in the other. When due attention was given,
the rotation of the bismuth sphere produced an induced current
in precisely the same direction as those obtained with the
copper and iron; and so far, therefore, it indicated precisely
the same direction of polarity for the magnetic force then acting
upon and in it.
3355. The hard steel sphere, having been previously examined
by a small needle and found to be unmagnetized, was placed in
the magnetic field. It was then revolved, and gave an induced
magneto-electric current in the same direction as the former
currents. Being removed and again examined by the magnetic
needle, it was found not to have received any sensible charge of
magnetism.
3356. So these four metal globes indicate like polarity of the
magnetic force, acting upon and within them, when examined
thus by the magneto-electric current due to movement across the
lines of force. By researches described elsewhere, it is known
that all metals, and all bodies which are sufficiently electro-con-
ductors, down even to aqueous fluids, give the same direction of
the magneto-electric current :-it is never reversed without re-
version of the polarity, and reversion of the polarity always re-
verses the current induced.
3357. The hard steel sphere was now made a magnet, and
DEC. 1854.]
561
Spherical magnet and sphere of bismuth.
•
though not of good shape to retain magnetism, yet because of
its hardness it was able to sustain being placed in the magnetic
field, in a position the reverse of the polarity there, and yet retained
its own polarity; for when taken out and examined by a magnetic
needle, the polarity was found to be the same as before. Such
being the case, it seemed to me that this magnet might be em-
ployed to represent, according to the view of those who conceive
that iron and bismuth are polarized in opposite directions in the
magnetic field, both iron and bismuth; inasmuch as it could be
placed in the field in that condition of polarity, which these are
supposed respectively to acquire there. The globe magnet was
therefore placed in the magnetic field in a position conformable
to that of the dominant magnet, i. e. with its N pole towards
the S pole of the magnet, &c.; and being rotated, it gave an
induced magneto-electric current like that of the standard and
of iron (3352. 3353.). The dominant magnet was then with-
drawn to a distance (3353.) and the globe rotated by itself; it
gave, as it ought to do, the same current as before; for it, by
its coercitive force, retains permanently that state of polarity,
which the iron could receive only temporarily whilst in the mag-
netic field: being now turned 180° in a horizontal direction,
the globe magnet was reversed as regarded the dominant magnet
(the latter being, however, still at a distance), and now the globe
magnet gave a current the reverse of the former, or of the
standard current; and yet a very consistent current in relation
to its own polarity.
3358. The dominant magnet was now gradually brought up,
and its effect on the reversed globe magnet observed. The cur-
rent from the latter became less and less, and at last was in-
verted, becoming like that of the standard current; nor can that
be wondered at, when it is considered that the dominant magnet
was the largest supplied by Logeman to the Great Exhibition,
and able to sustain a weight of 430 pounds, and the sphere
magnet only 0.8 of an inch in diameter, and very imperfectly
hardened in the interior. But when the dominant magnet was
withdrawn a little, a place was soon found for the globe magnet,
where its rotation in either direction produced no current at all.
Outside of this place, the rotated sphere gave a current, the
reverse of that of the standard; whilst the iron and bismuth
spheres in the same place, gave currents alike in kind and the
VOL. III.
20
562
[DEC. 1854.
Points of magnetic philosophy.
same as that of the standard. In this region, therefore (and it
is like the whole of the magnetic field of many inferior yet very
powerful magnets), if we represent bismuth by a magnet,
reversely polar, as bismuth is supposed to be, we obtain induced
magneto-electric currents, not like those of bismuth, but the
contrary; and if we turn the representative magnet round, so
as to give it the position in which it yields currents like those
of the bismuth, then its polarity contradicts, or is the reverse
of the assumed polarity of the bismuth.
3359. Now until the polarity or direction of the magnetic
force which determines the course of the induced magneto-elec-
tric currents produced in every moving conductor, is distin-
guished and separated from the polarity or direction which
causes movement amongst bodies subjected to the same force,
how can these phænomena be accounted for by the supposition
that the bismuth sphere is in the same polar condition as the
reversed globe magnet? The reversed magnet is, in fact, the
contrary to bismuth and to iron;-then bismuth and iron must
be the same. The direct magnet is the same as the bismuth, in
that polarity which induces a current ;-then the magnet and
the bismuth are the same. How easily all these effects present
themselves in a consistent form, if read by the principle of
representative lines of force! The reversed globe magnet at a
distance from the dominant, shows, in revolving, the effect of
the lines of force within it (3116.); as the magnet is ap-
proached, its external sphondyloid of power is compressed
inwards (3238. fig. 15), and at last the magnet is self-contained;
then showing the equalization of its own powers, and as yet the
absence from within it of any of the powers of the chief magnet;
so that it gives no induced currents, though in a place where
bismuth and iron would give them freely. Within that
distance the effect of the superior and overpowering force of
the great magnet appears (3358.), which, though it can take
partial possession of the little magnet, still, when removed,
suffers the force of the latter to develope itself again, and
present the same series of phænomena as before.
3360. Van Rees admits, I believe, that the moving wire
shows truly the presence, direction, and nature of the magnetic
force or forces; and it is very important to know that the set-
ting of a magnetic needle, or crystal of bismuth, and the produc-
DEC. 1854.]
563
Polarity, and the induced electric current.
tion of a current of electricity in a moving conductor, are like
correlative and consequent effects of the magnetic force; the
power of producing one or the other effect being rigidly the same.
Philosophers should either agree or differ distinctly on this point;
so that if they differ, they may distinguish clearly the physical
separation of the phænomena; which, if established, must lead
to new and important discoveries. The polarity direction which
the moving conductor makes manifest, whether that conductor
be one of the paramagnetic or diamagnetic bodies themselves, or
whether it be a conductor moving amongst them, either by itself
or with them, is always the same. The electric current pro-
duced never indicates a change in the direction of the polarity,
from that belonging to the first source or seat of the power;
whether it be a magnet, a solenoid, or of any other nature; the
only difference being in the strength of the electric current
produced, which difference is directly referable to the electro-
conducting power (3143. 3152. 3163.). If such be the natural
truth, how can the two modes of indication ever give opposite
results? If opposite results seem to appear, and only occa-
sionally, is it that mode of induction which gives one consistent
result that we should doubt, or that which seems to be incon-
sistent with itself? especially when similar contrary phænomena
in abundance are known to be produced by bodies having
like polarity (3316.), and when excellent physical reasons,
founded on differential action, offer themselves for their expli-
cation. There is sufficient reason to admit, that the mag-
netic needle cannot be always a true direct indicator of the
amount or the direction of magnetic action (2868. 2870. 3156.
3293.). Should we not therefore, in respect of the above pha-
nomena, rather conclude, for the time, that the simple and uni-
form results of the one mode of action, are the true indication;
and that where, in the other mode, the phænomena are reversed
or doubled, a part of them are compound in their nature?
may, in conclusion, remark, that the effects of motion and those
produced in the action of magnetism on light, are never reversed
in any case, whatever the medium in which they are observed;
both point to one direction of polarity only, namely that of the
dominant source of magnetism.
I
3361. I will bring these imperfect observations to an end, by
a very brief statement of what I suppose to be the condition of
202
564
[DEC. 1854.
Points of magnetic philosophy.
a magnet; and by a disclaimer, as to anything like conviction on
all points of that which I set forth as a supposition tending to
lead to inquiry. Contemplating a bar magnet by itself, I see
in it a source of dual power. I believe its dualities are essen-
tially related to each other, and cannot exist but by that rela-
tion. I think that though related through the magnet by sus-
taining power, they are not so related by discharging or inducing
power, a power equal in amount to the coercitive or sustaining
power. The relation externally appears to me to be through
the space around the magnet; in which space a sphondyloid of
power is present consisting of closed curves of magnetic force.
That the space is not magnetically dark (3305.) appears to me
by this; that when bodies occupy that space, having like rela-
tion by known phænomena to the power as the space has, as
copper, mercury, &c., they produce magneto-electric currents
when moved. When bodies (media) occupy the space around
the magnet, they modify its capability of transmitting and rela-
ting the dual forces of the magnet, and as they increase or
diminish that capability, are paramagnetic or diamagnetic in
their nature; giving rise to the phænomena which come under
the term of magnetic conduction (2797). The same magnet
can hold different charges, as the medium connecting its poles
varies; and so one, fully charged with a good medium, as iron
between its poles, falls in power when the iron is replaced by
air, or space, or bismuth. Corresponding effects occur with
longer or shorter magnets (3290.), or with magnets made thick
by adding many sideways together (3287.). The medium about
a magnet may be mixed in its nature, and then more dual
power is disposed of through the better conductor than the worse,
but the whole amount of power remains unchanged. The powers
and utility of the media, and of space itself, fail, if the dual force
or polar action be interrupted. The magnet could not exist with-
out a surrounding medium or space, and would be extinguished
if deprived of it, and is extinguished, if the space be occupied ad-
versely by the dual power of a dominant magnet of sufficient
force. The polarity of each line of force is in the same direction
throughout the whole of its closed course. Pointing in one direc-
tion or another, is a differential action due to the convergence or
divergence of the lines of force upon the substance acted on, accord-
ing as it is a better or a worse conductor of the magnetic force.
DEC. 1854.]
565
Difficulties—reservations.
3362. But though such is my view, I put it forth with all
the reservation made on former occasions (3244. 3299.). I
do not pretend to explain all points of difficulty. I have no
clear idea of the physical condition constituting the charged
magnetic state; i. e. the state of the source of magnetic
power-or of the coercitivity by which that state is either
resisted in its attainment, or sustained in its permanent condi-
tion; for the hypotheses as yet put forth give no satisfaction
to my
mind. I profess rather to point out the difficulties in
the way of the views, which are at present somewhat too easily
accepted, and to shake men's minds from their habitual trust in
them; for, next to developing and expounding, that appears to
me the most useful and effectual way of really advancing the
subject:—it is better to be aware, or even to suspect, we are
wrong, than to be unconsciously or easily led to accept an error
as right.
Royal Institution,
20 Dec. 1854.
566
On some Points of Magnetic Philosophy¹.
+
THE magnetic and electric forms of power, being dual in their
character, and also able to act at a distance, will probably aid
greatly in the development of the nature of physical force
generally; and if (as I believe) the dualities are essential to
the forces, are always equal and equivalent to each other, and
are so mutually dependent, that one cannot appear, or even
exist without the other, the proof of the truth of such condi-
tions would lead to many consequences of the highest import-
ance to the philosophy of force generally. A few brief
experiments with the electric power quickly place the dual
cases before the contemplative mind. Thus, if a metallic
vessel, as an ice-pail, be insulated and connected with a
delicate gold-leaf electrometer, or other like instrument, and
then an insulated metallic globe, half the diameter of the ice-
pail, be charged with positive electricity and placed in the
middle of the pail, the latter being for the moment uninsu-
lated by a touch outside, and then left insulated again, the
whole system will show no signs of electricity externally, nor
will the electrometer be affected; but a carrier applied to the
ball within the vessel will bring away from it positive electri-
city, showing its particular state of charge; or being applied
to the lower inside surface of the vessel will bring away
negative electricity, proving that it has the contrary state: or
the duality may be proved by withdrawing the ball, when the
vessel will show itself negative by the electrometer, and the
ball will be found positive. That these dualities are equal, is
further shown by replacing the ball within the vessel, obser-
ving the electrometer, bringing the ball and vessel in contact,
and again observing the electrometer, which will remain
unchanged; and finally withdrawing the ball, which comes
away perfectly discharged, and leaves the vessel externally in
its unchanged and previous state. So the electric dualities
are equal, equivalent, and mutually sustained. To show that
one cannot exist alone, insulate the metallic vessel, charge it
strongly by contact with the machine or a Leyden jar, and
¹ Proceedings of the Royal Institution, January 19, 1855.
JAN. 1855.]
567
Magnetic dualities-never separated.
then dip the insulated ball into it; and after touching the
bottom of the vessel with the ball, remove it, without
touching the sides: it would be found absolutely free from
charge, whatever its previous state may have been; for none
but a single state can exist at the bottom of such a metallic
vessel; and a single state, i. e. an unrelated duality, cannot
exist alone.
The corresponding dualities, i. e. the northness and the
southness, of the magnetic force are well known. For the
purpose of insulating, if possible, one of these, and separating
it in any degree from the other, numerous experiments have
been made. Thus six equal electro-magnets, formed of square
bars, were put together in the direction of three lines perpen-
dicular to each other, so that their inner ends, being all alike
in polarity, might enclose a cubical space and produce an
experimental chamber. When excited, these magnets were
very powerful in the outer direction, as was found by nails,
filings, spirals, and needles; but within the chamber, walled
in on every side by intense north poles, there was no power
of any kind filings were not arranged; small needles not
affected, except as they by their own inducing powers caused
arrangements of the force within; revolving wire helices pro-
duced no currents; the chamber was a place of no magnetic
action. Ordinary magnetic poles of like nature produced
corresponding results. A single pole presented its usual
character, attracting iron, repelling bismuth; a like pole, at
right angles to it, formed a re-entering angle, and there a
weak place of magnetic action was caused; iron was attracted
from it to the prominent corners; bismuth moved up into it;
and a third like pole on the opposite side made the place of
weak force still weaker and larger; another pole or two made
it very weak; six poles brought it to the condition above
described. Even four poles, put with their longer edges
together, produced a lengthened chamber with two entrances;
and a little needle being carried in at either entrance passed
rapidly through spaces of weaker and weaker force, and found
a part in the middle where magnetic action was not sensible.
Other very interesting results were obtained by making
chambers in the polar extremities of electro-magnets. A
cylinder magnet, whose core was 1.5 inch in diameter, had
568
Points of magnetic philosophy. [JAN. 1855.
a concentric cylindrical chamber formed in the end, 0·7 in
diameter, and 1.3 inch deep. When iron filings were
brought near this excited pole, they clung around the outside,
but none entered the cavity, except a very few near the outer
edge. When they were purposely placed inside on a card they
were quite indifferent to the excited pole, except that those near
the mouth of the chamber moved out and were attracted to
the outer edges. A piece of soft iron at the end of a copper
wire was strongly attracted by the outer parts of the pole,
but unaffected within. When the chamber was filled with
iron filings and inverted, the magnet being excited, all those
from the bottom and interior of the chamber fell out, many,
however, being caught up by the outer parts of the pole. If
pieces of iron, successively increasing from the size of a filing
to a nail, a spike, and so on to a long bar, were brought into
contact with the same point at the bottom of the inverted
chamber, though the filing could not be held by attraction,
nor the smaller pieces of iron, yet as soon as those were
employed which reached to the level of the chamber mouth,
or beyond it, attraction manifested itself; and with the larger
pieces it rose so high, that a bar of some pounds weight could
be held against the very spot that was not sufficient to retain
an iron filing.
These and many other results prove experimentally, that
the magnetic dualities cannot appear alone; and that when
they are developed they are in equal proportions and essen-
tially connected. For if not essentially connected, how could
a magnet exist alone? Its power, evident when other
magnets, or iron, or bismuth is near it, must, upon their
removal, then take up some other form, or exist without
action: the first has never been shown or even suspected;
the second is an impossibility, being inconsistent with the
conservation of force. But if the dualities of a single magnet
are thrown upon each other, and so become mutually related,
is that in right lines through the magnet, or in curved lines
through the space around? That it is not in right lines
through the magnet (it being a straight bar or sphere) is
shown by this, that the proper means as a helix round the
magnet, shows that the internal disposition of the force
(coercitive or other) is not affected when the magnet is exert-
JAN. 1855.] Polarity of bismuth, iron, steel, &c.
569
ing its power on other magnets, or when left to itself (Expe-
rimental Researches, 3119. 3121. 3215. &c.); and like means
show that the external disposition of the force is so affected:
so that the force in right lines through the magnet does not
change under the circumstances, whilst the force in external
(and necessarily) curved lines does.
The polarity of bismuth or phosphorus in the magnetic
field is one point amongst many others essentially dependent
upon, and highly illustrative of the nature of, the magnetic
force. The assumption that they have a polarity the reverse
of that of paramagnetic bodies involves the consequence, that
northness does not always repel northness or attract southness;
or else leads to the assumption that there are two northnesses
and two southnesses, and that these sometimes associate in
pairs one way, and at other times in the contrary way. But
leaving the assumptions and reverting to experiment, it was
hoped that a forcible imitation of the imagined state of
bismuth in the magnetic field, might illustrate its real state,
and, for this purpose, recourse was had to the indications
given by a moving conductor. Four spheres of copper, iron,
bismuth, and hard steel have been prepared, and rotated upon
an axis coincident with the magnetic axis of a powerful horse-
shoe magnet; each sphere has a ring of copper fixed on it as an
equator, and the ends of a galvanometer wire were brought into
contact with the axis and the equator of the revolving globe.
Under these circumstances, the electric current produced in
the moving globe was conveyed to the galvanometer, and
became the indicator of the magnetic polarity of the spheres;
the direction of rotation, and the poles of the magnet, being
in all cases the same. When the copper sphere, as a
standard, was revolved, deflection at the galvanometer
occurred in a certain direction. When the iron sphere
replaced the copper and was revolved, the deflection at the
galvanometer was the same. When the bismuth sphere was
employed, the deflection was still the same:—and it still
remained the same when the steel sphere was rotated in the
magnetic field. Hence, by this effect, which I believe to be
a truthful and unvarying indication of polarity, the state of
all the spheres was the same, and therefore the polarity of
the magnetic force in the iron, copper, and bismuth, in every
570
[JAN. 1855.
Points of magnetic philosophy.
case alike. (Experimental Researches, 3164. &c.) The steel
sphere was then magnetized in the direction of its axis, and
was found to be so hard as to retain its own magnetic state
when in a reverse direction between the poles of the domi-
nant magnet, for upon its removal its magnetism remained
unchanged. Experiments were then made in a selected posi-
tion, where the dominant magnetic force was not too strong
(a magnet able to lift 430 lbs. was used)-and it was found
that when the steel magnet was placed in accordance, i. e.
with its north pole opposite the south pole of the dominant
magnet, the deflection was in the same direction as with the
bismuth sphere; but when it was changed so as to be in the
magnetic condition assigned by some to bismuth (i. e. with
reversed polarities), it then differed from bismuth, producing
the contrary deflection. For a further account of these con-
siderations and investigations, a paper may be referred to,
which will appear in the Philosophical Magazine¹.
It is, probably, of great importance that our thoughts
should be stirred up at this time to a reconsideration of the
general nature of physical force, and especially to those forms
of it which are concerned in actions at a distance. These are,
by the dual powers, connected very intimately with those
which occur at insensible distances; and it is to be expected
that the progress which physical science has made in latter
times will enable us to approach this deep and difficult subject
with far more advantage than any possessed by philosophers
at former periods. At present we are accustomed to admit
action at sensible distances, as of one magnet upon another,
or of the sun upon the earth, as if such admission were itself
a perfect answer to any inquiry into the nature of the physical
means which cause distant bodies to affect each other; and
the man who hesitates to admit the sufficiency of the answer,
or of the assumption on which it rests, and asks for a more
satisfactory account, runs some risk of appearing ridiculous
or ignorant before the world of science. Yet Newton, who
did more than any other man in demonstrating the law of
action of distant bodies, including amongst such the sun and
Saturn, which are 900 millions of miles apart, did not leave
the subject without recording his well-considered judgement,
¹ See ante, p. 528; or Philosophical Magazine, 1855, vol. ix. p. 81.
JAN. 1855.]
571
Gravitation—its nature considered.
that the mere attraction of distant portions of matter was not
a sufficient or satisfactory thought for a philosopher. That
gravity should be innate, inherent, and essential to matter,
so that one body may act upon another at a distance through
a vacuum, without the mediation of anything else, by and
through which their action and force may be conveyed from
one to another, is, he says, to him a great absurdity. Gravity
must be caused by an agent, acting constantly according to
certain laws; but whether this agent be material or immaterial
he leaves to the consideration of his readers. This is the
onward-looking thought of one, who by his knowledge and
like quality of mind, saw in the diamond an unctuous sub-
stance coagulated, when as yet it was known but as a trans-
parent stone, and foretold the presence of a combustible
substance in water a century before water was decomposed
or hydrogen discovered; and I cannot help believing that
the time is near at hand, when his thought regarding gravity
will produce fruit :—and, with that impression, I shall venture
a few considerations upon what appears to me the insuffi-
ciency of the usually accepted notions of gravity, and of those
forces generally, which are supposed to act at a distance,
having respect to the modern and philosophic view of the
conservation and indestructibility of force.
The notion of the gravitating force is, with those who
admit Newton's law, but go with him no further, that matter
attracts matter with a strength which is inversely as the
square of the distance. Consider, then, a mass of matter (or
a particle), for which present purpose the sun will serve, and
consider a globe like one of the planets, as our earth, either
created or taken from distant space and placed near the sun
as our earth is ;-the attraction of gravity is then exerted,
and we say that the sun attracts the earth, and also that the
earth attracts the sun. But if the sun attracts the earth, that
force of attraction must either arise because of the presence of
the earth near the sun; or it must have pre-existed in the
sun when the earth was not there. If we consider the first
case, I think it will be exceedingly difficult to conceive that
the sudden presence of the earth, 95 millions of miles from
the sun, and having no previous physical connexion with it,
nor any physical connexion caused by the mere circumstance
572
[JAN. 1855.
Points of magnetic philosophy.
of juxtaposition, should be able to raise up in the sun a power
having no previous existence. As respects gravity, the earth
must be considered as inert, previously, as the sun; and can
have no more inducing or affecting power over the sun than
the sun over it: both are assumed to be without power in the
beginning of the case; how then can that power arise by
their mere approximation or coexistence? That
That a body
without force should raise up force in a body at a distance
from it, is too hard to imagine; but it is harder still, if that
can be possible, to accept the idea when we consider that it
includes the creation of force. Force may be opposed by
force, may be diverted, directed partially or exclusively, may
even be converted, as far as we understand the matter, dis-
appearing in one form to reappear in another; but it cannot
be created or annihilated, or truly suspended, i. e. rendered
existent without action or without its equivalent action. The
conservation of power is now a thought deeply impressed
upon the minds of philosophic men; and I think that, as a
body, they admit that the creation or annihilation of force is
equally impossible with the creation or annihilation of matter.
But if we conceive the sun existing alone in space, exerting
no force of gravitation exterior to it; and then conceive
another sphere in space having like conditions, and that the
two are brought towards each other; if we assume, that by
their mutual presence each causes the other to act,—this is to
assume not merely a creation of power, but a double creation,
for both are supposed to rise from a previously inert to a
powerful state. On their dissociation they, by the assump-
tion, pass into the powerless state again, and this would be
equivalent to the annihilation of force. It will be easily
understood, that the case of the sun or the earth, or of any
one of two or more acting bodies, is reciprocal;—and also
that the variation of attraction, with any degree of approach
or separation of the bodies, involves the same result of creation
or annihilation of power as the creation or annihilation (which
latter is only the total removal) of either of the acting bodies
would do.
Such, I think, must be the character of the conclusion, if
it be supposed that the attraction of the sun upon the earth
arises because of the presence of the earth, and the attraction
JAN. 1855.]
573
Gravitation-its nature considered.
of the earth upon the sun, because of the presence of the
sun; there remains the case of the power, or the efficient
source of the power, having pre-existed in the sun (or the
earth) before the earth (or the sun) was in presence. In the
latter view it appears to me that, consistently with the con-
servation of force, one of three sub-cases must occur: either
the gravitating force of the sun, when directed upon the
earth, must be removed in an equivalent degree from some
other bodies, and when taken off from the earth (by the
disappearance of the latter) be disposed of on some other
bodies ;—or else it must take up some new form of power when
it ceases to be gravitation, and consume some other form of
power when it is developed as gravitation; or else it must be
always existing around the sun through infinite space. The first
sub-case is not imagined by the usual hypothesis of gravita-
tion, and will hardly be supposed probable; for, if it were
true, it is scarcely possible that the effects should not have
been observed by astronomers, when considering the motions
of the planets in different positions with respect to each other
and the sun. Moreover, gravitation is not assumed to be a
dual power, and in them only as yet have such removals been
observed by experiment or conceived by the mind. The
second sub-case, or that of a new or another form of power,
is also one which has never been imagined by others, in
association with the theory of gravity. I made some
endeavours, experimentally, to connect gravity with electri-
city, having this very object in view (Phil. Trans. 1851, p. 1) ;
but the results were entirely negative. The view, if held for
a moment, would imply that not merely the sun, but all
matter, whatever its state, would have extra powers set up in
it, if removed in any degree from gravitation; that the
particles of a comet at its perihelion would have changed in
character, by the conversion of some portion of their molecular
force into the increased amount of gravitating force which
they would then exert; and that at its aphelion, this extra
gravitating force would have been converted back into some
other kind of molecular force, having either the former or a
new character: the conversion either way being to a perfectly
equivalent degree. One could not
One could not even conceive of the
diffusion of a cloud of dust, or its concentration into a stone,
574
[JAN. 1855.
Gravitation-magnetism, &c.
without supposing something of the same kind to occur; and
I suppose that nobody will accept the idea as possible. The
third sub-case remains, namely that the power is always
existing around the sun and through infinite space, whether
secondary bodies be there to be acted upon by gravitation or
not; and not only around the sun, but around every particle
of matter which has existence. This case of a constant
necessary condition to action in space, when as respects the
sun the earth is not in place, and of a certain gravitating
action as the result of that previous condition when the earth
is in place, I can conceive, consistently, as I think, with the
conservation of force: and I think the case is that which
Newton looked at in gravity; is, in philosophical respect,
the same as that admitted by all in regard to light, heat, and
radiant phænomena; and (in a sense even more general and
extensive) is that now driven upon our attention in an espe-
cially forcible and instructive manner, by the phænomena
of electricity and magnetism, because of their dependence on
dual forms of power.
January 22, 1855.
575
Further Observations on associated cases, in Electric Induction,
of Current and Static Effects'.
MELLONI, whose loss science must deeply feel, was engaged
in the latter part of his life in investigations relating to static
electricity, especially concerning inductoin, conduction, &c.
He desired, in refere ce to these and the results I had pub-
lished respecting the charge of, and conduction by, subter-
raneous and subaqueous insulated wires², to know whether there
was any difference in the time of transmission through such wires,
of currents having greater or less intensity, i. e. of currents from
batteries of different numbers of plates. I applied to Mr. Latimer
Clark on the subject; and he, with the same earnestness as on
the former occasion, sought and seized the opportunity of making
experiments of the like kind, and gave me the results, which I
sent to Melloni. The latter published them with some observa-
tions in an Italian Journal (whose title is not on the paper
which he sent to me), and soon after he was suddenly removed
from us by death. As Mr. Clark's results are not yet known
in this country, I have thought that a brief account of them
would be valuable. His process records, by the printing tele-
graph of Bain, the results obtained with 768 miles of copper
wire covered with gutta percha, and laid in the ground in four
lines between London and Manchester, so connected that the
beginning and the end of the whole length was in London.
The following are his words, dated May 31, 1854-
"I have tried a few experiments on the relative velocities of
currents of different intensities, and I enclose you some strips of
paper showing the results. I was unable to equalize the deflec-
tions of a galvanometer by currents of intensity with small plates
as compared with currents from a few large plates, for no size
of plate would make up for the deficiency in intensity. I allude
to the form of experiment suggested by Melloni ;-but I believe
they will be of interest to him.
"The experiments were made through 768 miles of gutta
percha wire, viz. from London to Manchester and back again
2
¹ From the Philosophical Magazine, for March 1855.
Ante, page 508; also Royal Institution Proceedings, i. 345; or Phil.
Mag. 1854, vii. p. 197.
576
Subterraneous telegraph wires. [FEB. 1855.
twice, with our ordinary sulphate of copper batteries, plates
3 inches square, and with intensities varying from 31 cells to
sixteen times 31 cells, or 500 cells.
"In the accompanying strips the upper line indicates the
time during which the current was sent, being made by a local
arrangement.
"The second line (of dots) indicates time by seconds, being
made by a pendulum vibrating seconds, and striking a light
spring at the centre or its arc of vibration.
"The third line indicates the time at which the current
appeared at (what we may call) the distant end of the line, 768
miles off.
"The fourth line merely shows the residual discharge from
the near end of the wire, which was allowed to communicate with
the earth as soon as the batteries were disconnected; this has no
reference to the subject of our inquiries.
"It will be seen by the third line, that about two-thirds of a
second elapsed in every case before the current became apparent
at the distance of 768 miles, indicating a velocity of about 1000
miles a second; but the most interesting part appears to be, that
this velocity is sensibly uniform for all intensities from 31 cells
to 500."
Melloni has then given a copy of the records made when 31 pair
and 500 pair of plates were employed; unfortunately the copy
is inaccurate, since it makes the fourth line commence as to time
at the termination of the third, whereas it ought to correspond
with the termination of the first; also the third line on each does
not thin off as those upon the record do. The following is a copy
from other slips obtained at the same time from the Bain's print-
ing apparatus. Experiments with 62, 125, and 250 cells, gave
like results with those of 31 and 500 cells.
31 cells.
500 cells.
After certain observations, which are mainly upon the manner
of the experiments, and the way in which practical difficulties
FEB. 1855.]
Time of the electric wave.
577
were avoided, Melloni says, "It appears, then, that when the
electric current possesses sufficient force to overcome the sum of
the resistance offered by a given conductor, whatever its length
may be, an augmentation of its intensity ten or twentyfold does
not alter the velocity of its propagation. This fact is in open
contradiction with the general meaning attributed to the deno-
minations of quantity and intensity; since the first compares the
mass of electricity to that of a fluid, and the second represents
its elasticity or tendency to motion. The equal velocity of cur-
rents of various tension offers, on the contrary, a fine argument
in favour of the opinion of those who suppose the electric current
to be analogous to the vibrations of air under the action of sono-
rous bodies. As sound, higher or lower in pitch, traverse in
air the same space in the same time, whatever be the length or
the intensity of the aërial wave formed by the vibration of the
sonorous body; so the vibrations, more or less rapid or more or
less vigorous, of the electric fluid excited by the action of bat-
teries of a greater or smaller number of plates, are propagated
in conductors with the same velocity. Every one will see how
the hypotheses imagined by us to give a reason for natural phæ-
nomena, will serve to suggest certain experimental investigations,
the results of which will test their validity or insufficiency."
Melloni then says that he shall shortly have occasion to publish
facts which clearly demonstrate the errors of certain conclusions
admitted up to the present time respecting electro-static induc-
tion; and I am aware, from written communications with him,
that he considered the results arrived at by Coulomb, Poisson,
and others since their time, as not accordant with the truth of
nature¹. In the mean time he died, and whether his researches
are sufficiently perfected for publication or not, I do not know.
¹ He says, "I deceive myself much, or else the fundamental theorem of
electrical induction, as we find it ordinarily announced, ought to be modi-
fied so as not to confound two effects completely distinct-the electric state
during induction, and after the contact and separation of the inducing body.
We know perfectly what occurs in the latter case, but not in the former,"
&c. Again, "In my last letter I raised doubts with regard to the con-
sequences which have up to the present been deduced from the experiments
serving as a base for the fundamental theorem of electro-static induction.
These doubts have passed to a state of certitude in my mind,. ... and
behold me at this time thoroughly convinced that the enunciation of that
theorem ought to be essentially modified." (July 1854.)
VOL. III.
2 P
578
Subterraneous telegraph wires. [FEB. 1855.
The uniformity in the time and appearance of currents of
different intensities at the further end of the same wire in the
same inductive state, is a very beautiful result. It might at first
be supposed to be in opposition to the views I set forth some
years ago on induction and conduction, and the statements more
recently made with regard to time. That, however, does not
appear to me to be the case, as a few further observations on Mr.
Clark's recent experiments will perhaps show. When the smaller
battery is used, much less electricity passes into the wire in a
given time, than when the larger one is employed. Suppose that
the batteries are so different that the quantities are as 1 to 10;
then, though a pulse from each would take the same time for
transmission through the wire, still it is evident that the wire
would be a tenfold better conductor for the weak current than
for the strong one; or in other words, that a wire having only
one-tenth of the mass of that used for the greater current should
be employed for the smaller one, if the resistence for equal quan-
tities of electricity having different intensities is to be rendered
equal.
My views connect the retardation of the transmitted current
with the momentary induction set up laterally by the insulated
and externally coated wire. The induction will be proportionate
to the intensity, and therefore its especial effect on the time of
retardation proportionately diminished with the less intense cur-
rent,—a result of action which will aid in rendering the time of
retardation of the two currents equal.
The difference of time in the former experiments with air wires,
and earth or water wires, very clearly depends upon the differ-
ence of lateral induction; the air wire presented a retardation
scarcely sensible, the earth wire one amounting to nearly two
seconds. If the insulating layer of gutta percha could be reduced
from 0.1 to 0.01 of an inch in thickness, and mercury could be
placed on the outside of that instead of water or earth, I do not
doubt that the time would be still more increased. Yet there is
every probability that in any one of these varying cases, electric
currents of high and of low intensity would appear at the end of
the same long wire after equal intervals of time.
Mr. Clark's results may be stated thus :-A given quantity of
electricity at a high intensity, or a smaller quantity at a propor-
tionally lower intensity, will appear at the further end of the
FEB. 1855.]
579
Time of the electric wave.
same wire after the lapse of the same period of time. My
statement assumed the discharge of the same quantity at different
intensities through the same wire, and the quantities in the illus-
trative experiments were measured by a Leyden jar. In the
consideration and further development of these results, it must be
remembered that it is not the difference either in time, velocity,
or tranmission of a continuous current which constitutes the
object in view, for that is the same both for an air wire and a
subterraneous wire, but it is the difference in the first appearance
only of the same current when wires under these different con-
ditions are employed. After the first appearance both wires are
alike in power unto the end of the current, and then a difference
again appears which is complementary to the first.
There are many variations of these experiments which one
would wish to make, if possible, and perhaps by degrees the pos-
sibility, or else equivalent experiments in other forms, may occur.
If the wire employed were changed from a cylinder to a flat
ribbon of equal weight, or to several small wires, all being equally
coated with gutta percha and submerged, differences would pro-
bably arise in the time of delay with the same currrent; and I
think that the ribbon, presenting more induction surface than the
cylinder would cause more delay; but probably any one of these,
or of like varieties, would cause the same delay for currents of
different intensities. Again, one can scarcely doubt that with
different conducting substances, as iron and copper, the delay
would vary, as is the case in the transmission of sound and light.
That the delay for currents of high and low intensity should be
the same for the same wire in any one of such cases may still be
expected, but it would be very interesting to know what would
be the fact.
The prosecution of these results and the principles concerned
in them, through the various forms they may assume by such
like variations of the conductors and also of the currents, offers,
as Melloni has observed, most extensive and interesting inquiries:
even the power of a current to induce a current in neighbouring
wires and conductors is involved in the inquiry, and also the
phænomena and principles of magneto-electric induction.
Royal Institution,
Feb. 7, 1855.
INDEX.
N.B. A dash rule represents the italics immediately preceding it. The references are
sometimes to the individual paragraph, and sometimes to that and such as succeed it.
Those which follow p. or pp. are to pages, the others to the paragraphs of the Experimental
Researches.
ACTION at a distance considered, p. 570.
Air, action of magnets on, 2400, 2432.
attracted in water, 2406.
unseparated by magnetism, p. 484.
Air, its magnetic character, 2791, 2853,
pp. 476, 484.
485.
affected by heat, 2855, 2859, pp. 473,
Annual variation, 2882, 2947.
Antimony, diamagnetic, 2295.
Antimony, magnecrystallic, 2508.
motion arrested, 2512, 2526.
> revulsive action, 2513, 2526.
Arsenic, its magnecrystallic action, 2532.
Associated magnets, their state 3215, 3218
Associated cases of current and static effect,
p. 508.
Assumptions, magnetic, 3301, 3311, 3317,
3326.
Atmosphere, its magnetic character, 2853.
2863, 2963.
its probable action, 2864, 2917, 2920,
2934, 2997.
Atmospheric magnetism, 2453, 2796, 2847,
2997, p. 323.
general principles, 2997, 2917, 2878.
laws of its action, 2969.
experimental analogies, 2969, 2997.
effect of cooled air, 2864, 2917, 3003,
3240.
effect of heated air, 2877, 2939, 3240.
variation upward, 2878, 2941.
in different latitudes, 2881.
by pressure, 2952.
by wind, 2954.
by rain or snow, 2955.
annual variation, 2882, 2947, 3001.
diurnal variation, 2892, 2920, 3000.
at night, 3002.
Axial and equatorial, 2252,
Bismuth, diamagnetic, 2295.
its motions at the magnet, 2297, 2308.
VOL III.
Bismuth, its static magnetic condition, 3319.
-, liquid, subjected to magnetism, 2502,
2572.
sphere revolved, 3354, p. 569.
at the magnet, in powder, 2302, 2304.
in various media, 2301.
2303.
"
surrounded by iron, 2301.
two pieces, no mutual action,
its magnecrystallic action, 2454.
Bismuth crystals, form and cleavage, 2474.
their magnetic position, 2175, 2480,
2574, 2840.
>
affected by iron, 2487.
magnets, 2491.
act upon a magnet, 2567.
non-magnecrystallic, when hot, 2570.
retain no magnetic power, 2504.
exert no mutual action, 2582.
and the earth power, 2581.
Bismuth, its magnetic polarity, 3309.
same as iron and copper, 3164, 3168.
, same as a direct magnet, 3358.
-, supposed reverse of iron, 3310.
, involves four sorts of magnetism,
3311.
sions, 3311.
3320.
involves contradictory conclu-
-,involves idea of perpetual motion,
Blood, diamagnetic, 2281, 2285.
Bodies not changed in volume by magnetism,
2752.
Bodies, their static magnetic condition,
3318.
Bubbles of gases magnetized, 2758, 2765.
, oxygen, 2766.
nitrogen, 2765.
Calcareous spar and magnets, 2595, 2600,
2842.
Cape of Good Hope variations, 3035, 3069,
tables.
2 Q
582
INDEX.

Carbonic acid gas, its magnetic characters,
2857.
Chamber of no magnetic action, 3341.
feeble magnetic action, 3344, 3347,
3350.
Circular polarization, magnetic, 2230.
essentially different to the natural, 2231.
Cobalt, heated, its magnetic state, p. 444.
Conduction and induction, connected, p. 513.
Conduction, magnetic, 2797, 2843, 3281.
Conduction, magnecrystallic, 2836.
Conductor, moving, 3351, 3360.
Conductors of magnetism, their effect, 2806,
2828.
•
paramagnetic, 2807, 2814, 2828.
diamagnetic, 2807, 2815, 2829.
Conservation of force, 3325.
Continuity, its effect in magnetism, p. 462.
Copper, a magnetic medium, 3339:
Copper block attracted and repelled, 2338.
Copper acted on by magnets, 2309, 2323,
2411.
peculiar actions, 2310, 2317, 2326,
2333.
revulsion, 2315, 2336, 2411.
Crystalline polarity of bismuth, 2457.
antimony, 2508,
arsenic, 2532.
various bodies, 2535.
salts, 2547.
calcareous spar, 2594.
sulphate of iron, 2615, 2546, 2554.
red ferro-prussiate of potassa, 2560.
Crystalline particles in solution, their mutual
relation, 2578.
Crystals, magnetic rotation of light in, 2177.
Current and static effects, associated, p. 508.
Curved lines of magnetic force, 3323, 3336.
Delineation of lines of magnetic force, 3234.
Diamagnetism, 2243, 2417.
Diamagnetic action, its nature, 2417, 2427.
Diamagnetic body defined, 2149, 2790.
Diamagnetic and paramagnetic bodies distin-
guished, p. 458.
Diamagnetic condition of flame and gases,
pp. 467, 487.
of smoke, pp. 469, 487.
Diamagnetic curves, 2270.
Diamagnetic force, relation to distance,
p. 504.
Diamagnetic motions, 2253, 2257, 2259,
2271.
Diamagnetic order, 2284, 2307, 2399.
Diamagnetic pointing, 2258, 2282.
Diamagnetic polarity, 2429.
its nature, 2497, 2640, 2820.
examined by inductive currents pro-
duced, 2655, 2663.
effects of approach and recession,
2640, 2665.
effects of time, 2681.
division, 2658.
into discs, 2659, 2661.
Diamagnetic polarity examined by division
into wires, 2659, 2662.
shortening the cores, 2657.
helices, 2668.
velocity, 2681.
Diamagnetic polarity, supposed proofs
doubtful, 2689, 3311, 3320.
Diamagnetic substances, 2275, 2279.
list of, 2280, 2399.
acted on by magnets, 2275.
suspension of, 2248.
precautions, 2250.
division of, 2283, 2302.
antimony, 2295.
bismuth, 2295.
crystals, 2278.
fluids, 2279.
metals, 2291, 2295, 2425.
phosphorus, 2277, 2284.
Differential magnetic action, 2361, 2422,
2757, 2405, 3298, 3316.
Direction, axial and equatorial, 2252.
Discs, metallic, revolving in lines of force,
3159, 3167.
of non-conductors, 3171.
Disintegration, its effect in magnetism,
p. 462.
Disposition of magnetic force, 3305.
Distance, differences with different bodies,
p. 503.
Diurnal variation, 2892, 2920.
Dual forces, p. 440.
always equal and dependent, 3324.
Dualities, electric, p. 566.
9
their equality, p. 566.
Dualities, magnetic, 3323, 3341, p. 567.
Earth, interior, its magnetic state p. 446.
Electric currents, their action on light, 2189,
2170.
Electric induction, p. 508.
Electric and magnetic forces, their relation,
3265.
Electric dualities, p. 566.
Electric lines of force, 2149, 3249, p. 440.
Electric rotation of light, 2189, 2195.
law of, 2199.
in fluids, 2201, 2183.
in iron tubes, 2209.
in rotating bodies, 2204.
in various bodies, 2211.
Electrical use of gutta percha, p. 494.
Electricity, light and magnetism, cases of
non-action, 2216.
Electricity, natural standard, p. 465.
its possible relation to gravity, 2702,
2717.
its velocity of conduction, pp. 514,
576.
Electro-magnet, the great, 2247.
Woolwich helix, 2246.
Electro-tonic state, 3172, 3269.
Equatorial and axial, 2252.
INDEX.
583
Flame, its diamagnetic condition, pp. 467,
487, 490.
surrounding currents of air, p. 471.
Fluids, magnetic rotation of light in, 2183.
Fluids, their non-expansion in the magnetic
field, 2172.
Force, its necessary conservation, 3326,
p. 571.
>
magnetic lines of, 3300.
Force, physical, considered, p. 570.
, gravity, 3245, p. 570.
Forces of nature, their unity, 2702.
Forces acting at a distance, 3245, p. 570.
Fort Simpson, variations, 2914, 2968, tables.
Fuse for electrical mining, p. 519.
Galvanometer of thick wire, 3123, 3137,
3178.
,
"
influential circumstances, 3124, 3179.
value of its indications, 3184.
contacts, 3126.
Gases do not expand by magnetism, 2718,
2750, 2756.
,
no magnetic rotation of light in,
2186.
their magnetic character, 2785, 2792,
P. 467.
affected magnetically by heat, 2855,
p. 485.
>
•
action of magnets on, 2400, 2432.
their magnetic relation, pp. 474, 480.
air, pp. 476, 481, 483.
ammonia, pp. 479, 485.
bromine vapour, p. 479.
carbonic acid, pp. 477, 481.
hot, p. 485.
carbonic oxide, pp. 477, 481.
chlorine, p. 479.
coal-gas, pp. 478, 483.
hot, p. 486.
, cyanogen, p. 479.
hydriodic acid, p. 478.
-, hydrogen, pp. 477, 481, 482, 485.
"
hot, p. 485.
iodine vapour, p. 479.
muriatic acid, pp. 478, 485.
nitrogen, pp. 476, 481, 483, 485.
nitric oxide, p. 478.
nitrous oxide, pp. 478, 481, 483.
nitrous acid gas, p. 478.
olefiant gas, pp. 478, 485.
oxygen, pp. 476, 481, 483, 485.
hot, p. 485.
sulphurous acid, p. 478.
Gases in the magnetic field examined, 2723,
2728, 2734, 2770.
by a ray of light, 2723.
in close vessels, 2730, 3737, 2743,
2749.
as bubbles, 2758, 2765.
hydrogen in air, 2740.
no currents, 2754.
Glass, heavy, 2151, 2176, 2214.
Globe magnet, its condition, 3331, 3357,
p. 570.
Gravitating force, Newton's conclusion,
3305, note.
•
considered, p. 570.
cases of its action, p. 570.
its possible relation to electricity,
2702, 2717.
its lines of force, 3245.
Greenwich variations, 2911, 3018.
Gutta percha, its electrical uses, p. 494.
Heat, its effect on the magnetism of gases,
2856, p. 485.
air, 2856, 2859, pp. 471, 485.
carbonic acid, 2857.
nitrogen, 2858.
oxygen, 2861.
Heavy glass, 2151, 2176, 2214.
action of magnets on, 2253, 2273.
points equatorially, 2253, 2264.
is repelled bodily, 2259, 2265, 2266.
rotation of light in it, 2152, 2171.
Helices for electric action on light, 2190,
2213.
Hobarton variations, 2896, 2948, 3027.
Hypotheses of magnetic force, 3301, 3303,
p. 524.
Illumination of magnetic lines of force,
2146.
Induced magneto-electric currents, 2327,
2526.
,
their force, 2514, note.
Induction, electric, p. 508,
Induction dependent upon intervening parti-
cles, 2240.
Induction and conduction connected, p. 513.
Induction of magneto-electric currents,
3087, 3270.
Insulation and conduction, connected,
p. 513.
Insulation by gutta percha, p. 494.
Intensity and quantity, p. 519.
Iron, hot, is magnetic, 2344.
Iron, copper, bismuth, have like polarity,
3164, 3168, 3356, p. 569.
Lake Athabasca variations, 2913, 2968,
tables.
Law of the electric rotation of light, 2199.
Law of inverse square of the distance, p. 503.
Law of magnecrystallic action, 2479, 2464.
Law of the magnetic rotation of light, 2155,
2160, 2175, 2200.
Light, electricity and magnetism, cases of
non-action, 2216.
its magnetic affection, p. 453.
by repeated reflexions, p. 453.
magnetization of, 2146, 2221.
affected by electricity, 2189, 2221.
affected by magnets, 2146, 2152, 2157,
p. 453.
magneto-rotation of, 2428.
time, p. 466.
gases, p. 489.
Lines of force, 3245, p. 450.
2Q 2
584
INDEX.
Lines of electric force, 2149.
dynamic electricity, 3276.
Lines of force, physical, 3303, pp. 438,
566, 570.
of light, p. 439.
of electricity, p. 440.
of magnetism, 3303, pp. 438, 441, 506,
528.
Lines of magnetic force, 2149, 3070, 3122,
3174, 3243, 3300, p. 566.
defined, 3071.
their definite character, 3073, 3103,
3109, 3121, 3129, 3165, 3199, 3232.
distribution within a magnet, 3084,
3116, 3120, 3273.
distribution through space, 3084, 3099,
3129, 3274.
their physical character, 3075, 3243,
3273.
polarity of, 3072, 3154, 3157.
true representatives of nature, 3074,
3122, 3174, 3243.
the unit, 3122.
are closed currents, 3117, 3230, 3264.
delineated, 3234.
recognized, 3076.
by induction of currents, 3077,
3083, 3123, 3159, 3177.
3116, 3156, 3176, 3280.
, advantages, 3078, 3115,
thick wire galvanometer,
3123, 3178.
, magnet and wire revolving together,
3084, 3091, 3095.
3106.
3111.
separately, 3094, 3095, 3097,
effect of time, 3104, 3114, 3135.
distance, 3107, 3109,
velocity, 3108, 3114, 3135.
and wires of different thicknesses,
3133, 3141, 3191, 3203.
in different planes, 3140.
of different substances, 3143, 3152.
effect of masses, 3137, 3150.
in varying media, 3292.
through hot and cold nickel, 3240.
round an electric current, 3239.
of associated magnets, coalesce, 3226.
no increase of force, 3227.
their course through one or more mag-
nets, 3230.
of opposed magnets, 3233.
their physical character, 3243, 3269,
3273, 3297.
,
relation to time, 3253.
in curved lines, 3254, 3258, 3261,
3263, 3297, 3323.
their amount limited, 3255.
dependent relation of the pola-
Lines of magnetic force, their physical cha-
racter, a state of tension, 3269.
manifested by moving conductors,
3270.
, competency, 3273.
disposition, 3273.
refraction, 3274.
condensation, 3275.
Lines of terrestrial magnetic force, 2849.
their disposition in the atmosphere,
2865, 2919.
their quantity and intensity, 2870.
Logeman magnet, p. 498.
Magnet, its physical condition considered,
3257, 3273.
its independent condition, 3331, 3357,
3336, 3361.
its internal constitution, 3117.
its relation to the space around it,
3278, 3284.
its external disposition of power, 3305,
3332, 3336, 3361.
globular, its condition, 3331, 3357,
p. 570.
tubular, its character, 3346.
lines of force, within it, 3100, 3116,
3120.
around it, 3099, 3101, 3117.
its examination by induced currents,
3177, 3215.
when associated with other
magnets, 3215.
Magnets, variable and invariable, 3224.
supersaturated, 3285.
>
action of the keepers, 3283.
their surrounding medium, 3278.
varied, 3292.
proportion of small to large, 3286.
influence of shape and size, 3282, 3287.
over-long, 3290.
associated, 3294.
their analogy to voltaic batteries, 3228,
3276, 3282.
habitations of lines of force, 3295.
definite amount of their power, 3121,
3215.
when associated with other mag-
nets, 3218.
their action on light, 2146, 2152,
2157, 2170, 2609.
their action on heavy glass, 2253, 2273.
repel it, 2259, 2265, 2266,
their action on metals, &c., 2287, 2295,
2309, 2333.
rities, 3257, 3323.
3265.
relation to lines of electric force,
p. 569.
air and gases, 2400, 2432.
antimony, 2391, 2306, 2508.
arsenic, 2383, 2532.
bismuth, 2392, 2306, 2457.
a bismuth sphere, 2298, 3354,
cerium, 2373.
chromium, 2374.
INDEX.
585
Magnets, their action on cobalt, 2351, 2358.
copper, 2537.
earths, 2395.
gold, 2540...
iridium, 2386, 2542.
hot iron, 2344.
compounds of iron, 2349.
sulphate of iron, 2546, 2554, 2615.
lead, 2378, 2539.
magnetic salts, 2352.
magnetic solutions, 2357, 2361.
manganese, 2372.
nickel, 2346, 2350, 2358.
nitrogen, 2770, 2783, 2854, 2858.
osmium, 2385.
oxygen, 2770, 2780, 2793, 2861, 2966,
P. 476.
palladium, 2382.
platinum, 2379.
rhodium, 2387, 2542.
silver, 2390.
sodium, 2393.
tellurium, 2541.
tin, 2538.
titanium, 2371, 2536.
tungsten, 2389.
zinc, 2535.
compounds of magnetic metals, 2349,
2379.
cold metals, 2348.
Magnecrystallic action, 2454, 2479, 2550.
not attraction or repulsion, 2551.
Magnecrystallic conduction, 2836.
Magnecrystallic force, 2469, 2550, 2585, 2836.
its law, 2479.
its nature, 2562, 2576, 2624, 2836.
not measurable by vibration, 2529.
compared to radiant force, 2591.
Magnecrystallic polarity, 2454, 2550. 2624,
2639.
Magnetic action, new, 2243, 2343, 2417.
at different distances, p. 503.
•
differential, 2365, 2405, 2438, 2757.
terrestrial, 2447.
by contiguous particles, 2443.
on copper, &c., 2309, 2333.
places of none, 3311.
places of feeble force, 3344, 3347,
3350, p. 567.
bismuth there, 3350.
Magnetic assumptions, 3317, 3301, 3311,
3326.
Magnetic attraction and repulsion, its phy-
sical cause, 3280.
Magnetic chamber of no force, 3341, p. 567.
Magnetic condition of gases, pp. 474, 480.
of all matter, 2226, 2243, 2286,
p. 457.
Magnetic conduction, 2797, 2843, 3281.
polarity, 2818, 2835, 3166, 3307.
Magnetic conductors, their action in the
magnetic field, 2810, 2828, 2839, 3313.
Magnetic curves delineated, 3234.
Magnetic dualities, 3257, 3323, 3341,
p. 567.
never alone, 3257, p. 567.
related in curved lines, 3258, 3336,
p. 568.
-, not related through the magnet, 3332,
3260, p. 568.
Magnetic effect of disintegration, p. 462.
Magnetic field, condition of metals in, 3172.
disturbed by conduction, 2806, 2831.
of equal force, 2463, 2465.
Magnetic force, observations on, p. 497.
its disposition, 3305.
its relation to light, 2221.
its physical nature, 3301, 3303.
turned in various directions, 3328.
relation to distance, p. 504.
no loss by distance, 3111.
never single, 3277.
lines of, 3300.
reasons for considering it anew, 3305.
Magnetic forces, dual, 3257, 3323.
are always equal, 3324.
essentially connected, 3258, 3327,
3331, 3341.
ร
never destroyed, 3325, 3330.
their conservation, 3325.
definite in amount, 3328.
never appear separated, 3258, 3329,
3341.
not compensated through the magnet,
3260, 3332, 3335.
are in curved lines, 3258, 3336.
Magnetic forces examined by induced cur-
rents, 3177.
galvanometer employed, 3178.
3133.
value of its indications, 3184,
metallic loops employed, 3184.
those of the earth, 3192.
by moving rings, 3212.
by moving rectangles, &c., 3192.
of different sizes, 3195, 3211.
of different substances, 3231.
of different thicknesses,
at different velocities, 3196,
of different forms, 3198.
of several convolutions,
3201, 3203, 3208, 3231.
3200, 3202.
3206.
Magnetic and electric forces, their relation,
3265.
Magnetic hypotheses, 3301, 3303, p. 524.
Magnetic lines of force, 2149. See Lines of
magnetic force.
their relation to light, 2146, 2223.
of the earth, 2449, 2849, p. 324.
in the atmosphere, 2847, p. 325.
Magnetic media, their actions, 3313, 3337,
p. 500.
586
INDEX.
Magnetic media, point as if polar, 3313.
-, point either equatorially or axially,
3315.
give differential results, 3316.
at rest and in motion, 3160, 3337,
3351.
Magnetic needle not a perfect measure of
earth's force, 2871.
fails in its indications, 3280, 3293.
Magnetic order of bodies, 2424.
Magnetic philosophy, points of, 3300.
Magnetic pointing east and west, 2258,
2269, 2282.
Magnetic polarity, 3304, 3307, 3360.
various meanings and interpretations,
3307.
defined, 3154.
its nature, 2832, 3154.
not always shown by attractions and
repulsions, 3155.
is shown by the induced currents,
3156, 3158, 3164.
in a field of equal force, 3157.
3157.
not shown by a magnetic needle,
shown by revolving discs, 3159.
shown by revolving spheres, 3360,
p. 569.
alike in iron, copper, bismuth, &c.,
3164, 3356.
true reverse cases, 3321, 3357.
of copper, 3352.
of iron, 3356.
of bismuth, 3354, 3309.
not reverse of a magnet, 3358.
of hard steel, 3355.
of hard magnet, 3357.
of differing solutions, 3316.
Magnetic pole, wire moving round it, 3272.
Magnetic poles, association of like, 3347.
Magnetic poles pierced, p. 487.
Magnetic pole chambers, 3341, p. 567.
Magnetic relations of metals, p. 444.
Magnetic repulsion without polarity, 2274.
Magnetic revulsion, 2315, 2336, 2514,
2516, 2684.
Magnetic rotation of light, its law, 2155,
2160, 2175, 2200.
its peculiarities, 2231.
related to time, 2170, p. 466.
increases with the diamagnetic, 2163.
intensity of the magnetic force,
2164.
occurs with various bodies, 2165, 2173.
not affected by motion, 2166.
intervention of extra-diamagnetic
bodies, 2167.
is affected by the intervention of iron,
2168.
in bodies generally, 2173, 2189, 2215,
2609.
crystalline bodies, 2177, 2237, p. 456.
fluid bodies, 2183, 2194.
Magnetic rotation of light not in gases,
2186, 2212, 2237, p. 456.
in rotating bodies, 2187, 2235.
in heavy glass, 2152, 2171.
by repeated reflexions, p. 453.
Magnetic scale, Centigrade, p. 501.
Magnetic scale of bodies, p. 502.
Magnetic solutions, relative actions of, 2357,
2361, 3313.
their action at the pole, p. 462.
Magnetic state requires time for its assump-
tion, 3319, p. 466.
Magnetic storms, 2958.
Magnetic variations of the earth, 2847,
p. 326.
Magnetism tested for, 2290.
does not change volume of bodies, 2752.
does not expand gases, 2718, 2750,
2756.
,
its zero, pp. 465, 488.
electricity and light, cases of non-
action, 2216.
atmospheric, 2796, 2847, 2997, p. 323.
transverse, pp. 458, 464.
Magnetization of light, 2146, 2221.
Magneto-electric currents, induced, 2327,
3087, 3270.
induction, nature of its action, 2696.
Man is diamagnetic, 2281.
Manganese its magnetic condition, 2372,
p. 445.
Matter and force, p. 448.
Matter, all is magnetic, 2243, 2286.
, a new magnetic condition of, 2227,
2242, 2274, 2286, 2417.
its relation to magnetism, 2226, 2286,
2443.
and light, 2224.
Media, their relative magnetic action, 2405,
2414, 3313.
their magnetic relation, 3313, p. 500.
magnetic, considered, 3313, 3337.
Medium about a magnet, considered, 3278.
Metallic spheres in the magnetic field, 3352,
p. 569.
Metals acted on by magnets, 2287.
"
their condition in the magnetic field,
3172.
>
,
their magnetic order, 2399.
their magnetic relations, p. 444.
cooled, their magnetic state, p. 445.
heated, their magnetic state, p. 444.
different under induction, 3145, 3152,
3164.
-, magneto-electric currents induced in,
2294, 2309, 2327, 2340.
their feeble intensity, 3123.
Metals diamagnetic, 2291, 2295, 2425.
heated, 2397.
Metals, magnetic, 2288, 2292, 2425.
"
cooled, 2398.
Mining by electricity-the fuse, p. 519.
Moving conductors, 3076, 3159, 3351, 3360.
INDEX.
587
Moving conductors in the magnetic field,
3270.
Moving magnetic media, 3159, 3337, 3351.
Moving wire, its value as an examiner, 3176.
its magnetic indications, p. 442.
results, 3338.
Mutual magnetic action of bodies, 2814.
Newton's conclusion as to gravitating force,
3305, note, p. 571.
New magnetic actions, 2243, 2343, 2417.
New magnetic condition of matter, 2227,
2242, 2274, 2286.
Nickel, its magnetism at different tempera-
tures, 2346, 3240.
Nitrogen, its magnetic character, 2770, 2783,
2854, 2858.
Non-expansion of gases in the magnetic field,
2718, 2750, 2756.
fluids in the magnetic field, 2172.
Nuclei of matter, p. 449
Observations on the magnetic force, p. 497.
Oxygen, its magnetic character, 2770, 2780,
2793, 2861, 2966, p. 476.
Oxygen bubble, magnetic, 2766.
Paramagnetic bodies defined, 2790.
and diamagnetic bodies distinguished,
p. 458.
Peroxide of iron, its magnetic behaviour.
p. 459.
Perpetual motion, if bismuth reversely polar-
ized, 3320.
Phosphorus, diamagnetic, 2277, 2284.
its magnetic polarity, p. 569.
Physical force considered, 3245, p. 570.
Physical character of magnetic force, 3303.
Physical lines of force, 3243, p. 439.
of gravity, 3245, p. 571.
of radiant agencies, 3247.
of static electricity, 3249, 3264.
of dynamic electricity, 3250, 3276.
of magnetic force, 3243, 3251, 3300, pp.
438,441,506. See Lines of magnetic force.
Places of force, 3306.
Places of no magnetic action, 3341, p. 568.
Pointing, magnetic, east and west, 2258,
2269.
Points of magnetic philosophy, on, 3300,
p. 566.
Polarity, magnetic, 3154, 3307. See magnetic
polarity.
>
of bismuth, 3309.
its nature, 2497, 2640, 2820,
diamagnetic, 2429.
magnecrystallic, 2454, 2550.
its nature, 2639.
>
Polarity of magnetic conduction, 2818, 2835,
3166.
Quantity and intensity, p. 519.
Ray vibrations, thoughts on, p. 447.
Radiant lines of force, 3247.
Rectangles and rings, revolving 3192, 3212.
Relation of natural forces, 2146, 2221, 2238.
Repulsion, magnetic, without polarity, 2274.
Revulsion, magnetic, 2315, 2336, 2514, 2516,
2684.
Rotation of a ray of light by magnetism,
2151.
Scale, Centigrade of magnetic bodies,
p. 501.
Singapore variations, 3058, 3069, tables.
Smoke, its diamagnetic condition, pp. 469,
487.
Soap-bubbles of gases, magnetized, 2758,
2765.
Space, its magnetic relations, 2400, 2787.
Speculation regarding physical lines of force,
3244.
Sphere magnet, direct and reverse, 3357,
p. 570.
Spheres, metallic, at the magnet, 3352, p. 569.
the polarity of copper, 3352.
iron, 3353.
bismuth, 3354.
hard steel, 3355.
a hard magnet, 3357.
Sphondyloid of magnetic force, 3271, 3276.
St. Helena variations, 3045, 3069, tables.
St. Petersburgh variations, 2915,2968, tables,
3009.
Standard of electricity, p. 465.
Static condition of bodies generally, 3318.
Static and current effects, associated, p. 508.
Steel ring magnet, 3331.
Steel magnet reversed, 3357.
not as bismuth, 3358, p. 569.
Storms, magnetic, 2958.
Sulphate of iron, its magnetic relations,
2546, 2554, 2615.
Telegraph wires, insulated, pp. 508, 575.
in the air, pp. 510, 511, 513, 579.
-, subaqueous, charged with electricity,
p. 509.
their conduction, pp. 510, 575.
their induction, pp. 511, 579.
subterraneous, pp. 512, 521, 575.
their charge, p. 512.
their lateral induction, pp. 513,
518, 578.
578.
512, 517, 575.
their conduction, pp. 512, 517,
time of the current, pp.
simultaneous waves, p.512.
Terrestrial magnetic action, 2447.
at the equator and poles, 2449.
Terrestrial magnetic force, its disposition,
variation of direction, 2874.
2849.
588
INDEX.
Thoughts on ray-vibrations, p. 447.
Time in development of magnetism, 2332.
3319, p. 466.
Time, its influence in magnetic induction,
2170, 2650, 2688.
in magnetic rotation of light, p. 466.
with iron and bismuth, 3318.
Toronto variations, 2905, 2948, 2968, tables,
3027.
Torsion-balance for magnetic observations,
p. 498.
Transverse magnetism, pp. 458, 464.
Unity of natural forces, 2702.
Vacuum, its magnetic character, 2770, 2786,
3277.
Vacuum in water, 2412.
the zero of magnetism pp. 465, 488.
Variation, annual, 2882, 2947.
diurnal, 2892, 2920.
Velocity of electricity in wires, pp. 514, 575.
very variable, p. 515, 579.
Wire, retardation of electricity in, pp. 514,
575.
Zantedeschi on magnetic motions of flame,
p. 490.
Zero of magnetic action, 2790.
Zero of magnetism, pp. 465, 488.
Zero of static electricity, p. 465.
THE END.
PRINTED BY
TAYLOR AND FRANCIS, RED LION COURT, FLEET STREET, LONDON.
Plate 1. Vol. 3. Exp. Researches
June.
Summer.
Phil Trans. MDCCCLI Plate I. p.p. 57 & 60.

11
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Plate II. Vol. 3. Exp. Researches.

Phil. Trans. MDCCCLLPlate II. p.g6.
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