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1
2
3
1
2
3
4
5
6
1. :
decide
When
a 8uc<
Boundt
curren
discovi
ferent
teleph(
were <
♦ a
1837, J
1838, X
t J.
I'ifelectr
t W
(2(1 seri
§ Gc
II De
Apch. c
p. 1287
Chim. e
vol
^i^
PROCEEDINGS
or THE
AMERICAN ACADEMY
ov
ARTS AND SCIENCES.
VOL. xn.
PAPERS READ BEFORE THE ACADEMY.
RESEARCHES IN TELEPHONY.
\ By A. Graham Bell.
Prmeiited May 10, 1876, by the Corresponding Secretary.
1. It has long been known that an electro-magnet gives forth a
decided sound when it^is suddenly magnetized or demagnetized.
When the circuit upon which it is placed is rapidly made and broken,
a succession of explosive noises proceeds from the magnet. Those
sounds produce upon the ear the effect of a musical note, when the
current is interrupted a sufficient number of times per second. The
discovery of " Galvanic Music," by Page,* in 1837, led inquirers in dif-
ferent parts of the world almost simultaneously to enter into the field of
telephonic research ; and the acoustical effects produced by m.ignetization
were carefully studied by Marrian,t Beatson,}: Gassiot,? De la Rive,||
V
* C. G. Page. "The Production of Galvanic Music." Silliman's Journ.,
1837, XXXII., p. 336; Silliman's Juurn., July, 1887, p. :]54; Silliman's Journ.,
1838, XXXIII., p. 118; Bibl. Univ. (new scries), 1839, II., p. 8U8.
t J. P. Mnrrian. Phil. Mag., XXV., p. 382; Inst., 1846, p. 20; Arch, do
rfelectr.,V., p. 196.
t W. Bmtson. Arch, de rfjlectr., V., p. 197 ; Arch, de Sc. Phys. et Nat.
(2d series), II., p. 118.
§ Gassiot. See " Treatise on Electricity," by De la Rive, I., p. 800.
II De la Rive. Treatise on Electricity, I., p. 800; Phil. Mug., XXXV., p. 422 ;
Arch, de I'^lectr., V., p 200; Inst., 1846, p. 83; Comptes Rendus, XX.,
p. 1287; Comp. Rend., XXII., p. 482; Pogg. Ann., LXXVL, p. 637; Ann. do
Chim. et de Phys., XXVI., p. 168.
VOL. XII. (n. 8. IV.) 1
-'^k.
2
PROCEEDINnR OP THE AMERICAN ACADEMY
Mattoucci,* Guillemin,t W(>rtlioim,| Wnrtmanii,§ Janiiiar,|| Joulclf
Laliordc,** Lt'gat,tt Rt'iH.lt l*oggeii(lorfr,§§ Du Moncel,|||| Dele-
zenne,1[ir mu\ otliers.***
2. In the autumn of 1H74, T discovered that the sounds emitted by
an elect ro-mngnct under the influence of a discontinuous current of
electricity are not dui; wholly to sudden changes in the magnetic con-
dition of the iron core (as heretofore supposed), but that a portion of
the uftect resulta from vibrations in the insulated copper-wires comivosing
the coils. An electro-magnet was arranged upon circuit with an in-
strument for interrupting the current, — the rheotome being placed
in a distant room, so as to avoid interference with the experiment.
Upon applying the ear to the magnet, a musical note was clearly per-
ceived, and the sound pc^rsisted after the iron core had been removed.
It was then much feebler in intensity, but was otherwise unchangitd,
— the curious crackling noise accompanying the sound being well
marked. #
The effect may probably be explained by the attraction of the coils
of the wire for one auotlier during the passage of the galvanic current,
* MalUHcri. Inst., 1845. p. 316; Arch, dc I'tlectr., V., 889.
t GuilUmin. Ccjinp. Rt'nil., XXII., p. 2G4 ; Inst., 184G, p. 30; Arch. d. Sc.
Phys. (2il scrk'g), I., p. I'Jl.
X G. W'-rlfwlm. Comp. Rend., XXII., pp. 330, 544; Inst, 1846, pp. 65, 100;
Poptf Ann., LXVIII.p. 140; Comp. Hend.. XXVI., p. 506; Inst, 1848, p. 142;
Ann. de Cliini. et de Pliy.s., XXIII., p. :502; Arcli. d. Sc. Phys. et Nat, VIII.,
p. 20(5; Vofig. Ann., LXXVII., p. 43; Hcrl. Her., IV., p. 121.
§ A7/V W'lirtiiiaun. Comp. Rend., XXII., p. 544; Phil. iVlag. (3d series),
XXVIII., p. 644 ; Arcli. d. Sc. Piiys. et Nut. (2d series), I., p. 419; Inst., 1840,
p. 290; Monatsclier. d. Rerl. Akad., 1846, p. 111.
II Jmtnlar. Comp. Rend., XXIII., p. 819; Inst., 1846, p. 269; Arch. d. Sc.
Phys. et Nat. (2d series), II., p. 394.
1[ ./. /'. Joule. Pl.il. Mag., XXV., pp. 76, 225 ; Berl. Ber., III., p. 489.
•* Lalwde. Comp. Rend., L., p. 692 ; Cosmos, XVII., p. 514.
tt Leifat. Brix. Z. S., IX., p. 125.
n IMx. " Tolephonie-." Polytechnic Journ , CLXVIil., p. 185; Bottger's
Notizl.l., 1863, No. 6.
§§ ./. C. Po<i(jfndorff. Pogg. Ann., XCVIII., p. 192; Berliner Monatsbcr.,
186(J, p. 133; Cosmos, IX., p. 49; Berl. Ber., XII., p. 241; Pogg. Ann.,
LXXXVII., p. 139.
nil Itn Moncel. Expose, 11., p. 125; also. III., p. 83.
IIT Deli-cuiw. " Sound produced by Magnetization," Bibl. Univ. (new series),
1841, XVI., p. 406.
*»• See London Journ., XXXII., p. 402; Polytechnic Joum., CX., p. 16;
Cosmos, IV., p. 43; fil.isener Traitc g(<ndral, &c.,p.350; Dove.-Repert.,VI.,
p. 68 ; I'ojjg. Ann., XLIII., p. 411 ; Birl. Ber., I., p. 144; Arch. d. Sc, Phys. et
Nat, XVI., p. 406; Kuhn's Eneyelopaedia der Physik, pp. 1014-1021.
trGSB//0f6 '^^ ^^"^ ■'^ND SCIENCES.
8
and tlie sudden cessation of such attraction when the current is inter-
rupted. Wlien a spiral of fine wire is made to dip into a cup of mer-
cury, HO as thereby to close a galvanic circuit, it is well known that
the spiral coils up and shortens. Ferguson * constructed a rheotonie
upon this principle. The shortening of the spiral lifted the end of the
wire out of the mercury, thus opening the circuit, and the weight of
the wire sufliced to bring the end down again, — so that the spiral was*
thrown into continuous vibration. I conceive that a somewhat similar
motion is occasioned in a helix of wire by the passage of a discontinu-
ous current, although further research has convincwl me that other
causes also conspire to produce the etVect noted above. Tlit! extra
currents occasioned by the induction of the voltaic current upon itself
in the coils of the helix no doubt play an important part in the pro-
duction of the sound, as very curious audible etlects are produced by
electrical impulses of high tension. It is probalde, too, that a molecular
vibration is occasioned in the conducting wire, as sounds are emitteil
by many substances when a discontinuous current is passed through
them. Very distinct sounds proctied from straight piece» of iron,
steel, retort-carbon, and plumbago. I believe that 1 have also obtained
audible effects from thin platinum and (Jerman-silver wires, and from
mercurv contained in a narrow groove about four feet loim. In tiu-se
cases, however, the sounds were so faint and outside noises so loud that
the experiments recjuire verilication. \V ell-marktsd sounds |n"oceed
from conductors of all kinds when formed into spirals or helices. I
find that I)e la Hive had noticed the production of sound irom iron
and steel during the passage of an intermittent current, ultlioiigh he
faile<l to obtain audible results from other substances. In order that
aich efl'eets should be observed, extrenu; <iuietiH;ss is necessary. The
rheotonu! itself is a great source of annoyance, as it always produces
a sound of similar [titclt to the one which it is desired to hear. It
is absolutely requisite that it should be placed out of earshot of the
observer, and at such a distance as to exclude the possibility of soum<1s
Ix-'ing me(;hanically conducted along the wire.
li. \'ery striking audible effects can be produced u[)0ii a short circuit by
means of two Grove eh'tnents. I had a helix of insulated copper-wire
(No. 2.'») constructed, having a resistance of about twelve ohms. It
was placed in circuit with a rheotomc which interrupted the current
one hundred times per second. Upon i)lacing the helix to my ear I
* FtriiiiHon. I'liKoediiifis of Uo\'al Scottisli lijoc. of Arts, April 9, 1866;
Taper on "A New Current Interrupter." .
PROCEEDINGS OP THE AMERICAN ACADEMY
. \
couhl hear the unison of the note produced by the rlieotome. The
intiMiHity of the sound was much increaticd by phuring a wrought-irou
nail iiisidu the helix. In both tliuHe cuhcs, a crackling eil'uut accumpa-
niiMl the MOund. When the nuil was held in the fingera 8o that no
portion of it touched the helix, the crackling effect disappeared, and a
pure nui.si(*nl note resulted.
• When the nail was placed inside the helix, between two cylindrical
pieceH of iron, a loud sountl resulted that could be hi'ard all over a largo
room. The nail seemed to vibrate bodily, striking the cylindrical |»iecos
of metal alternately, and the iron cylinders themselves were violently
agitated.
4. Loud sounds are emitted by pieces of iron and steel when sub-
jected to the attraction of an electro-magnet which is placed in cir-
cuit with a rheotomc. Under such circumstances, the armatures of
Morse-sounders and IJclays produce sonorous eHects. 1 have
8ucc«'e<led in rendering the sounds audible to large aiidi«'n('es by
interiK)sing a tense membVane between the electro-magnet and its
armature. * The armature in this case consisted of a jHece of clock-
spring glued to the membrane. This form of a))paratus I have fomid
invaluable in all my experiments. The instrument was connected
with a parlor organ, the reeds of which were so arranged as t(» open
and close the circuit (Juring their vibration. When the organ was
plajtid the music was loudly reproduced by the telephonic receiver
in a distant room. When chords were played upon the organ, the
various notes composing the chords were emitted simultaneously by
the arnuUure of the receiver.
o. The simultaneous production of musical notes of different pitch
by the electric current, was lbi'<!seen by me as early as 1870, and
demonstrated during the year 1873. Elisha Gray,* of Chicago, and
Paul La Cour,f of Copenhagen, lay claim to the same discovery.
The fact that sounds of different pitch can be simultaneously produced
u})on any i)art of a telegraphic circuit is of great practical importance;
for the duration of a musical note can be made to signify the dot or
dash of the Morse alphabet, and thus a number of telegraphic mes-
sages may be sent simult.aneously over the same wire without confusion
by making signals of a definite pitch for each message.
G. If the armature of an electro-magnet has a definite rate of oscil-
lation of its own, it is thrown botlily into vibration when the interrup-
• Elislifi Gray. Eng. Pat. .Spec, No. 974. See " Kngiucer," March 26, 1876.
t Paid la Coiir. TL'U'jjrapliic Journal, Nov. 1, lb76.
OP ARTS AND SCIKNCE^. 6
tions of tlio current arc timed to its movemcnU}. For iiiRtiincc, present
un ductro-mai^net to the strings of a piano. It will he round that thu
string which is in unison witli tho rheotonio included in tlio circuit
will Im) tlirown into vihration hy the attraction of tho magnet.
Ilehnholtz,* in his experiments upon the synthesis of vowel sounds
caused continuous vibration in tuning-forks which wero used as tho
armatures of electro-magnets. One of the forks was employed as a
rhcotome. Platinum wires attached to the prongs dipped into mer-
cury.
The intermittent current occasioned hy the vibration of tho fork
traversed a circuit containing a number of electro-magnets hetw«;en
the poles of which wero placed tuning-forks whose normal rates of
viltration were multiples of that of the transmitting fork. All the
forks were kept in continuous vibration l)y the passage of the iiiter-
ru|)ted current. l\y re-enforcing the tones of the forks in diHerent
degrees by means of resonators, Ilelmholtz succeeded in reproducing
a.'tificially certain vow(d sounds.
I havt! caused intense vibration in a steel strip, one extremity of
which was (irndy clamped to the pole of a U-^^'i'M'^'*' electro-maguist, tho
free en<i overhanging the other pole. The amplitude of tho vibration
was greatest wlu'ii the coil was removed from tho leg of the magnet to
which the armature was attached.
7. All the ert'ects noted above result from rapid interruptions of a
voltjiic current, but sounds may be produced electrically in many other
ways.
The Canon Gottoin de Coma,t in 178"), observed that noises we:e
emitted by iron rods [daced in the open air during certain electrical
conditions of the atmosphere ; Beatson t produced a sound from an
iron wire hy the discharge of a Leyden jar; Gore§ obtained loud
musical notes from mercury, accompanied by singularly beautiful ciis-
pations of the surface during the course of experiments in electrolysis ;
and I'ag'' || produced musical tones from Trevelyan's bars by the action
of the galvanic current.
8. When an intermittent current is passed through the thick wires
of a Kuhmkorir's coil, very curious audible effects are produced by the
* Ilelmholtz. Die Lelire von ilom Tonempflntlungen.
t See " Treatise on Electricity," hy De la Uive, I., p. 300.
X Ibid.
§ (!i>re. Procecilings of Hoynl Society, XII., p. 217.
II l\uie. " Vibration of Tri'velyaii's burs by tiie galvanic current." Silli»
roan's Journal, 1H50, IX., pp. 106-108.
\
G
PKOCKKDINCS OK THB AMBIUCAN ACADEMY
' (
"I
* »■
currents iii<!nco(l in tlie sccondnry wins. A rhcotonin was pl.-UM'd in
circuit witli tlit> illicit wiics of :i Hulinikortf'H coil, iiiul the tine wircH
were connected with two -strips of hr.iss (A and H), insulated from oiio
another l»v uieaus of a sheet of |ia|>er. V\hu\ phicii.;? the ear »<;.iiiist
one of the strips of hra-^s, ii s(»uud was |)ereeivt'd like that (leseriliejl
uli(»v»' as proceedinjf from an empty helix of wire during the |»assa<,'e of
an intermittent voltni<; current. A similar sound, oidy mu<-h moro
inti-nse, was (>mitted hy a tin-foil condenser when cunn<-cted with the
tint! wires of the coil.
One of the strips (»f bniHs. A (mentioned iiljove), was held closely
a<;ainst the ear. A loud sound cnmc! from A whenever the slip \\ was
touched with the other hand. It is douhtfnl in all thes(> cases whether
the sounds proc'eeded from the metals or from the imperfect conductors
intciposed between them. Further experiments seem to favor the
hitter supposition. The strips of brass A and H w(U'e held one in each
hand. TIk; induced currents occasioned a muscular tremor in the
liiij^t I's. I 'poll placinj; my forefin;ier to my ear ji loud crackliii<j noise
was audil)le, seeminirly proceedinj^ from the fiii<;er itself. A friend
who was present pla(«'d my limber to his ear. but heard nothiti<^. I
r('<pii'stcd him to hold the strips A and 11 himself. IU> was then dis-
tinctly conscious of a noise (which I was umilde to perceive) proceed-
\i\<l from his hmier. In these cases a portion of the induced currents
passed thronnh the head of the observer when he placed his ear a;;aiiist
his own liii'fer ; and it is uossilde that the sound was occusioned bv i*
vil)ration of the surfaces of the ear and tiiiiier iii contact.
When two persons receive a shock from a Kuhmkortt"s coil by claspinj^
hands, each takinj; liohl of oiu^ win^ (»f the coil with the free hand, a
sound proceeds from tlu! clasped hands. The etl'ect is not produced when
the hands are moist. When either of the two touches the boily of the
other a loud sound comes from the parts in contact. When the arm
of one is placed aj^ainst the arm of the other, the noise produced can be
heard at a distance of several feet. In all these cases a slight shock
is experienced so long as the contact is preserved. The introduction
of a piece of paper between the parts in contact does not materially
interfere with the production of the sounds, while the unpleasant
etl'ects of the shock are avoided.
When a powerful current is passed throu<rh the body, a nmsiciil note
can hv. perceiv(;d when the ear is closely ap))lied to the arm of the
person experimented upon. Tins sound seems to proceed from the
nuiscles of the fore-arm and from the biceps muscile. The musical
note is the unison of the rheotome employed to interrupt the primary
OF ARTS AND fiCIKNCES.
|.l:i('«'(l ill
line wirt'H
from olio
nr ii<i:iiiiKt
icissuji;*' «>f
luch inoro
<) with the
•111 I'loHcly
slip i^ wiH
ICS wlu'tlltT
wmliu't^^i''*
, favor tlu>
Olio ill t'lu'li
nior ill tlio
I'kliiijj noise
, A frioml
iiothiiif?- I
ftB then <liH-
VI') pro(H'0<l-
icimI curnMitrt
H e:ir a^'iiinf^t.
rtsioned by »■
,il by clnspin,!;
fire liiunl. ii
roduc'od when
I, iKxly of the
VluMi tlu! iinn
ndiiced can be
a slight shock
le introdurtioii
not niiitcriiiUy
ho unpleasant
a nnisical note
he arm of the
coed from the
The musical
pt the primary
circuit. I faihtd to obtain uiidil)Io ('(TectH in tluH wny when tlic pilrli
of tlio rhootoino was lii^h. Klisha (<niy * has also produced niidibh)
efrects by the passaj^o of indiiecMl electricity throii;,'li tlie human body.
A musical note is o(;casioned by tlu; spark of a Kniimkortr's coil wlim
the primary ciriMiit is made and broken suHiciently rapidly. Wlnu
two rheottmics of ditrerent pitch are causeil Himiiitaneously to open and
close the primary circuit, a doiiblu tone proceeds from the spark.
S>. When a voltaic battery is common to two closed circuits, the
current is divi(h'il between them. If one of the circuits is rapidly
opened and closed, a pulsatory action of the current is occasioned upon
the other.
All the aiiilible etTects resulting from the passage! of an intermittent
current can also be produced, though in less degree, by means of a
pnlsatory current.
lU. When a permanent magnet is caused to vibrate in front of the
pole of an electro-magnet, an undiilatory or oscillatory current <tf
electricitv is induced in the coils of the electro-maynet, and sounds
pn»ce«'d from the armatures of other electro-magnets placed upon the
circuit. The telephonic receiver referred to above (par. I ), was coii-
ni'Cted in circuit with a single-pole electro-nuigiiet, no liutteiy being
used. A steel tnniiig-fork which had lieeii previously magnetized was
cjiiised to vibrate in front of the polo of the olectro-magnet. A
musical note similar in pitch to that produced by the tiiniiig-fork
proceeded from the tele|)honic receiver in a distant room.
11. The ell'ect was much increased when a iiattciry was iiKiliided in
the circuit. In this case, the vibration "f tlu! permanent magnet threw
the battery-current into waves. A similar etlect was produced by the
vibration of an uninagnetized tuning-fork in front of the electro-magnet.
The vibration of a soft iron armature, or of a small piece of steel spring
no larger than the pole of the electro-iiiagiiet in front of which it was
placed, sutfict'd to prodm.'o andililo effects in the distant room.
12. Two single-pole electro-magnets, each having a resistaiu-o of
ten ohms, were arranged upon a cinuiit with a battery of five carbon
elements. The total resistance of the circuit, exclusive of the battery,
was about twenty-five ohms. A drum-head of gold-beater's skin,
seven centimetres in diameter, was placed in front of each (rlectro-
magnet, and a circular |)iece of dock-spring, one centimetre in
diameter, was glued to the middle of each memlirane. The telephones
80 constrncted were placed in diflerent rooms. One was retained in
* Klisha Gray. Ent?. I'at. Spec, No. 2040, see "Engineer," Aug. 14, 1874.
PROrEKDINOS OF TIIR AMERICAN ACADEMY
I
'#•'
tilt' (>x|)(>riiii(>iitiil room, and tliu other takuti to thu luiHOiUfiit of a:i
atljoiiiiiiir liniiHt'.
l.'|Hiii Hiii;,'iii^ into i\w l«'I('|tIion<», llic toncn of tlm voice \v<'ro ro-
produt'ctl Ity th«- inHtrnnit^nt in lli«! dixtant room. Wlit-n two pcrHonH
Hang HinudtancouHly into thu iiiHtrun)t>nt, two nol«>M w(>n> uniittcd Niniul-
tancoiisly liy tlio Iflcphon*' in th«; other house. A friend wiih sent
into tilt adjoinin;; l)tiildin!{ to noti; tlie etf'cct prtMhieed l)y arlindato
speech. I phicetl tliu nieinl>rane of tiie teleplione near my moiitli, and
uttered tlio Kcutenot), "Do yoii understantl what I say?" iVesentiy
an answer was returned tlirou<;h the iiiHtrument in my liand. Artieu-
hile woihIh proceeded from the clocli-xjirin}; atta<-lied to llie memhranu,
and I iieard the 8enten<'e : " Ych ; I understand yon perfectly."
Tlio articulation was somewliat mutlietl and indistinct, altliou;r|i in
this ca-MO il was intelli<rii)h'. Familiar tpiotations, such as, '*To lie. or
not tu 1m;; that is the question." "A horse, a horse, my kiii<rdom for
a horse." " What hath (Jod wroujfht," &.v., were jjenerully utidersto<Hl
alter a few repetilions. The cHecis were not sutliciently distinct to
admit of sustained convi-rsalion throii<{h the wire. Ind«-ed, as a ;;en-
eral rule, the articulation was uninteHi;;ilile, nxceptin<; when familiar
sentences were «'niploy«'il. Occasionally, howev«'r, a sentence wouhl
C(miti out with such startling distinctness as to render it ditlicult to
believe that the spniker was not i-lose at hand. No sound was iiudiide
when the t-lock-spring was removed from th<i mcnd>rane.
The elementary sounds of the Knglish laiigiiiige were uttered sm*-
cessively into one of the telephones and the ettects noteil at the (tther.
C'onsommtal sounds, with the exception (»f Fj and M, wi're unre<'og-
ni/ahle. Vowel-Kounds in most cases were <listiii(*t. Diplitlioitgal
vowels, such as (t (in ale), o (in old), t (in isle), i>w (in now), i>i/ (in
hoy), our (in poor), out' (in door), ere (in here), ere (in there), were
well marked.
Triphthongal vowels, stjch as ire (in fire), our (in flour), oicer
(in mower), ni/) r (in player), were also distinct. Of the elementary
vowel-sounds, the most distinct wcr«! those which had the largest oral
apertures. Such were a (In fur), aw (in law), a (in man), and e (in
men).
1.'5. Electricjd utidulations can be produced directly in the voltaic
current by vibrating the conducting wire in a licpiid of high resistance
included in the circuit.
The stem of a tuning-fork wjis comiected with a wire leading to one
of the telephones described in the preceding paragraph. While the
tuning-fork w;i8 in vibration, the end of one oi" the prongs was dipped
OF ARTS AND BCIENCES.
it of ilil
rtiTt' TV-
JHTHOIIH
ll sillUll-
kVilH HCIlt
rticiiltiti)
nth, uikI
'n-sfiitly
Artirii-
luliniiit!,
lion;;!) in
I'd 1h'. or
;.'il(im for
lult-rstoiMl
istinct to
l!^ II ;;t'ii.
I i'liiiiiliur
(•»' would
liriciilt to
lis aiidililu
tJTcfl sne-
tlio otlicr.
' iiiin-coy-
i|llltllOll<{lll
w). Ill/ (in
on;), wcro
lur), nwer
ilciiu'utary
irfjcst onil
, und e (in
the voltaic
rosistunco
liii;^ to one
Whih- the
was tiiitped
into wiilfi iii«'lii«l(Hl in tlio circuit. A hoiiiuI pHNTcilcil from tlic diittiiiit
tclr|ihoi;c. When two tiiiiiii)r-t'orkM of ililVcrcnt pitrh were coiiiicrlcd
loj^rtlifr, mill Hiniiihaiu'oiiHly chiihc<I Iu vihniti^ in tho wntcr, two iiiiiHicul
not(*H (the uniHoiiH rciiM^ctivcly of thoHu produced hy the furkH) wcru
emitted HimultancouHly hy ihu lelcplionc.
A phitinnin wire attach*'*! to a Htrctchc<1 mmilirain^ nipli-tcd a
voltaic circuit l)y dipping into water. Tpon Hpcukiii;r to the iiicmiiraiie,
arliciihite hoiiikIm procee<h-d from tlie tch'phoiiu in the distant room.
The soiiiidH produced liy tiie teh'phoiie h<-camu K>iider wlieii dilute siil-
phuri«; acid, or a Hatnratcd Hohition of Halt, was Hiiltsiitnteil for tli«
water. Aiidihle ctl'ects weru also produced hy tln^ vihration of pliuiiha^o
in mercury, in u Molution of hichromate of potash, in salt and water, in
dilute sulphuric acid, and in pure water.
I \. Sullivan * disc*»vcred that a current of (electricity is peiierated
l»y the vihration of a wire <;oni|M)«ed partly of one metal and partly of
another: and it is prohahle that electrical iindulatioiiH were caused hy
the vihration. Tin; current was produced ho loii); as the wire emittiHl
u musical note, hut Htopped immediately upon the cessation of tlio
(iouiid.
I.'). Altliou<;h sounds proceed from the armatures of elect ri>-iiiai;iiels
under the iiitluem-e of iiiidiilatory currents of electricity, 1 have heeii nii-
aide to det«'Ct any audihie ettects diu! to the electro-maj^nets theniselvus.
An iiiidiilatory current was passed through the coils of au electro-
magnet which was held closely against the ear. No sound was per-
ceiveil until a piece of iron or steel was pn-sentcd to the pole of llio
mauiiet. No sounds either were ohserved when the undulatnrv cur-
I'eiit was passed through iron, stetd, retort-carhon, or plumbago. In
these respects an undiilatory current is curiously diirerent from an inter-
mittent on*'. (See par. 2.)
](>. The telephonic efiects descrih.ni above are produced by three
distinct varieties of currents, which I term resp<'Ctively intermitlent,
pulsatory, and midulatory. Jntcrnuttfnt rurrt-nts are chaiaclerlzed by
the alternate presence and absence of electricity up(»n the circuit;
Piihntory ciirrentg result fi-om Kiidden or instantaneous changes in the
intensity of a coiitiiiuous current; and iiinhdiitury riirnnts are pro-
duced by gradual <"liaiiges in the intensity of a current analo<;ous to
the (changes in tin- di-iisity of air occasioned by simjde peiididous
vibrations. The varying intensity of an undulatory current can be
* Siillimn. " Currents of Kluctricity produccil by tliu vibration of Mt-tala.
riiil. Mag., 1845, p. 201 ; Arch, de rfilcctr., X., p. 4»0.
10
PROCEEDINGS OP THE AMERICAN ACADEMY
i
ropreseiite<l by a sinusoidal curve, or by the resultant of several sinus-
oidu! curves.
Intermittent, pulsatory, and undulutory currents may bo of two
kinds, — voltaic, or induced; and these varieties maybe still further
discriminated into direct and reversed currents ; or those in which
the ehictriciil impulses are all positive or negative, and those in which
they are alternately [wsitive and negative.
<^ u u
So. a
9 5
Intermittent.
K 5 ^ ^I'ulsatory.
— i, il
4) "3 O
Undulatory.
V
( Voltaic. I ^^''''' (f "« P'^""- *' 2' ^' ^' ^' ^>
J \ Keversed.
J T 1 1 i Direct.
( Induced. < ,, , /o q\
'^ ( Uevcrscd (See par. H).
^ Direct (See par. 'J).
^ Iltnersed.
< Direct.
( Reversed.
S Din<t (See par. 11, 12, 13, 15).
\ Hciversed.
j Direct.
^ Reversed (S(!e par. 10).
17. In conclusion, I wouhl say that the diHerent kinds of currents
described above may be studied optically by means of Ki'mi^'s luano-
metric capsule.* The instrument, as I hav(^ empl<»yed it, consists
simply of a gas-chamber closed by a meml»rane to which is attached
a piece of clock-spring. When the spring is sultjected to the attraction
of an electro-magnet, through the coils of wliich a "telephonic" current
of electricity is passed, tl ' Hami' is thrown into vibration.
I find the instrum(>nt invaluable as a rheimieter, for an ordinary
galvanometer is of little or no use when "telephonic" currents are to
l)e tested. For instance, the galvanometer needle is insensitive to the
most jiowerful undulatory current when the impulses are reversed, and
is only slightly deflected wlien they are direct. The nuinonietric cap-
sule, on the other hand, affords a means of testing the aniplitu<le of
the electrical undulations; that is, of deciding the diHerence between
the maximum and minimum intensity of the current.
♦ Kiiiwi. " Upon Manometric Flames," Thil. Mag., 1873, XLV., No. 297,
2'J8.
il sinus-
of two
furtluT
in which
PURCHASED FROM
HKut^»^»\^.Cvv9^v^ Vv^ViCi
, 4, 5, 6).
^X LIBl^jQ
2, 13, 15).
)•
of currents
lli.r's lUiUlO-
it, rousists
is attiicheil
e attnii'tiou
ic" current
in ordinary
[rents are to
sitive
to tlie
■vi-rsed, and
oinetric cap-
unplitude of
JACOBl SOUS COHEN.
ICC
between
LV., No. 297,