SB 
 
GIFT OF 
 
THE DYNAMO. 
 
THE DYNAMO 
 
 HOW MADE AND HOW USED. 
 
 for 3 
 
 S. R BOTTONE, 
 
 CERTIFICATED SCIENCE TEACHER, SOUTH KENSINGTON, 
 LATE OF THE ISTITUTO BELLING, NOVARA, 
 
 AND OF THE 
 
 COLLEGIO DEL CARMINE, TURIN. 
 
 
 FOURTH EDITION. 
 
 LONDON : 
 
 SWAN SONNENSCHEIN, LOWEEY AND CO., 
 PATERNOSTER SQUARE. 
 
 1887. 
 
34 
 
PKEFACE. 
 
 THIS work was not written for the manufacturer of large 
 Dynamos : it originally appeared in the pages of the English 
 Mechanic in answer to the demands of many amateurs, who, 
 desirous of constructing a small dynamo, capable of being 
 worked by hand, and of giving a current sufficiently powerful 
 for experimental purposes, were in need of such practical 
 information, as to the correct proportion of the various parts, 
 and the precautions necessary to ensure success, as they had 
 been unable to gather elsewhere. 
 
 Encouraged by the flattering reception with which it has met, 
 the author places it before the public in a separate form, trusting 
 that it may lead many to taste the pleasures which can bs 
 extracted from even a slight acquaintance with the science of 
 Electricity, 
 
 & K. BOTTONE. 
 
 46452 
 
THE DYNAMO: 
 
 HOW MADE AND HOW USED. 
 
 THE interest awakened in machines for the generation of current 
 electricity, consequent upon the demand for electric lighting and 
 transmission of power, has induced many amateurs to turn their 
 energies to the construction of small dynamos, such as might 
 replace a battery of eight or ten cells, without the disagreeable 
 concomitants of changing acids, cleaning plates, etc., provided 
 such dynamos could be afterwards worked without the employ- 
 ment of power. Such efforts have not generally met with 
 success, owing to the fact that no work of a practical nature ha? 
 yet appeared in which the construction of the dynamo is fully 
 explained. When the principles which control the manufacture 
 of such machines is understood, dynamos can be constructed 
 with as much ease and certainty as induction coils ; and in the 
 following pages these principles will be elucidated sufficiently to 
 enable the amateur to carry out his work in an intelligent 
 manner. 
 
 1. What a Dynamo is. As understood at present, the dynamo- 
 electric machine may be defined as a machine whereby energy 
 (motion) is converted into electricity by the aid of the residual 
 magnetism present in certain iron portions : which electricity is 
 caused to react on the iron and so heighten its magnetism ; and 
 this increased magnetism in its turn gives rise to more powerful 
 electrical effects, and so on, until a limit is reached, depending 
 partly on the velocity of the motion, partly upon the relative 
 apportionments of the size and quantity of the wire and iron 
 
 1 
 
Tht Dyna'mo:' *Hoiv Made and how Used. 
 
 employed in its construction, and partly on the resistance through- 
 out the circuit. Although this principle was fully understood, 
 and described by Soren Hjorth, of Copenhagen, in his patents, 
 dated October, 1854, and April, 1855, yet the name 'dynamo' 
 (from dynamis, Gr., force) does not appear to have been used in 
 this connection until Dr. Werner Siemens employed it in a com- 
 munication to the Berlin Academy, January 17, 1867. 
 
 2. Faraday's Discovery. The closeness of the relationship 
 between the phenomena which we call electricity and magnetism 
 had struck many philosophers of the eighteenth century. Oersted, 
 of Copenhagen, in 1819, was the first to prove, by a series of 
 masterly experiments, the magnetic properties of current elec- 
 tricity ; Ampere, and Arago in France, and Sir Humphry Davy 
 in England, then distinguished themselves by their zeal and 
 activity in this research ; but the keystone of the arch was laid 
 when Faraday, in November, 1831, showed that it was possible 
 to call forth electric currents by means of a magnet. In order 
 that the reader should have an intelligent knowledge of the 
 principles which underlie the construction of the dynamo, it 
 would be well for him to repeat some of the experiments about 
 to be described, more especially as they are easy of performance 
 and trifling in cost. 
 
 The first thing required will be a galvanometer, an instrument 
 for indicating the presence of current electricity (and in some cases 
 to measure its quantity). To make this, a piece of crinoline steel, 
 2 inches long and -J of an inch in width, is * softened ' by heating 
 the middle portion over a gas jet or other flame, until red hot, then 
 allowed to cool gradually. By laying this across a knife blade 
 the exact centre is found and marked. By means of a screw-drill 
 a hole about -% of an inch diameter clear through the centre of this 
 steel ' needle/ as it is called, is bored. By filing from the centre 
 towards the side the needle is brought to the shape of a lozenge, 
 as seen at Fig. 1, A. Holding this needle by means of a piece of 
 copper wire passed through the hole, it is heated to dull redness 
 over a flame and plunged into cold water to restore its temper. 
 A piece of brass rod, J of an inch in diameter, and about J of an 
 inch long, is now soldered centrally, just over the hole. This is 
 easily done by cleaning the needle with a bit of sandpaper, 
 
The Dynamo : How Made and how Used. 3 
 
 12 
 
4 The Dynamo : How Made and how Used. 
 
 specially round the hole, cleaning also the little piece of brass 
 rod, on its end, then putting a little piece (as big as a grain of 
 mustard-seed) of plumbers' solder just over the hole bored in the 
 needle. Holding the needle with a pair of forceps (a little rosin 
 powder having been previously applied round about the hole) 
 over the flame of a spirit-lamp or gas-burner, will cause the 
 solder to melt and adhere to the steel. The piece of brass is 
 now taken up with another pair of forceps, and laid (flat side 
 downwards) as centrally as possible over the hole. Keeping the 
 needle still over the flame, the solder will also flow round the 
 brass and adhere to it, making a firm junction, when it may be 
 removed from the flame, and placed at once on a cold metal or 
 stone surface. It should now present the appearance shown at 
 Fig 1, B. Any solder which may have exuded from between the 
 brass and the steel should be filed away. Using the same bit in 
 the screw-drill that was employed originally to bore the hole 
 through the steel, a conical hole, reaching nearly but not quite to 
 the opposite surface of the brass piece, is drilled from the hole in 
 the steel. This serves as a pivot on which to poise the needle. 
 A trial may now be made to find whether the needle is fairly 
 centred ; but no attempt need be made yet to balance it if not 
 true. Having cut off the head of a fine-pointed pin, let us drive 
 it, blunt end downwards, into the centre of a little slab of well- 
 seasoned pine 3 inches by 3 inches by J an inch, leaving not less 
 than J of an inch protruding. On the point we can poise the 
 needle, and mark with a pencil the end which hangs (if either 
 does). Fig 1, C, will show what is meant. The needle must now 
 be magnetized by being allowed to remain for some time (twenty 
 minutes or half an hour) across, and in contact with the poles of 
 a horse-shoe magnet, care being taken that having once placed 
 the needle in one position it should not be reversed, as its polarity 
 would be reversed if this were done ; and since in our latitude 
 the north-seeking pole of a freely suspended needle hangs dowmvards, 
 if the needle, when tried previous to magnetizing, had one end 
 heavier than the other, that end must be placed against the north 
 pole of the horse-shoe magnet, by which means it will acquire 
 south-seeking polarity, and consequently neutralize to a certain 
 extent the inclination of the poised needle. After magnetization 
 
The Dynamo : How Made and how Used. 5 
 
 it should be again poised, any deviation from the horizontal line 
 noted and corrected by cautiously filing the needle on one of its 
 flat sides, at its heavier extremity, with a fine file, until perfect 
 equilibrium is obtained. Fig. 1, D, illustrates the position in which 
 the needle should be placed with relation to the magnet during 
 magnetization. AVhen the needle has been well balanced it ought 
 to turn very freely on its pivot, making several free swings, but 
 finally taking up a position pointing north and south. It should 
 also show decided polarity when tested with a magnet ; that is to 
 say, one extremity should be strongly attracted, and the other just 
 as strongly repelled on the approach of the north pole of a horse- 
 shoe or bar magnet. When all these conditions have been satisfied, 
 it will be well to mark with a pencil the letter 1ST on the extremity 
 of the needle, which is repelled by the north-seeking (or marked) 
 end of the magnet. This extremity will be the north-seeking end 
 of the needle, and is generally (though inaccurately) called its 
 north pole. 
 
 3. We have now succeeded in making and poising a magnetic 
 needle. In so doing we have learnt two important facts : (a) that 
 steel becomes permanently magnetic when placed in proximity to 
 a magnet ; (b) that each pole of the new magnet thus formed 
 evinces a polarity of opposite kind to that possessed by the pole 
 of the original magnet which induced its magnetic condition : in 
 other words, the north pole of the original magnet induces south 
 polarity in that portion of the steel nearest to it, while the south 
 pole induces north polarity. 
 
 Our next step is to surround the needle with' a coil of insulated 
 copper wire. To this end a piece of wood 2J inches wide by 
 1 J inch thick, and of convenient length to hold in the hand, is 
 prepared as a form, the edges being slightly rounded to admit of 
 the wire being slipped off; this is then wound with about 10 feet 
 of No. 30 silk-covered copper wire, as shown at Fig. 2, A, leaving 
 about 3 inches of wire projecting at each extremity. The four 
 corners of the rectangle thus formed should be bound with silk, 
 so as to prevent uncoiling when the rectangle is drawn off the 
 wooden form. The coil, on removal from -the form, should pre- 
 sent the appearance shown at B, in which the ends of the silk 
 vised to tie the corners are purposely exaggerated in length, the 
 
6 The Dynamo : How Made and how Used. 
 
 better to show their position. The centre of the coil being 
 found, the wires forming one of the flat sides are slightly parted 
 by means of a blunt pin (care being taken not to abrade the 
 silken covering, and the coil passed over the pin-point fastened in 
 the centre of the little baseboard above described ( 2,) and attached 
 thereto with a little dab of hot sealing-wax, or better still, with 
 Front's elastic cement. The needle is then replaced, and tried, to 
 see whether it oscillates freely without catching at any point in 
 the coil. The two free ends of the wire are now to be denuded 
 of their silk covering, cleaned with a bit of sand or glass paper, 
 and attached to two small binding screws (those known as tele- 
 phone binding-screws, and sold at most electricians at Is. 6d. per 
 dozen, will do admirably), inserted one at each corner of the base- 
 board. The galvanometer or multiplier is now complete, and 
 should appear as figured at C. When all is in position, note from 
 which binding-screw starts the wire which goes over the needle. 
 Mark this binding-screw by writing * over ' near it. The gal- 
 vanometer is used to detect the presence of current electricity by 
 causing any such current to pass through the coils of the instru- 
 ment. For this purpose the two opposite extremities of [any 
 circuit, through which it is supposed a current is flowing, are 
 each connected to one of the binding-screws. If a current passes, 
 the needle (which previously must be made to lie parallel with 
 the coil, by turning the baseboard round until the coil points 
 north and south, like the needle) will immediately start out from 
 its position of parallelism with the coil, and take up a position 
 which will approach nearer to right angles with the coil, in pro- 
 portion as the current is stronger. To test whether the galvano- 
 meter just made be fairly delicate, attach a piece of copper wire 
 about ^g- of an inch thick and 6 inches long to one of the binding- 
 screws ; to the other attach a similar piece ol iron wire. Now 
 bring the free ends of the wire (by bending) within J of an inch 
 of each other. Turn the baseboard round until the north end 
 of the needle points between the two binding-screws, perfectly 
 parallel to the coil. Put a single drop of vinegar on a little piece 
 of glass, and bring it under the two ends of the wires, which must 
 be lowered until they are both in the drop of vinegar, but do not 
 touch each other. By the action of the vinegar on the two 
 
The Dynamo : How Made and how Used. 7 
 
 F/C.Z 
 
8 The Dynamo : How Made and hoiv Used. 
 
 metals, an electrical disturbance is set up, which produces a so- 
 called ' current ' which starts from the iron, passes through the 
 vinegar, along the copper wire, through the coils of the galvano- 
 meter, and back again into the iron, this action being continuous 
 as long as the vinegar acts on the iron. Simultaneously with 
 this, the needle is seen to deflect from the line of the coil, and if 
 our galvanometer is a success, it should stand out at least 20 from 
 the central line of the coil. Faraday's great discovery, on which 
 all dynamos are based, consisted in proving that a magnet could 
 be caused to excite a current, similar to that produced by the 
 action of acids on metals. We can now repeat his experiment 
 with the aid of our galvanometer. Let A, Fig. 3, be a rod of 
 \ inch soft iron, about 6 inches long, bent to the shape of the 
 letter U, and wound round its central portion with about 100 feet of 
 No. 24 cotton-covered copper wire, the two ends of which (about 
 a yard each end) having been stripped of their covering, must be 
 attached to the binding-screws of the galvanometer. If a good 
 horse-shoe magnet, B, be placed in contact with the two legs of the 
 coiled U, this latter being kept motionless, while the magnet is 
 alternately approached to and separated from it, it will be found 
 that the needle of the galvanometer is powerfully affected, first in 
 one sense and then in the other, according to whether we make, 
 or break contact with the U, or armature, as it is called. We 
 shall also find that, although the most powerful effects are noticed 
 when actual contact and actual separation take place, yet currents 
 are also produced on approaching or removing the magnet to or 
 from a distance. In other words, motion in the field of a magnet 
 gives rise to electricity. A contributor to Blackuwd's Magazine 
 embodied this fact in the following lines : 
 
 ' Around the magnet, Faraday 
 Is sure that Volta's lightnings play ; 
 
 But how to draw them from the wirs ? 
 He took a lesson from the heart ; 
 "Tis when we meet, 'tis when we part, 
 Breaks forth the electric fire.' 
 
 If we study the effects thus obtained, we shall find that they 
 differ in some points very markedly from those obtained by the 
 action of acids on metals (voltaic electricity galvanism), inasmuch 
 
The Dynamo : How Made and how Used. 9 
 
 FIG. 4. 
 
io The Dynamo: How Made and how Used. 
 
 as first, the action is not continuous ; secondly, it is contrary in 
 direction when contact is made to what it is when it is broken, 
 
 4. The student will do well to compare the effects produced 
 on the galvanometer by the battery current, and by the current 
 obtained from the magnet. Any single cell will do for this pur- 
 pose; and in order to have an intelligent perception of what 
 takes place, the student must bear in mind, that in the battery 
 itself, the electricity (undulatory movement of the molecules) 
 passes from the zinc to the negative plate (be it copper, silver, 
 platinum, or graphite), while outside the battery, the electricity 
 passes from this latter round through the wires, galvanometer, or 
 other circuit open to its passage, back again to the zinc plate. 
 (See Fig. 4, where the direction of the undulation, or * current,' is 
 shown by the arrows ; the plate marked Z being zinc, the one 
 marked C being carbon, copper, or other conductor ; W W being 
 the wires forming the poles or electrodes). If the positive pole 
 (the one from which the ' current ' is flowing, the wire attached 
 to the C plate) of such a battery be connected to the galvanometer 
 by means of the binding-screw marked 'over,' the other pole 
 being attached to the other binding-screw, the north pole of the 
 needle having previously been adjusted so as to lie between the 
 two binding-screws, it will be found that the north pole of the 
 needle will deflect to the left of the line of the coil ; the operator 
 being supposed to be standing at the binding-screw end of the 
 galvanometer. Since the w r ire of our coil returns below the needle, 
 it is evident that a positive current (an outflow of undulation) 
 passing over the north pole of a horizontally suspended needle, or 
 a negative current (an influx of undulation) passing under such a 
 north pole, causes it to deflect to the left. 
 
 If we disconnect the battery and reverse the connections id 
 est, join the negative pole (the wire coming from the zinc) to the 
 binding-screw marked ' over,' the other pole being connected to 
 the other screw the opposite effect results : viz., the north pole 
 now deflects to the right of the coil. This will be understood by 
 reference to Fig. 5, in which a represents the effect of the positive 
 current flowing from the operator over the needle, the north pole 
 in both illustrations being nearest to him; in b the positive 
 
The Dynamo : How Made and hoiv Used. 1 1 
 
[2 The Dynamo : Hoiv Made and how Used. 
 
 current is supposed to be flowing from the operator, below the 
 needle, in either case returning to the battery the opposite way. 
 
 5. This effect will enable us at once to recognise, by means of 
 our galvanometer, the direction in which a current is travelling ; 
 for, on connecting the two terminals of any source of electricity 
 to the binding-screws of the galvanometer, whilst the north pole 
 is in a line with the coils, between the two binding-screws, the 
 operator facing the north pole of the needle, it is evident that if 
 the north pole of the needle is deflected to the left, the terminal 
 attached to the binding-screw marked ' over ' is positive ; but that 
 if the north pole deflects to the right, then the said terminal is 
 negative. It must be borne in mind that by the term positive in 
 this connection is meant the point from which electricity is flow- 
 ing, negative being the point towards which it is flowing, or at 
 which it enters.* This power of recognising the direction of a 
 current will be found of great service to us in the construction of 
 the dynamo. 
 
 6. Eeturning now to our experiments with the magnet (see 
 latter portion of 3), and using in preference a straight soft iron 
 rod, about 6 inches in length, and ^ an inch in diameter, coiled 
 with about 100 feet of No. 24 covered wire as our armature, and 
 a good bar magnet to produce the electrical effects, we shall find, 
 on coupling up the armature wires to the galvanometer, and 
 approaching one end of the armature to or receding it from the 
 north pole of the magnet, that the electrical flow set up is alwaj*s 
 in one direction in approaching or making contact, and in the 
 opposite direction on receding or breaking contact. Fig. 6 will 
 make this clear. The arrow at a shows the direction of the 
 current produced on approaching or making contact with the 
 north po^e of a magnet; b illustrates the direction of current 
 produced on receding from or breaking contact with the north 
 pole of a magnet. If now we reverse the experiment by pre- 
 senting the south pole of the magnet to the coiled armature, we 
 
 * We have no desire to enter into any theoretical matters in these pages ; 
 but comparing electricity to sound, we may say that in blowing a blast in a 
 trumpet, the trumpet may be considered as positive, while the ear of the 
 listener may be considered as being negative. The chief difference seems to 
 be that electrical undulations seem to require a complete circuit wherein to 
 display their effects, sound undulations being bound by no such conditions. 
 
The Dynamo : How Made and how Used. 1 3 
 
 FIG. G. 
 
14 The Dynamo: How Made and how Used. 
 
 shall find that the direction of flow is also reversed ; that is to 
 say, the withdrawal of a south pole produces the same effect as 
 the approach of a north pole, and vice versd, the approach of a 
 south pole is equivalent in its effects to the recession of a north 
 pole. It must be noted that the direction in which the wire is 
 coiled round the soft iron rod (or armature), while it has no 
 influence on the direction of the electrical current set up round 
 the iron rod (which is always the reverse to the hands of a clock 
 in the face approaching the north pole) determines the extremity 
 of the said wire at which the current leaves or enters the coil. 
 In the figure we have supposed the wire to he wound from left 
 OVER towards right ; had we wound our rod from left UNDER 
 towards right, the opposite ends of the wire would have been 
 respectively -h and . This must be borne in mind when we 
 proceed to actual work. 
 
 7. Currents can produce Magnetism. If we take the coiled soft 
 iron U, of which we made use 3, and apply it to pieces of soft 
 iron, nails, filings, etc., we shall find that it possesses little or no 
 magnetic power of attraction ; but if we couple the projecting 
 ends of the coiled wires one to each terminal of a single-cell 
 battery, we shall find that the U will become powerfully magnetic, 
 retaining its magnetism as long as electricity flows around the 
 coils, but losing nearly all the instant that the flow is caused to 
 cease, either by breaking connection with the battery, or by any 
 other interruption. The rapidity and completeness with which 
 the iron loses its magnetism depends almost entirely on its softness 
 and purity. Anything which tends to put a strain on the mole- 
 cules of the iron, such as hammering, filing, twisting, sudden 
 cooling, vibration, etc., render it liable to retain magnetism, or 
 increase its coercitive force ; whereas raising to a high temperature 
 and very gradual cooling, which allows the molecules to range 
 themselves with little or no strain, furnishes a soft iron, eminently 
 incapable of retaining magnetism, or possessing little coercitive 
 force. 
 
 8. The direction in which the flow of electricity takes place 
 around the iron bar decides which end of the bar acquires north- 
 seeking, and which south-seeking polarity. Let us suppose, as in 
 Fig. 7, A, that one extremity of the bar be made to face us, and 
 
The Dynamo : How Made and how Used. 1 5 
 
1 6 The Dynamo: How Made and how Used. 
 
 that the current be caused to flow in the direction of the motion 
 of the hands of the clock ; in this case, the farther extremity of 
 the bar becomes a north-seeking pole, while the nearer extremity 
 becomes south-seeking. The direction of the current, and conse- 
 quently the polarity of the bar, may be reversed by joining up 
 the opposite electrodes of the battery (or other source of electricity) 
 to the ends of the wire coiled round the bar, as shown at B ; 
 where, as the wire is joined to the electrodes in a manner just 
 the reverse to that shown at A, so also the current enters at the 
 opposite end of the wire, and produces contrary magnetic effects. 
 The same result may also be attained by coiling the wire around 
 the bar in the contrary direction, while leaving the connection 
 with the electrodes unchanged, as represented at C (Fig. 7). 
 Perhaps the simplest means of remembering the relation which 
 exists between the direction of the current and the position of the 
 magnetic poles produced, is one known as 'Ampere's Rule/ in 
 which the experimenter considers himself to be swimming head 
 foremost, with the current, along the wire, always facing the iron 
 core ; then the NORTH-SEEKING POLE will always be at his LEFT 
 HAND. (See Fig. 8.) 
 
 9. It must be borne in mind, as being of the greatest impor- 
 tance in the construction of successful dynamos, that although 
 steel, or hard iron, when subjected to this inducing action of the 
 current, becomes magnetic, yet it does not acquire nearly such 
 powerful magnetism as soft iron ; and, in fact, the softness of the 
 iron, and its capacity for becoming powerfully magnetic, run side 
 by side. On the other hand, it must not be forgotten, as we 
 learnt at 7, that the softer the iron the sooner it loses the 
 magnetism imparted to it ; while the harder brands of iron (and 
 more especially steel) retain nearly all the magnetism which it is 
 possible to confer upon them. 
 
 10. The student who has carefully and intelligently performed 
 the experiments described in the previous sections, will now find 
 himself in a position to understand the principles which underlie 
 the construction of the dynamo, even though he may have little 
 or no previous knowledge of electricity. The first machine con- 
 structed after Faraday's discovery was that of H. Pixii, in 1832. 
 In this machine a powerful horseshoe magnet was caused to rotate 
 
The Dynamo: How 'Made and how Used. 17 
 
 Fig. 8. 
 
1 8 The Dynamo : How Made and how Used. 
 
 rapidly before a soft iron U-piece, wound with insulated copper 
 wire, the two extremities of which were prolonged by two brass 
 springs pressing against a rotating split collar of brass, whose 
 office was to rectify the direction of the currents produced by 
 rotation of the magnet, before the iron core ; currents which, as 
 we have seen ( 4), are in different directions, according to whether 
 a, given pole of a magnet is approaching to or receding from the 
 core. This arrangement for causing alternating currents to flow 
 in one direction, is known as the commutator, and it, or some 
 modification of it, is most extensively used in all dynamos in 
 which it is of importance that the current should flow in one 
 direction only. The chief disadvantage in this machine was that 
 of having to rotate a heavy magnet (built up of a number of thin 
 steel plates), since the mere rotation tended to destroy, or at all 
 events, to weaken its magnetism. In 1833 Mr. Saxton had the 
 happy idea of fixing the heavier and causing the lighter portions 
 of the apparatus to rotate : in other words, the magnet (or 
 magnets) was now made a fixture, while the U-shaped soft iron 
 armature, with its surrounding coils of wire, was caused to rotate 
 rapidly before it, on axis or spindle, either by gear-wheels or 
 wheel and band. Mr. E. M. Clarke, in 1834, noticed that the 
 thickness of the wire coiled round the armature had a consider- 
 able influence on the nature of the current produced by these 
 machines. If the wire employed be very thin, say about the T l^j 
 of an inch in diameter, and a large number of convolutions be 
 coiled around the legs of the armature, the electricity produced is 
 of high tension, capable of overcoming considerable resistances, 
 and of giving severe shocks. If, on the contrary, a smaller 
 quantity of a much thicker wire, say from the -f T to the y 1 ^ of an 
 inch be made use of, the current produced is that known as a 
 quantity current, or a * large ' current, possessing but little power of 
 overcoming resistances, not capable of giving shocks, but giving 
 fine large sparks, and able to decompose water, and other chemical 
 bodies. Clarke usually furnished two armatures with his machines, 
 one wound with about 1,500 yards of covered wire ^ of an inch 
 in diameter, which he designated the ' intensity ' armature ; the 
 other, wound with about 40 yards of wire ^ of an inch thick, to 
 which he gave the name of the * quantity ' armature. One pecu- 
 
The Dynamo: How Made and how Used. 19 
 
 liarity of the machines turned out by Clarke was the fact of the 
 rotating U-shaped armature being made to rotate near the flat 
 sides of the magnet instead of in front of the poles. This, though 
 it facilitates somewhat the mechanical arrangements, is open to 
 some objections on the score of lesser efficiency, since the most 
 active portion of the magnet is certainly in front of the poles. As 
 Clarke's machine embodies nearly all the principles found in later 
 dynamos, we shall give an illustration^ together with detailed 
 explanation of the commutator, etc., in our next paragraph. 
 
 11. In Clarke's machine the horseshoe magnet, A, Fig. 9, is 
 clamped to a rigid backboard, which is mortised to the baseboard. 
 In front of this magnet, and in close proximity to its poles, is the 
 armature B B', which can be made to rotate on its axis at c, which 
 passes right through the backboard, behind which it is supported 
 on bearings. The distant end of the axis is fitted with a pulle}', 
 around which plays a band or gut coming from the fly-wheel /. 
 On turning the handle of /, the small pulley enters into rotation, 
 carrying with it the armature. This armature (which represents 
 the U-piece described at 3, Fig. 3) is really constructed of three 
 pieces of very soft iron, two short circular bars and a cross-piece, 
 held together by screws, as shown at b. Around the two bars is 
 carefully coiled the insulated* copper wire, in such a manner that, 
 if the bars were straightened out, the winding would be always in 
 one continuous direction, either from left over to right, or vice versa, 
 and the two extreme ends of the wire are brought out and joined 
 metallically with the two metal half-cylinders which form the 
 commutator c. This commutator is illustrated more fully at 
 Fig. 10 c. Against the commutator press the two brass springs 
 d and d' t to which are connected the wires e and e', which form 
 the real electrodes or poles of the machine. Fig. 10 shows how the 
 wire is wound round the two soft iron cores B and B', which are 
 screwed to the soft iron cross-piece at A and A', thus constituting 
 virtually a coiled U-piece. The two ends of the wire which forms 
 these bobbins come out at opposite sides of the bobbins, and are 
 soldered or screwed to the two half-cylinders (of brass) c and c', 
 as shown at b and b'. In order that the two cheeks of the com- 
 
 * A body is said to be insulated when surrounded by substances which pre- 
 vent the passage of electricity. 
 
 22 
 
2O The Dynamo : How Made and hoiv Used. 
 
 mutator, c and c' (which are shown separately to the right-hand 
 of Fig. 10), should not allow the electricity to escape from one tc 
 the other, the spindle which carries the bobbins B B' and the cross- 
 piece A A', is encased in a thick ring of ivory, baked boxwood, 01 
 other insulator, which in the illustration is shaded darkly. 
 
 FUNCTION OF THE COMMUTATOR. 
 
 12. If we follow one of the bobbins of the armature during 
 its revolution before the poles of the magnet, we shall find that it 
 changes its magnetic condition, and consequently its electrical 
 state, twice, during each revolution. Let us take, for instance, the 
 bobbin B' in either figure in its rotation from the north pole of 
 the magnet towards the south pole : as we learnt at 6, leaving a 
 north pole or approaching a south pole produces the same effect; 
 and this effect will be that a current will flow round the bobbin 
 from the right over towards the left. Hence, if the wire (which is 
 coiled round the bobbin in the same direction) have its correspond- 
 ing extremity joined to any circuit, this extremity will be found 
 to be negative. In practice this extremity is actually connected 
 with the cheek c' of the commutator. This cheek c' during the 
 whole of the semi-revolution of the bobbin B' from north to south, 
 is being pressed against by the spring d', which, with its wire e', 
 is consequently kept continuously in a negative state until the 
 bobbin B' has arrived quite opposite the south pole of the magnet. 
 At this instant the spring d' touches neither of the brass half- 
 cylinders, but presses against the ivory, boxwood, or other insu- 
 lator, which separates the two half -cylinders of the commutator 
 c and c'. Hence, no current flows; but directly B' leaves the 
 middle of the south pole and begins to complete the under-half of 
 the revolution, its cheek comes into contact with the spring on 
 the opposite side, d. But now we find that the bobbin B' is 
 leaving a south pole to approach a north pole ; therefore, according 
 to 6, the current is flowing in the opposite direction round the 
 bobbin. Therefore the spring d collects from the cheek c' positive 
 electricity. What has been said of bobbin B' is, of course, equally 
 true of bobbin B at similar points of its revolution ; hence we seo 
 that, although each bobbin becomes alternately north and south 
 AS it approaches the south or north pole of the permanent magnet, 
 
The Dynamo : How Made and how Used. 2 1 
 
 Fig 9. 
 
22 The Dynamo : How Made and how Used. 
 
 and sends therefore a current alternately in contrary directions, 
 yet, since (owing to the insulated half-cylinders) we are able to 
 cause one spring to pick up the current from the bobbins whilst 
 the free extremity of their encircling wire is sending a positive 
 current only (the other spring picking up the current only whilst 
 the free extremity of the coiled wire is negative), it follows that 
 the springs d and d' are maintained in oppositely electrified con- 
 ditions. It must be borne in mind that the wire is coiled con- 
 tinuously round both bobbins ; hence, that as the bobbins are 
 always exposed at the same time to opposite magnetic influences, 
 so the conditions of the two extremities of the coiled wires are 
 electrically opposite viz., while one is positive the other is negative, 
 and vice versd ; but that as the bobbin, whichever it be, which 
 travels from north over to south has the free extremity of its wire 
 always negative and in connection with the spring d', while the 
 bobbin (each in turn) which passes under from south to north has 
 its extremity always positive and in connection with the spring d', 
 it follows that, providing always the motion be that indicated by 
 the arrow in Fig. 10, the spring d' will always be kept in a negative 
 condition, while the spring d will simultaneously be positive. 
 
 Since the comprehension of the function of the commutator is 
 of the highest importance in the manufacture of the dynamo, we 
 recommend the amateur to digest carefully the contents of this 
 last section. 
 
 13. The next great step in the development of the dynamo 
 was the application of the current generated by the armature to 
 the heightening of the magnetism of the magnets which set up 
 that current in the armature. We have seen ( 7) that a current 
 sent round a mass of soft iron converts that iron into a magnet; 
 and we find that the intensity of magnetisation is, up to the point 
 of saturation, proportionate to the quantity of electricity flowing 
 round the iron. We also know that magnets produced by such 
 means (id est, the passage of currents around soft iron cores) are 
 much more powerful than permanent steel magnets of equal size 
 and weight. Hence, apart from the question of less expense and 
 greater constancy (for steel magnets gradually lose their power by 
 the continuous motion of the armatures before their poles), there 
 is actually a great gain in efficiency in employing electro-magnets 
 
The Dynamo : Plow Made and how Used. 23 
 
24 The Dynamo : How Made and how Used. 
 
 instead of permanent magnets wherewith to induce the current. In 
 Hjorth's machine (which was perfected so far back as October, 
 1854) two compound cast-iron magnets, A A (Fig. 11), which may 
 or may not be surrounded by a coil of wire, are bolted to the 
 frame of the machine. These magnets are shaped like the letter C ; 
 and in the gap between the poles rotates a wheel, B B, on the 
 circumference of which are fastened several armatures consisting 
 of soft iron cores wound with insulated copper wire, the ends of 
 which are brought out to a peculiarly constructed commutator, 
 which rectifies the dissimilar currents produced. The wheel (and 
 consequently the armatures) is caused to rotate by means of the 
 rigger C and driving-axle. Around these movable armatures, and 
 also bolted to the frame, are several soft iron cores wound with 
 
 insulated copper wire, D D D D. The currents produced in the 
 first instance by the passage of the armatures before the poles of 
 the magnets, A, after being rendered uni-direction by means of a 
 commutator, are led on through wires to the coils which surround 
 the soft iron cores, D D D D. These become, therefore, powerful 
 electro-magnets, and induce in their turn more powerful currents 
 in the armatures. The larger currents thus produced, again re- 
 acting in their passage on the electro-magnets, superinduce a 
 higher state of magnetism in them, and this again exalts the 
 electricity generated in the armatures, and so on until the limit 
 of saturation is reached. The current, after traversing the coils, 
 is led to terminals to which connection can be made for exterior 
 work. 
 
 It is remarkable that, although this discovery was so important, 
 and the description and designs were so clear in the specification, 
 
The Dynamo: Hoiv Made and ho^v Used. 2$ 
 
 so little attention should have been attracted to it. Soren Hjorth 
 was, indeed, much before his time, many of the machines now 
 doing excellent work being simply trifling modifications of his 
 'magneto-electric battery.' 
 
 THE SIEMENS ARMATURE. 
 
 14. The intensity of electric and magnetic effects does not 
 increase in the simple proportion of the nearness of the bodies 
 acted on, but in a much greater ratio, which, in the case of 
 electrified bodies and permanent magnets, is directly as the square 
 of the nearness, or (what amounts to the same thing) is inversely as 
 the square of the distance. For instance, we find that a magnet 
 which exerts a ' pull ' of 1 Ib. on a given piece of iron at 6 inches, 
 if placed at 3 inches, or twice the nearness, pulls with a force of 
 2 x 2 = 4 Ib. ; and if placed four times as near, namely, 1 J inches, 
 pulls with a force of 4 x 4 = 16 Ib. 
 
 It would appear that in the case of electro-magnets the ratio 
 between the distance and the effect increases even more rapidly, 
 being, according to the best authorities, equal to inversely the cube 
 of the distance nearly. Hence, it struck Dr. Werner Siemens, of 
 Berlin, that if the armature could be constructed of such a form 
 as to allow of its remaining always very close to the poles of the 
 magnet during its rotation, greatly exalted electrical effects would 
 result; and in 1856 he patented in this country the special form 
 of armature represented at Fig. 12 a, so well known as the 
 * Siemens ' or ' H -girder ' armature. On reference to the armatures 
 depicted at Figs. 9 and 10, it will be seen that during a consider- 
 able portion of their rotation they are at some distance from the 
 legs of the magnets, and even when near them are not at the 
 points of greatest action. 
 
 On the contrary, the Siemens armature is placed as nearly as 
 possible at the most active portion of the magnet's poles viz., 
 their extremities, and at every portion of its rotation some 
 portion of the armature is exposed to the action of the said 
 poles. The Siemens armature, as shown at Fig. 12 a, consists of 
 a cylinder of soft iron, between three and four times as long as 
 its diameter, around the sides and ends of which is cut a deep 
 groove or channel, rather more than one-third the diameter of 
 
26 The Dynamo : How Made and how Used. 
 
 the cylinder. This is shown in section at b. The soft iron 
 cylinder, c, has brass heads and axes fitted to it, as shown at / 
 and' g the latter carrying a pulley or rigger, by which the 
 armature can be rotated ; while the former is encircled by the 
 commutator, e e, to which are attached the two ends of the in- 
 sulated wire, which is wound in the channel. When in action 
 this armature is placed between the poles of a compound horse- 
 shoe magnet, and supported on trunnions or bearings at both 
 ends ; two springs pressing against the commutator carry off the 
 electricity generated by the rotation of the armature, the motion 
 being imparted by means of a band passing over the pulley at 
 the farther end of the armature. A general idea of this arrange- 
 ment may be gathered by inspecting Fig. 12 H. 
 
 CURRENTS GIVEN BY THESE MACHINES NOT CONTINUOUS. 
 
 15. Since the direction of the current changes at every semi- 
 revolution of the armature in such machines as those of Clarke, 
 Pixii, and Siemens, and at every passage of the compound 
 armature before the poles of the inducing magnets in Soren 
 Hjorth's machine, we are constrained to use a commutator when- 
 ever we desire to produce a current in one direction only. But 
 the commutator, by the very fact of its being necessarily con- 
 structed of two or more portions of a metallic cylinder, separated 
 by intervals of insulating material, interrupts the passage of the 
 electricity every time that the springs press against the insulating 
 spaces. Hence the electricity furnished by these machines 
 partakes more of the nature of rapidly succeeding waves, than 
 of a steady continuous current, like that furnished by the battery. 
 Still, when the armature is rotated at a high speed (and the 
 Siemens requires to be driven at about 3,000 revolutions per 
 minute, to give the best effects), these waves succeed each other 
 with such rapidity as to simulate a steady current, no break in 
 continuity being perceptible to ordinary tests. 
 
 RAPID MAGNETISATION AND DEMAGNETISATION PRODUCES 
 
 HEAT. 
 
 16. It is found that the sudden change from north magnetism 
 to south magnetism, which takes place in each half of the above 
 
The Dynamo : How Made and how Used. 2? 
 
 L 
 
 fro. 
 
23 The Dynamo : How Made and how Used. 
 
 described armatures, as they pass over from before a south pole 
 to before a north pole of the inducing magnets, is accompanied 
 l>y a very considerable rise in temperature ; and that this rise 
 increases with the rapidity of change of magnetism, which in its 
 turn depends on the rapidity of rotation. So marked is this rise 
 of temperature, that a dynamo fitted with a Siemens armature 
 of the pattern figured at 14, and started at an initial temperature 
 at 10 C., rises in about twenty minutes to nearly 50 C., when 
 driven at 3,000 revolutions per minute. This rise in temperature 
 is detrimental to the efficiency of the machine : 1st. Because 
 the wires of the armature, becoming heated, conduct less freely ; 
 hence loss of current. 2nd. Because the armature itself is not 
 capable of such intense magnetisation when hot as when cold (a 
 red-hot mass of iron is hardly affected by the magnet) ; hence 
 another loss of current. 3rd. Because the insulating covering of 
 the wire is impaired, even if not actually ruined, if the temperature 
 exceeds a very moderate limit. 
 
 For these reasons it is important to keep the temperature of 
 the armature as low as possible. The first successful step in this 
 direction was taken by Dr. Pacinotti, of Florence, in 1860, who 
 constructed an armature of soft iron, in the shape of a ring, 
 around which were coiled, in successive sections, helices of in- 
 sulated copper wire, the ends of which were joined up to a 
 divided ring commutator. The ring armature of soft iron, with 
 its covering of wire, was supported on a central axle, and rotated 
 before the poles of a magnet, either permanent or electro. At 
 no part of the revolution is such a ring taken as a whole farther 
 from, or nearer to, the poles of the magnet ; and although its 
 magnetism is constantly changing, yet the change is not abrupt, 
 but gradual and continuous ; as will be explained in the follow- 
 ing paragraph. 
 
 PACINOTTI'S KING ARMATURE. 
 
 17. The description and illustration of this machine is to be 
 found in the Nuovo Cimento for the year 1864, under the heading 
 of * Una Descrizione d'una Piccola Macchina Elettro-Magnetica.' 
 The machine itself, as described, can be used either as a motor, 
 or. as a generator of electricity ; and its adaptability to either 
 
The Dynamo : How Made and how Used. 
 
 \ 
 
 PACINOTTI'S EING ARMATUKE. A A, The iron ring, enveloped with coils 
 of wire. B B B' B', Soft iron prolongations, or ' horns ' of the electro 
 magnets S N. CD, Central axis, on which the ring A turns. E, The 
 commutator, to which the ends of the coils of wire are joined. F F, The 
 brushes. G, The pulley, driven by the band H. 
 
30 The Dynamo : Hoiv Made and how Used. 
 
 purpose was specially dwelt upon by Dr. A. Pacinotti, in his 
 communication ; but it is only under the aspect of a generator 
 that we shall stop to consider it here. 
 
 Two electro-magnets, S, N, Fig. 13 (which may, or may not, 
 be united together below), are fastened to a base-board, and so 
 arranged that the upper extremity of one is a north pole, while 
 the other is a south pole. These poles are furnished with semi- 
 circular prolongations B B, B' B', between which is poised, on 
 the axis C D, a soft iron ring A A. This ring is attached to the 
 axis by means of radial arms. Coils of insulated wire are wrapped 
 found the ring at short intervals about its periphery, the end of 
 each coil being brought down the axis at D and attached to one 
 &f the small copper strips at E (of which there are as many as 
 there are coils around the ring), the wire beginning the next coil 
 being also metallically connected to this same strip. The wire 
 terminating the next coil is fastened to the next strip, from 
 whence starts a fresh coil, and so on, until all the strips, which 
 form the compound commutator E are connected to the coils in 
 s.uch a manner that the end of one coil, by its attachment to its 
 strip, forms the commencement of the next. Consequently, the 
 wire forming the coils, although capable of communicating 
 electrically with the springs F F at opposite points of the diameter 
 of the commutator, is really continuous. The ring A A is caused 
 to rotate by means of the rigger G and the driving belt H. 
 
 It will be evident on reflection that the half of ring opposite 
 the pole marked N will acquire by induction south magnetism, 
 while the half facing the pole S will for a similar reason become 
 north. Hence the ring, whether in motion or at rest, will, pro- 
 vided the electro-magnets be active, become a circular magnet, 
 with the south pole facing the north pole of the electro-magnet, 
 and its north pole facing the south pole of the electro. When 
 the ring is rotated, though, if viewed as a whole, this magnetic 
 condition remains unaltered, yet, of course, any given portion of 
 the ring will gradually change as it passes over from one ' horn ' 
 ojr prolongation of the magnets to the other. Still, the change 
 which takes place is not abrupt, but gradual, and partakes more 
 ojf the nature of a wave than of shock. So also, since the springs 
 olE the commutator press on several strips at the same time, at no 
 
The Dynamo : How Made and how Used. 3 r 
 
 time is contact ever entirely broken between the commutator and 
 the springs ; therefore the current which is produced as a con- 
 tinuous wave, always in one direction, is collected in a similar con- 
 tinuous manner by the springs F F, and may be employed where 
 required by coupling up the wires II. - * 
 
 This machine, discovered more than twenty years ago, embodies 
 all the essential characteristics of the best modern machines, and 
 the much-vaunted machines of Gramme, Brush, Siemens- Alteneck, 
 Maxim, Edison, etc., are, at best, but trifling modifications of the 
 Pacinotti ring machine modifications which have not always 
 been improvements. Having now brought our brief sketch of 
 the essentials of a dynamo to a close, we shall proceed in our 
 next section to constructive details. 
 
 THE PATTERNS. 
 
 18. In the dynamo we are about to construct, three separate 
 pieces for patterns are absolutely necessary viz., one for the 
 armature, one for the legs of the field magnets, and one for the 
 standard which supports the flywheel. There is no necessity for 
 the amateur to put himself to the trouble of cutting out a pattern 
 for the flywheel, since such wheels with handles already fixed 
 can be had for two or three shillings. In constructing the 
 wooden patterns, from which the iron castings are afterwards to 
 be procured, the amateur should remember to choose dry, well 
 seasoned wood, free from knots. Red pine, for such small work 
 as is required, will be found as good as any. Any joints that 
 are absolutely necessary (and joints should be avoided as much 
 as possible) should be attached together with dowels and Prout/s 
 elastic glue. It must be borne in mind that the pattern-moulder 
 places the patterns in green (moist) sand, and that this moisture 
 causes ordinary glued joints to come undone or expand. Any 
 roughnesses left on the pattern also swell up, catch the sand, and 
 thus destroy the sharpness and beauty of the mould, and there- 
 fore of the resulting casting. It is therefore advisable, after 
 having got the wooden pattern to the highest possible degree of 
 smoothness and trueness by means of emery-paper, etc., to give 
 it a coating of melted paraffin wax, and polish the surfaces care- 
 fully with a roll of flannel. This renders the surfaces not only 
 
32 The Dynamo : How Made and how Used. 
 
 extremely smooth but impervious to moisture, so that the pattern 
 does not warp or swell when placed in the sand. In order that 
 the pattern should come clean out of the sand and not break 
 away any portion of the mould, care must be taken that the 
 edges be slightly rounded, so as to give what is technically called 
 clearance. The possessor of a lathe can turn up many portions of 
 the fittings with much greater accuracy and rapidity than one 
 provided with only ordinary tools ; but in the ensuing directions 
 the amateur is supposed to possess tools of the simplest kind 
 only. 
 
 19. The pattern for the armature first demands our attention. 
 When completed, it presents the appearance shown at Fig. 14, a 
 being the elevation and b the section, on a scale of about half the 
 real size, and consists of a wooden cylinder 1 J inches in diameter 
 by 3| inches in length, with a deep channel round the ends 
 and sides. To construct this pattern, procure a piece of pine 
 8 inches long by 1J inches wide and f of an inch thick. Lay 
 this on a table on its widest side, and draw a line along its whole 
 length, that shall divide it into two halves of f of an inch each. 
 Now, draw a line on each side of this central line, rather better 
 than I of an inch from it. Holding a metal rule against one of 
 these side lines, with a sharp penknife, cut into the wood along 
 the line to a depth of about f of an inch rather less than more. 
 Now, perform the same operation on the other side line to the 
 same depth. With a sharp J inch chisel, shave away the wood 
 on the outside of the cut lines to the depth of f of an inch on the 
 outsides, but rising up very slightly toward the centre, as shown at 
 Fig. 14 c. This precaution will ensure the pattern lifting out 
 clear from the mould. 
 
 Now, take a piece of stout cardboard, and with a pair of com- 
 passes strike out a circle 1J inches in diameter. Cut the circle 
 out of the cardboard so as to leave a clean circular aperture of the 
 diameter specified. This is to serve as the templet, or gauge, of 
 the size and general truth of our arrrxiture. Strike out, also, in a 
 similar manner a circle in a piece of stoutish zinc, or tinned iron, 
 also 1J inches in diameter, and cut this in two halves (one of 
 which is shown at d). These will serve to shave away the last 
 irregularities from the wood, when it has been roughly trimmed 
 
The Dynamo : How Made and how Used, 33 
 
34 The Dynamo : How Made and how Used. 
 
 up to the shape shown at e, by means of a small plane, or pen- 
 knife. The piece may now be cut into two halves across its 
 length, dowelled and fastened together with Front's elastic glue, 
 and cut down to the exact length required namely, 3| 
 inches. All roughnesses should now be carefully sand-papered, 
 and care should be taken that the finished pattern should pass 
 exactly through the cardboard pattern, being appreciably neither 
 thicker nor thinner at any part. When this has been effected 
 satisfactorily, a small quantity of paraffin wax (a piece of paraffin 
 candle will do) should be melted in an iron spoon, and well rubbed 
 into the pattern at all points with a roll of flannel until it is 
 thoroughly impregnated with the wax ; rubbing the pattern until 
 it acquires a polish completes the operation, and renders it ready 
 for the founder. The thin central portion, which joins the semi- 
 circular portions, should be about 2J inches in length, having 
 rather more than J an inch cut away at each end, so that the 
 channel is continuous round the armature, being f of an inch wide 
 and about J an inch deep all round. 
 
 20. The pattern for the legs of the electro-magnet (field 
 magnets, exciting magnets) will next require our care. Since the 
 two legs are exact counterparts, the one of the other, so we need 
 only make one pattern, from which, however, two castings must 
 be obtained. Fig. 15 illustrates the form and dimensions of this 
 pattern on a scale of about one-quarter the real size. The dimen- 
 sions are marked in inches. A represents the outside view, i.e., 
 as seen from the side which is farthest from the armature ; B 
 gives the view from the inside (close to which the armature 
 rotates). 
 
 To make this pattern, procure a piece of pine 6 inches in length, 
 4 inches in width, and J an inch thick, planed smooth, and 
 free from knots and roughness. Glue and dowel along the bottom 
 edge a strip 1J inch wide, 4 inches long, and \ of an inch 
 thick, as shown at Fig. 16, a. Now, with a sharp plane, remove 
 half the inner edge, as shown at Fig. 16, b, so that it makes an 
 angle with the edge of the 6-inch piece. With a fine saw cut a 
 recess on each side of the jointed piece 1 finches long by 4 inches 
 deep, as shown at c, and glue and dowel in each recess the two 
 flanges, made of ^-inch stuff, of the shape and dimensions 
 
The Dynamo: How Made and how Used. 35 
 
 '6 'J 
 
36 The Dynamo: How Made and how Used 
 
 given at d. To insure the slot e being exactly at the same point 
 in each flange, the two flanges, after being roughly shaped with a 
 fretsaw, or otherwise, should be clamped together, and the finish- 
 ing touches given with a rat-tail file, for the slot e, and with 
 sandpaper along the rounded edges. Care must be taken that 
 these flanges should be a trifle thinner near the edge marked 1 J 
 than on the opposite edge, to insure the pattern coming out clean 
 from the mould. For this reason the slot e must not be narrower 
 at the outside than at the inside, but rather the contrary. The 
 slot e must be J of an inch wide, and must reach in depth to the 
 6-inch piece, to which the flanges are attached. At this point 
 our pattern will present somewhat the appearance shown at /. 
 A piece of wood 4 inches long by 1 J inches wide, and J of an 
 inch thi'ck, perfectly smooth, square, and free from knots, must 
 now be chosen, and the two sides planed away, on the upper side 
 to such an extent as to make an angle of 60 with the base. (See 
 Fig. 17, #.) With some good thin, hot glue (not Prout's), this 
 piece is to be glued along the bottom edge of the 6-inch piece, on 
 the side opposite the flanges, and in such a manner that the slope 
 of the base is continued by the slope of the piece, as shown at 
 Fig. 17, b. When the glue is quite dry, by means of an inch 
 gouge, cautiously hollow out along the entire length of this piece, 
 in a semicircular form, nearly to the depth of the original 6-inch 
 piece, so as to fit accurately the pattern of the armature which 
 has already been made. ( 19.) When this is as true and smooth 
 as it can be made with the gouge, fold a piece of fine glasspaper 
 over the pattern of the armature, rough side outwards, lay the 
 armature in the channel, and work it backward and forward until 
 perfect smoothness and a perfect fit are insured. The pattern 
 should now present the appearance given at Fig. 17 c. When 
 this end has been attained, four small dowels should be inserted 
 into the thicker portions of this semicircular piece, to hold it 
 firmly down to the 6-inch piece. We now need only make the 
 top flange, by which the bracket or standard that bears the wheel 
 is clamped to the legs of the dynamo. This is made most easily 
 in two pieces, one being squared up to 4 inches long, f of an inch 
 thick by f of an inch wide. The other piece is to be f of an inch 
 thick, and must be cut into a perfect semicircle, with a radius of 
 
The Dynamo : How Made and how Used. 37 
 
 PORTIONS OP THE PATTERN OF THE FlELD-MAGNET. a, The unfinished j 
 
 cheek ; b, The limb with the cheek in its place ; c, The cheek ' 
 hollowed out ; d, The top flange, to which the bracket is fastened. 
 
The Dynamo : How Made and how Used. 
 
 1J inches. By means of Front's glue and a couple of dowels, 
 this is neatly attached to one side of the other square piece, as 
 illustrated at Fig. 17 d, and then the whole is carefully and 
 squarely glued and dowelled, in like manner, to the top of the 
 G-inch piece, so that it now presents the appearance shown at A 
 and B, Fig. 15. The holes shown in the bottom and top flanges 
 may be bored, and core prints inserted, if the founder will take the 
 /.rouble to put them in his mould ; but, as a rule, founders do not 
 care to cast small castings with holes in them, as they seldom 
 come true, so that it will be, perhaps, as well to have them bored 
 afterwards, which can be done at a cost not exceeding 2d. a hole. 
 This pattern must now be carefully smoothed, the sharp edges 
 
 rounded, to insure parting from the mould, and finally paraffined 
 and polished, as recommended for the armature ( 19), when it 
 will be ready for the moulder. 
 
 21. The next pattern to be made is that of the standard, 
 which supports the driving-wheel. This should be made out of 
 -|-inch stuff, a piece of which 5J inches long by 2f inches wide 
 must be cut to the shape shown at A, Fig. 17* (one-quarter the 
 real size). In order not to split the top while boring the hole, it 
 is as well to bore the hole (which should be J an inch in diameter) 
 before shaping the piece. For the same reason, the piece marked 
 C, which should be |- an inch thick and 1 inch in diameter when 
 finished, should be glued to the centre of the top end of the piece 
 
The Dynamo: How Made and how Used. 39 
 
 A, and the whole bored (by means of a brace and sharp J-inch 
 centre-bit) before trimming up to shape. From the same J-inch 
 stuff, another piece, figured at B, is cut out, being J an inch wide at 
 the top, sloping gradually, and becoming wider to about half its 
 length (d) when it should sharply curve to a width of 4 inches. 
 The length of this piece should be 5 inches, and it is to be glued 
 and dowelled to the centre of the piece A, close against the boss 
 C, as shown at B. A small piece e must now be glued and 
 dowelled to the edge of the curved flange, so as to make it flush 
 with the front A. When this has been smoothed arid polished 
 with paraffin, the patterns are ready for the foundry. The three 
 holes shown at d may be bored in the castings. 
 
 THE CASTINGS. 
 
 22. The patterns may now be sent to the foundry, with the 
 following instructions : First, the armature should be carefully 
 annealed, so as to constitute a malleable iron casting; second, two 
 legs should be cast from the pattern shown at Fig. 15, and these 
 also must be carefully annealed, and be made as soft as possible ; 
 third, the standard (Fig. 17*, B) will be better if left pretty hard, 
 as in this way it will retain sufficient magnetism to start the 
 machine without adventitious aid. Particular stress must be laid 
 on the importance of the iron in the armature and legs being very 
 soft, since much of the efficiency of the dynamo will depend on 
 this point. (See 9.) When the castings return from the foundry, 
 their degree of hardness may be tested by -trying with a rather 
 coarse file. If the file bites easily, the iron is fairly soft ; if it 
 slips over without filing, it is altogether too hard. (This does not 
 apply to the standard, which may be left quite hard without any 
 detriment to the machine. ) The armature must now be cleaned 
 and trued up. If the student be the happy possessor of a lathe, 
 this will not prove a difficult job; if otherwise, he may, by 
 careful filing, remove any irregularities, and square up the ends. 
 These must be made quite true ; otherwise it will be impossible 
 to centre the armature so as to rotate it between the poles of the 
 magnet. The thin central portion shown at a, Fig. 14, and there 
 marked 2J, must have its edges rounded, so as not to cut the 
 wire, which will have to be wound round it. No trouble should 
 
4O The Dynamo : How Made and how Used. 
 
 be spared to get the armature as truly cylindrical as possible ; as 
 care expended at this portion of the process will render the 
 remainder of the work very much easier, and more satisfactory. 
 The armature having been thus rendered true, the legs will 
 demand our attention. Having gone over the surface with a 
 bastard file to remove any irregularities, the curved channels, 
 shown at A and B, Fig. 15, must be carefully cleaned out. 
 Perhaps the quickest way to do this, and to clean the armature 
 at the same time, is to lay the two pieces, channels uppermost, 
 on a table, putting a little fine sand and water in the channels, 
 and then to work the armature up and down the channels, first 
 in one and then in the other, alternating also the sides of the 
 armature, until the channels, as well as the external surfaces of 
 the armature, are rendered quite smooth and bright. The sharp 
 .corners of the legs of the magnets around which, the wire has to 
 be coiled must also be rounded, and the top semicircular flanges, 
 between which the standard has to be clamped, must be filed 
 quite flat on their inner surfaces, and made perfectly parallel with 
 the portions marked 3J B, Fig. 15. The standard must also be 
 cleaned in like manner, particular care being taken that the two 
 sides of the piece marked B, Fig. 1 7*, be perfectly parallel. The 
 edges of the front piece e must be made perfectly square and true, 
 so as to fit exactly on to the top of the two legs of the magnets, 
 Fig. 15. 
 
 23. Before winding the armature and field-magnets with 
 the wire in which the electricity is at once generated and con- 
 ducted, it is necessary to fit together accurately the different 
 portions, and mark them, so as to be able to put them together 
 again in precisely the same position after winding ; since no filing 
 or fitting can be attempted on the castings after the wire has 
 been wound without almost certain destruction of the insulation, 
 and certain ruin to the neat appearance of the evenly-laid 
 wire. 
 
 The part that calls for the greatest care and attention is the 
 armature, which, as it must rotate in very close proximity to the 
 poles of the field-magnets at a rate varying from 1,000 to 3,000 
 revolutions per minute, requires to be centred most accurately on 
 its bearings or trunnions. This to the possessor of a lathe 
 
The Dynamo: How Made and how Used. 41 
 
 presents but little difficulty ; for the benefit of those who depend 
 on ordinary tools only, the following method, by which the 
 armature can be mounted on its bearings in a fairly accurate 
 manner, is described. With a pair of calipers, the diameters of 
 the two opposite extremities of the armature are taken, as shown 
 at Fig. 18, a and b. (If the armature casting were finished up 
 quite exactly, these two measurements would be exactly alike, 
 viz., a trifle under 1J inches each. But unless turned on the 
 lathe, it is very rare to get such precision.) Two circles, of 
 exactly the same diameters as the two extremities of the arma- 
 ture, are now to be struck out of a piece of hard sheet brass, J of 
 an inch thick, care being taken to mark the centre and the cir- 
 cumference in an exact and bold manner with the compasses. 
 These circles will have to be cut out of the brass with a saw or 
 file, so as to get two discs, fitting each one to its respective arma- 
 ture extremity ; but before cutting out the circles thus marked, 
 three holes should be drilled in each, viz., one in the exact centre 
 Y\ of an inch in diameter, which is to take the driving shaft or 
 trunnion, and one on each side of this centre, J- of an inch in 
 diameter, to admit the screws which serve to attach these heads 
 or discs to the iron portion of the armature. Besides these three 
 holes, which are common to both * heads/ another pair, also -J- of 
 an inch in diameter, must be drilled in one of the heads, to allow 
 the ends of the wire which is to be coiled around the armature to 
 emerge from them, and pass through to the commutator. All 
 these holes are shown full size, and in their, correct- position at 
 Fig. 19, where a is the central aperture, to take the shaft ; b b the 
 two holes to admit the screws, whereby the heads are attached to 
 the armature ; and c c holes drilled in one head only, to admit of 
 the passage of wires to the commutator. These holes being bored, 
 and the discs accurately cut out, two pieces of hard-drawn iron 
 wire (not galvanized) J of an inch diameter and 2 inches long, 
 are carefully straightened, and by means of a screw-plate, a thread 
 is put on one end of each. With the corresponding tap, a female 
 screw is cut in the central hole of each brass disc. The two iron 
 rods are then screwed in, particular care being taken that they 
 enter perpendicularly and centrally. They must be screwed in 
 until they just protrude through to the other side ; then the long 
 
42 The Dynamo : How Made and how Used. 
 
 end being allowed to slip between the jaws of a vice, while the 
 disc rests flat upon the surface of the jaws, a few steady blows 
 with a flat-pened hammer will spread the head of the screw end 
 of the iron rod, so as to rivet it firmly to the disc, and thus 
 prevent it working out. To render assurance doubly sure, a drop 
 or two of soft solder may be run round the flat side of the end of 
 the rod and disc. Now we come to a part of the work that very 
 few amateurs can do at home viz., drilling the holes in the faces 
 of the armature. Any blacksmith will, however, do this for a 
 few pence. Four holes are required, two at each end of the 
 armature (one end is shown real size at d d), and these holes must 
 be tapped with a female screw, so as to take the screws which 
 serve to unite the whole together. It will be well to let the black- 
 smith drill and tap these holes to any sized screw that he has 
 nearest approaching J of an inch in diameter. Now will be also 
 
 Fi,. 
 
 a/ 
 
 the time to get the blacksmith to drill the three holes, right 
 through the top end of the legs and standard, which serve to 
 allow these portions to be clamped together by means of bolts 
 and nuts. These holes should be about \ of an inch in diameter. 
 Further details as to position and size will be given a little farther 
 on. If our work has been properly performed, the heads may 
 now be screwed down to the armature with flat-headed screws, 
 which should project about ~ of an inch above the level of the 
 discs. Fig. 20 gives a representation of the finished armature 
 about half the real size. 
 
 24. Our next proceeding is to clamp together the standard, 
 or bracket, which serves to support the wheel to the two legs of 
 the field-magnets. At the concluding portion of 23, we adverted 
 to the advisability of getting the holes bored right through the 
 top end of the legs and standard, at the same time that the holes 
 
The Dynamo : How Made and how Used. 45 
 
44 The Dynamo : Hoiv Made and how Used. 
 
 were being drilled in the armature. The position of these holes 
 is indicated at Fig. 21 ; they should be about J of an inch in 
 diameter, and the two lower ones should be at least f of an inch 
 from the bend of the flange, so as to allow the nuts to be easily 
 turned and tightened up. These two bottom holes should be 
 about 2 inches apart, while the upper one should stand equi- 
 distant from the others, but at about \ an inch from the top of 
 the flange. The amateur will find at any of the good furnishing 
 ironmongers, very neat skate-screws with nuts to fit, of the form 
 illustrated at Fig. 22. These screws have usually rounded heads, 
 without the slot for the screw-driver to enter ; but these can be 
 easily cut with a metal-saw. Of course, any small bolts and nuts 
 
 liaving a section of about J of an inch will do, but the ones men- 
 tioned are very neat in appearance. The holes being drilled and 
 the bolts and nuts chosen, the bracket and limbs of the field- 
 magnet may be temporarily clamped together, in order to see 
 what opening is left between the legs for the armature to turn 
 in, at a, Fig. 23. In all probability some filing of the faces of the 
 flanges and of the bracket will be necessary to insure a proper fit. 
 A well-fitted armature, if placed in the centre of the channels at 
 a, should leave a space of a trifle more than -^ of an inch to turn 
 in ; that is to say, there should be rather more than T \ of an inch 
 clear space all round between the armature and the field-magnets. 
 Perhaps the quickest way to insure this distance being obtained 
 is to roll tightly a single fold of stout brown paper round the 
 
The Dynamo: Hoiv Made and how Used. 45: 
 
 Jl FL 
 
 Zj [* 
 
 d 
 
 A 
 
 o 
 
46 The Dynamo: How Made and how Used. 
 
 armature and seal down the edge to prevent it slipping; then, 
 having inserted the armature in the channels, to file away at the 
 inner faces of the flanges, either towards the lower portions at 
 b b, if the channels are too wide apart, or at the upper extremi- 
 ties at c c, if too close, until the whole fits accurately together. It 
 is needless to remark that when the armature thus wrapped in 
 paper is placed between the field-magnets, to obtain a correct fit, 
 the solid portions of the armature should lie against the legs, and not 
 the portion of the armature which is hollowed out for the recep- 
 tion of the wire. (See Fig. 23.) 
 
 25. The magnets and brackets being thus properly clamped 
 together, the hole in the top of the bracket (which ought to have 
 been left in the casting, but if not may be bored now) should be 
 cleaned out to J- an inch in diameter. When this is done, two 
 pieces of hard rolled brass sheet of an inch thick, 6 inches long 
 by 1 inch wide, must be cut out and squared up. One of these, 
 which we shall for the future call the * back bearing/ and which 
 must be made to fit that end of the dynamo at which the driving 
 wheel is to be placed, and which we shall henceforward call the 
 * back ' of the dynamo, is to be bent four times at right angles, as 
 shown at Fig. 24, a, where the dimensions are given. In order 
 not to crack the brass while bending to shape, it will be well, 
 after having given the general form by bending gently and gradu- 
 ally over the jaws of a vice, to heat the bends over the flame of a 
 spirit-lamp until nearly red hot, and then to hammer up more 
 exactly to shape, repeating the heating after each hammering 
 until the desired sharpness of outline has been obtained. 
 
 When this object has been attained, another almost similar 
 bearing is formed out of the remaining piece of sheet brass, the 
 principal difference being that, as this is to be the front bearing, 
 between which the commutator will have to turn, a much greater 
 depth must be given to the central bent portion, as may be seen 
 at Fig. 24, b, the dimensions being given in inches as before. 
 When the brass has been bent to these forms, the bearings thus 
 produced should be laid each against its own respective end of the 
 dynamo, in such a position that the centre of the bend comes in 
 the centre of the channel, the two flat extensions lying close to, 
 and flat against, the slotted lugs shown at Fig. 23, d, d. The 
 
The Dynamo : How Made and how Used. 47 
 
 bearings should now be cut in a sloping fashion to follow the out- 
 line of the lugs, as shown at Fig. 24, c; but the outline of the 
 slotted portion should not be followed, as a ^-inch hole must be 
 drilled in the brass at this point to take a 5-inch bolt and nut. 
 The exact position of these holes may be obtained by holding 
 each bearing in succession against its own proper extremity, and 
 scratching with a steel point on to the brass the position in which 
 the slots in the lugs fall; then, with an Archimedean drill, a 
 ^-inch hole can be drilled at each extremity nearest to the centre 
 of the bearing, as shown at Fig. 24, d. 
 
 Having got so far, let us clamp the back bearing in its place 
 by means of two bolts about 5 inches long, passing through the 
 holes in the bearings and through the slots in the lugs, held in 
 their places by two nuts screwed down on to the front lugs of the 
 dynamo. Taking the armature in one hand, we roll, as before, 
 one fold of paper round it, and put a dot of Brunswick black on 
 the extremity of the trunnion rod at the back end of the armature 
 (the end where the holes are bored for the wire to come out is 
 the front, the other is the back), and then insert it into the 
 channel between the legs of the field-magnets, until the trunnion 
 rod on shaft touches the brass forming the back bearing. In so 
 doing it will leave a mark of Brunswick black, which will be the 
 point at which a J-inch hole must be bored. This must be 
 done most carefully, so as to preserve centricity ; and when done 
 must be rimed out and bushed with a piece of brass tubing of 
 about T 5 g- external diameter, the internal diameter of which must 
 exactly correspond with the external diameter of the driving-shaft 
 or trunnion of the armature ; in fact, this latter must fit exactly 
 into the tube, without any shake. This piece of tubing should 
 be about 1J inches in length, and should be soldered into the 
 central hole in the back bearing, and should extend inwards to 
 such a degree that when the back bearing is clamped in its place, 
 with the armature in its position, with the back trunnion in the 
 tube, and the back head flush with the back of the magnets, it 
 should just rest against the back head of the armature. 
 
 In a precisely similar manner the centre of the front bearing is 
 found ; that is to say, the back bearing being removed, the front 
 bearing is clamped to the front of the dynamo, the armature, 
 
48 The Dynamo : Hoiu Made and how Used, 
 
 rolled in one fold of paper, is inserted from the back end of the 
 dynamo, front end forwards, and care taken to moisten the front 
 end of the driving-shaft with Brunswick black or other colour, so 
 as to get a mark where it touches. The hole being drilled and 
 rimed out, as in the previous case, is to be likewise bushed with 
 the same kind of brass tubing ; but, in the front bearing, the tube 
 should be only flush with the inside of the bearing, and should not 
 extend in towards the armature. 
 
 26. The Commutator next claims our care. This essential 
 piece of apparatus serves, as the student may remember ( 12), to 
 rectify, or send in one direction, the vibrations or currents which 
 are produced in opposite directions, as each pole of the armature 
 passes alternately before the north and south pole of the field- 
 magnets. In screwing the brass heads down to the armature, the 
 student was advised ( 23, Fig. 20) to employ flat-headed screws, 
 projecting about -f^ of an inch above the level of the discs. The 
 use of the projecting heads is to prevent the commutator slipping 
 round the axis or trunnion of' the armature when the latter re- 
 volves. The body of the commutator may be turned up out of a 
 piece of sound boxwood, which previous to turning up should 
 have been allowed to soak for a couple of hours in melted 
 paraflin. It should, when finished, present the appearance shown 
 at Fig. 25, a. While on the lathe, a hole, perfectly central, 
 should be drilled right through it, into which the front shaft or 
 trunnion of the armature fits tightly. The length of this should 
 be |4 of an inch, so. that it just clears the front bearing when in 
 its place. The diameter should be about -J of an inch, so tha.t 
 the two flat-headed screws of the front armature head should be 
 covered by the cylinder on opposite sides of its circumference to 
 the extent of about ^ of an inch. Two semicircular nicks must 
 be cut out of the bottom of the cylinder to allow these screw 
 heads to enter, so that the cylinder when driven home rests quite 
 against the disc or head. The front of this cylinder (the part 
 farthest from the disc) must be rounded slightly, so as not to 
 present too great a surface for friction against the front bearing. 
 A piece of brass tube, -J of an inch shorter than the cjdinder, and 
 of such internal diameter as to fit tightly on it, is now cleaned up 
 and cut into two exactly equal halves longitudinally. The cuts 
 
The Dynamo : How Made and how Used. 49 
 
 must not be quite parallel to the axis of the cylinder, but must 
 make a small angle with it, in order that the * brush ' or spring 
 which takes the current off the commutator should at no time 
 abruptly leave one half tube before it rests on the other ; other- 
 wise the commutator sparks badly while at work, and the sparks 
 injure both commutator and brushes, besides entailing loss of 
 current. The amount of angular deviation from the line of axis 
 should not, in this machine, exceed two or three degrees of arc, 
 and care must be taken they are equi-distant, and both inclined 
 in the same direction. To insure this, stand the tube (already 
 cut to length and cleaned) on one end. Take the exact diameter 
 with a pair of compasses, and strike out on a piece of card a 
 circle of exactly similar diameter. Eule two fine lines across 
 this circle, both cutting the centre, but exactly \ of an inch apart 
 at the circumference, like a letter X. Lay this card on the top 
 of a tube, and with a steel point or file make a mark on the rim 
 of the tube at each of the points where the lines touch the cir- 
 cumference of the circle. Now lay the tube on its side, and draw 
 four lines straight along the length of the tube, starting from the 
 points just marked. Each opposite pair of lines will be exactly 
 \ of an inch apart, and quite parallel. Having done this, bring 
 one pair of lines uppermost, and draw a diagonal line from the 
 top of the right hand to the bottom of the left-hand line. Now 
 turn the tube half a revolution, so as to bring the lower pair of 
 lines uppermost, and draw a similar diagonal line, in the same 
 direction viz., from the top of the right-hand line to the bottom 
 of the left-hand line. Now, with a fine fretsaw cut the tube 
 into two halves in the direction of the two diagonal lines just 
 described. The tube, with the diagonal lines marked ready for 
 cutting, is shown, as if transparent, at Fig. 25, b. It will be noticed 
 that though, when seen through, these lines cross each other, yet 
 when either portion of the marked tube is uppermost, the line of 
 division is from right downwards to left. The split tube is now 
 to be fastened to the boxwood cylinder in such a position that the 
 middles of the lines of division shall be exactly in a line with the 
 middle of the channel of the armature. (See Fig. 26.) These 
 two half-tubes may be attached to the boxwood cylinder or core 
 by means of two short flat-headed screws, care being taken that 
 
 4 
 
50 The Dynamo: How Made and how Used. 
 
 these screws do not reach to make contact with the trunnion or 
 touch the * head ' of the armature. The split ring, when fastened 
 in its place, should reach to within about ^ of an inch of each 
 end of the boxwood core; and if screws are used to fasten it 
 down, these should be placed at the end nearer the armature. 
 But another very neat and effective way of attaching the split 
 tube or ring to the core is by means of two narrow ivory or bone 
 rings, forced over the split tube, one at each end. Care must be 
 taken, in either case, that the divisions in the split tube are main- 
 tained ; for, of course, if the two halves of the tube were allowed 
 to touch at any point, the current would flow round at that point 
 or 'short-circuit,' and no current would be perceptible on the 
 outside. To insure the distance being maintained, it is well to 
 place a shaving of paraffined wood of the same thickness as the 
 sawcuts between the two halves of the split tube on both sides. 
 
 27. Those who have not a lathe can make a very fair substitute 
 for the boxwood cylinder by rolling and gluing a stout piece of 
 brown paper, just as if making a rocket-case, around a piece of 
 the same iron rod that served for the trunnions of the armature, 
 until a cylinder | of an inch thick and f J of an inch long has 
 been produced. This should be rolled very hard while on the 
 iron rod, so as to insure its being truly cylindrical ; the rod on 
 which it was rolled should then be pulled out, and the tube 
 allowed to dry thoroughly. When dry, it should be soaked for 
 half an hour in melted paraffin, then reared on end to drain and 
 cool. It will be found to work extremely well. Of course the 
 split ring can be attached to this, either by screws or by two 
 rings, as in the former case. 
 
 28. Two rectangular pieces of boxwood (previously boiled in 
 paraffin) must now be cut, planed, and drilled. These are the 
 ' brush blocks,' which serve to support the metallic springs or 
 ' brushes ' which press against the commutator.' Some operators 
 prefer to mount their blocks on the stand, separate from the 
 dynamo castings ; here, the plan followed is to cause the bolts 
 which clamp the bearings to the field-magnets to carry the brush 
 blocks. To this end, the two pieces of boxwood should be cut so 
 as to fit exactly the space left between the shoulders of the front 
 bearings on the outside, and bored so as to allow the bolts to come 
 
The Dynamo: How Made and how Used. 51 
 
 42 
 
5 2 The Dynamo : How Made and how Used. 
 
 right through to take the nuts ; that is to say, the blocks will be 
 almost cubical in shape, being 1 inch long, \~ of an inch wide, by 
 | of an inch thick. Fig. 27 shows one of these blocks in its 
 place, clamped to the bearing by the nut and bolt. 
 
 29. In order to communicate the motion from the flywheel to 
 the armature, a small pulley-wheel, either of iron or brass, is fitted 
 to the back trunnion, just outside the bearing. Such a pulley- 
 wheel may be bought at any ironmonger's, and should be about 
 \\ inches in diameter, and rather over \ of an inch thick, with 
 the central hole somewhat smaller than the diameter of the rod 
 which serves for the armature trunnion. This may be attached 
 to the trunnion in either of the two following ways : 1st. By 
 ' keying,' which consists in filing the trunnion along its length, in 
 one direction only, so as to produce a flattened side ; then, having 
 with a rat's tail file cleaned out the central hole of the pulley to 
 such an extent that the said trunnion will only just enter, to 
 deepen one side (corresponding to the flattened side of the 
 trunnion) so as to admit of a small steel wedge or ' key ' being- 
 inserted. (See Fig. 28, a.) 2nd. By filing the trunnion-rod to a 
 slightly conical shape, and producing a similar ' coning ' in the 
 interior of the pulley hole, which may then be driven on. (See 
 Fig. 28, b, where the ' coning ' of the trunnion is exaggerated, to 
 render this mode of attachment more plainly visible.) Which- 
 ever mode of attachment is adopted, one precaution must be 
 taken viz., that the distance between the back of the field- 
 magnets and the pulley should not be less than 1 J inches ; other- 
 wise, when the limbs of magnets are wound with wire, the fly- 
 wheel will run too close to them to be altogether safe. 
 
 30. The flywheel which gives motion to the armature should 
 be a pretty heavy wheel, about 13 inches in diameter, with a 
 groove in the rim to take the band which drives the pulley, 
 furnished with a wooden handle for convenience of rotating. 
 Such wheels may be obtained ready made in cast-iron, from most 
 ironmongers, as they are sent out with 'rotary blowers,' * portable 
 forges,' etc. Fig. 29a gives an idea of the kind of wheel necessary, 
 on a scale of i J inches to the foot. The central hole is turned, 
 and only requires fitting with an iron pin, on which it turns, 
 the aperture in these wheels is about f of an inch in 
 
The Dynamo: How Made and how Used. 53 
 
 * 13 
 
 Fvg.30. 
 
54 The Dynamo : How Made and how Used. 
 
 diameter, the pin must be filed down to J an inch diameter, 
 where it has to fit the hole in the flange at the top of the- 
 dynamo. 
 
 The farthest end should have a rounded head, to prevent the 
 wheel from working off, while the portion which passes into the 
 eye at the top of the flange must have a thread put on it, so as to 
 take a nut, (See Fig. 29, b.) 
 
 31. All the portions of the dynamo being now fitted, they 
 should be marked so as to insure putting together again in right 
 order after winding. When this has been done, the limbs of the 
 field-magnets, at all parts except the channel for the armature, 
 and the inner face of the semicircular top which rests against the 
 wheel bracket, should receive a coat of good Brunswick-black, 
 allowing them to dry between each application, in a warm oven. 
 The bracket should likewise receive a coat or two of the same 
 varnish, except where the semicircular tops clinch it. This 
 portion must be left metallic, so as to ensure magnetic contact ; 
 otherwise much magnetic power is lost. Two strips of silk (colour 
 immaterial) 10 inches long by 3J inches wide, should now be 
 quickly brushed over with Brunswick-black, and wrapped, while 
 still sticky, one round the one limb, and the other round the other 
 limb of the field-magnets, in the space between the armature 
 channel and the bend at the top. (See Fig. 15, where the 
 portions indicated are marked respectively 4" and 3J".) The 
 object of this silk wrapping is to insulate the wire thoroughly 
 from the iron, and to prevent any accidental abrasion of the 
 covering wire, which may take place during careless winding from 
 short-circuiting to the iron below. When the silk has been laid 
 smoothly and tightly on, the limbs may be returned to the oven, 
 and allowed to dry at a gentle heat. In precisely the same 
 manner, the interior faces and their central portion of the arma- 
 ture {technically known as the * web ') must be varnished with 
 Brunswick-black, and wrapped with one layer of similarly-pre- 
 pared silk. Three pieces will be required to do this effectually 
 viz., two pieces 3f inches long by 1J inches wide, shaped as in 
 Fig. 30, to fit against the inner faces, and one piece 6 inches long, 
 by f of an inch wide, to wrap round the web. Particular care 
 must be taken that every portion of the inside of the armature's 
 
The Dynamo : How Made and how Used. 5 5 
 
 channel be entirely covered in silk. When this has been satis- 
 factorily performed, another coat of Brunswick-black may be 
 given (avoiding to soil the outside), and the armature allowed to 
 dry thoroughly in a warm oven. 
 
 32. Our dynamo is now ready for wiring. For this purpose 
 we shall require about 7 Ib. of No. 1 6 single cotton-covered copper 
 wire for the field-magnets, and about \ Ib. No. 20 double silk- 
 covered for the armature. The amateur should be careful to get 
 new wire, of the highest conductivity, and very soft ; the em- 
 ployment of old, kinky, and hard wire is fatal to success. 
 
 33. The quantity of wire above mentioned having been duly 
 selected, it should be tested for continuity. The No. 16 will give 
 evidence to the sight alone, whether there be any break in it or 
 not. Should there be such, the covering from the two broken 
 ends should be uncovered for about an inch on each end, the two 
 extremities filed down to a fine flat wedge, so as to fit one another, 
 when each one separately should be warmed for a second over the 
 flame of a spirit-lamp, dipped into powdered resin, and rubbed, 
 while being held in the flame of the lamp, with a rod of solder, 
 until each has taken a good coating of solder. The two ends may 
 then be applied with their flattened portions together over the 
 flame of the spirit-lamp until the solder coating melts. Keeping 
 the ends pressed together, the wire is to be removed from the 
 flame. The solder soon hardens, and the wires will be found 
 firmly united. It is now only necessary to file away any rough- 
 ness, and rewind the cotton covering over the bared portion, 
 adding a little darning-cotton if the covering be deficient. The 
 finer wire, which is generally bought on reels, had better be tested 
 with the galvanometer (Fig. 2). To this end, find the two 
 extremities of the wire, attach one to one binding-screw of the 
 galvanometer, the other extremity being in good metallic contact 
 with the pole of any single- cell battery. Connect the other pole 
 of the battery with the other binding-screw of the galvanometer. 
 An immediate and large deflection of the needle will show that 
 the wire is continuous. If not, the wire must be unwound from 
 the reel, and carefully wound on to another until the point at 
 which the break occurs has been discovered. The two broken 
 ends may be joined as described above, great care being taken 
 
56 The Dynamo : How Made and how Used. 
 
 after joining to re-cover the point of junction thoroughly, so as to 
 preclude all danger of leakage, more silk being used to this end if 
 necessary. It having been ascertained that the wire is perfect 
 and in good condition, the next step is to soak it in melted paraffin 
 wax. The good effect of this is twofold : (a) The insulation is 
 thereby rendered very much better ; (b) a damp atmosphere has 
 then little or no effect on the insulation, since the paraffined 
 cotton and silk covering is no longer hygroscopic, and may 
 actually be pumped upon without becoming wetted or spoiling 
 the insulation. To paraffin nicely the wire should be laid in a 
 shallow dish large enough to contain it easily a circular tin 
 baking dish will do admirably. It should then be placed in a 
 warm oven, not too hot, until it is about the heat of the hand 
 say, 90 Fahr. About | Ib. of good paraffin wax should now be 
 placed in the tin, and the oven closed until the paraffin is all 
 melted. The wire may then be turned over two or three times 
 until it is seen to be thoroughly soaked with the paraffin. Two 
 or three metal rods should now be placed across the top of the 
 dish, on which the wire may be placed to drain for a few seconds 
 while still in the oven. When it ceases to drip it may be removed 
 from the oven and allowed to cool. The superfluous paraffin, 
 while still hot, may be poured into a cup (which has been just 
 previously breathed into) to set, when it may be used for other 
 insulations. 
 
 34. Winding the armature next claims our attention. Having 
 marked the heads, so as to know which belongs to a given 
 extremity of the armature, we unscrew and remove them ; about 
 6 inches of the extremity of the No. 20 wire should be coiled 
 tightly round the end of a pencil, so as to form a tight helix from 
 which the pencil must then be slipped out. This helix will form 
 one of the spare ends of the wire which will be attached to the 
 commutator, and should be, pro tempore, tied with a bit of silk to 
 the outside of the armature, so as to be out of the way while 
 winding. Holding the armature in the left hand, with the end 
 which corresponds to the commutator facing us, and beginning at 
 the left-hand cheek, we wind the wire in the channel, continuing 
 to wind until we reach the right-hand cheek, taking care to lay 
 the wire on as closely as possible, never allowing it to ride over 
 
The Dynamo : How Made and how Used. 57 
 
 its neighbour, nor yet to leave gaps between. When one layer 
 has thus been carefully wound on, as shown at Fig. 31, it should 
 be tested for insulation, since the amateur is very apt to wind 
 carelessly and cut the insulating covering, either by catching in the 
 sharp corners of the channel or otherwise. To test for insulation, 
 tie the end of the wire (without detaching it from the reel or 
 hank) against one cheek of the armature, to prevent its unwinding 
 during the trial ; then connect one pole of a battery to one binding- 
 screw of a galvanometer, and the helix end of the wound wire to 
 the other binding-screw. On touching the iron of the armature 
 at any point with the other pole of the battery, no deflection of the 
 needle should take place. Should a deflection show itself, evincing 
 a metallic contact and want of insulation at some point, the wire 
 must be unwound, the flaw localized and remedied by a fresh 
 covering of silk, basted with paraffin, and again wound on and 
 tested until the insulation is satisfactory. A layer of thin 
 paraffined paper should now be laid over the first layer of wire, 
 and the winding proceeded with in exactly similar manner, until 
 the second layer has been laid on, remembering that the essentials 
 of success are to wind the wire as closely as possible in each layer 
 without overlapping ; to avoid grazing the covering of the wire, 
 so as to maintain insulation, and to wind always in one direction 
 viz., from us, over to under. There is no necessity (when using 
 silk-covered wire) to place a stratum of paraffined paper between 
 each layer of wire, as this, by increasing the distance between the 
 layers, somewhat decreases the efficiency of .the machine : this is 
 only advisable when the insulation of the wire has been found to 
 be imperfect. The winding should be proceeded with, layer after 
 layer, evenly, tightly, and smoothly, until the wire just fills the 
 channel. Care must be taken that it does not exceed this, for if 
 it comes higher than the cheeks it will surely catch in the limbs 
 of the field-magnets during rotation. From eight to nine layers 
 of wire may be laid on, according to the tightness with which it 
 is pulled during winding. When the due proportion of wire has 
 been laid on, it should be fastened down by tying, so as not to 
 unwind, with its free end at the same extremity (the commutator 
 end) as we started from. The helix may now be straightened 
 out, and its condition observed, to insure that it is well insulated. 
 
The Dynamo: How Made and hoiv Used. 
 
 The end at which we finished winding should also be straightened 
 out and examined for good covering. Then a stick of Front's 
 elastic glue should be heated and rubbed over the covered ends 
 right up to the armature, so as to thicken them to such an extent 
 that they will only just pass through the holes bored in the head 
 to which the commutator is attached. (See Fig. 19, c, c.) The 
 wire ends should be passed one through each of these holes (care 
 being taken that the head be put on as it was previous to removal), 
 
 pulled pretty tightly, but not so roughly as to graze or injure the 
 covering, and having been cut so as to just reach the heads of the 
 screws, which fasten the two halves of the split tube of the com- 
 mutator to its cylinder (see Fig. 26), should have their extreme 
 ends unwound and cleaned, and then be soldered down, one to 
 each half of the split tube, care being taken that neither the 
 solder nor the wire passes beyond the line of the screws, so as to 
 leave plenty of room for the brushes to press against the commu- 
 tator. The heads may now be screwed up in their place, and a 
 
The Dynamo : How Made and how Used. 59 
 
 coat of good sealing-wax varnish (best made by dissolving good 
 scarlet sealing-wax in methylated spirit) painted over the layers 
 of wire, both for the sake of appearance and to keep the wires 
 from moving out of place during rotation, though if the wires are 
 tightly wound this will be hardly needful. This coat of varnish 
 must be allowed to dry off in a warm atmosphere (not in tho 
 oven), and the armature will be complete. 
 
 35. Our labours are now drawing to a close. To wind the 
 field-magnets it will be as well to rig up a little piece of apparatus, 
 since, although they may be wound without, it is very difficult to- 
 lay the wire as closely, as tightly, and as neatly as can be done 
 by its aid ; and since the efficiency of the machine is greatly 
 exalted by the greater proximity of the wire to the core, it is a 
 matter of considerable importance that this should be attended to. 
 The apparatus necessary consists of a handle fastened to an axle 
 passing through a standard supported on a base ; the axle having 
 a prolongation to which each limb of the field-magnets can be 
 screwed down in its turn. On turning the handle, it is evident 
 that the iron mass of the field-magnet will rotate on its axis, and 
 if care be taken that the centre of the mass coincides with the 
 centre of motion, the motion imparted to the iron will be smooth 
 and even, and the wire may be laid on with great exactitude and 
 closeness. This apparatus is illustrated at Fig. 32, a, with one of 
 the limbs of the field-magnets screwed in its place, ready for 
 winding. It should be made out of f-inch stuff, the base being 
 about 5 inches wide by 6 inches long. The upright through which 
 the axle passes should also be about the same size, and screwed 
 to the edge of the base-board, so as to stand at right angles to it. 
 A short piece of broomstick, about f of an inch in diameter, may 
 be used as the axle, and a hole must be bored in the upright, 
 at about 4 inches from this base, to admit this axle. To the ex- 
 ternal portion of the axle is fastened a handle; while to the 
 internal portion, which should protrude about \\ inches, is 
 screwed a piece of J-inch stuff about 1 \ inches square, half the 
 axle being cut away to admit of its lying flat. Previous to- 
 screwing down, the handle, as well as this latter square piece, 
 should be rubbed over with a little good hot glue at the places 
 where they touch the axle, to insure a good sound joint. This. 
 
Co The Dynamo : How Made and how Used. 
 
 4 winder ' being completed, it may be clamped to a bench or table 
 by means of a sewing-machine or fretsaw clamp, the leg of the 
 iield-magnet having been previously screwed to it by means of 
 the three holes in the flange, in the position shown in the figure. 
 Though shown in the cut to the left, the handle of the winder 
 should be to the right of the operator, unless he be left-handed. 
 In commencing to wind the wire, the operator should stand over 
 his work, a sheet of paper having been placed on the floor, and 
 the coil of paraffined wire at his feet, with a two-gallon stone 
 bottle filled with water in the centre of the coil to prevent its 
 entangling or kinking. The surface of this jar being glazed, the 
 wire slips from it without injuring the covering. The winding 
 should be commenced at the extremity farthest from the handle 
 id est, nearest to the channel in the field-magnets in which the 
 armature rotates. Six or eight inches of the wire should be coiled 
 round a pencil, and so as to form a tight helix, which, with a 
 piece of strong twine, should be tied to the leg of the magnet, as 
 shown in Fig. 32, b. Holding the loose end of the wire in the left 
 hand, keeping it pretty tightly pulled, and straightening it out 
 from its coiled shape as it passes through the fingers, it is easy in 
 this manner to wind the wire perfectly flat and smooth by turning 
 the handle of the winder in the direction of the motion of the 
 hands of a watch. (In order to prevent any accidental contact 
 through abrasion against the corners, etc., it is advisable pre- 
 viously to cover the legs of the field-magnets, at all events as far 
 as the wire is to extend viz., from c to d in the present figure 
 with a band of silk dipped in melted paraffin, and applied hot to 
 the iron, when it will immediately adhere. This band must be 
 carefully smoothed down, so as not to cause unevenness in the 
 winding of the wire.) If the wire be nicely laid on, it will be 
 found possible to wind forty rows between c and d. Before 
 arriving at d it will be necessary to place two pieces of tape about 
 J an inch wide and 3 inches long, as shown at e e in the figure, 
 the free ends of which must be turned back smoothly and tightly 
 over the layer just put on when d is reached. Continuing the 
 rotation of the handle in the same direction, another layer of 
 wire is now laid over the first ; by holding the ends of the tape 
 fast while beginning to wind this second layer, all tendency of 
 
The Dynamo: How Made and how Used. 61 
 
 Fig. 32 
 
 ARRANGEMENTS FOR WINDING THE FIELD-MAGNET. a, The winder, with 
 one limb of the field-magnet in position ; &, Position of wire on 
 starting the right limb ; c, The wire ; d, The flange ; e, The tapes ; 
 /, Position of wire on starting the left limb. 
 
2 The Dynamo : How Made and how Used, 
 
 sinking into the layer beneath, which may be displayed by the 
 second layer, is overcome. Without this precaution it is almost 
 impossible to prevent the outer layers of wire sinking into the 
 interspaces of the layers below. Continuing in this manner, layer 
 after layer should be laid on until seven layers have been wound, 
 remembering to use tapes towards the end of each layer, and that 
 ach layer will diminish by two rows. When the seven layers 
 have been laid on, the wire must be tied down to the magnet to 
 prevent uncoiling, arid cut off from the hank of wire, leaving 
 about 6 inches free for attachment. 
 
 In exactly a similar manner as regards attachment, direction of 
 winding, etc., must the second limb be wound. The only differ- 
 ence that need be made is that, for convenience of having both 
 ends of wire at the same end of the dynamo, it will be well to 
 fasten the beginning of the wire (the helix) to the inside of the 
 leg instead of to the outside. Fig. 32, /, will make this clear. 
 
 36. Both for the sake of appearance and to further protect 
 the insulation from damp air, etc., it is advisable to give the wires 
 on the limbs of the field-magnets a coat of good varnish. The 
 best for this purpose is made by mixing about 2 ounces of the 
 best red lead with J an ounce of good white hard varnish, which 
 can be procured of any oilman. The two should be well incor- 
 porated together by working with the brush intended to be used 
 for laying on the varnish. 
 
 The varnish should be applied in a thin layer with a soft brush, 
 so as to disturb the paraffin coating as little as possible, since if 
 the paraffin mixes with the varnish, this latter never dries, but 
 remains a sticky mess. For this reason the 'coating of varnish 
 should be allowed to dry without the application of heat, which, 
 if the ' white hard ' be good, it will do in about eight to twelve 
 hours. A second coat may be given if desired ; but as this 
 generally fills up the interstices between the layers of wire, it 
 detracts somewhat from the neatness of the appearance. 
 
 37. The varnish being quite dry; the dynamo may again be put 
 together, care being taken that the parts are adjusted in the posi- 
 tion which they occupied after fitting. If this has been properly 
 done, the armature ought to turn freely in its bearings quite cluse 
 to the limbs of the field-magnets, but without catching any 
 where. 
 
The Dynamo: How Made arid how Used. 63 
 
 ATTACHMENT OF WIRES AT UPPER PORTION OF THE FIELD-MAGNET. 
 a, Wires cleaned and uncovered ready for joining ; b, Wires twisted 
 and soldered ; c, Brass spring, or * brush,' to collect the electricity 
 from the commutator. 
 
64 The Dynamo : How Made and how Used. 
 
 Supposing this to be all right (and it must be so, or the dynamo 
 cannot work properly), the dynamo must be screwed down to a 
 base-board, which should consist of a slab of oak, walnut, or 
 mahogany, 10 inches long by 8 inches wide, and at least 1 inch 
 thick. The two holes in the lower flange in the limb of the field- 
 magnets, near the channel in which the armature revolves, are 
 expressly for the purpose of clamping the dynamo to its base- 
 board. The base-board should be chosen of a well-seasoned 
 nature polished, for appearance' sake ; and the dynamo should 
 be screwed to it centrally, with the narrowest portion of the 
 dynamo parallel with the narrowest portion of the baseboard. 
 
 ATTACHMENT OF THE WIRES. 
 
 38. The dynamo having been wound as described (and care 
 must be taken to have fulfilled the instructions exactly, or else 
 the resulting magnet will have two north poles, or two south poles, 
 instead of one north and one south), we can proceed to couple 
 up the various parts. To this end we begin by joining the wires 
 at the two extremities at which we left off winding. This may be 
 effected by removing a portion of the covering of the wires (by 
 scraping with a sharp knife) for about an inch along the places 
 where the two wires cross each other if made to touch. (See 
 Fig. 33, a.) 
 
 The wire must be made quite bright and clean by rubbing with 
 a bit of sandpaper at this point, and then the wires are twisted 
 tightly together by the aid of a pair of pincers. A drop of solder, 
 taken up on a hot soldering-iron and run along the twisted portion 
 will insure the contact remaining good. The excess of wire should 
 now be cut off from the twisted end with a pair of cutting pliers ; 
 the bared twist bound round with a layer of darning-cotton, 
 varnished with the red varnish ( 36), and turned in out of the 
 way between the limbs of the magnet. (Fig. 33, b.) 
 
 We may now proceed to magnetize the field-magnets. For this 
 purpose we need only attach the poles of a single-cell bichromate 
 battery, exposing from 8 to 1 square inches of negative surface, 
 to the wires of the dynamo for a few seconds ; but in order to 
 obtain results winch may be deducible from reason, and which 
 
The Dynamo : How Made and how Used. 
 
 Fig. 34-. 
 
 THE BRUSHES AND BRUSH BLOCKS. Fig. 34. a, a, The commutator. 
 1) b, Brush blocks, c c, The brushes, d d, Screws to tighten up the 
 brushes. 
 
 Fig. 35 a. Wire loop to connect brushes with binding-screws. 
 
 Fig. 35 b. The same in position on the brush-block. 
 
66 The Dynamo : How Made and how Used. 
 
 can be corrected if mistakes are made, it is desirable to determine 
 beforehand which shall be the north pole of our future magnet. 
 It will be remembered ( 8) that we have it in our power to pro- 
 duce a north pole, to our left, in a mass of iron, by passing a current 
 of electricity aivay from us, over it ; and if we wish to produce a 
 north pole to the right, the current must come toicards us, over 
 the mass. 
 
 Let us decide to make a north pole of the limb on which we 
 began to wind the wire on the outside. (See Fig. 32, c.) To do 
 this the current ought evidently to fLowfrom the limb of the magnet 
 to the observer ; in other words, this wire must be attached to the 
 negative pole of the cell. (The negative pole of the bichromate 
 cell is the wire proceeding from the zinc, the one attached to the 
 graphite being positive.) The positive pole of the cell must be 
 coupled to the other wire id est, the one which was started from 
 the inside in winding. (See Fig. 32, /.) 
 
 While the battery is thus coupled up to the dynamo, we can 
 test if we have produced the effect desired by bringing a suspended 
 magnetized needle near the supposed north pole of the dynamo. 
 If all has been properly performed, it will be found to attract 
 the south pole of the poised needle, and repel its north pole. 
 
 A few seconds' connection with the battery will impart as 
 much magnetism to the field-magnet as it will retain ; but that 
 little will be sufficient for our purpose. Our next step is to dis- 
 cover in which direction the current flows in our armature, when 
 we rotate the flywheel in the usual way with the right hand (in 
 the direction of the motion of the hands of a clock). Before 
 we can do this we must fasten two * brushes ' or collectors on 
 the brush-blocks, in order to collect the electricity generated by 
 the revolution of the armature. 
 
 THE BRUSHES. 
 
 39. These consist of two pieces of springy sheet brass, -^ of 
 an inch thick, 3J inches long, and about f of an inch wide. They 
 must be bent twice at right angles, so as to fit tightly on to the 
 brush-blocks ( 28, Fig. 27), and slightly curved inwards at the 
 longer portion, so as to press with some force against the com- 
 
The Dynamo : How Made and how Used. 67 
 
 mutator. (See Fig. 33, c.) To fasten these on to the blocks, a 
 lateral slot is cut about half-way into each brush, at about J- of 
 an inch from the longest portion, of such a width as to admit 
 the shank of a small screw passing into it. The portion of the 
 brush which rests against the agnfttpfe^ should be slit into two or 
 three divisions, and curved slightly upwards to avoid scratching 
 the armature. 
 
 These two brushes, though alike in shape, must be put in 
 opposite positions on the dynamo ; that is to say, the one which 
 goes on the block to the right of the observer has the longer 
 portion above the block, while the one which goes on the left- 
 hand block has the longer portion below the block. Thus the 
 commutator is rubbed by these two brushes at diametrically 
 opposite points. Care must be taken that the two screws which 
 serve to fasten the brushes to the blocks do not touch the metal 
 of the bolts which clamp the bearings to the dynamo, for if they 
 did the current would short-circuit, and the machine would not 
 work. It will also be necessary to observe that sufficient curvature 
 be given to the longer portion of the brushes to clear the bearings 
 altogether, otherwise, of course, the current would pass into the 
 bearings and be short-circuited. Fig. 34 shows the brushes in 
 their proper position ; a, a being the commutator (exaggerated 
 in size somewhat to show its position), &, b the brush-blocks, e, c 
 the brushes, and d, d the screws which, by being tightened or 
 loosened, can increase or decrease the pressure of the springs on 
 the commutator, and to which the two wires which form the 
 electrodes of the commutator are to be attached. These two 
 wires, which in our machine may be about 3 inches long, with a 
 loop at each end, as shown at Fig. 350, should be of No. 16 
 cotton-covered copper wire, the covering being removed from the 
 two loops, which must be made quite bright. Before putting in 
 the screws d, d, Fig. 34, each one should be passed into one eye 
 of one of the said wires, then screwed partly into the brush- 
 block, when the brush itself may be pushed into its place over 
 the block, and under the screw, the slot in the side admitting of 
 this ; lastly, the screw is tightened up until the desired pressure 
 on the commutator is obtained. 
 
 Fig. 356 shows the position of the wire, screw, and left-hand 
 
 52 
 
68 The Dynamo : How Made and hoiv Used. 
 
 brush on the left-hand block. The two free ends of the wires 
 just described project straight forward to the front of the 
 machine ; they may be screwed down on the baseboard, at the 
 distance of about 3 inches apart, by means of a small pair of 
 binding screws ; the long screws of which are passed through the 
 free eyes. 
 
 We can now test the direction of the current in our armature. 
 To do this we place the flywheel on its bracket, put a leather 
 band (such as is used for treadle sewing-machines) round the fly- 
 wheel and driving pulley, then by means of two thin wires, 
 which T7e will screw into the holes of the binding-screws just 
 
 Fig. 36. 
 
 arranged, we couple up the brushes to our galvanometer ( 3), 
 and rotate the handle of the flywheel gently, in the direction we 
 intend to work the machine for the future. 
 
 A deflection of the north pole of the needle, either to right or 
 left, shows us in which direction the current is travelling ; we 
 carefully note, and mark with a paper label, which is the binding- 
 screw which is sending the positive current (which, if coupled to 
 the wire over the needle, causes the north pole to turn to the left), 
 since this is the binding-screw which must substitute the positive 
 pole of the battery, and to which we must attach the wire which 
 comes from the S limb of our dynamo. 
 
 40. Two binding-screws are now to be inserted into the base- 
 
The Dynamo : How Made and how Used. 69 
 
 MODES OF ATTACHING LAMPS. , For series, b, For parallel arc. 
 
7O The Dynamo : How Made and how Used. 
 
 board, to which the wires proceeding from the limbs of the field- 
 magnet must be clamped. These should be placed about 1 \ inches 
 from the side of each limb, the wires proceeding therefrom being 
 denuded of their covering and sandpapered at the extremities 
 where they are clamped to the binding-screws. These binding- 
 screws (as also those connected with the brushes) should, for the 
 convenience of being able to couple up at one and the same time 
 two or more wires, be of the pattern shown at Fig. 36, in which 
 case the extremities of the field-magnets may be also formed into 
 rings, as shown at Fig. 35a, and either clamped down to the base- 
 board by passing the long screw c (Fig. 35) into the ring, or, the 
 nut a having been removed pro tern., the ring may be slipped over 
 the screw 5, and then clamped by the nut a. 
 
 Connection is now to be made between the binding-screw 
 attached to the current-sending or positive brush (the one which 
 we have marked with a paper label), and the binding-screw 
 coupled to the wire, starting from the inside of the limb of the 
 field-magnet (see Fig. 32, c) by means of a short length of No. 16 
 copper wire, well cleaned, bent into rings at the ends, and clamped 
 down as advised above. 
 
 If all the instructions have been carefully carried out, more 
 especially those contained in the last six paragraphs, we shall 
 find that on rotating the flywheel a powerful current will flow 
 between the two remaining binding -screws viz., the one con- 
 nected with the outside wire of the field-magnets, and the other 
 with the negative brush of the commutator a current which will 
 be sufficient to heat to bright redness 4J inches to 5 inches of 
 No. 42 platinum wire, or to light four 5-candle power lamps, 
 arranged in parallel arc. 
 
 The current actually flowing through the circuit (the number 
 of amperes) will naturally depend largely on the resistance 
 interposed between the poles that is to say, between the binding- 
 screws connected with the outside wire of the field-magnet, and 
 the negative brush of the commutators respectively : and since 
 the magnetism of the field-magnet depends entirely on the 
 amount of current flowing around it, and this again influences 
 the current set up in the armature, it is evident that every varia- 
 tion in the resistance of the interpolar or outside circuit will 
 
The Dynamo : Hoiv Made and hoiv Used. 71 
 
72 The Dynamo : How Made and how Used. 
 
 produce a corresponding variation in the current, if the dynamo 
 be connected up as above described ; and that a very much larger 
 current will traverse the circuit when the resistance is small, than 
 when the resistance is great. When the machine is doing its 
 best work that is to say, when the resistance of the interpolar is 
 equal to the internal resistance of the machine the current is 
 equal to that of eight or ten Bunsen's cells against an equal 
 resistance. Sometimes it is necessary to send the current 
 through a greater resistance ; in this case, in order not to weaken 
 too greatly the magnetism of the field-magnet by diminishing so 
 greatly the current, it is necessary to shunt off a portion of the 
 current, and send it round the limbs of the field-magnet by 
 another circuit, which diminishes the total resistance. 
 
 To render this clearer, let us suppose that we wish to light up 
 four 5-candle lamps, having each an approximate resistance of 
 8 ohms, and requiring a current of about 1 ampere each to 
 cause them to give out their proper light. If we arrange them 
 in series, as in Fig. 37, a, when the total resistance is the sum of 
 their separate resistances = 32 ohms, then, as the electromotive 
 force of our machine when at best is about 10 volts, so \^ re- 
 presents the current flowing through the lamps, supposing even 
 that the dynamo lost no power by the diminution of current 
 (which it does to a very great extent), and this current is not 
 sufficient to light the lamps. But if we arrange the lamps in 
 parallel arc, as at Fig. 37, &, then the total resistance falls to a 
 quarter of one single lamp that is to say, it is equal to 2 ohms 
 only ; hence, the current now flowing becomes V = 5 amperes, 
 and this divided among the four lamps gives 1 \ amperes each, 
 which is ample. 
 
 Again, we find that coupling up one single lamp to the dynamo 
 presents too great a resistance, so that no light is given off, since 
 not sufficient current can pass round the field-magnets to give 
 an electromotive force of 10 volts. But if we insert a ' shunt/ 
 consisting of about a dozen inches of No. 30 iron wire, between 
 the two binding-screws aforesaid, as shown at Fig. 38, and then 
 connect the lamp also to the said screws or terminals, more 
 current circulates round the field-magnets, since two roads are 
 now open to the current, the field-magnet becomes more power- 
 
The Dynamo : Hew' -Mads and/ '&$&)''&&&. 73 
 
 fully magnetic, and in its turn induces a much more powerful 
 current in the armature, and so on until current enough is pro- 
 duced to light up the lamp. The resistance of the * shunt ' to be 
 inserted between the terminals, to produce the best result, will 
 depend on the resistance of the interpolar. If this latter be low, 
 no ' shunt ' (or one of very great resistance) will be required ; 
 but if the resistance of the interpolar be very high, the resistance 
 of the * shunt ' must be correspondingly low, or else not enough 
 current will pass to magnetize the field-magnet, and the dynamo 
 will give no current. 
 
 Fig. 39 represents the dynamo completed. 
 
INDEX. 
 
 N.B. The Numbers refer to the PARAGRAPHS, not to ttie Pages?. 
 
 AMPERE'S Kule . 
 
 , 8 Insulation, of armature 
 
 31 
 
 Armature, Clarke's 
 
 - 11 
 
 of field magnets , 
 
 31 
 
 Siemen's, H. 
 
 , 14 
 
 of wires 
 
 33 
 
 Pacinotti's . 
 
 . 17 
 
 general . , 
 
 31; 
 
 tracing up the : , 
 
 , 22 
 
 
 
 fitting the . 
 
 , 23 
 
 Law, Ampere's . . . . 
 
 s 
 
 heads for . 
 
 . 23 
 
 of deflection 
 
 4 
 
 winding the 
 
 . 34 
 
 ,, of magnetic attraction 
 
 11 
 
 Base board . . . ., 
 Battery, Galvanic 
 
 . 37 
 
 4 
 
 Magnetic attraction 
 ,, induction 
 
 li 
 3 
 
 Bearings, to fit . 
 , , to make 
 Binding screws . 
 
 . 25 
 . 25 
 
 39,40 
 
 Magnetism produced by currents 
 Magnetizing the field magnets . 
 Magneto, Clark's ... 10, 
 
 7 
 38 
 
 11 
 
 Bracket, how to finish . 
 
 . 24 
 
 Pixii's .... 
 
 10 
 
 ,, or standard . 
 
 . 21 
 
 ,, Saxton's 
 
 10 
 
 Casting, how to finish . 
 
 . 22 
 
 Pacinotti's machine 
 
 17 
 
 ,, must be soft . 
 
 . 22 
 
 Patterns, general instructions for 
 
 IS 
 
 Clarke's machine . 
 
 10,11 
 
 ,, for armature 
 
 1'.) 
 
 
 9 
 
 for field mafriets 
 
 20 
 
 Commutator, how made 
 
 . 26 
 
 ,, for standard ., * 
 
 21 
 
 ,, its functions . 
 
 . 12 
 
 Pixii's machine 
 
 10 
 
 Cumulative principle . 
 
 , 13 
 
 Pulley ,..** 
 
 2 1 .) 
 
 Currents, battery 
 
 4 
 
 
 
 ,, direction of . 
 
 . 12 
 
 Rigger. , 
 
 2<> 
 
 ,, not continuous . 
 
 . 15 
 
 
 
 produced by magnet 
 
 6 
 
 Saxton's machine . 
 
 10 
 
 ,, produce magnetism 
 
 7 
 
 Shunt, use of a 
 
 40 
 
 voltaic . 
 
 3 
 
 Siemen's, H., armature ., 
 
 14 
 
 
 
 ,, machine . , * 
 
 14 
 
 Deflection of needle 
 
 4 
 
 Soren Hjorth's machine 
 
 i;j 
 
 Dynamo, how to use , , 
 
 . 40 
 
 
 
 ,, power of 
 
 . 40 
 
 Varnish, electric .... 
 
 3f 
 
 ,, what is a 
 
 1 
 
 Varnishing ., 
 
 3G 
 
 Faraday's discovery . , 
 
 . 2, 3 
 
 Winder . 
 
 35 
 
 Fly-wheel 
 
 , 30 
 
 Winding the armature . 
 
 34 
 
 
 
 the field magnets 
 
 35 
 
 Galvanometer, to make a . 
 
 2 
 
 Wire, attachment of 
 
 37 
 
 
 
 ,, insulation cf 
 
 33 
 
 Heat, evolved . . , 
 
 . 15 
 
 ., joining 
 
 33 
 
 Hjorth's machine , , 
 
 . 13 
 
 ., required 
 
 32 
 
 
 
 ,, testing = 
 
 33 
 
 Induction, magnetic 9 
 
 3 
 
 
 
 
 THE END. 
 
 
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