91 4 



UNDULATORY FORCES. ELECTRO-METALLURGY. [sormriM or POWER. 



electricity is developed ill the wiro in one direction by 



the piece of iron 

 witliin it gaining 

 magnetism; and 

 *whon the bar U 

 moving from the 

 polo of the mag- 

 not, a current is 

 produced in an 

 opposite dirootion 

 by the iron bar 

 lonng its magnet- 

 urn; and these 

 cunvnts arc both 

 reversed in di- 

 rection, if the 

 pole of tho mag- 

 not be reversed ; 

 BO that tho cur- 

 rent developed 

 in a wire, coiled upon an iron bar, by moving that 

 bar toward* the south polo of a magnet, is the saino 

 in direction as that produced by moving it from the 

 north pole. Wo will now suppose that tho current pro- 

 duced in tho coil of wiro upon bar B, moving from S to 

 N, is iu the direction of the small arrow surrounding 

 that bar viz., (eft-handed motion; if so, tho current of 

 tho wiro of bar D will also bo /'/{-handed in direction, 

 because it also is moving from a south to a north polo ; 

 whilst tho currents in the wires of bars C and E will bo 

 ri;/M-haiidod, because both those bars and coils are 

 moving from north to south polos. 



From those remarks, it may bo perceived 1st, that 

 the currents of electricity, in all tho coils, are reversed 

 in direction every time the bars pass the centres of the 

 poles of the magnets, i.e., four times in every revolu- 

 tion; 2nd, that to obtain a current of ono uniform 

 direction from all the four coils (by conducting tho 

 whole four into one stream), during only one quarter of 

 a revolution, . e. , from one pole to the next one, it is 

 necessary to connect the ends of tho wires of tho coils of 

 B and D in an opposite manner with the semi -cylinders 

 of tho commutator or break-piece (Fig. 81), to those of 

 the coils of C and E ; and, 3ra, that as the currents in 

 all tho coils arc reversed in direction every time tho bars 

 pass the centre of tho poles of the magnets, tho two 

 springs which press upon tho semi-cylinders, must, by 

 some means or other, bo reversed in their order of con- 

 nection with all the wires every time, and at the same 

 moment that tho bars pass the centres of tho polos, in 

 order to throw the whole of tho currents, during a 

 complete revolution, into one uniform direction in the 

 springs and in tho wires which proceed to the depositing 

 n -~ !. 



To enable us to understand how tho opposite currents 

 of the different coils arc thrown into ono uniform direc- 

 tion during ono quarter of a revolution, and how tho 

 whole of tho currents are alternately conducted into one 



Fig. 83. 



uniform stream 

 during rapid revo- 

 1 ut ion, we will 

 suppose a (Fig. 

 83) to bo the axle, 

 and 1, 2, H, :ind -I, 

 the semi-cylinders 

 in itilated from tin? 

 axle by a tube of 

 gutta-percha. In 

 the first place 1 

 - are con- 

 nected together by 

 a short piece of 

 thick copper or 

 brass wiro, or a 

 i strip of sheet cop- 

 per behind (not 

 shown in the cut), 

 and 3 nd 4 are connected together by another and 

 similar piece of metal; next tho ends of the wires 



A, A, A, A are gathered into one bundle. :ui.l connected 

 by soldering with the wire or strip of metal of tho .- 

 cylinders 1 and 2, and tho ends B, B, B, B arc con- 

 nected in like manner with thu semi-cylinders 3 and -1 ; 

 and by this arrangement, on careful attention, it will lx> 

 perceived that the whole of tho currents are thrown 

 into one direction during one quarter of a revolution. 

 In the sketch, tho bars are just approaching the centre* 

 of the poles, and the senii-cyhnd- r 1 is just about 

 breaking contact with spring C', and semi-cylinder 4 is 

 about making contact with it ; semi-rylinder 3 U about 

 passing from spring D 1 , and semicircle 1 is about making 

 contact with it. In this position of tho bars, it will be 

 perceived that all the A ends of tho wires, the semi- 

 cylinders 1 and 2, and the spring C', are positive, as 

 indicated by the arrows; whilst the B ends, the semi- 

 cylinders 3 and 4, and the spring D' are negative : but 

 immediately tho bars pass the centres of the poles, tho 

 currents are all reversed in direction all the B ends of 

 the wires, and the semi-cylinders 3 and 4 become posi- 

 tive, and the A ends, and the semi-cylinders 1 and '1 

 negative; but as the rotation of tho nxle shifts the 

 points of contact of semi-cylinder 1 to spring -D', and of 

 semi-cylinder 4 to spring CX, at the same moment, tho 

 spring C' still remains positive, and D' negative, as 

 before. The connections of tho springs with the semi- 

 cylinders in the other two quarters of the revolution, 

 alternate in a similar manner; and these alternations 

 take place regularly, and synchronously with the re- 

 versals of the currents, during the most rapid revolu- 

 tions ; and notwithstanding the incessant and indefinitely 

 rapid changes of these currents, one uniform stream of 

 electricity is obtained. In the practical machine, the 

 bars of iron rotate as closely as possible to the ends of 

 the magnets without absolutely touching them, in order 

 to obtain the greatest amount of power ; and the power 

 is regulated by placing the soft iron keepers which are 

 upon tho magnets (Fig. 80) nearer or further from the 

 poles ; the keepers are secured to the magnet, that thoy 

 may not fall off by the vibration of tho machine. The 

 wires proceeding from the springs are connected, one 

 with the dissolving plates, and the other with tho re- 

 ceiving articles in the vat. Tho machine may contain 

 eight revolving armatures, and either four or eight mag- 

 nets, according to the amount of work to bo effected. 



70. Vottaic Batteries. Each of tho arrangements of 

 metals and liquids which have been described under tho 

 head of " Facts," and which develop a current of elec- 

 tricity, constitutes an elementary voltaic battery a 

 battery in all its essential parts, but not in outward 

 form. All voltaic batteries consist of one or other of 

 those theoretical arrangements modified and adapted for 

 practical use, and are composed either of two metals and 

 one liquid, or two metals and two liquids ; because those 

 two arrangements develop the greatest amount of elec- 

 tricity, and are most convenient in use. In the theo- 

 retical form, any kind of metal, of any size or si 

 with almost any conducting liquid, and with any kind, 

 shape, or size of containing vessel, will develop a cm-- 

 rent of electricity and produce deposition ; but a true 

 voltaic battery consists of particular metals and liquids, 

 of particular sizes, shapes, and proportions, and at 



i distances apart, with suitable screws attached 

 for connections, and with eontaining-vessels made of 

 particular materials, and of special forms and sizes. 



71. Arrangements of various voltaic batteries havo 

 already been fully described in our previous pages.* 



72. Battery CW/J. Tho form of cells for those bat- 

 teries is generally either round or square ; for small 

 batteries, either of tho old zinc and copper kind, or of 

 Mr. Smee's arrangement, square ones are generally 

 used ; but for small Oanioll's batteries, or for largo bat- 

 teries of either of these kinds, round vessels ore almost 

 invariably adopted. They are made of stoneware, glass, 

 or gutta-percha; tho first of these is universally used 

 for largo batteries of all kinds: glass is too expensive 

 for largo vessels, but it possesses tho great advantage 

 of enabling tho operator to watch the action of tho 



Sw anlf, p. 197, tt Iff. 



