CHAMBERS'S INFORMATION FOR THE PEOPLE. 



communicate with the ends, m, , of the coil), to 

 give us a constant flow of electricity in one 

 direction. 



With electricity obtained in this way, we may 

 have all the ordinary current effects. Water may 

 be decomposed, platinum wire heated red-hot, 

 and soft iron magnetised. It has been much used 

 for medical purposes, and the physiological effects 

 are very powerful Magneto-electric machines 

 have also been used for firing gunpowder. Abel 

 has lately constructed fuses which may be readily 

 fired with a pocket-machine of this kind. 



Such a machine forms a link of the chain that 

 binds all the physical forces together. The force 

 of a magnet, and the force of a man turning .a 

 handle, may seem very different, and they do 

 differ widely. Yet they differ only inform. With 

 a suitable arrangement, the one form of energy 

 may be, as it were, remoulded and brought forth 

 in the shape of the other. 



Recent Magneto-electric Machines. The mag- 

 neto-electric machine has now come into extensive 

 use, as being a readier, steadier, and cleanlier 

 source of current electricity than the galvanic 

 battery. Very powerful machines have been con- 

 structed on much the same principle as that we 

 have just described. They have been employed 

 for the electric light in lighthouses, and are driven 

 by small steam-engines. We are to look upon 

 them as simply the means of converting mechani- 

 cal into electrical force or energy. But important 

 modifications in the construction of these have 

 been made in recent years. 



Siemen^ Armature. In 1854, Siemens intro- 

 duced a new form of armature, which brings the 

 coil and its core nearer the poles of the inducing 

 magnet or magnetic magazine. It has the wire 

 wound lengthways or parallel to the axis of its 

 core, and not across its length, as in common 

 electro-magnets. The core is a cylinder of soft 

 iron, with a large hollow scooped out on each side, 

 leaving it somewhat like a piece of an iron rail. 

 Insulated copper wire is wound along it till this 

 hollow is filled up, and the cylindrical form restored. 

 The faces of the core or rail, and not the ends, 

 form the poles of this electro-magnet. It is not 

 rotated before the poles of a steel magnet, as in 

 the common machine, but between the poles of a 

 series of magnets spanning it like a bridge, whose 

 breadth is the length of the armature. A very 

 rapid rotation can be given to the cylinder round 

 its axis, and the iron faces are magnetised and 

 demagnetised with corresponding rapidity. 



Wilde's Machine. Wilde of Manchester con- 

 structed in 1865 a magneto-electric machine of 

 unequalled simplicity, which can be made to con- 

 vert any amount of mechanical energy into elec- 

 tricity. It is formed on a new and seemingly 

 paradoxical principle namely, that the weakest 

 current or magnet may be made to induce any 

 desired strength of current or magnet. 



Wilde's machine consists of two magneto- 

 electric machines, a small one surmounting a 

 large one of precisely similar principle, but of 

 enormously greater strength. The figure (fig. 42), 

 represents an end view of the machine. In the 

 small machine, the inducing power is a magnetic 

 magazine, m, of twelve to sixteen steel horse-shoe 

 magnets. It evokes currents in a Siemens arma- 

 ture, which revolves between the poles, a, b, of the 

 magnets, some 2500 times a minute. Two springs, 



connected with n and p, press on the commutator 

 of the Siemens, and are the poles of the upper 



N P '^TSfrO. 



- -- , , -___-.,_ 



Fig. 42. 



current. This current is not used directly, but is 

 sent through the coils, E, E, of the huge electro- 

 magnet of the lower machine. It has a Siemens 

 armature, S, revolving between its poles, A, B, 

 some 1800 times a minute. Both machines are 

 precisely alike in action, and differ only in power. 

 The armatures are both driven by belts from the 

 same shaft. The arrangement of the magnetic 

 poles is very ingenious. It is the same in both, 

 but we shall refer only to the lower. They con- 

 sist of two masses of soft iron, A and B, hollowed 

 out so as to form the two sides of a tube to inclose 

 the Siemens armature. Pieces of brass, L, L, 

 serve to insulate the two poles magnetically, and 

 to complete the tube. This protects the armature 

 from the resistance of the air, and brings it as 

 near as possible to the inductive influence of the 

 poles. 



The effects which this machine is capable of 

 producing are almost incredible. When worked 

 with a three horse-power engine, the current of 

 the second armature consumes carbon sticks three- 

 eighths of an inch square, and evolves a light of 

 insupportable brilliancy. With one that consumes 

 carbons half an inch square, a light so intense is 

 got that, when put on a lofty building, it casts 

 shadows from the flames of street-lamps, a quarter 

 of a mile away. Mr Wilde succeeded in melting 

 an iron rod fifteen inches long, and a quarter of an 

 inch thick. Wilde has .even employed the current 

 of the second armature to magnetise a second 

 electro-magnet still more powerful than the first. 

 The whole required a fifteen horse-power engine 

 to drive it, and the heat of the current was 

 sufficient to melt a platinum bar two feet long and 

 a quarter of an inch thick. Indeed, the only limit 

 to the amount of electricity which might thus be 



