2/6 SCIENTIFIC RECREATIONS. 



The Maxim machine is constructed on the principle of sets of coils rotating 

 between powerful electro-magnets. The Wallace machine was invented by the 

 inventor of the Wallace-Farmer lamp. It consists of two horse-shoe electro- 

 magnets placed side by side, the opposing poles facing each other. Each 

 magnet has a rotating armature of twenty-five bobbins, on which the wire is 

 wound quadruply, and the current generated by these coils is conducted 

 away, passing through and exciting the electro-magnets, thus utilizing the 

 residual and terrestrial magnetism before mentioned in connection with the 

 Ladd machine ; otherwise it partakes of the nature of the Niaudet machine. 



We now come to what is perhaps the most perfect magneto-electric 

 machine, which was first constructed by M. Gramme, a Parisian, in 1872, 

 and differs in principle and construction from all those hitherto noticed. Its 

 essential characteristic is a soft iron ring, round which is coiled one single 

 continuous wire (i.e., the two ends are joined). Round the exterior surface 

 of the wire coil a band is bared, and on this bared part two friction springs 

 act. If the ring and coil be placed before the poles of a magnet, the ring 



Fig. 276. The Gramme Machine. 



will have two poles, S. and N., induced opposite the opposing poles N. and 

 S. of the magnet ; and if the ring revolve the poles will remain stationary, 

 and as the coil revolves each coil of the wire will pass this induced pole, and 

 as naturally half the coil will be inducted with one current, the other half 

 (acted on by the other pole) will be charged with another or opposite 

 current, which two kinds of electricity are carried away by the friction springs 

 before mentioned. In the machine, as actually constructed, the soft iron ring 

 is composed like the magnet or wire bundle of an induction coil, and the 

 coils are set upon it side by side. Inside the ring are radially set insulated 

 pieces, to each of which is attached the issuing end of one and the entering 

 end of another bobbin ; these answer the same purpose as the denudation of 

 the external layer of wire. These pieces are bent so as to come out of the 

 centre of the ring at right angles, and lay side by side (insulated) round a 

 small cylinder. These, as they revolve, are touched by friction springs, which 

 draw off the electricity induced in the coils in one continuous current. No 

 sparks are produced at the contact of the friction springs, and there is no 

 tendency to become heated. To obviate the inconvenience of the secondary 



