64 FJ.ECTRIC LIGHTING. 



Sixteen coils are placed on a bronze wheel provided with 

 suitable receptacles and fastening-collars by which they are 

 strongly clasped. This arrangement, which for brevity we 

 shall call the disc, revolves between two rows of horseshoe 

 magnets, fixed parallel to the plane of the disc on a particu- 

 lar kind of frame constructed of wood only, at least in the 

 vicinity of the magnets. Each row contains eight magnets, 

 and thus presents sixteen poles at uniform distances .apart. 

 Thus there are as many poles as coils, and when any one of 

 the latter is opposite a pole the remaining fifteen are in a 

 like position. 



One machine may have several discs mounted on the same 

 axle, with several rows of magnets fixed on the same frame. 

 The number of discs does not usually exceed six, as the 

 machines would be too long, and it would be difficult to 

 avoid flexure of the axle and the frame. It should be borne 

 in mind that the coils must revolve as close as possible to 

 the magnets, but without touching them. At the present 

 time nearly all these machines have only four discs. 



Fig. 15 shows a general view of a six-disc machine, and 

 Fig. 1 6 indicates the manner in which each coil E is pre- 

 sented before the poles A, B ; B", A"; a, b ; //, a', &c., of the 

 different magnets, which are so placed in the contiguous 

 rows that a north pole may be opposite to a south pole in 

 order to polarize in opposite directions the magnetic core of 

 each coil. The ends of the wires of the coils are attached 

 to flat pieces of wood fixed on the bronze wheel, and on these 

 the coils may be arranged either for tension or for quantity, 

 like the elements of an hydro- electric battery. One pole of 

 the total current is connected with the axle' c, which com- 

 municates with the frame through the bearings ; the other 

 pole ends in a metallic collar, D c, concentric with the axle, 

 and insulated from it by wood or ebonite, and these two poles 

 are connected with the external circuit by the cast-iron frame 

 of the apparatus, and by a friction-spring which, by means of 

 a wire, is in communication with a binding screw. 



