July I, 1875J 



NATURE 



171 



By uniting two or more machines to- 

 gether, electrical currents of high tension 

 may be obtained. But a more useful 

 arrangement is to divide into two each 

 ring, so that the two halves may be joined 

 either for quantity or tension, and varied 

 effects thus obtained from the same ma- 

 chine. This is effected in the following 

 manner. Suppose the machine to contain 

 sixty bobbins or hehces round the ring. 

 If the entrance of the thirty alternate 

 bobbins is placed on one side of the ring 

 and of the thirty other bobbins on the 

 other side, there will be in reality two 

 ring-armatures in one, interlaced as it 

 were into each other ; and by collecting 

 the currents by means of two systems of 

 rubbers, one to the right and the other to 

 the left of the ring, we may obtain from 

 each one half of the electricity pioduced 

 by the rotation of the ring. By applying 

 this principle to machines for producing 

 the electric light, the same machine may 

 give two distinct lights instead of one. 

 In its industrial applications, this is a 

 point of capital importance. The use of 

 the electric light is at present greatly in- 

 terfered with by its excessive brightness, 

 and the deep shadows which by contrast 

 are produced at the same time. These 

 defects will be to a large extent remedied 

 by the use of two lights, so that the 

 shadow from one may be illuminated by 

 the other. It is proposed to use four 

 electric lights, each of the strength of lifty 

 Carcel burners, for lighting foundries and 

 large workshops. In support of this pro- 

 posal I may remark that I find Duboscq's 

 lamp of the latest construction gives a 

 singularly steady and mild light, with 

 only twenty Bunsen's cells, and would of 

 course work equally well with currents of 

 the same intensity from a magneto-elec- 

 tric machine. 



It would be impossible, within the limits 

 of this lecture, to give an account of the 

 proposed improvements in magneto-elec- 

 tric machines, which will be found in the 

 records of the Patent Office during the 

 last three years. I cannot, however, pass 

 over without notice the machine of Sie- 

 mens and Alteneck, in which electrical 

 currents are obtained solely by the rota- 

 tion of a longitudinal helix of insulated 

 wire. This helix revolves in an annular 

 space bounded externally by two semi- 

 cylindrical magnetic poles, and internally 

 by a stationary cylinder of iron, which 

 latter may also be an independent mag- 

 net. The following account of this appa- 

 ratus I give nearly in the words of the 

 inventors. Between the poles of one or 

 more magnets or electro-magnets, an iron 

 core or cylinder is placed so as to leave a 

 space between it and the faces of the 

 magnetic poles, which have a cylindrical 

 form, and are concentric with the iron 

 cylinder. In this annular space a cylin- 

 drical shell of light metal is made to 

 revolve, on which a coil of insulated wire 

 is wound parallel to the axis of the shell, 

 and crossing its ends from one side to tlu 

 other. There may be several such coil 

 each covering an arc of the periphery ot 

 the shell. The ends of these wires are 



Fig. 9,— Gramme iiiaghiue for electric i!,; ■ 



