72 ELECTRIC LIGHTING. 



duced in one of the coils was used to successively augment 

 the power of the inducing electro-magnet, while the other 

 coil was utilized for the external work. This combination, 

 however, was, as we have seen, the same as Wilde's. It was 

 at first expected that great advantages would result from this 

 arrangement, especially as regards the electric light, for it 

 was supposed that a working current so variable in its in- 

 tensity would, in consequence of passing completely through 

 the inducing electro-magnet, increase the effects of the varia- 

 tions in the ratio of the simple power to the square, since 

 the electo-magnetic forces are proportional to the squares of 

 the intensities of the current. But numerous experiments 

 since made by Gramme and Lontin showed that there was 

 infinitely more advantage gained by causing the whole in- 

 duced current to traverse the inducing electro-magnet ; so 

 that at the present day the original arrangement of Siemens 

 has been reverted to, and what is still more curious, a rather 

 lively controversy regarding this matter has been carried on 

 by Lontin, who thinks he discovered this kind of action.* 



Be that as it may, Ladd's machine was in 1867 regarded 

 as one of the wonders of the Exhibition, and the small di- 

 mensions of the apparatus were specially a matter for surprise. 

 At that period people were accustomed to the large machines 

 of Holmes and of the Alliance Co., and a machine of 70 to 

 80 centimetres in length, 35 or 40 in breadth, and 20 or 30 

 in depth, capable of producing a relatively intense electric 

 light, was really a matter for astonishment. Nevertheless, 

 the great velocity of rotation that had to be given to the 

 machine, and the large quantity of heat it generated, soon 

 showed that the problem of the economical production of 

 the electric light was far from having been solved in this 

 way. But the principle of the dynamo-electric system was 

 regarded as in itself an advance, and we shall see that the 



* It would nppear that Siemens had invented his apparatus simultaneously 

 with Wheatstone, and had announced it to the Royal Society of London on 

 the same day. 



