150 ELECTRIC LIGHTING. 



It is surprising that with a current having so little tension 

 such results could be obtained, and some sceptical persons 

 would at first have denied the fact, contending that in order 

 to obtain a focus of electric light an electro-motive force 

 equal to that of at least 30 Bunsen cells was required ; but 

 such persons did not observe that with incandescent lamps 

 there is no appreciable solution of continuity in the metallic 

 circuit, and that a source of electricity of quantity suffices 

 to produce incandescence in such a circuit. If from the 

 resistance of a light circuit, four or five thousand metres 

 of telegraph wire be taken away, together with the nearly 

 equivalent resistance of the battery, and that of the electro- 

 magnetic apparatus of the regulator, it may be understood 

 how an electro-motive force equal to that of only 4 Daniell 

 cells can produce effects of incandescence in a circuit of 

 extremely small resistance, and even produce several points of 

 light, by derivations from the current, since the total resistance 

 of the circuit is then in a manner diminished proportionably 

 to the number of derivations. We are not sufficiently 

 familiarized with effects of this kind, and mistakes are often 

 made by confounding phenomena that are produced under 

 very different electrical conditions. 



Light produced by means of an inductive action* 



A short time before his death, Fuller, who had been one 

 of Edison's fellow labourers, invented a system of electric 

 lighting, on which we think it right to say a few words, 

 although it appears to us scarcely practical. Here, however, 

 is the description of it given in the Telegraphic Journal ' : 



In this system the principal current does not produce the 

 light, but it engenders another current in a series of induction 

 coils, and each lamp is lighted by the current of one of the 

 coils. An alternating current must be used. The induction 

 coils were constructed as follows: Two magnetic cores, 

 placed parallel to each other, were magnetically connected 

 at one end. Round the centre of each of these cores was a 



