THE ELECTRIC LIGHT 459 



by the use of thin wires, the convolutions of the rotating 

 armature as, a moment ago, we augmented the cells of our 

 voltaic battery. Each additional convolution, like each 

 additional cell, adds its electro-motive force to that of all 

 the others; and though it also adds its resistance, thereby 

 diminishing the quantity of current contributed by each 

 convolution, the integrated current becomes endowed with 

 the power of leaping across the successive spaces neces- 

 sary for the production of a series of lights in its course. 

 The current is, as it were, rendered at once thinner and 

 more piercing by the simultaneous addition of internal re- 

 sistance and electro- motive power. The machines, on the 

 other hand, which produce only a single light have a 

 small internal resistance associated with a small electro- 

 motive force. In such machines the wire of the rotating 

 armature is comparatively short and thick, copper ribbon 

 instead of wire being commonly employed. Such ma- 

 chines deliver a large quantity of electricity of low ten- 

 sion — in other words, of low leaping power. Hence, 

 though competent, when their power is converged upon 

 a single interval, to produce one splendid light, their cur- 

 rents are unable to force a passage when the number of 

 intervals is increased. Thus, by augmenting the convo- 

 lutions of our machines we sacrifice quantity and gain 

 electro-motive force; while, by lessening the number of 

 the convolutions, we sacrifice electro- motive force and 

 gain quantity. 



Whether we ought to choose the one form of ma- 

 chine or the other depends entirely upon the exter- 

 nal work the machine has to perform. If the object 

 be to obtain a single light of great splendor, machines of 

 low resistance and large quantity must be employed. If 



