1879.J on the Electric Light. 13 



niftcliinos cajmblc of sustaining several liglits. The Gramme machine, 

 for example, which ignites the Jahlochkoff candles on the Tliames 

 Embankment and at the Ilolborn Viaduct, delivers four currents, each 

 flowing through its own circuit. In each circuit are five lamps through 

 which the current belonging to the circuit j^asses in succession. The 

 lights correspond to so many resisting spaces, over which, as already 

 explained, the current has to leap ; the force which accom2)lislies the 

 leap being that which produces the light. Whether the current is to 

 be competent to pass through five lamias in succession, or to sustain 

 only a single lamp, depends entirely upon the will and skill of the 

 maker of the machine. He has, to guide him, definite laws laid down 

 half a century ago, by which he must abide. 



Ohm has taught us how to arrange the elements of our battery so 

 as to augment indefinitely its electro-motive force. We have only to 

 link its cells together so that the current generated by each shall 

 pass through all the others, and add its electro-motive force to 

 that of all the others. We increase, it is true, at the same time the 

 resistance of the battery, diminishing thereby the quantity of the 

 current from each cell, but we augment the power of the integrated 

 current to overcome external hindrances. The battery resistance 

 may, indeed, be rendered so great that the external resistance shall 

 vanish in comparison. What is here said regarding the voltaic 

 battery is equally true of magneto-electric machines. If we wish our 

 current to leaj? over five intervals, and produce five lights in succes- 

 sion, we must invoke a sufficient electro-motive force. This is done 

 simply by multiplying, by the use of thin wire, 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 

 necessary for the production of a series of lights in its course. The 

 machines, on the other hand, which i)roduce 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 com- 

 paratively short and thick, copper riband instead of wire being 

 sometimes employed. Such machines deliver a large quantity of 

 electricity of low tension — in other words, of low leaping power. 

 Hence, though competent, when their power is converged ujion a 

 single interval, to produce one splendid light, their currents are 

 unable to force a passage when the number of intervals is increased. 

 Thus, by augmenting the convolutions 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 machine or the other 

 depends entirely upon the external work it has to perform. If the 

 object be to obtain a single light of great splendour, machines of low 



