458 FRAGMENTS OF SCIENCE 



Jablochkoff candles on the Thames Embankment and at 

 the Holborn Yiaduct, delivers four currents, each passing 

 through its own circuit. In each circuit are five lamps 

 through which the current belonging to the circuit passes 

 in succession. The lights correspond to so many resist- 

 ing spaces, over which, as already explained, the current 

 has to leap; the force which accomplishes the leap being 

 that which produces the light. Whether the current is to 

 be competent to pass through five lamps 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 by Ohm half a century 

 ago, by which he must abide. 



Ohm has taught us how to arrange the elements of a 

 Voltaic battery so as to augment indefinitely its electro- 

 motive force — that force, namely, which urges the current 

 forward and enables it to surmount external obstacles. 

 We have only to link the cells together so that the cur- 

 rent generated by each cell 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 quanti- 

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

 of the integrated current to overcome external hinderances. 

 The resistance of the battery itself may, indeed, be ren- 

 dered 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 leap over five intervals, and produce 

 five lights in succession, we must invoke a sufficient 

 electro -motive force. This is done through multiplying, 



