468 FRAGMENTS OF SCIENCE 



heat. From one end of a voltaic battery runs a wire, 

 dividing at a certain point into two branches, which re- 

 unite in a single wire connected with the other end of the 

 battery. From the positive end of the battery the current 

 passes first through the single wire to the point of junc- 

 tion, where it divides itself between the branches accord- 

 ing to a well-known law. If the branches be equally re- 

 sistant, the current divides itself equally between them. 

 If one branch be less resistant than the other, more than 

 half the current will choose the freer path. The strict 

 law is that the quantity of current is inversely proportional 

 to the resistance. A clear image of the process is derived 

 from the deportment of water. When a river meets an 

 island it divides, passing right and left of the obstacle, 

 and afterward reuniting. If the two branch beds be equal 

 in depth, width, and inclination, the water will divide it- 

 self equally between them. If they be unequal, the larger 

 quantity of water will flow through the more open course. 

 And, as in the case of the water, we may have an in- 

 definite number of islands, producing an indefinite sub- 

 division of the trunk stream, so in the case of electric- 

 ity we may have, instead of two branches, any number 

 of branches, the current dividing itself among them, in 

 accordance with the law which fixes the relation of flow 

 to resistance. 



Let us apply this knowledge. Suppose an insulated 

 copper rod, which we may call an "electric main," to be 

 laid down along one of our streets, say along the Strand. 

 Let this rod be connected with one end of a powerful vol- 

 taic battery, a good metallic connection being established 

 between the other end of the battery and the water-pipes 

 under the street. As long as the electric main continues 



