448 FEAGMENTS OF SCIENCE. 



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 deport- 

 ment of water. When a river meets an island it divides, 

 passing right and left of the obstacle, and afterwards 

 reuniting. If the two branch beds be equal in depth, 

 width, and inclination, the water will divide itself 

 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 indefinite number of islands, producing an indefinite 

 subdivision of the trunk stream, so in the case of elec- 

 tricity 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 re- 

 lation of flow to resistance. 



Let us apply this knowledge. Suppose an insulated 

 copper rod, which we may call an c 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 

 voltaic battery, a good metallic connection being esta- 

 blished between the other end of the battery and the 

 water-pipes under the street. As long as the electric 

 main continues unconnected with the water-pipes, the 

 circuit is incomplete and no current will flow ; but if 

 any part of the main, however distant from the battery, 

 be connected with the adjacent water-pipes, the circuit 

 will be completed and the current will flow. Supposing 

 our battery to be at Charing Cross, and our rod of 

 copper to be tapped opposite Somerset House, a wire 

 can be carried from the rod into the building, and the 

 current passing through the wire may be subdivided into 

 any number of subordinate branches, which reunite 

 afterwards and return through the water-pipes to the 

 battery. The branch currents may be employed to 



