446 FRAGMENTS OF SCIENCE. 



will choose the freer path. The strict law is that the 

 quantity of current is inversely proportional to the re- 

 sistance. 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 

 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 in- 

 definite subdivision of the trunk stream, so in the case 

 of electricity 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 ' 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 cop- 

 per to be tapped opposite Somerset House, a wire can 

 be carried from the rod into the building, and the cur- 

 rent 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 



