682 VRA QMENTS OF 8C1KNCK. 



may luive an iiulefinite number of islands, producing an 

 indefinite 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 relation of How 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 

 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 oppo- 

 site 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 afterward and return through the 

 water-pipes to the battery. The branch currents may be 

 employed to raise to vivid incandescence a refractory metal 

 like iridiuni or one of its alloys. Instead of being tapped at 

 one point, our main may be tapped at one hundred points. 

 The current will divide in strict accordance with law, its 

 power to produce light being solely limited by its strength. 

 The process of division closely resembles the circulation of 

 the blood; the electric main carrying the outgoing current 

 representing a great artery, the water-pipes carrying the 

 return current representing a great vein, while the inter- 

 mediate branches represent the various vessels by which 

 the blood is distributed through the system. This, if I 

 understand aright, is Mr. Edison's proposed mode of illu- 

 mination. The electric force is at hand. Metals suffici- 

 ently refractory to bear being raised to vivid incandescence 

 are also at hand. The principles which regulate the divi- 

 sion of the current and the development of its light and 

 heat are perfectly well known. There is no room for a 

 " discovery," in the scientific sense of the term, but there 

 is ample room for the exercise of that mechanical ingenuity 



