270 PROCEEDINGS OP THE AMERICAN ACADEMY 



With a double-wire cable when used to form a metallic circuit, the 

 two wires being connected to the two poles of the battery or trans- 

 mitter, or whatever the electric source may be, the quantity of elec- 

 tricity flowing across any section of the cable on one of the wires 

 will be equal and of opposite sign to that on the other. 



Hence the total quantity flowing across any section of the cable 

 will be zero, and dQ will be zero. So that the potential to which the 

 condenser, consisting of the two wires and the outside surface of 

 the cable, will be raised will be zero, and the energy required from 

 the battery no greater on account of the nearness of the water, the 

 second conducting surface of the condenser. 



There is one thing to be considered, that the wires, being covered 

 with some insulating material which cannot be made perfectly homo- 

 geneous, they, with the broken nature of the dielectric about them, 

 will each form a condenser to some extent. 



It would therefore appear that, as far as the retardation is due to 

 the static capacity of a cable, it can be greatly reduced by using a 

 double wire cable with homogeneous insulating material. 



In support of this view there are the experiments made by "Wheat- 

 stone, and described in the Proceedings of the Royal Society for 

 1854-55. Wheatstone made experiments on a cable of six wires 

 intended for use in the Mediterranean. The length of the cable was 

 one hundred and ten miles. On connecting one of the wires with one 

 pole of his battery, the other pole being to ground, he found that quite 

 a time was required before the flow into the cable fell to the rate due 

 to leakage. On connecting one pole of the battery with one wire and 

 the other with another, the charge which the cable wires would take 

 was reached instantly. 



On long land lines the static capacity of the line is due, outside of 

 the capacity of the wire, to the neighborhood of the earth. This has 

 been found to affect the articulation in telephoning on the line from 

 Boston to Baltimore, five hundred miles in lengtli. By the use of a 

 complete metallic circuit the articulation was greatly improved. 



Salem, Mass., U. S. A., 

 May 9th, 1882. 



