164 STUDIES IN ELECTRO-PHYSIOLOGY: 



is first covered with three wrappings of paper, the 

 first of which may be either spiral or longitudinal, but the 

 other two are invariably applied spirally. The spiral 

 wrappings are applied so as to form a helical air-space 

 throughout the length of the core. The conductor thus 

 insulated is then enclosed in a final wrapping of paper, 

 forming a closed helix without overlap. Over this is laid 

 a helical winding of copper tape, with an overlap. . . . The 

 whole of the cores are laid together, and a seamless cylin- 

 drical sheathing of lead, at a temperature of 600 F., is 

 applied to the cable." 



This description refers, needless to say, to a land cable, 

 and the paper and air insulation are designed to reduce the 

 capacity. 



" The copper tape forms a continuous conducting tube 

 around the wire, and as this tube is earth-connected, either 

 by direct contact with the lead sheathing or indirectly by 

 the tapes of the other cores, it will be obvious that induction 

 between the wires cannot occur. Firstly, Faraday's 

 experiments showed that variations in the differences of 

 potential existing or produced between conductors within 

 a metallic covering produce no effect outside that covering. 

 Secondly, any source of inductive disturbances brought to 

 bear upon a screened conductor produces the whole of its 

 effects upon the copper tape. The magnetic lines of force 

 induce currents along the tape covering the wire, and as this 

 path is highly conductive, practically the whole of the 

 energy is absorbed by it. In order to produce an inductive 

 effect, currents must be generated in the tape of the 

 disturbing wire and also in the tape of the disturbed wire 

 before the second conductor is reached." 



It is at least a coincidence that in the " flex," the cable 

 and the nerve, the axis cylinder should be composed of a 

 bundle of funiculi instead of one wire, and that the insula- 

 tion should take the form of several layers of a semi-plastic 



