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PROCEEDINGS OF THE AMERICAN ACADEMY 



TABLE VI. — Copper Wire. 



But we need also to know the capacity per mile of various sizes of 

 pole wire when suspended at various heights above the earth, (for the 

 capacity of a pole wire depends both upon its size and the distance 

 it is suspended above the earth,) and we need further to know the 

 various capacities of various sizes of cable conductors when insulated 

 to various thicknesses, and when insulated with various substances ; 

 for the capacity of a cable conductor depends upon its size, upon the 

 distance it is removed from neighboring conductors by the thickness 

 of the insulating coating, and upon the specific inductive capacity of 

 the particular insulating coating used. 



Now the available data regarding capacities of pole lines and of 

 cables (excepting ocean telegraph cables which have only one con- 

 ductor, and in which the conductors are quite different from that of 

 the multiple conductor cables used in telephony) are very meagre, and 

 I have therefore been obliged to undertake an experimental investi- 

 gation into the capacities of wires of different sizes, suspended on poles 

 of varying heights, and a further investigation into the capacities of 

 various sizes of cable conductors when separated from the neighbor- 

 ing conductors by varying thicknesses of insulating material, and 

 when insulated with various materials differing in specific inductive 

 capacity. 



The results are given in Tables VII., VIII., and IX. 



