OF ARTS AND SCIENCES. 125 



VIII. 



AN EMPIRICAL RULE FOR CONSTRUCTING TELE- 

 PHONE CIRCUITS. 



By William W. Jacques. 



Presented June 15, 1887. 



The following paper describes some investigations I have made as to 

 the proper dimensions to be given to pole lines and cable conductors, 

 in order that they shall be best fitted to transmit speech telephonically. 



The experiments were made by selecting cables varying in size 

 of conductor, thickness of insulating coating, and material used for 

 insulating, and measuring in each case the greatest length in miles 

 through which good business conversation could be carried on. 



Similar experiments were then made with pole lines, in which the 

 size of the wire was varied, the distance it was suspended above the 

 earth was varied, and both iron and copper wires were used. 



Further experiments were then made in which mixed cable and 

 pole lines were used, varying the proportionate length of cable to pole 

 line in each case, and also the position of the cables in the line. 



These experiments were made upon a large number of underground 

 cables, varying in length from one mile to one hundred miles, in re- 

 sistance per mile from 2.8 ohms to 48.0 ohms and in electro-static 

 capacity per mile from 0.11 microfarad to 0.35 microfarad, in use in 

 France and Germany, (an abstract of which was published in the 

 Proceedings of the Society of Arts of November 13, 1884,) and were 

 continued upon a large number of cables and pole lines in our own 

 country. 



The method of experiment was to connect up varying lengths of 

 cable or pole line until the greatest length at which it was possible to 

 transmit good business conversation was reached, and then to measure 

 the electrical resistance and capacity of the circuit. 



Some of the experiments are given in Tables I. to IV., to illustrate 

 the method of experiment, and prove the results stated later. 



