224 



BELL SYSTEM TECHNICAL JOURNAL 



grade insulation suitable for many purposes where more expensive 

 combinations of silk and cotton have been required heretofore. 



From the telephone transmission standpoint, the a-c. characteristics 

 of capacitance and conductance are of particular importance because 

 they determine the loss in transmission of energy at voice and carrier 

 frequencies, which must be kept at a minimum to maintain high quality 

 of telephone communication. A comparison of a-c. capacitance and 

 conductance at a frequency of 1,000 cycles for commercial and purihed 



§ 4000 



5 3000 



5 



p t 85 

 < Q 



a. 3 



5 

 TIME 



7 

 DAYS 



Fig. 6 — A-C. capacitance of 50 feet of twisted pair 22-gauge wire insulated with 

 double servings of equal thickness. 



silk and cotton with and without cellulose acetate treatment is shown 

 in Figs. 4, 5, 6 and 7. The data represented by these graphs converted 

 into transmission loss units are shown in Figs. 8 and 9. These data 

 derive their main significance from the large reduction in capacitance 

 and conductance at the higher humidities, and the fact that it is the 

 variation of these transmission loss characteristics which is of the 

 greatest importance from the telephone transmission standpoint. 

 Losses, if fixed in value, can be compensated for, but if they are sub- 

 ject to wide variations such as those illustrated by the samples of 



