A STUDY OF TELEPHONE LINE INSULATORS 



701 



ing ratio would have been 25,000. These ratios are higher than would 

 be commonly found because the line was quite new but they serve to 

 indicate the wide range in the magnitude of this type of leakage. 



Fortunately, direct surface leakage even at its higher values in a 

 sufficiently small part of the total leakage, especially at carrier fre- 

 quencies, to make its wide variations substantially less serious than the 

 foregoing ratios have indicated. 



Fig. 3 — Standard C. W. insulator and pin thimble. 



2. Influence of Insulator Design. To make this leakage conduc- 

 tance small it will be apparent from elementary considerations alone 

 that the length of the path should be as great and its cross-section as 

 small as possible. The latter depends on both the thickness and width 

 of the moisture film, the width, in turn, depending upon the diameter of 

 the surfaces. 



The length of path may be increased by simply lengthening the in- 

 sulator. The cross-section of the film may be made small by decreasing 

 the diameter of the surfaces. Both methods are employed in the 

 experimental design shown in Fig. 5 which will be recognized as ex- 



