A STUDY OF TELEPHONE LINE INSULATORS 



709 



This particular test which was made after more than a year of exposure 

 shows only a small difference between the two glasses. A previous 

 test (exposure of nine months) showed quite the same results while 



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Fig. 11 — Illustrates effect of insulator material on d.-c. surface leakage. 



still earlier tests had indicated the borosilicate as quite superior to the 

 alkali glass. 



Fig. 12 — Standard C. S. design for use with standard steel pin. 



While the foregoing tests illustrate the point made above as to the 

 relative importance of design vs. material they cannot be considered as 

 conclusive evidence on the relative merits of these two glasses for 

 direct surface leakage. 



