A STUDY OF TELEPHONE LINE INSULATORS 



725 



into place over the thimbles, forcing the latter well into the threads of 

 the wood. The thimbles are constructed of thin copper and are bonded 

 together by a tinned copper strip. 



The other new type is designed to screw directly over a steel pin. 

 This is known as the C. S. insulator and its design is shown in Fig. 12. 

 At each crossarm the two steel pins are bonded by means of a wire 

 underneath the arm. 



10 20 30 



FREQUENCY-KILOCYCLES 



40 



50 



Fig. 24 — Estimated allocation of leakage for D. P. insulator. 



Both new designs are molded from borosilicate glass. This glass Is 

 more expensive than the alkali glass used in the old D. P. design. On 

 this account, and on account of the pin thimbles in one case and the 

 steel pins in the other, the new insulators cost more to install than did 

 the old ones. 



Both of the new designs were brought out several years ago before 

 this study had conclusively demonstrated the importance of surface 



