No. 1 .—Tests on 66,000-volt Thomas Insulators, Nos. 722-29 (First Dozen). 
1920.] 
Birks and Ferguson. — High-tension Insulators 
189 
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Notation.— 50 means that the shell stood. 0 means that the insulator broke down under 20,000 volts (the lowest reading on the voltmeter 
scale). 45/10 means that the shell withstood 45,000 volts for 10 seconds and then broke down. 
