490 Dr. H. H. Poole on the Electrical 



The specimen to be tested is represented by S, which 

 shows the earthed guard-ring designed to eliminate the 



Ffc. 1. 



effect o£ surface leakage. The current passing through the 

 specimen is measured by the very sensitive galvanometer G x 

 when the key K, is depressed. This key prevents the com- 

 paratively large currents flowing when the system is quickly 



