TESTING IN VACUO 113 



contact drjdng or partly drying up before the other 

 was similarly affected. 



3. If the object under examination (or the electrodes 

 when they were in contact with it) were touched 

 with the bare fingers the natural charge was inter- 

 fered with, and for this reason 



4. Dry rubber gloves should be worn throughout the 



tests and the utmost care exercised in keeping the 

 gloves absolutely free from moisture. 

 6. If the above conditions are observed the object, 

 whatever it may be, under examination loses its 

 charge when earthed in vacuo much more quickly 

 than it does when earthed in air, and 

 6. Some things, such as an Onion or an Apple, will 

 not when earthed in air lose more than a fraction 

 of their charge in several weeks or even months. 

 I cannot too strongly emphasize the importance of 

 making firm contacts with the Needles and of avoiding the 

 " shorting " which would result from diffusion and lead to 

 false readings. Care should be taken in every instance in 

 recording the immediate or initial deflection that there is 

 not a quickly commencing fall as that is an indication either 

 of charge from some external source of energy other than 

 the air or of diffusion. 



A very interesting experiment was with the same half 

 of the apple mentioned in Experiment No. 4. After the 

 deflection had remained subject to a weak and fluctuating 

 negative earth-current for some little time it was disconnected 

 and placed in the open air, in the sun, for three-quarters of 

 an hour, to see if it would recover. 



The Needles had been cleaned and were replaced in the 

 same holes and switched to earth (in air) for forty-five 

 minutes. 



The full initial deflection was 3080 mm., and after the 

 forty-five minutes earthing 



D =3080 mm., showing that it had not lost even 

 one division of the Scale. It was then earthed for 

 forty-five minutes in vacuo, when 

 D =275 mm., with a very faulty vacuum. 



