638 



Prof, P. Whiddiiiffton 



(a) 



change that could be detected with certainty was that pro- 

 duced by 1 m.gm. at 5 inches — the number of beats (about 

 2 per sec.) changing perceptibly and by a constant amount. 



Fiff. 2. 



(5) 



TWO- METHODS USED FOR MAKING 

 SMALL CHANGES IN 3C 



SCALE - Y Z FULL SIZE 

 (EXCEPTING x) 



I i i . I . i . I ■ i.I.i.I.i 



This shift is approximately 



reVo-x 6 x 10" 6 inch = 4-3 x 10~ 9 inch = l'6- 8 cm. (approx.), 



or about ^yo millionth part of an inch. 



It will be noticed that this figure is not so small as that 

 estimated in the introduction (2 X 10~ 9 )*. 



* Probably due to the plates not beiug so close as ^oo inch, the value 

 of x assumed in the initial calculation. It is to be noted in this con- 

 nexion that when oscillations occur a voltage maybe set up between the 

 plates whose mean square value can easily be of the same order as the 

 constant voltage supplied by the anode battery — in this case 50 volts. 

 This fact in itself sets a limit to the pcssible closeness of approach of the 

 plates. 



