Barus — Displacement In terferometer. 



75 



Table I. 



Cylindrical electrometer ; movable cylinder within. 



I. — M = 1-105 g. ; M — 207 cm. ; r = 1*7 cm. ; I = 21 cm. 



r n =v 3 = o. 



10 S AN V 3 



•08 15 



•25 28 



•60 43 



1-12 60 



1-87 77 



II.— M= 1-189, g. ; R = 2-07 cm. 



V 2 = ; V 1 = 250 volts. 



lO 3 ^ V a 



Voltmeter 

 15 

 29 

 41 

 61 

 81 



r = 1-90 cm. ; I = 21 cm. 



1-74 

 2-17 

 331 

 4-53 



5-85 



•1 



11-6 



16-0 

 20-6 



Voltmeter 



5 



7 



11-5 



15 



19 









Fig 



3. 







60 















40 







^Q 









w 



"t 









W 



/ i? 







VI 



A- 











y 



W 40 60 80 20 



Fig. 3. Electrometer data compared with actual voltages. 



The observations with the needle charged at 250 volts show 

 the maximum sensitiveness obtained with short suspensions. 

 These results and those by the idiostatic method are quite 

 satisfactory and the differences are more liable to be sought 

 for in the voltmeter with which the comparison was made 

 than in the electrometer. It indicates the sufficiency of the 

 equation assumed, apart from correction for the end of the 

 cylinder, so that the latter cannot be menacing. 



In addition to these experiments, a long suspension (I = 150 

 centimeters) in which the sensitiveness would have been 

 increased 7 times or equivalent to 5xl0 -3 centimeter per volt 

 or '006 volt per vanishing ring was installed. The ellipses 

 were easily found but they were continually in motion, owing 

 to the friction of air currents moving across the wires. To 

 make the adjustment available it would have been necessary 

 to build a closed case around the bifilar suspension over 1*5 



