Conductivity of Air enclosed in Metallic Receivers. 301 



To show how the determination of " q" with this instrument 

 was arrived at, and to give an estimation of the magnitudes 



Ffe: 4. 



involved, a measurement taken with the same cylinder and 

 under the same conditions as obtained in the case of the 

 determination with the Wilson instrument, is given in 

 Table III. These values for " q," as obtained with the two 

 instruments, are seen to be practically the same, and so afford 

 a conclusive test of the accuracy of the measurements. 



Table III. 



(1) Date March 19, 4.00 p.m. 



(2) Lead Cylinder No. 1. 



(3) Locality. — Basement of Physics Laboratory. 



(4) Potential applied to needle +250 volts. 



(5) Eate of motion of needle without condenser= 13'0 mm. per min. 



(6) Eate of motion of needle with condenser=-f 7*4 ram . 



(7) Eate of motion of needle due to defective insulation cylinder 



being removed and electrode capped =4-1-0 mm. 

 .*. Eate due to conduction in air in cylinder alone 

 = + 12-0 mm. 



(8) Sensitiveness = 832 - 2 mm. per volt. 



(9) Capacity of auxiliary condenser =128'04 cms. 



(10) Temp. 10° 0., voltage on cylinder 4-85 volts. 



(11) Volume of cylinder =26700 c.cs. 

 From this we obtain 



Capacity of electrometer 169-1 cms. 



The calculation to determine " q " is then 



109-1x12 



?x3-4x 10-10x60x26700. 



8322x300 



Whence q 



1493 



