Recovery of Residual Charge hi Electric Condensers. 581 



trometer E, one quadrant o£ which was earthed. P and Q 

 are the two parallel plates, the uranium fluoride being spread 

 on the bottom one Q. M the movable shutter was initially 

 drawn right back, thus exposing the whole o£ the uranium 

 fluoride surface. 



Fiar. 1. 



On connecting K to E the deflexion increased at first, but 

 owing to the leak introduced the turning point was soon 

 reached ; at this instant the shutter M was moved in by means 

 of the wheel S, which engaged in the milling of a brass strip 

 connected to M. The motion of the shutter was recorded by a 

 pointer P (attached to the brass strip), which traced a path over 

 a blackened surface of paper on a cylindrical drum D which 

 revolved at a known speed by means of a motor, to which it 

 was connected by a system of gearing-down countershafting. 



In this way the amount of active area exposed at each 

 moment was recorded. This was proportional to the con- 

 ductivity, and consequently to the current developed at each 

 moment by the recovering dielectric. 



In controlling the motion of the shutter bv hand one is 

 very apt to overshoot the mark, due no doubt to air remaining 

 ionized for a short interval after the shutter has covered the 

 ionizing surface, this making the apparatus slow in respond- 

 ing to any alteration in area. If S is turned too quickly, the 

 leak is being cut too rapidly and the deflexion on the scale 

 increases, so that S has to be stopped for a short interval in 

 order that the deflexion may return to its former value. On 

 account of this the curve traced out bv P on the drum was 



