Dielectrics in a Steady Field of Force. 



405 



case, a flint-glass ellipsoid was suspended in a glass cell 

 (fig. 3), the upper part having pole plates, so that a field 



Fig-. 3. — Testing Cell for exposure to Radium. 



W 



^^\\Wc: W^W^W^ 



could be maintained there, and the lower being filled with 

 disulphide of carbon. Outside the cell a massive iron cylinder 

 was placed, having a small central hole pointing towards the 

 line of suspension. The ellipsoid was exposed to the field for 

 several days, and its steady period noted. It was then 

 lowered into the liquid and exposed to the radiation from a 

 strong tube of radium bromide placed in the end of the iron 

 cylinder. After five minutes' exposure the ellipsoid was 

 raised, allowed to stand in the field for the same time that it 

 had been removed from it, and its period then found to be 

 unchanged. The liquid was used to shield the specimen 

 from any ions which might possibly gather on it from the 

 poles, and to prevent any change in the gradient betw r een 

 the poles by the diffusion of ions from the line of the radium 



discharge. 



If the charge on the ellipsoid had been in any sense free, 

 whether residing on the surface or inside, it would have been 

 rapidly removed and the period lengthened by exposure to 



