On the Capacity and Residual Charge of Dielectrics. 425 



"On the Capacity and Residual Charge of Dielectrics as 

 affected by Temperature and Time." By J. HoPKlNSOk; 

 F.R.S., and E. WILSON. Received December 15, 1896, 

 Read January 28, 1897. 



(Abstract.) 



The major portion of the experiments described in the paper 

 have been made on window glass and ice. It is shown that for long 

 times residual charge diminishes with rise of temperature in the 

 case of glass, but for short times it increases both for glass and ice. 

 The capacity of glass when measured for ordinary durations of time, 

 such. as l/100th to l/10th second, increases much with rise of tem- 

 perature, but when measured for short periods, such as 1/10 6 second, 

 , it does not sensibly increase. The difference is shown to be due to 

 the residual charge, which comes out between l/50,000th second and 

 l/100fch second. The capacity of ice when measured for periods of 

 l/100th to l/10th second increases both with rise of temperature, 

 and with increase of time, its value is of the order of 80, but when 

 measured for periods such as 1/10 6 second, its value is less than 3. 

 , The difference again is due to residual charge coming out during 

 short times. In the case of glass, conductivity has been observed at 

 fairly high temperatures and after short times of electrification ; it is 

 found that the conductivity after l/50,000th second electrification is 

 much greater than after l/10,000th, but for longer times is sensibly 

 constant. Thus a continuity is shown between the conduction in 

 dielectrics which exhibit residual charge and deviation from Max- 

 well's law and ordinary electrolytes. 



'' On the Electrical Resistivity of Electrolytic Bismuth at Low 

 Temperatures, and in Magnetic Fields." By JAMES DEWAR, 

 M.A., LL.D., F.R.S., Fullerian Professor of Chemistry in 

 the Royal Institution; and J. A. FLEMING, M.A., D.Sc,. 

 F.R.S., Professor of Electrical Engineering in University 

 College, London. Received January 4, Read January 28, 

 1897. 



In a previous communication to the Royal Society we have pointed 

 out the behaviour of electrolytically prepared bismuth when cooled to 

 very low temperatures, and at the same time subjected to transverse 

 magnetisation.* During the last summer we have extended these 



* See ' Proc. Roy. Soc.,' vol. 60, p. 72, 1896. " On the Electrical Resistivity of 

 Bismuth at the Temperature of Liquid Air," by James Dewar and J. A. Fleming. 

 See also ' Phil. Mag.,' September, 1895, Dewar and Fleming " On the Variation in 

 the Electrical Resistance of Bismuth when cooled to the Temperature of Solid Air." 



2 K 2 



