1895.] On the Question of Dielectric Hysteresis. 469 



Density of Density of Density of 



cathode fraction oxygen cathode fraction 



with long sparks. unsparked. with short sparks. 



15-78 15-88 16-00 



1579 15-87 16-01; 



15-80 15-89 16-02 



15-79 15-88 16-04 



15-88 16-06 



16-05 



Mean of results of other observers = 15'887. 



Density of cathode fraction from oxygen, previously for three days 

 fractionated with short sparks, 15*75. 

 The experiments are still in progress. 



V. "On the Question of Dielectric Hysteresis." By ALFRED 

 W. PORTER, B.Sc., Demonstrator of Physics, University 

 College, London, and DAVID K. MORRIS, 1851 Exhibition 

 Scholar, University College, London. Communicated by 

 Professor G. CAREY FOSTER, F.R.S. Received March 2, 

 1895. 



The condenser on which the following experiments were made is 

 the one referred to in a paper by one of us read before the Royal 

 Society on June 1st, 1893 (' Roy. Soc. Proc.,' vol. 54, p. 7). It is a 

 5-microfarad condenser of tinfoil and paraffined paper, made by Messrs. 

 Muirhead. In the paper referred to it was shown that when it is 

 allowed to discharge itself through a coil containing induction the 

 rate of dissipation of energy (calculated from the damping of the 

 oscillations that occur) is greater than that due to the resistance of 

 the outside circuit : the additional dissipation being equal to what 

 would have taken place if about 59 ohms had been added to the 

 circuit resistance. 



The following experiments were made with the idea of ascertaining 

 whether this additional dissipation is the result simply of viscosity in 

 the dielectric of the condenser or to true hysteresis of the charge 

 with respect to the potential difference between the condenser plates. 

 A sharp distinction is not always made between the two phenomena ; 

 it cannot be too clearly borne in mind that, on the one hand, viscosity 

 is a " time " effect i.e., it depends on the rate of change of the 

 variables ; while, on the other hand, the phenomenon of hysteresis 

 does not in any way involve the rate at which the changes in the 

 quantities are made. 



Rapidly performed series of cycles, such as occur during an 



