578 Prof. F. T. Trouton and Mr. S. Buss on the Rate of 



The conclusions to be drawn from these experiments are 

 the following : — 



(1) The beam of Bontgen rays from a focus-tube which 



yields a magnetic cathode spectrum is hetero- 

 geneous. 



(2) A metallic sheet shows selective absorption of the 



different rays. 



(3) This selective absorption does not follow the same 



law in all metals : in certain pairs of metals the 

 absorption is relatively selective. 



Jefferson Physical Laboratory, 

 Harvard University, Cambridge, U.S.A. 



XLIX. The Rate of Recovery of Residual Charge in Electric 

 Condensers. By Feed. T. Trouton, F.R.S., and Sidney 

 Buss, B.Sc* 



[Plate XV.] 



THE analogy between the phenomenon of residual charge 

 in Leyden jars and the recovery from elastic overstrain 

 in solids has often been pointed out. The theoretical inves- 

 tigations of Boltzmann and the experiments of Kohlrausch 

 and Hopkinson have thrown considerable light on the 

 subject. 



In view, however, of recent work done by Mr. A. 0. 

 Bankinef, and subsequently confirmed by Mr. Phillips J, on 

 the recovery of solids from overstrain by a method in 

 which the strain was kept constant while the stress disappears, 

 it seemed desirable to experimentally examine the relations 

 governing the rate at which residual charge makes its 

 appearance in a discharged condenser under conditions 

 analogous to those of their experiments. 



The explanation of the phenomenon of residual charge has 

 been referred § to a heterogeneity in the structure of the 

 dielectric due to its consisting of parts having diverse con- 

 ducting and dielectric properties, all however subject to simple 

 linear laws. This hypothesis leads to an exponential ex- 

 pression for the rate of recovery of the residual charge. This 



* Communicated bv the Physical Society : read March 8, 190/ 

 t Phil. Mag. [6] vol. viii. 1904, p. 538. 

 X Phil. Mag. [6] vol. ix. 1905, p. 513. 

 § Maxwell, vol. i. p. 414. 



