242 Prof. W. M. Thornton on the Cause of Lowered 



An extensive series of experiments were further under- 

 taken in Christiania in 1910. The absorption was studied in 

 pure nitrogen with a number of electrodes of various metals, 

 and found to follow essentially the same law as already stated 

 for oxygen. Further, the rate of disintegration of the 

 cathode was measured with the same tube as that used for the 

 absorption experiments and for gold and platinum electrodes. 



The results of my experiments on electric absorption were 

 published in the Proceedings of the Christiania Academy*. 



Reading the paper of Dr Brodetsky and Dr. Hodgson, 

 I was very glad to notice that they have confirmed the 

 results which I obtained in 1909. As regards the view 

 taken about the mechanism, w r e also agree in the essential 

 points. Thus they assume the absorption to be due to the 

 velocity (energy or momentum) of the positive ions before 

 the cathode, and they suppose the gas to be attached to the 

 disintegrated metal. 



Still I do not quite agree with the assumptions on which 

 they base their theoretical deduction of the absorption curve, 

 for both assumptions would for a constant current make the 

 velocity of absorption increase continually with increase of 

 cathode-fall^ while all experimental evidence goes to show 

 that there is an upper limit for the velocity of absorption. 



Yours faithfully, 



University of Christiania, L. VeGARD. 



May 12, 1916. 



XXIX. The Cause of Lowered Dielectric Strength in High 

 Frequency Fields. By W. M. Thornton, D.Sc, D.Eng., 

 Professor of Electrical Engineering in Armstrong College, 

 Newcastle -upon- Tyne t • 



1. JT^HE breakdown strength of dielectrics falls with rise 

 J. of frequency of the field, up to the frequencies used 

 in wireless telegraphy. The experimental evidence for this 

 is not extensive, but it is found in solid, liquid, and gaseous 

 media. For example, glass having a strength of 320 kilo- 

 volts per centimetre at 50 cycles a second bears only 128 

 kilovolts at 8500 cycles J. A light petroleum oil failing at 

 170 kilovolts at 60 cycles, fails at 67 kilovolts at 90,000 



* " Uber die elektrische Absorption in Entladungsrohren." Kristiania 

 Vid. Selsk. Skr. Nr. 7 (1913). 

 t Communicated by the Author. 

 X Moscicki, .E. T. Z., 1904, p. 527. 



