JOURNAL 



OF THE 



WASHINGTON ACADEMY OF SCIENCES 



Vol. VI OCTOBER 19, 1916 No. 17 



PHYSICS. — A note on electrical conduction in metals at low tem- 

 peratures. F. B. Silsbee, Bureau of Standards. (Com- 

 municated by P. G. Agnew.) 



Some time ago I had occasion to study the accounts of the 

 brilliant experiments of Kamerlingh Onnes on the resistivity of 

 various metals at liquid helium temperatures. In so doing I 

 have noticed a certain correlation between the phenomena of 

 critical current density and critical magnetic field. Though the 

 relationship seems quite obvious I have come across no mention 

 of it in the literature of the subject, and think it worthy of notice 

 as furnishing a possible clue to further theories of metallic 

 conduction. 



The present state of our experimental knowledge of the sub- 

 ject is somewhat as follows. Certain metals — mercury, tin, and 

 lead — at the very low temperatures obtainable in a bath of 

 liquid helium show a very greatly increased electrical conduc- 

 tivity, to which Kamerlingh Onnes has given the name " super- 

 conductivity." The actual resistivity of the metal in this state 

 is too small to measure but lias been shown 1 to be less than 

 2 X 10 -u times the resistivity at 0°C. As the temperature of 

 any of these metals is lowered from room temperature, the re- 

 sistance decreases uniformly with the normal coefficient of about 

 0.4 per cent per degree until the temperature has become very 

 low, then the rate of decrease becomes for a time less rapid. At 

 a certain critical temperature (4?2 K for mercury, 3?8 K for 



1 Kon. Akad. v. Weten. Amsterdam, 17 : 2S0. 



597 



