450 



If we assume, that in super-conductivity tlie curtent runs only 

 in an extremely thin layer at or along the surface of the wire 

 and that each element of a section of this layer ceases to be super- 

 conducting at a certain current saturation dependent upon the tem- 

 perature, integration over the whole layer yields the threshold current 



1 



and for wires of different diameter we get the constancy of -. 



The assumption of current saturation along the surface does not, 

 however, explain the connection, suggested by Silsbee, between the 

 threshold values of the current and the magnetic field. 



