680 



y. Experiments concerning the influence of the contact with an 

 ordinary conductor of a metal which can become super-conducting, 

 upon its super-conducting properties, were in continuation of tliose 

 of § 10 made with tin in two different ways, first witli a german 

 silver tube, which was tinned, and through the layer of tin of 

 which a spiral was cut, and second with a constantin wire which 

 w^as tinned. In the first experiment the resistance did not disappear, 

 in the second, as already said in § 10, it did ; from which we 

 conclude that the continuity of the layer of tin in the first case was 

 not sufficient. In the second experiment the threshold value was, 

 however, also very low, even at the lowest temperature l.°6 K. it 

 remained below 0.095 amp. for the bare wire immersed in liquid 

 helium. It is simplest to assume iu the mean time, that the layer 

 of tin becomes super-conducting, but that the section of it, which 

 was, deduced from the resistance, 0,0125 mm'., according to measure- 

 ments down to 0,1 mm'., was very small here and there. There 

 was in this case no reason to suppose a want of contact between 

 tin and constantin, as in the corresponding experiment with mercury 

 between it and the steel. 



§ 15. Farther examination of lead. In the fii-st place we will 

 mention a few experiments on the heating of a wire which was at 

 a temperature below the vanishing point, which correspond to those 



