988 



generate in a supra-conductor, and I immediately prepared experi- 

 ments in connection with this. Tiiat 1 was firmly convinced that the 

 action would be only small, is shown by the fact that [ arranged 

 the apparatus for these experiments as if for a phenomenon that 

 could only be studied with profit in fields of 10 kilo-gauss, but it 

 now appears that even then without further preparation, I might 

 have made the observations described below quite easily with the 

 field of 2 kilo-gauss that I then had at my disposal. 



For our experiments a coil was prepared as described aboAe, but 

 wound non-inductively. When (17 January 1914) it was brought 

 into a field of 10 kilo-gauss, it showed a considerable resistance. 

 We had not been so successful in the construction of this coil as in 

 the previous one, as it did not become supra-conducting. It was 

 therefore possible that not much value could be attached to this 

 experiment. A coil with tin wire prepared in the same way as the 

 above described non-inductive lead coil also showed a considerable 

 resistance in a field of 10 kilo-gauss when cooled to 2" K., which 

 decreased more slowly than proportionally, when the field was 

 reduced to 5 kilo-gauss. In this case again we had not succeeded 

 in making the coil so that it would become supra-conducting, but 

 (always assuming a regular decrease with the field, and supposing 

 that the fact that the coil did not become supra-conducting only 

 gives a non-essential disturbance) the results of both experiments did 

 not seem to be reconcilable with the above mentioned observations, 

 in which the magnetic field generated no resistance in supra-conductors. 



The first thing to do was therefore to repeat the experiments with 

 the coils of tin and lead, which had become supra-conducting in the 

 former experiments, notwithstanding that the windings were in a 

 magnetic field. That these coils were not wound induction-free, was 

 of no consequence, now that it was a question of such comparatively 

 large resistances. 



§ 2. Further experiments with lead and tin which shoio a sudden 

 change in the resistance at a threshold value of the magnetic field. 



The lead coil of Tal)le XII Comm. N". 133, as it was not wound 

 induction-free, was placed in the cryostat of the apparatus to be 

 described in a future paper for magnetic measurements in liquid 

 helium, so that the plane of the windings coincided with the lines 

 of force of the magnetic field which is to be applied. This last acts 

 therefore partly transversely upon the conductor (lines of force at 

 right angles to the current), partly longitudinally (lines of force in 

 the direction of the current). 



It was first ascertained that the coil was supra-conducting at the 



