989 



boiling-point of lieiiurii. Fnrther tliut it remained ,su|)ra-conductiiig 

 when a current of 0.4 ampere was sent through it ; even tijen tlie 

 windings were in a not inconsiderable field of their own current. 



For fnrther confirmation it was ascertained that the current 

 actually passed through the windings by bringing a small cardani- 

 cally suspended magnet (pole seeker} near the cryostat ; it showed the 

 movements which were to be expected. 



Then the mas'iietic field 



'tO 



iO 



V10' 



-^ 



10000 Qm»i. 



was applied. With a field of 

 10 Kilogauss there was a 

 considerabfe resistance, at 5 

 Kilo-gauss it was somewhat 

 less. This made it fairly cer- 

 tain that the magnetic field 

 created resistance in supra- h" 

 conductors at larger intensi- j ^o 

 ties, and not at smaller ones. 

 The apj>arent contradiction 



that so far liad existed be- o isoo sooo fsoo 



tween the different experi- I'^ig- 1- 



nients, was hereby solved. Later it appeared that 500 gauss was 

 below the threshold value, and 700 above it. Further investigation 

 gave for the resistance (expressed in parts of the resistance at 0° C) 

 as function of the field, the curve that is given diagrammatically 

 completed in tig. J. The numerical values, in so far as they are 

 necessary for the descri|)tion of the phenomenon, can be read from 

 the figure, so that they need not be separately detailed here. 



It will be seen that the Iransilion from the supra-conducting con- 

 dition to the ordinary conducting condition through the magnetic 

 field takes place fairly suddenly. The curve, which represents the 

 change of the resistance with the field is closely analogous to th.at 

 which represents the change of the i-esistance with the temperature 

 'comp. / =1 0,004 amp. in fig. 7 in ('omm. N". 133). The resistance 

 measurements were made with a current of 0,006 ampère. Of the 

 two curves in fig. 1, one refers to 4°. 25 K, and the other to 2° A". 

 The sudden change in the resistance moves at low temperatures 

 towards higher fields; beyond this point the resistance increases at 

 lower temperatures (2° K.) almost in the same way as at higher ones, 

 it seems as if the introduction of the mugnetic /ield has the same effect 

 as heating the conductor. 



The tin coil of Comm. N" 133 Table IX was examined in the 

 same way. With this too we have a resuU in which longitudinal 



(34* ■ 



