279 



ol' relaxaiioii, with /y=:\0', would como lo about 270000 seconds 

 01' 75 lioiirs. lil that case the cuiTcnt would fall l>y 4 7o J^^ three 

 hours. It w^as hoped that it woidd tie possilile with the improved 

 arrangement to establish a diminution of that amount. 



The experiment was made w^ith a field of 189 gauss at a tempe- 

 rature of l.°7 K. The current amounted to about 0.4 amp. (as 

 before no account was taken of the possibility of magnetisation or 

 of induced circulating currents inside the snpraconducting material) 

 and during about '2^/^ hours no diminution of the current was 

 observed; it was then uecessarv lo admit a fiesh supply of helium 

 into the cryostat: during this operation the temperature rose tem- 

 porarily to 4.°25 K. During the next hour the current was found 

 to undergo a gradual diminution and to apjiroach asymptotically a 

 new value of about 0.36 amp. which did not show any further 

 change for V/^ hours. The observations during the two periods 

 mentioned render it probable, that the change does not attain the 

 value of 4 7o i" ^ hours as calculated above. 



It was considered' possible, that the changes of shape of the 

 helium-liquefier and the cryostat dnring the process of condensation 

 and transfer of the liquid helium, as well as a possible change of 

 zero of the compass-needle which after the magnet has been removed 

 is still near various iron parts of the appai'atns, might have had an 

 influence on the values of the current as measured at different 

 moments. Judging by the correspondence of the various readings 

 the accuracy was smaller than had been expected. In again repeat- 

 ing the experiment therefore two compensating coils were used by 

 which compensations on the east and on the west could be effected. 

 They were mounted each in a small vessel with liquid air on a 

 fork-shaped stand and could be rotated about vertical axes in such 

 a manner that the distance of the axes could not change. The same 

 needle served for the compensation on both sides. Guiding pins 

 guaranteed the same position each time of the needle relatively to 

 the compensating cod wdiich was being used. The common support 

 of the two coils was moveable parallel to itself in a horizontal 

 direction on a slide and by means of marks it was possible to place 

 it each time in the same direction and the same position relatively 

 to the vertical axis of the ex jieri mental coil. The axes of the three 

 coils were provided with horizontal divided circles moving along 

 fixed pointers. Each measurement consisted of 8 readings in the 

 obvious combinations of 4 positions both with compensation on the 



left and on the right. 



In the experiment with this improved method of reading care was 



19* 



