from it of 8 cms pointed almost at right angles') to the meridian. 

 When the action on the magnet was compensated by means of a 

 second coil placed on the other side (West) of it of abont the same 

 dimensions as the experimental coil and ot 800 turns, it was found 

 that the coil was carrying a current of about 0.5 to 0.6 amp. *). 

 This was further confirmed by turning the coil and by mox'ing the 

 compass-needle to various positions abont the cryostat ^). During an 

 hour the current was observed not to decrease perceptibly (as far 

 as could be judged by the deviation of the needle with an accuracy 

 of 107o)- During the last half hour the coil was no longer at 

 1°.8 K. but at 4°. 25 K. the tem|)ei'ature of helium boiling under normal 

 atmospheric pressure. ITndoubtedly even at this temperature the 

 observation might have been continued much longer without much 

 diminution of the current. A coil cooled iji liquid helium and provided 

 vyith current at fjeiden, might, if kept irnmersed in liquid helium, 

 be conveyed to a considerable distance and there be used to demon- 

 strate the permanent magnetic action of a supra-conductor carrying a 

 current. I should have liked to show the phenomenon in this meeting 

 (Kon. Acad. Amsterdam), in th^ same way as I brought liquid 

 hydrogen here in 190(i, but the aj)plianees at my disposal do not 

 yet allow the transportation of liquid helium. 



Whereas the experiment, so far as described, shows, that a current 

 when started in a supra-conducting wire continues to flow, the 

 process is immediately stopped as soon as ordinary resistance is 

 generated in the circuit. When the coil is lifted out of the helium, 

 the current is instantaneously destroyed. The temperature of the 

 coil is thereby xery quickly raised above the vanishing point of 

 lead (6° K) and the very long relaxation-time is replaced by a very 

 short one. Reimmersion of the coil, if not too soon after the lifting 

 out, does not again produce magnetic action. 



If the experiment is made with the windings of the coil parallel 

 to the field, no effect") is to be expected. This expectation was in so 

 far confirmed as only a slight effect was observed : this effect can 



i) The field of the. earth beilig distorted by machinery the action of the latter 

 Was compensated by magnets and there resulted a weaker field (note added in 

 the translation.) 



2) [Calculated from the moment, comp. N". liÜtZ g 8, end. Added in the trans- 

 lation]. The coil has a magnetic moment of about 180 C.G.S. and behaves as if the 

 lead possessed remanent magnetisation of some 200 C.G.S. units. 



3) On repeating the experiment at 4°. 25 K. nearly 0.5 amp. was obtained; a 

 later experiment with larger initial field at 2°.3 K. gave 0.7 amp. (see further down). 



-••) Nearer consideration points to a small effect Comp. N". 140c (Note added in 

 the translation). 



2 

 Proceedings Royal Acad. Amsterdam. Vol. XVII. 



