( 180 ) 



some delay in consequence of insignificant disturbances, the filling 

 of the graduated vacuum glass and the hydrogen refrigerator with 

 hydrogen began at 4.20 p.m. 



At the same time the helium was conducted in circulation through 

 the liquefactor. The pressure under which the hydrogen evaporated, 

 was gradually decreased to 6 cm., at which it remained from 5.20 

 p.m. The level in the refrigerator was continually regulated according 

 to the indication of the thermometer-level-indicator and the reading 

 of the graduated glass, and care was taken to add liquid hydrogen 

 {Hydr. a, Hydr b PI. II) and liquid air wherever necessary {a, b, c,d, 

 PI. II). In the meantime the pressure of the helium in the coil 

 was slowly increased, and gradually raised from 80 to 100 atms. 

 between 5.35 and 6.35 p.m. 



At first the fall of the helium thermometer which indicated the 

 temperature under the expansion cock, was so insignificant, that we 

 feared that it had got defect, which would have been a double disap- 

 pointment because just before also in the gold-silver thermo-element, 

 which served to indicate the same temperature, some irregularity 

 had occurred. After a long time, however, the at first insignificant 

 fall began to be appreciable, and then to accelerate. Not before at 

 6.35 an accelerated expansion was applied, on which the pressure 

 in the coil decreased from 95 to 40 atms., the temperature of the 

 thermometer fell below that of the hydrogen. In successive accele- 

 rated expansions, especially when the pressure was not too high, a 

 distinct fluctuation of the temperature towards lower values was clearly 

 observed Thus the thermometer indicated e.g. once roughly 6° K. 



In the meantime the last bottle of the store of liquid hydrogen 

 was connected with the apparatus : and still nothing had as yet been 

 observed but some slight waving distortions of images near the cock. The 

 thermometer indicated first even an increase of temperature with accele- 

 rated expansion from 100 atms., which was an indication for us to lower 

 the circulation pressure to 75 atms. Nothing was obsarved in the 

 helium space then either, but the thermometer began to be remar- 

 kably constant from this moment with an indication of less than 

 5° K. When once more accelerated expansion from 100 atms. was 

 tried, the temperature first rose, and returned then to the same 

 constant point. 



It was, as prof. Schreinemakers, who was present at this part 

 of the experiment, observed, as if the thermometer was placed in 

 a liquid. This proved really to be the case. In the construction of 

 the apparatus (see § 2) it had been foreseen that it might fill with 



