51 



I 



capillary H, a simple helium thermometer') for ascertaining the 



mean temperature of' the portion of the 

 small reservoir capillary within the cryo- 

 stat, bill above the liquid, as well as the 

 necessary tubes for the introduction and 

 removal of the etiiylene. 



The connections, required for the reg- 

 ulation of the pressure within the cryo- 

 stat may be seen in Plate I of Comm. 

 N°. 97". 



Tiie method of stirring the gaseous 

 and liquid phases within the small reser- 

 voir bulb was as follows : round the 

 bulb was fitted a soft iron sheath, which 

 could be moved vertically up and down 

 by means of an electro-magnet E above 

 the cryostat, in the same way as the 

 liquid stirrer is worked.') In the lowest 

 position of the sheath ?/; (which is of 

 about the same length as the reservoir R, 

 and about three times as long as the 

 stirrer), the lower edge was at the level 

 of the bottom of the bulb R\ in the 

 highest position of in its lower edge was 

 raised to fully two thirds of the height 

 of the bulb R. In order to be able to 

 obtain a clear view of the whole length 

 of the bulb R, two slits were cut out of 

 opposite sides of the sheath m, and the 

 latter so arranged that Ihese slits were 

 in line with the clear strips in the silver 

 surfaces of the vacuum-glasses. Round 

 the outer glass a ring electro-magnel m 

 was placed with the bottom surfaces slightly 

 above the level of the top of the bulb R. 

 By a correct adjustment of (he current 

 circulating through this and the weight 

 of the iron sheath ?», it was possible to 



n 



Fig. 1. 



raise and lower the latter, which carried the small stirrer r with 



1) These Proc. IX pg. 754. (Dec. 1906). Leiden Comm. N». 97a. 



■\ These Proc. XX (2) pg. 991 (June 1917). Leiden Comm. No. 152« l§ 3). 



4* 



