( 180 ) 



Fig. 5. 



shut Cj and disconnect the india rubber tube at a and remove the 

 whole apparatus to the measuring apparatus which is to be filled 

 with pure hydrogen; to this end the apparatus is connected with the 

 mercury pump, intended for this purpose, at c^. To take care that 

 the hydrogen in B should evaporate but slowly and the quantity 

 in C should not be lost before we begin to fill the pieces of appa- 

 ratus, B is placed in a vacuum glass with liquid air. 



Physics. — "■(Jn the measurement of very loio temperatures. IX. 

 Comparison of a theimio-element constantiii-steel with the hydrogen 

 thermometer y By Prof. H. Kamerlingh Onnes and C. A. 

 Crommelin. Communication N" Sö*^ from the Physical Labora- 

 tory at Leiden. 



(Communicated in the meeting of June 30, 1906). 



^ 1. Introduction. The measurements communicated in this paper 

 form part of a series, which was undertaken long ago with a view 

 to obtain data about the trustworthiness of the determination of 

 low temperatures which are as far as possible independent and 

 intercomparable. Therefore the plan had been made to compare 

 a thermo-element^), a gold- and a platinum-resistance thermometer'') 



1) Gomp. comms. N". 27 and 89. (Proc. Roy. Ac. May 189G, June 1896, and 

 Feb. 1904). 



3) Gomp. comms. N». 77 and 93. (Idem Febr. 1902 and Oct. 1904). 



