582 



Professor Sir James Deivar 



[Jan. 19, 



charcoal is theu brought into play hj a quarter turn of D. The 

 consequent reduction of pressure on the ice in the cotton wool on A» 

 and therefore of its temperature, is such that in two minutes the 

 mercury at each end of the tube freezes, the centre portion remain- 

 ing liquid ; in four minutes the mercury becomes solid, which may 

 be seen when the bulb is rotated. By this method a temperature of 

 - 70° C. can be reached. Experiments made with various bodies as 

 cooling agents give the following limits of temperature : — 



Table II.- 



-Limits op Temperature attainable with various 

 Cooling Agents. 



Solid 



Ice 



CO^ . 







N 



H 



Helium 



"X" . 



Absolute Tempera- 

 ture attainable. 

 Deg. 



132 



51 



37 

 9 



1-8 

 0-4 



In this table X is a hypothetical body as volatile compared to 

 helium, as helium is to hydrogen. "With the aid of such a substance it 

 may be inferred that a temperature of within h" of the absolute zero 



should be reached. It will be seen from the table that the tempera- 

 ture attained was almost invariably the same fraction of the critical 

 temperature of the body, a face which further emphasizes the 



