gas in such a receptacle of this substance, so faced as 

 to permit egress but not entrance of the heat, and the 

 gas thus enclosed, were it hydrogen itself, would very- 

 soon become liquid and solid, through spontaneous 

 giving off of its energy, without any manipulation 

 whatever. Contrariwise, were the faces of the recep- 

 tacle reversed, a piece of iron placed within it would be 

 made red-hot and melted though the receptacle were 

 kept packed in salt and ice and no heat applied ex- 

 cept such as came from this freezing mixture. One 

 could cook a beefsteak with a cake of ice had he but 

 such a material as this with which to make his stove. 

 Not even Rumford or our modern Edward Atkinson 

 ever dreamed of such economy of fuel as that. 



But, unfortunately, no such substance as this is 

 known, nor, indeed, any substance that will fully pre- 

 vent the passage of heat-impulses in either direction. 

 Hence one of the greatest tasks of the experimenters 

 has been to find a receptacle that would insulate a 

 cooled substance even partially from the incessant 

 bombardment of heat - impulses from without. It is 

 obvious that unless such an insulating receptacle could 

 be provided none of the more resistent gases, such as 

 oxygen, could be long kept liquid, even when once 

 brought to that condition, since an environment of 

 requisite frigidity could not practicably be provided. 



But now another phase of the problem presents it- 

 self to the experimenter. Oxygen has assumed the 

 quiescent liquid state, to be sure, but in so doing it has 

 fallen below the temperature of its cooling medium; 

 hence it is now receiving from that medium more en- 

 ergy of vibration than it gives, and unless this is pre- 

 52 



