1893.] 



on Liquid Atmospheric Air. 



3 



diminishes the rate of evaporation to one-fifth part of what it is 

 when the substance is surrounded with air at atmospheric pressure, 

 or, in other words, liquid oxygen or ethylene lasts five times longer 

 when surrounded with a vacuous space. 



The next step was to construct a series of glass vessels sur- 

 rounded by a vacuous space, suitable for various experiments, and 

 such are represented in Fig. 2. In vessels of this kind, if the vacuum 

 is very high, no ice appears on the surface of the outer vessel, even 

 although the walls of the vacuous space are within half an inch of 

 each other, and the liquid oxygen or air evaporates almost solely 

 from the surface, no bubbles of gas being given off throughout the 

 mass of the liquid. So far the convective transference of heat has 

 been stopped by the use of a high vacuum, but if the inner vessel 

 is coated with a bright deposit of silver, then the radiation is 



Fig. 2. 





diminished also, with the result that the rate of evaporation is 

 further reduced to more than a half. In such vessels liquid oxygen 

 or liquid air can be kept for hours, and the economy and ease of 

 manipulation greatly improved. 



The arrangements represented in Fig. 2 may be employed to 

 study the law of radiation at low temperatures. All that is necessary 

 for the purpose is to immerse the outer vessel in liquids maintained 

 at different temperatures. The following preliminary results have 

 been obtained, using oxygen, which boils at — 180° C, in the inner 

 sphere : — 



Temperature. Radiation. 



-115°C 60 cc. 



- 78° C 120 „ 



+ 6°C 300 „ 



+ 65° 600 „ 



These results show that radiation (along with such convective 

 transference as remains) grows approximately at the rate of the cube 



b 2 



