Professor Dewar 



[Jan. 20, 



Koy. Soc. Ed., vol. xxvii.) and the subsequent investigations of 

 Crookes, and especially of Bottomley, having confirmed the great 

 importance to be attached to the gas particles in the gain or loss of 

 heat, it naturally occurred to me that the use of high vacua surround- 

 ing the vessels containing liquid gases would be advantageous. 

 In order to arrive at definite data, some means of conducting com- 

 parative experiments between the amount of convective and radiant 

 heat at such low temperatures had to be devised. 



The apparatus shown in Fig. 1 measures the relative volumes of gas 

 distilled in a given time under definite conditions, so that the measure 

 of the gas distilled is proportional to the amount of heat conveyed 

 to the liquid. The experiments are made in the following way : the 

 distilling vessel to the right consists of two concentric spherical 

 chambers, the space between being highly exhausted by a mercurial 

 air-pump. The inner sphere is filled with liquid ethylene, oxygen, 



Fig. 1. 



or air, and the whole apparatus immersed in water maintained at a 

 constant temperature. Distillation begins immediately and continues 

 at a constant rate provided the liquid in the bulb is maintained at 

 the same level. This is not possible, but a sufficient uniformity 

 is attained by making the observations during the evaporation of the 

 first fourth of the contents. Having measured the volume of gas 

 produced per minute when the sphere is surrounded with a high 

 vacuum, the vessel is taken out of the water, the end nipped off, air 

 allowed to enter, and then again closed. In this condition the inner 

 sphere is filled up again with the liquid and the above experiment 

 repeated. The following results were obtained, using ethylene and 

 oxygen respectively : 



Liquid Oxygen, Vacuum . . . . 170 cc. per minute. 



» » Air 840 „ „ 



„ Ethylene, Vacuum .. 56 „ „ 



» Air 250 „ 



These results prove that under the same conditions a high vacuum 



