APPENDIX 289 



the atmosphere ; and it is most likely that these mole- 

 cules are so sensitive to external forces that the 

 slightest reaction from the sun operates upon them, 

 producing the depressions and the atmospheric altera- 

 tions man finds in the lower regions of the air. 



We have now our factors. Let us consider two 

 gaseous molecules, in contact, of like dimensions, as 

 illustrated below (fig. 2). And we want to liquefy 

 1. We wry quickly remove pressure from a ; it 

 seizes Ether from b ; a becomes higher in tempera- 

 ture, b lower in temperature (fig. 3). It would 

 appear, however, that this must be done quicldy, other- 



Fig. 2. Fig. 3. 



wise, as a increases in temperature, b picks up Ether as 

 fast, or nearly as fast, as it parts Ether to a. In 

 this case there is no decrease of temperature in b ; it 

 remains constant in temperature, or nearly so. 



Now, if we assist this reaction by putting pressure 

 upon b at the same time as we are removing pressure 

 from , b will be so reduced in volume (i.e. tempera- 

 ture) that it will become of the dimensions of a 

 liquid molecule. This is only seen in a mass of 

 molecules. 



This illustration explains the principle involved. Of 

 course we cannot do this with two molecules, but we 



u 



