82 ESSAYS AND OBSERVATIONS 



upward pure air lodged in the water, 

 what ground have we to fuppofe that it 

 can force upward air inclofed within a 

 watery film? 



In the next place, fuppofing thefe bub- 

 bles to be raifed to the furface of the wa- 

 ter, I cannot find a caufe for their ri- 

 fing higher. The air in the bubble is in- 

 deed fuppofed to be rarified by heat ; but 

 muft not the circumambient air be alfo 

 rarified by the fame heat ? 



In the third place, fuppofing the bub- 

 ble fairly lodged in the atmofphere, in 

 fpite of all thefe difhculties, the power of 

 gravity will never account for its conti- 

 nuing there: It muft inftantaneoufly be 

 condenfed, fo as to be in aqiiilibrio with 

 the lurrounding air, leaving the film of 

 water to defcend by its gravity, till it fet- 

 tle in its own element. Let me not be 

 mifunderflood in this argument, which 

 is not intended to contradict a notorious 

 fadt, that water may continue long fuf- 

 pended in air, but only to evince, that 

 gravity cannot be the caufe of that phe- 

 nomenon. 



It will occur at the fame time, that 

 the foregoing account of evaporation is 



contradi(5led 



