Chap. 9-] Compreffibiiity of Air. 429 



becaufe the moment the force of attraction is over- 

 come by the repulfive power of the heat, the particles 

 would feparate themfelves indefinitely, having nothing 

 to limit their expanfion, unlefs their own gravity might 

 collect them together, fo as to form an atmolphere *. 



Air, being an elaftic fluid, is confequently COM- 

 PRESSIBLE, as the very word implies; the weight, 

 therefore, of the atmofphsre compreflcs its lower 

 parts, for in low vallies it is more comprefTed, and 

 has more denfity than upon high mountains ; but this 

 is not the cafe with water, which not being elaflic in 

 its ordinary ftate, is hardly compreffible at all ; fo that 

 the different portions of the fame mafs of water have 

 nearly the fame denfity throughout its whole depth. 



IV! . Amontons contends, that there is no fixing any 

 bounds to the condenfation of air. Dr. Hal ley has 

 afierted, in the Philofophical Tranfactions, that, from 

 the experiments made at London and Florence, it 

 might be fafejy concluded, that no force whatever is 

 able to reduce air into 8co times lefs fpace than that 

 which it naturally poffefles on the furface of our 

 earth. 



It has been proved by various experiments, that a 

 column of cotnprefied air is diminifhed in proportion 

 to the augmentation of the preflure by which it is 

 condenfcd. 



The fimplcfb of thefe experiments is, to pour a 

 quantity of 'quickfilver into the 'tube ABC (Plate 

 XXIX. Fig. 6.) clcfed at A, and open at C. When 

 the tube is filled with quickfilver to E, then the air. 

 inclofed in the leg A B, will prevent its rifmg higher 

 than D, and the column D B will be in equilibrium with 

 FB ; confequentiy the quickfilver contained between 

 FD will not at all prefs on the air between A and D ; 



* 'Lavoificr's Elem. of Chemift. p. 8. 



but 



