Chap. 9-] Llaflidiy of Air. 43 1 



placed under the receiver of an air-pump, and rhe ma- 

 chine fet in rnocion to exhault the air furrounuing the 

 bladder, it will begin to open and fwell, and tint in 

 proportion to the diminution of the deniity of the air 

 in the receiver *. 



Philosophers have doubted whether this elaftic power 

 of the air is capable of being deftroyed or diminiflied. 

 Mr. Boyle endeavoured to difcover how long air 

 would retain its fpring after having aflumed the greareft 

 degree of expanfion his air-pump could give it ; but he 

 never obferved any fenfible diminution. Defaguliers 

 fays, that air, which had been enclofed half a year iii 

 a wind-gun, had loft none of its elafticity ; and Rober- 

 val afferts, that he has preferved air in the fame man- 

 ner for fixteen years j and that after that period he ob- 

 ferved, that its expanfive projectile force was the fame 

 as if it had been newly condenfed. Dr. Hales and 

 Mr. Haukfoee on the contrary conclude, from other 

 experiments, that the elafticity of the air is capable of 

 being impaired and diminiflied by a variety of caufes. 

 M. Lavoifier, however, has folved thefe difficulties, 

 by proving, that the elafticity of all gaffes or elaftic 

 fluids depends upon that of caloric, which feems to 

 be the moft eminently elaftic body in nature. No- 

 thing, fays he, is more readily conceived, than that one 

 body fliould become elaftic by entering into combina- 

 tion with another body porTefied of that quality. We 

 muft allow that this is only an explanation of elafti- 

 city, by an afTumption of elafticity; and that we thus 

 only remove the difficulty one ftep farther j and that 

 the nature of elafticity, and the reafon for caloric being 

 elaftic, remain ftill unexplained f.' 



On the elafticity and compreflibility of air depend 

 the ftructure and ufes of the air-gun. In thefe inftru- 



* Briflbn, torn. ii. p. 103. f Elem. of Chem. p. 22. 



MCflO 



