86 Mifiellanea Curio fa. 



to 1 1 i,fo the Semi-diamter of the Earth fuppofed 

 4000 Miles, to 44, 4 Miles; which will be 

 the height of the whole Air, if the Places £, S y 

 whofe vifible Portions of the Atmofphere EZ^Jf, 

 and S H K^B, juft touch one the other, be 1 8 

 Degrees afonder. 



At this height the Air is expanded into a- 

 bove 3000 times the fpace it occupies here, and 

 we have feen the Experience of condenling it 

 into the 60th part of the fame Space 3 - fo that 

 it fhould feem, that the Air is, a Subftance ca- 

 pable of being comprefTed into the 180000th 

 part of the Space it would naturally take up, 

 when free from preflure. Now what Texture 

 Or Compofition of Parts (hall be capable of this 

 great Expanfionand Contraction* feems a ver yhard 

 Queftion ; and which, I fuppofe, is fcarce fuffici- 

 ently accounted for, by comparing it to Wool, 

 Cotten, and the like fpringy Bodies. 

 . Hitherto 1 fiave only confider'd the Air and 

 Atmofphere, as one unalter'd Body, as having 

 conftantly at the Earth's Surface the 800th 

 part of the weight of Water, and being capa- 

 ble of Rarifa£tion and Condenfation in infini- 

 tum \ neither of which Hypothefes are rigidly true : 

 For here in England it is notorioufly known, 

 that the weight, of the whole Atmofphere is va- 

 rious, being counterpoifed fbmetimes by 282 

 Inches of Mercury, and at other times by no 

 lefs than gOj ; fo that the under parts being 

 preffed by about a 1 5th part, lefs weight, the 

 fpecifick. Gravity of the Air upon that fcore will 

 fomeiimes be a 1 $rth part lighter than another ; 

 befides Heat and Cold, does very considerably 

 dilate and contract the Air, and confequently 

 alter its Gravity j to which add the mixture of 

 f$uvia> or fteams arifing from almoft all Bo- 



