[ 350 ] 



ducSs, this air be iinprifoned in the barrel and the piilon be 

 then railed to the top the air in the cavities will be expanded 

 in the cyl"", and whatever is its rarefadion then, no greater 

 can ever be produced in the rec^ ; but its denfity then will 

 be to what it was when confined in the cavities, reciprocally 

 as the fpaces occupied, or as the contents of thofe cavities to 

 the whole content of the cyl^, that is, the rarefacflion will be 

 expreffed by the cjuotient of the latter divided by the former ; 

 and this I call the rarefatlion produced in the cyU per fe : 

 now one of thefe cavities is ith, and the other ^th of an 

 inch in diameter ; the depth of both being ^th of an inch ; 

 fo the fum of their contents is about --/--ths of a cubic inch : 

 alfo the content of the cyl"", which is about 13V inches long 

 under the pifton, and two inches in diameter, is nearly 42,4 

 cubic inches ; the quotient of which, divided by the former, 

 is 471 1 : and this No. expreffcs the rarefadion in the cyl"", and 

 what ought to be produced in the rec^ by this pump, if it were 

 even open at the top (in which ftate it would in fadl be the 

 fame as Mr. Boyle's original one) but as the pifkon can hardly 

 be made fo exadlly to fit and fill the bottom, as not to leave 

 a farther vacuity under it, perhaps equal to ^ of that of the 

 cavities under the plate, fo this rarefaction fhould be reduced 

 -1- viz. to 3530 ; and if the performance of the inftrument de- 

 pended only on its mechanifm, it would not fail of rarefying 

 the air to this degree, every part being made perfcdly air-tight. 



Accordingly 



