ON THE STANDARD OF WEIGHT AND MEASURE". *' 37 



preflure, is always of the fame fpecific gravity. This we know 

 is not the cafe ; confiderable variations in this refpect being 

 occafioned by its different ftates of drynefs, ele&ricity, and 

 perhaps other caufes : as, however, experiments are wanting 

 for the correct eftimation of thefe differences, we will take the 

 firft fuppofition to be true, and apply the corrections accord- 

 ingly from Sir G. S. Evelyn's tables for this purpofe, in his 

 note fubjoined to § 23. 



This gentleman tells us in the Philofophical Tranfaclions for Air expands 

 1777, that the fpecific gravity of air at 51°, under a preflure *j!XLheit. 9 ° f 

 equal to 29.27 inches of mercury, is to that of water as 1 to 

 836, or = .001208; taking the latter as unity. Afluming 

 therefore that the expanflon of air, for each degree of Fahren- 

 heit's thermometer between 51° and 60^, is .0027 of the 

 whole, we get the fpecific gravity of air at 60 under the like 

 preflure = .001179, and 29.27 : .001179 : : 29.5 : .001188 Sp.^gr. ofair at 

 = the fpecific gravity of air at 60° when the barometer ftands Jl ' 00 7i88 9 — •' 

 at 29§ ; and a cubic inch of fuch air confequently weighs T s ^ of -3 &> for each 

 a grain very nearly. cubic inch ' 



Now the cube was weighed in air at 62° under a preflure of Denfities of the 

 29 inches (§ 20) ; the cylinder in air at 62° under a preflure ^Vies^re ** 

 of 29 inches (§ 21 ) ; and the fphere in air at 67° under a pre/"- weighed, 

 fure of 29.74 inches (§29). 



And the excefles of the weights, of the refpeclive quantities 

 ef diftilled water difplaced by thefe bodies, on their being af- 

 terwards weighed in this fluid, over thofe of fimilar quantities 

 of air at the feveral temperatures and denfities above-men- 

 tioned, were as follow ; viz. 



That of the water difplaced by the cube (§ 22), 32084.82- The apparent 

 703.03 = 31381.79 g rains; ^SSXS 



That of the water difplaced by the cylinder (fecond experi- 

 ment § 23), 21560.05 - 2553.22 = 19006.83 grains; 



And that of the water difplaced by the fphere (§ 30), 

 28673.51 grains. 



The air in which each of the bodies was weighed being, Correction for 



however, lighter than air at 60? when the barometer ftands at P reffurc and 



° temperature ap- 



29|, we rauft correct thefe excefles of weight in the (everal plied* 

 quantities of water, fo as to find how much the weight of 

 each of them exceeds that of an equal quantity of air of fuch 

 ftandard fpecific gravity ; or in other words, how much the 

 iveight of each of the bodies in water differs from that which 



it 



