180 



TABLE XTII. 



FOR COXFASISG TEE "vTEI&ET OT A CTBIC FOOT OP I'llT AVD OF SATTRaTZT AIZ. 



This table is cc r - ' - I'zmnd m the Greenicich Meieorohgical 



OhserratioTis for 1'^^, . - ; the fiist containing the weight of a 



cubic foot of diy air, under a barometric pressure of 30 inches, at temperatures be- 

 tween 0^ and 90^ F : t're ::ber giving the weight of a cubic foot of saturated air 

 under the same barci-r:.; : ressore and temperature, together with the excess of the 

 first above the lasL 



The we.gb: of e : - ' - -' -y air, on which the tables are based, is assumed to 

 be 563 grains Troy. : _ . value, in round numbere, between the determina- 



tions of Shuckburgh, wnien is 557.T295 grains, and that of Biot and Arago. 568.7013. 

 The true mean is 563.2154, bu: 563 is the number used in the calculations. 



The coefficient of the expansion of the air is that of Gay-Lussac, viz. 0.00375 for 

 1= Centigrade, or 0.0020S3 of its bulk for 1= Fahrenheit 



C*e of ihf Table. 



This t£'" - - - •"' " — • " " lyaBcy imparted to ine air oy me adainon of 

 rDoisnre : i : and the relative humiditv of the air being 



known, the weight of a eut>ic foot of air, in the actual condition of the atmosphere at 

 the lime of an observation, car. - - - - - - - - 



It suffices to take in the : : ^ec " Excess," the qtiantitv corre- 



sz.:o fiiLg :j 'ie tempera: iir m tne nist, multiply h into the given Relative 



Hjmidiry. -^-^ - - — - • : :t from the number in the second column. The 



re=r;^: w:l. . :: ;. :jbic foot of air at the existing temperature and 



moisture, under a iarometrie pre^^ire of 30 inches. 



:>e reduced to its true value, under the barometric pressure given 

 Hd^it of Barometer 



-r-':: -^■ 



oy multiplying it by 



ao 



Hxample. 



7 ^ : is 60' F. ; the relative humidity, 0.852 ; the barom- 

 e*ei res IS 'Z':' .- 



Tbe t->> r fair, 60= : excess. 3.35 x 0.852 = 2.85, which, 



5 531.91 m : ctdumn. = 529.12, weight of a cubic foot 



of an rs of presnre: and 529.12 x " ^'' = 511.48, ibe weight of 



T 2iven couditicHis of temperature, moisture, and barooaetric 



B 144 



