[ 43r J 



degrees above 32'', the quantity thus found is called the calorific 

 rejidt or fupplemental height; the union of both gives the com- 

 pleat height. 



Hence we fee the neceffity of having four thermometers, one 

 attached to each barometer to indicate the temperature of the mer- 

 cury in each, and two detached, one at the top and the other at 

 the bottom, to indicate the temperature of the air; the mean heat 

 of both is fuppofed to indicate the mean temperature of the air, 

 and the difference of this mean and 32® muft alfo be expreffed^ 

 This I call i\\e fundamental difference. 



3tio. The indications of the inftruments being minuted, and 

 the barometers, or rather theirlogarithms, rorrif^f^, as fhewn, p. 438, 

 the logarithmic refult is obtained by fubftrading the logarithm of 

 the barometrical height at the top from that of the barometrical 

 height at the bottom of the elevation, as fhewn, p. 439.- This is 

 alfo cailed the approximate height. 



4to. To obtain the calorific refult., ox fupplemental height, two 

 produds are neceffary. For, iP. the fundamental difference mufl 

 be multiplied into 2,5, and divided by 1000 ; or, more fhortly, 

 into ,0025, which is the fame thing. The reafon is this, 1000 

 meafures of air at 32° gain by a heat of one degree above 32'', 2,5 



meafures ; 



