BAROMETRICAL MEASUREMENT OF HEIGHTS. 



In Table I., with the argument 2 T, take r f ; 



In Table III., with the arguments h and T, take C ; 



In Table IV., with the arguments h and <, take C' ; 



Make, further, 



u = h + C + C' and ^ r 1 ; 

 And if b' be given, and b required, 



In Table II., with the argument J, take H ; 



then is H = H' -\- ( u T T/ ) 



and the height of the barometer, in Table II., due .to H, is b required. 

 If b be given, and b' required for a level higher by h toises, then, 



In Table II., with the argument 5, take H'. 

 o Make, further, 



" 100 '' 

 and b' is the height of the barometer in Table II., corresponding to H'. 



Example 1. 



I Suppose the height of the barometer reduced to the freezing point to be b' = 

 1295.39 Paris lines ; the temperature of the air t' 11.8 Reaumur; and the latitude 

 J> = 51.48 ; the increase of heat downwards being 1 Reaumur for 100 toises. 

 'What is the height of the barometer reduced to the freezing point, at a station lower 

 3y h 498.2 toises ? 



In this case, t' = 11.8 ; t = 11.8 + 4.98 ;* + *' = 28.58 ; 



2r= '-f=14".29; r = 7.15; 

 md according to Table I. r 1 + 6.67. 



With h and T, in Table III., we find C = 1.4 

 With h and <, in Table IV., we find C' = + 0.3 



We add h = 498.2 

 and we have u = 497.1 ; ioo= *-Wl 



T. = + 6.67 



.34 



463.95 . 



With b', in Table II., we find H' = 367.86 10 



H = 831.81 



Finally, with H, in Table II., we find b = 330.91 Paris lines, which is the required 

 weight of the barometer at the lower station. Gauss's tables (IV.) would give b = 

 130.90 lines. 



D 61 



