400 BAROMETRICAL MEASUREMENT OF HEIGHTS. 



r 



Example 2. 



Suppose I 1 = 330.46 Paris lines ; t 1 12.3 Reaumur ; 7i' = 92.7 toises ; 

 < = 62. 



In this case, assuming t = t', 



2 T= -Ltl' == _i2o.3; 1-= 6.15; 



and according to Table I. r' = 6.55. 



With h and r, in Table III., take C = 0.2 

 With h and 0, in Table IV., take C' = + 0.1 



Add h = 92/7 



We have u = 92.6 ^ = 0>926 



u T = - 6.55 



- loo ' = + 6 ' 07 6 | 



98.67 _M^ 



With i', in Table II., take H' = 826.22 T ' 



H = 924.89 



With PI, in Table II., we find I = 338.53 Paris lines. Gauss's tables (IV.) would 

 give b = 338.54 lines. 



II. For Computing Differences of Elevation from Barometrical Observations. 

 Suppose to be given B, B', T, T', /, t 1 , $ ; required h. 



Make first r = '-^ and T T'. 

 Then in Table II., with the argument yo/ 



and make 



u = (H - H') + *=^ r - (T - T'), 



in which each full degree of T T' corresponds to a toise. 



Further, in Table III., with u and T, take C reversing the sign ; 



in Table IV., with u and 0, take C' reversing the sign ; 



in Table V., with T T' and r, take C ' with the signs of T T'. 

 Then the difference of elevation required is 



h = u + C + C' + C". 

 If the heights of the barometer, reduced to the freezing point, or b and &', are given, 



then in Table II., with the argument, < ,, . TT/ 

 and make 



Further, in Table III., take C reversing the sign ; 

 in Table IV., take C' reversing the sign ; 

 and 



h = u + C + C'. 



D 60 



