548 ON BAROMETRICAL MEASUREMENT OF HEIGHTS. 



7. The true difference of height is the approximate^ + the differ- 

 ence of the two small corrections %vhich are obtained 

 from Table IV., with the arguments of the greater and 

 lesser height. 



I take, as an example, one of D'Aubuisson's measurements of 

 the height of Monte Gregorio, above a point at an elevation 

 h = 128-3 toises (Traite de Geognosie, i. p. 481.). There be- 

 ing no observation of the psychrometer, I take a. = a! = ^. 



b = 329-013, t = 19-85, t = 19-95 



6'= 268-215, i' = 10-5, t'= 9-9 



log 6 =2-51721; 7.^=139; log A, = 2-51582 ^ half 

 logy = 2-42848; '] .t' - 73*5; log 6/ = 2-42774-5 J sum.* 



log T7 = O-O88O75 

 "t 



B = 8-94485 



Table B = 8-94485 



I. t + t'= 29°85 (A:=0-00375) logV =3-99782 logW = 0-0397 



II. Arg. = 7-5679 logV'= 161 * . . 2-4718 



III. <p=45°32' logG= —2 7-5679 



2-94426 

 Approximate height 879^-54 



IV. h!= 1007-8, h = 128-3 +0 -31 



h' — h = 879'r-85 ^ 



D'Aubuisson himself computes the height 879^-7; from Gauss's 

 tables we should have 879'^-63. If ^ be taken = 0-003648, we 

 have l'^-26 less. If we take the air as dry, we obtain 3^-24 less ; 

 and if as saturated, 3'^-28 more. 



Bessel. 



