BAR 



of Barometric heights in tenths of an inch ; tn rr mean Barometric heights ; 

 & difference of mercurial temperatures ; then ; 



Height = 30xOn+ft*K/-3;)xrf - s x 2 . 33, 



when the attached thermometer is highest at the lower station, and 

 r, r. 



Sir G. ShucJfburgh's formula in fathoms. 



Let / difference of logarithms of the heights of Barometer in inches ; 

 d = difference of mercurial temperatures ; /as before ; then 



Height (1000W + 440rf) x + / 32 X .00244), 



when the attached thermometer is highest at the lower station, and 

 v, v. 



Playfair^s formula in fathoms, which does not differ much from La 



Place's. 



Let b and (3 be the height of the Barometer at the lowest and highest 

 stations, t and t' the temperatures of the air (Fahr.) at those stations, 

 q and q' the temperatures of the mercury in the two stations j then 



Height = 10000 5l -f .00244. 



-^r~ 3 20 ) ? lo #- - - 



1 ' + 



Formula Encyc. Met r op. 

 The height in feet is 



< 1+ -^) 



where t and t' denote the number of degrees above the freezing point of 

 Fahrenheit. This formula differs very little from the last. 



3. Barometer, correction of observed heights in. 



When the mercury in the tube of a Barometer sinks, and the surface 

 of that in the basin rises ; to determine the correction. 



Let a = the section of the tube, and b that of the basin, supposed 

 cylindrical ; then apparent diminution of height I the real diminution 

 Z ; b a I b. In the best Barometers there is a contrivance for bring- 

 ing the mercury in the basin always to the same level, which obviates the 

 necessity of this correction. 



Jtarometer, correction ofobserced heights in, as far as regards a change 

 of temperature, 

 39 



