LEVELING 93 



Let 2 = difference in elevation of the two stations, in feet; 

 h = the reading, in inches, of the barometer at the lower 



station; 

 H = the reading, in inches, of the barometer at the 



higher station; 



t and T = temperatures of the air at the two stations. 

 Then, 



z = 60,384.3 (log h- log H) (] 



EXAMPLE. Suppose that the barometer at the lower sta- 

 tion reads 26.25 in. with the temperature at 72 F. and that 

 at the upper station it reads 24.95 in, with the temperature 

 at 46 F. What is the difference in elevation? 



SOLUTION. Substituting known values in the preceding 

 formula, 



2 = 60,384.3 (log 26.25 - log 24.95) (l-f 



or s = 60,384.3 X. 02206X1.06 = 1,412 ft. 



The accompanying table was compiled from the preceding 

 formula for a mean temperature of 50 F.; that is, for 



= 50 F. Therefore, for this condition, the heights cor- 

 responding to the barometer readings may be taken directly 

 from the table. If the heights at the upper and lower stations 

 as taken from the table are denoted by H and h, respectively, 

 the difference in elevation is 



z = H-h 



When the mean temperature is more or less than 50 F., 

 the result, as obtained by means of the table, must be multi- 



) 



plied by the factor --- \-.Q , Then, 



