lii INTRODUCTION. 



For convenience in computing, the tabulated values of A are for 



_ ( -1 ^^ ^ Y The side and top arguments are air and vapor pressures, re- 

 2 \o .00367 ) 



spectively, in mm. on p. 150 and in mb. on p. 151. Instead of computing 

 A 6 from the mean of the values of B and e at the upper and lower stations 

 it is computed for each station separately, and the sum of the two deter- 

 minations is added to 6. 



Table 62 gives the correction for gravity, and for the effect of the 

 variation of gravity with altitude on the weight of the mercurial column. 

 When altitudes are determined with aneroid barometers the latter factor 

 does not enter the formula. In this case the effect of the latitude factor can 

 be obtained by subtracting the tabular value for latitude 45° 29' from the 

 tabular value for the latitude in question. 



The side argument is the approximate difference of elevation Z varying 

 by intervals of 100 meters from 100 to 4000, and by 500 meters from 4000 

 to 7000. The top argument is the latitude, varying by intervals of 5° from 



o°to75.° 



Table 63 gives the correction for the variation of gravity with altitude 



in its effect on the weight of the air. 



The side argument is the same as in Table 62 ; the top argument is the 

 height of the lower station, varying by intervals of 200 meters from o to 

 2000, with additional columns for 2500, 3000 and 4000 meters. 



The corrections given in Table 62 and Table 63 apply to the approxi- 

 mate heights computed from metric or dynamic measures by the use of 

 Tables 56 to 61, inclusive, and are additive. 



Example: (Metric Measures.) 



Let the barometric reading (reduced to 0° C.) at the upper station be 

 655.7 mm. ; at the lower station, 772.4 mm. Let the mean tempera- 

 ture of the air column be 9 =12.3 C, the mean vapor pressure g = 

 9 mm. and the latitude </> = 32°. 

 Table 56, with argument 655.7, gives 1179 meters. 



Table 56, " " 7724, " - 129 



Approximate value of Z = 1308 



Table 59, with Z ^ 1308 and B = I2°3 C, gives 59 



Table 60, with g = 9 mm. and Z = 1370, gives 7 



Table 62, with Z = 1370 and = 32°, gives 5 



Table 63, with Z = 1370 and /?o = o, gives o 



Corrected value of Z = 1379 meters. 



Example : (Dynamic Measures.) 



Let the barometer reading (reduced to 0° C.) at the upper station be 

 448.6 mb.; at the lower station, 1000.3 mb. Let the vapor pres- 



