xlvi 



INTRODUCTION. 



Attention is called to the fact that the formula is linear with respect 

 to 6, and hence that the correction, for example, for 59?8 C. equals the cor- 

 rection for 50.8 plus the correction for 9 or .186 + .033 = .219, and is to 

 be added. 



Table 59 is an amplification of Table 58 and gives the temperature 

 correction 0.00367 6 X Z. 



The side argument is the approximate difference of elevation Z and 

 the top argument is the mean temperature of the air column. The values 

 of Z vary by intervals of 100 m. from 100 to 4000 meters and the tempera- 

 ture varies by intervals of i° from i° C. to io C. with additional columns 

 for 20 , 30 , and 40 C. This formula also is linear with respect to 6, and 

 hence the correction, for example, for 27 equals the correction for 20 plus 

 the correction for 7 . When the table is used for temperatures below O C. 

 the tabular correction must be subtracted from, instead of added to, the 

 approximate value of Z. 



Table 60 (pp. 149 and 150) gives the correction for humidity resulting 



from the factor 0.378 % X Z = /3 Z. 

 b 



Page 149 gives the value of 0.378 7 multiplied by 10000. The side argu- 

 es 



ment is the mean pressure of aqueous vapor, e, which serves to repre- 

 sent the mean state of humidity of the air between the two stations. 

 e = |(e x + e ) (e z and e being the vapor pressures observed at the two sta- 

 tions) has been written at the head of the table, but the value to be as- 

 signed to e is in reality left to the observer, independently of all hypothesis. 

 The top argument is the mean barometric pressure \ (B + B ). 



The vapor pressure varies by millimeters from 1 to 40, and the mean 

 barometric pressure varies by intervals of 20 mm. from 500 mm. to 760 mm. 



The tabular values represent the humidity factor fi, or 0.378 -, multiplied by 

 ioooo. 



Page 150 gives the correction for humidity, with Z and ioooo X 0.378 - 

 (derived from page 149) as arguments. 



The approximate difference of altitude is given by intervals of 100 

 meters from 100 to 4000 meters, with additional lines for 5000, 6000, and 

 7000 meters. The values of ioooo /3 vary by intervals of 25 from 25 to 300. 

 The tabular values are given in tenths of meters to facilitate and increase 

 the accuracy of interpolation. 



Table 61 . Humidity correction : Value of - ( ).- It has been 



2 V0.00367/ 



found advantageous to express the humidity term, (3Z, as a correction to 



the temperature term, ad Z. 



Let aA9Z = l3Z; then, A 9 = - = °' 378f . 



a 0.00367 



