Ixxii INTRODUCTION. 



Corrections for barometric pressure. The computation has been made 

 for B = /6o mm. but on each page of the table is given a correction, 

 AeXi^B, computed for B=66o, or AP=ioo mm., and for the vakies of 

 t' indicated. The correction is a hnear function of a5. For atmospheric 

 pressures less than 760 mm. it is to be added to the tabular values of c, 

 while for atmospheric pressures greater than 760 mm. it is to be subtracted. 

 The values of e are given to o.ooi mm. for t' less than — 5°o, and to o.oi 

 mm. for /' greater than — 5°o. 



Example : 



Given, t=io°4 C; /' = 8°3 C. and ^ = 740 mm. With t' = S°7, and 

 t — t' = 2°i as arguments, Table 84 gives for e the value 7.15 mm. 



AB=- ^^=0.2. AeXAB = 0.14x0.2 



= 0.0^. 

 100 ■ ^ 



Corrected value of c =7.18 mm. 



For t — t'=:0 a vapor pressure of 7.18 mm. corresponds to a tempera- 

 ture t' = t = 6°2, C., which is the saturation, or dew-point tempera- 

 ture for the data given. 



TABLE 85. 



Table 85. Relative humidity — Temperature Centigrade. 



This table gives the vapor pressure corresponding to air temperatures 

 from —45° C. to 4-55° C. at degree intervals (side argument) and for per- 

 centage of saturation at 10 per cent intervals (top argument). It is com- 

 puted from the same formula as Table 83, namely, 



e = esX relative humidity. 



Below a temperature of -|-5?0 the values of e are given to o.oi mm.; 

 above 5°o they are given to o.i mm. 



Example: 



In the dew-point example given above, the computed vapor pressure 

 is 7.18 mm. Entering Table 85 with air temperature 10.4 as side ar- 

 gument, we obtain vapor pressure 



6.6 mm. = relative humidity 70 



and 



7.18-6.6 = 0.58 mm. = " " — = 6 



^ -J 10 



therefore, vapor pressure 



7.18 mm. with ^=10.4 C.= " " = 76 



TABLE 86. 



Table 86. Rate of decrease of vapor pressure zvith altitude for mountain 

 stations. 

 From hygrometric observations made at various mountain stations on 

 the Himalayas, Mount Ararat, Teneriffe, and the Alps, Dr. J. Hann 

 (Lehrbuch der Meteorologie Dritte Aiifiage, S. 230) has deduced the fol- 

 lowing empirical formula showing the average relation between the vapor 



