HYGROMETRICAL TABLES. Ixxi 



For ^ — ^' = o?o a vapor pressure of 0.118 inch corresponds to a tem- 

 perature ^' = ^ = 23° (see page 182), which is the saturation or dew- 

 point temperature for the data given. 



Table 83. Relative humidity — Temperature Fahrenheit. 



The table gives the vapor pressure corresponding to air temperatures 

 from —30° to -|-I20° at degree intervals (side argument) and for percen- 

 tages of saturation at 10 per cent intervals (top argument). It is computed 

 from the formula 



e = esX relative humidity, 



where Cs is the saturation vapor pressure at the given air temperature. Below 

 a temperature of 20° the values of e are given to o.oooi inch ; above 20° 

 they are given to 0.00 1 inch. 



Examples: 



1. In dew-point example i, above, the computed vapor pressure is 

 0.462 inch. Entering Table 83 with air temperature 84?3 as side 

 argument, we obtain vapor pressure 



0.356 inch = relative humidity 30 



and 



90 



0.462 inch — 0.356 inch = o.io6 inch= " " 7^ ~ 9 



therefore, vapor pressure — 



0.462 inch with t = 84°s F. = " " 39 



2. In dew-point example 2, above, the computed vapor pressure is 

 0.1 18 inch. Entering Table 83 with air temperature 34°5 as side 

 argument, we obtain, vapor pressure 



0.1 00 inch = relative humidity 50 



and 



00 



0.1 18 inch — 0.1 00 inch = 0.018 inch = " " — =9 



therefore, vapior pressure — 



0.1 18 inch with ^ = 34?5 F. = " " 59 



Table 84. Reduction of Psychrometric Observations — Metric measures. 



Values of e = e' — 0.000660 B{t — t'){i-\- o.ooiis t') 



This table provides for computing the vapor pressure from observations 

 of ventilated wet- and dry-bulb Centigrade thermometers. From the vapor 

 pressure thus computed the dew-point and relative humidity of the at- 

 mosphere may be obtained. 



The tabular values of the vapor pressure, e, are computed for degree 

 intervals of t' from —30° to +45° C. Below — 5°o the interval for t — t' 

 is o?i, and above — 5°0 the interval is 1°, 



