::ygrometrical tables. xli 



It is computed 1)y the formula 



Relative humidity = -p. 



f and F are the maximum pressures of vapor corresponding respectively to 

 the temperatures d and / as given in Table 35 for temperatures above 32" F. 

 and in Table 37 for temperatures below 32° F. 



The top argument is t — d, extending by half degree intervals from o" to 

 15" /\, and by increasing intervals from 15° to 75° F. 



The side argviment is the air temperature /, given for intervals of four 

 degrees from —32° to 120° F. 



Example: 



Let the air temperature be 62° F. and the dew-point 51°/^., to find the 

 relative humidity. 



With / — rt^ = 1 1° for the top argument, and / = 62° for the side argument, 

 the table gives 67.5 per cent as the relative humidity. 



TABLES 43, 44.. 

 Reduction of Psychrometric Observatmis — Metric measures. 



TABLE 43. Pressure of aqueous vapor. 



TABLE 4.4. Values of 0.000660 B {t — /,) ( i + -5 — ^) • 



\ 873 / 



These two tables provide for computing the vapor pressure and dew- 

 point from observations of ventilated wet and dry-bulb thermometers 

 Centigrade. 



Table 43, with the wet-bulb temperature /, as an argument, gives the 

 value of/,, the first term of the formula for the vapor pressure/, viz : 



f=f— 0.000660 B {t — t,)\.i -fo.ooii5 (^ — /,)]• 



It gives the vapor pressure to hundredths of a millimetre from — 30°o C. 

 to 45.°9 C, the intervals being 1° for temperatures below 0° C. and ofi for 

 temperatures above 0° C. 



Table 44, with the depression of the wet-bulb / — /,, and the barometric 

 pressure B as arguments, gives the value of the second term of the formula. 



The top argument is given for every 10 millimetres from 770 to 460 mm. ; 

 the side argument t — t^ is given for every whole degree up to 20. Tabular 

 values are given to hundredths of a millimetre. 



From the two parts of the table we then have 



Vapor pressure, /(ww) = Table 43 — Table 44. 



The temperature in Table 43, corresponding to the vapor pressure thus 

 obtained, is the dew-point. 



