xl INTRODUCTION. 



Table 40, with the wet-bulb temperature /, as an argument, gives the 

 value of y, , the first term of the formula for the vapor pressure /, given 

 above. It is simply an abbreviation of Table 35 for temperatures above 

 32° F., and of Table 37 for temperatures below 32° F., reprinted for 

 convenience. 



Table 41, with / — /, and B as arguments, gives the value of the second 

 term of the formula, viz : 



0.000367 ^(/-/J^i +^— ^) 



The top argument is given for every half inch from 30.5 to 18.5 inches; 

 the side argument, / — /, , is given for every whole degree up to 40° F. 

 Tabular values are given to thousandths of inches. 



With the two tables we then have, 



/ (vapor pressure) = Table 40 — Table 41. 



The value of / in Table 40, corresponding to the vapor pressure thus 

 obtained, is the dew-point. 



Examples : 



1. Given / = 84°3; /, = 66.°7, and B = 2,0.00 inches, to find the vapor 



pressure and dew-point. 



Table 40, with t^ = 66^7, gives /, = 0,654 inches. 



Table 41, with t — t^ = 84f3 — 66.°7 = 17^6 and B = 30.00 inches 



as arguments, gives o.ig6 inch as the value of the last term 



of the expression above. Hence we have the vapor pressure 



/= 0.654 — 0.196 = 0.458 inch. The temperature (Table 40) 



corresponding to this value of/ is the dew-point, d = 56.°6 F. 



2. Given / = 34°5; /, = 29f4, and ^-^22.3 inches, tq find the vapor 



pressure and dew-point. 



Table 40, with /, = 29°4, gives/, = 0.162 inch. 



Table 41, with / — /, = 34f5 — 29^4 = 5!! and ^=22.5 inches (the 

 nearest value in the table to 22.3 inches) as arguments, gives 0.042 

 inch as the value of the second term of the expression for/ Hence 

 we have the vapor pressure/ = o. 162 — 0.042 = o. 120 inch. 



The temperature in Table 40, corresponding to this value of/ is the 



dew-point, fl^== 2 2.°o. 



« 



Note— In using Table 40, the proportional part for tenths of the argument, t-t„ 

 may be easily obtained by taking one-tenth of the tabular value belonging to the same 

 number of degrees ; for instance, in the first example, the tabular value for 17° is 0.189, 

 and the proportional part for o?6 is one-tenth the tabular value for 6?o, viz., one-tenth 

 of .066, or .007. Hence we get o. 189 4- 0.007 = o. 196. 



Table 42. Relative humidify — Te7nperature Fahrenheit. 



Table 42 gives the relative humidity of the air in hundredths, having 

 given the air temperature t and the dew-point d in Fahrenheit degrees. 



