599 



TABLE 633.— MAINTENANCE OF AIR AT DEFINITE HUMIDITIES 



The relative humidity and vapor pressure of aqueous vapor of moist air in equilibrium 

 conditions above aqueous solutions of sulfuric acid are given below. 



TABLE 634.— PRESSURE OF AQUEOUS VAPOR IN THE ATMOSPHERE 



For various altitudes (barometric readings) 



The amount of water vapor in the atmosphere may be determined by the use of the 

 wet-bulb-dry-bulb hygrometer. 



The first column gives the depression of the wet-bulb temperature ti below the air tem- 

 perature t. The value corresponding to the barometric height at the altitude of observation 

 is to be subtracted from the vapor pressure corresponding to the wet-bulb temperature 

 taken from Part 3, Table 635. The temperature corresponding to this vapor pressure 

 taken from Part 3, Table 635 is the dew point. The wet bulb should be ventilated about 

 3 meters per second. For sea-level use Table 640. Example : t = 35°, U = 30°, barometer 

 74 cmHg. Then 31.83 — 2.46 = 29.37 mm = aqueous vapor pressure; the dew point is 

 28.6°C. 



SMITHSONIAN PHYSICAL TABLES 



