. Preventive medicine and hygiene. l also gives only a very gen-eral indication of the humidity of the atmosphere. A place with highrainfall may have low absolute and relative humidity, and vice versa;that is, a rainy district is not necessarily a damp district, so far as the•atmosphere is concerned. Dew also bears no constant relationship to the humidity of the atmos-phere, for a clear sky and a dry atmosphere favor its formation. Aircontaining mist is obviously moist. Methods of Determining Humidity in the Air.—The amount of watervapor in the air may be determined either by (1) weighing, (2)
. Preventive medicine and hygiene. l also gives only a very gen-eral indication of the humidity of the atmosphere. A place with highrainfall may have low absolute and relative humidity, and vice versa;that is, a rainy district is not necessarily a damp district, so far as the•atmosphere is concerned. Dew also bears no constant relationship to the humidity of the atmos-phere, for a clear sky and a dry atmosphere favor its formation. Aircontaining mist is obviously moist. Methods of Determining Humidity in the Air.—The amount of watervapor in the air may be determined either by (1) weighing, (2) psy-chrometers or hygrometers, (3) the dew-point. Weighing.—The amount of moisture in the air may be determinedby passing a given volume of air through a tube or flask containing anhygroscopic substance, such as calcium chlorid or sulphuric acid. Ifsulphuric acid is used small flasks are filled with pieces of pumice whichhave been heated to a high temperature over a Bunsen burner, and 694 PEESSUEE, TEMPEEATUEE, AXD HUMIDITY. r Fig. 86.—Slingpstchkometeh. dropped while liot in concentrated sulphuric acid; re-moved, and quickl}^ drained. The increase in weight represents the amount ofmoisture in the volume of air passed through thefiasks, or the absolute humidity. Knowing the tem-perature of the air, it is then easy to determine therelative humidity by reference to tables of maximumwater capacity for certain volumes of air at varyingdegrees of temperature. PsYCHROMETERS.—The most convenient of allmethods for measuring atmospheric moisture is toobserve the temperature of evaporation, that is, thedifference between the temperatures indicated by wetand dry bulb thermometers. The United StatesWeather Bureau regards the sling psychrometer as themost reliable instrument for this purpose. In specialcases rotary fans or other means may be employed tomove the air rapidly over stationary thermometerbulbs. The sling psyclirometer consists of a pair of ther-mometers provided with
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Keywords: ., bookauthorwh, bookcentury1900, bookdecade1910, booksubjecthygiene
