Text-book of hygiene : a comprehensive treatise on the principles and practice of preventive medicine from an American standpoint / by George H. Rohé and Albert Robin.

  • Rohé, George H. (George Henry), 1851-1899.
Date:
1908
Catalogue details

Licence: Public Domain Mark

Credit: Text-book of hygiene : a comprehensive treatise on the principles and practice of preventive medicine from an American standpoint / by George H. Rohé and Albert Robin. Source: Wellcome Collection.

Provider: This material has been provided by the Augustus C. Long Health Sciences Library at Columbia University and Columbia University Libraries/Information Services, through the Medical Heritage Library. The original may be consulted at the the Augustus C. Long Health Sciences Library at Columbia University and Columbia University.

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    to appropriate instruments, would be considered as ''dry at the latter temperature, although the actual amount of vapor present, or absolute humidity, is the same in both cases. In meteorological observations for sanitary purposes, the relative humidity is the condition deserving especially careful study. It must be borne in mind that the mere statement of the per- centage of relative humidity, without taking into account the tem- perature of the air, is of little significance. A ]ike remark is justi- fied with regard to statements of absolute humidity, when used to illustrate the apparent effects of atmospheric moisture upon life and health. The following table shows the absolute humidity correspond- ing to the same relative humidity at different temperatures. It also includes the total possible absolute humidity and the difference be- tween the actual and possible humidity (deficiency of saturation) at the temperatures given:— Table II. Tempera- ture °C. Relative Humidity (percent). Absolute Humidity (grammes per cubic metre). Greatest Possible Absolute Humidity. Deficiency of Saturation. —20 —10 0 -flO 20 30 60 60 60 60 60 60 0.638 1.380 2.924 5.623 10.298 18.083 1.064 2.300 4.874 9.372 17.164 30.139 0.426 0.920 1.950 3.749 6.866 12.056 In forests the relative humidity is usually higher than over un- wooded districts, although the absolute humidity may be the same, or, perhaps, even less. The evaporation is usually much greater in the open air than in forests. In closed apartments the evaporation may be greater or less than in the open air, depending upon the local conditions present. ^By absolute humidity is meant the total amount of vapor present in a certain mass of air. By the term relative humidity meteorologists designate the proportion of vapor present at certain temperatures, compared with full saturation of the air Avith vapor, which is reckoned 100. Thus, air which is satu7-ated, or whose relative humidity is 100 at 4°, would have a relative humidity of only 24, if the temperature were raised to 27°, because in the latter case the capacity of the air for aqueous vapor is increased. Relative humidity is always desif^Tiated in percentages; absolute humidity in grammes per cubic metre or grains per cubic foot.