Tables of physical and chemical constants and some mathematical functions / by G.W.C. Kaye and T.H. Laby.

  • G. W. C. Kaye
Date:
1911
Catalogue details

Licence: Public Domain Mark

Credit: Tables of physical and chemical constants and some mathematical functions / by G.W.C. Kaye and T.H. Laby. Source: Wellcome Collection.

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    HYGROMETRY Relative humidity = RELATIVE M* IPX HUMIDITY AND DEW-POINT . ico, where [p\ is the actual pressure of water-vapour at temperature /°, and is equal to [Pjd/>, the saturated vapour-pressure at the dew¬ point (dp) ; [pjf is the pressure of saturated vapour at t°. For a table of saturated water-vapour pressures, see p. 40. (See “Smithsonian Meteorological Tables.”) Percentage relative humidities for different dew-points and dew-point depressions are tabulated below. Dew-point Depression of dew-point = t°—(dp)°. (dp). o°c. 1° 2° 3° 4° 5° 6° 7° 8° 9° O © tH 12° 0 H 16° 18 - 15° C. 100 92 85 79 73 67 62 58 53 49 46 39 34 29 26 0 ICO 93 87 81 75 70 65 61 57 53 5° 44 38 34 30 + 10 IOD 94 88 82 77 7 2 68 64 60 56 53 47 4i 37 33 20 100 94 89 83 78 74 70 66 62 58 55 49 44 39 35 30 100 94 89 84 80 75 7i 68 64 61 57 52 46 42 38 WET AND DRY BULB HYGROMETER Apjohn (1835), August (1825), and others, by making various assumptions (some of doubtful legitimacy), have derived formulas of the type— IPX, ~ iPlt = AH(/ - 4) [1 + B(7 - 4)] where t is the temperature of the dry bulb, 4 that of the wet, [p]t is the actual pressure of water-vapour in the air (at temperature 7), [J>X is the saturated vapour pressure of water at the temperature (4) of the wet bulb, H is the barometric height, and A and B are constants. (See Preston’s “Pleat.”) The indications of this hygrometer are so dependent on its environment that for most purposes B may be taken as zero, and H as constant, say 760 mms. If H is measured in millimetres, and temperatures in Centigrade degrees, the following values of A are suitable for the conditions mentioned :— A = *0007 if wet bulb is caused to swing for a short time. A = *00075 *n a Stevenson screen as used by Meteorological Office. A = *0008 in open air with slight wind. A = *0009 in open air with no wind. A = *ooi in a small closed room. Rizzo (1897) takes A = '00075 and B = — *008, and the table below is derived by employing these values. [pjw can be got from the table of saturated vapour pressures on p. 40, and thus the desired vapour pressure [p\ can be determined. VALUES OF [/]’ - [fi\ (Rizzo) Barom. Difference of temperature of dry and wet bulb thermometers (t — tw). Press. H. 1° C. ' 2° 3° 4° 5° 6° 7° 8 9° 10° mm. mm. mm. mm. mm. mm. mm. mm. mm. mm. mm. 770 •57 1*13 1*69 2*23 2*78 3*30 3*81 4*32 4*87 5*31 760 *56 1*12 1*67 2*20 2*74 3-25 3*76 4*27 475 5*24 750 •55 I'll 1*65 2*17 2*71 3*21 37i 4*21 4*69 5*i7 730 •54 ro8 1*60 2*12 2*63 3*12 3*61 4*10 4*56 5'°3 700 *52 1*03 1*54 2*03 2*52 3*00 3'46 3‘93 4‘37 4*82 670 •50 '99 1*47 1*94 2*42 2*8 7 3‘32 376 4‘J9 4*62 11° c. 12° 13° 14° 15° 16° 0 H M CO 0 19° 20° 770 5*78 6*26 6*72 7*i7 7* 62 8*06 8*47 8*89 9*30 969 760 5*71 6*18 6*63 7*08 7*52 7*95 8*36 8*77 9* 18 9*56 750 5*63 6*09 6*54 6*98 7*42 784 8*25 8*66 9*06 9*44 • 730 5*48 5*93 6*37 6*79 7*22 7*63 8*03 8*43 8*82 9* 18 700 5*26 5*69 6*i 1 6*52 6*93 r 32 770 8*o8 8*46 8*82 670 | 5‘°3 5*44 5*84 6*24. 6*63 7*01 7'37 773 8*o8 i 8*43
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