Hygrometrical tables : adapted to the use of the dry- and wet-bulb thermometer / by James Glaisher.

  • James Glaisher
Date:
1869
Catalogue details

Licence: Public Domain Mark

Credit: Hygrometrical tables : adapted to the use of the dry- and wet-bulb thermometer / by James Glaisher. Source: Wellcome Collection.

    14/62
    Before use, the cotton lamp-wick should be washed in a solution of carbo- nate of soda, and pressed whilst under water throughout its length. In use it should be of such extent that the water conveyed be sufficient in quantity to keep the muslin on the bulb as moist as when the air is saturated with va- pour. The amount of water supplied can be increased or diminished by in- creasing or decreasing the extent of the conducting-thread. In observing, the eye should be placed on a level with the top of the mer- cury in the tube ; and the observer should be careful to refrain from breathing whilst taking the observation. Temperatures of the Air and of Evaporation are given by the readings of the two thermometers. Temperature of the Dew-Point. If a mass of air be gradually cooled, it will descend to a degree of tempe- rature at which, it will be saturated by the quantity of vapour then mixed with it. This temperature is called the dew-point. It can be found directly by the use of either Daniell’s or Regnaulfs Hygrometer, or by the use of the dry- and wet-bulb thermometers noth these Tables. Determination of the Dew-Point from observations of the Dry- and Wet-bulb Thermometers. Table I.—Factors by which it is necessary to multiply the excess of the reading of the dry thermometer over that of the wet, to give the excess of the temperature of the air above that of the Dew-Point, for every de- gree of air-temperature, from 10° to 100°. Reading of Diy-Bulb Therm. Factor. Heading of Dry-Bulb Therm. Factor. Reading of Dry-bulb Therm. Factor. Reading of Dry-bulb Therm. Factor. o IO 878 O 33 3*oi 0 56 1'94 0 79 i-69 II 878 34 277 57 1*92 80 i-68 12 878 35 260 58 I '9O 81 i-68 i3 8-77 36 2*50 59 1^89 82 1 '67 I •- 876 37 2*42 6o* i;88 83 1-67 iS 875 38 276 61 i's7 84 166 16 870 39 2*32 62 i-86 85 165 ll 8-62 40 2’29 63 1-85 86 1-65 18 8-50 41 2*26 64 i's3 87 i'64 19 8-34 42 2*23 65 i 82 88 1 64 20 S'i4 43 2’20 66 i-Si 89 163 21 7-88 44 2‘l8 67 i-8o 90 1 63 22 7 60 45 2-i6 68 179 91 1-62 23 7'28 46 2*14 69 178 92 162 24 6'92 47 2'1 2 70 177 93 1 -61 25 6 53 48 2*10 7i 176 94 i'6o 26 6-o8 49 2'o8 72 175 95 i-6o 27 5'6i 50 2-o6 73 174 96 r59 28 S-I2 9* 2*04 74 173 97 ,-59 a9 4-63 52 2*02 75 172 98 1-58 30 4-' 5 53 2*00 76 171 99 i'5s 31 37° 54 rgS 77 170 IOO 1 '57 32 3'32 55 1’96 78 r69 The numbers in this Table have been found from the combination of many thousand simultaneous observations of the dry- and wet-bulb thermo- meters with DanielFs Hygrometer, taken at the Royal Observatory, Green- wich from the year 1811 to 1851, with observations taken at high temperatures in India, and others at low and medium temperatures at Toronto. The results