52 Meteorological Observations, [Jan. 



of a centigrade degree, that is, for the degrees of the mille- 

 simal scale. This table enables us, by a simple observation 

 of the dry and wet bulb themometers, to ascertain the 

 dew point, the dryness, and the actual quantity of moisture 

 in the air ; and the nfiode of using it will be readily understood 

 from the following examples. Suppose the wet bulb thermo- 

 ineter to mark 15.1, and the dry thermometer, at the same 

 time, to stand at 19.0, the difference will be 3.9, which must 

 be considered as a whole number. Look in the table for 

 temperature 15.1, and opposite to it in the column of mois- 

 ture will be found 200.9, from which subtract the above 

 number 3.9, the remainder 161.9 is the exact quantity of 

 moisture in grains in a cubic mass of air 40 inches everyway. 

 Look now in the column moisture for the nearest number to 

 161.9, and it will be found to be 161.7, and opposite to it is 

 the temperature 10.4, which is the dew point. Now to find 

 the dryness, search the table for temperature 19.0, and itwill 

 be seen to correspond to the number 240.6, in the adjoining 

 column, from which subtract 161.9, and the remainder 78.7, 

 will be the dryness, or the number of grains of moisture it 

 would be necessary to add, to render the air prefectly damp. 

 Let us take another example. 



Dry thermometer 24.0 



Wet bulb thermometer. . 19.5 difference 45. 



19.5 in table 246.9 



Subtract 45 



2(i\, 9 quantity of moisture 



201.9 in table. 15.2 dew point 



24.0in table. .. ....303.1 



Subtract 201.9 



101.2 dryness. 



Since the condition of the air, in relation to moisture, must 

 be always regulated, in a certain measure, by the temperature, 

 it is not improbable that we may obtain an approximation to 

 the average of the dew point, moisture, and dryness of the 

 air for the whole 24 hours^ by taking the mean of 10 .A m. 



