204 W. MAREIOTT — REDUCTIOX OF METEOROLOGICAL OBSERVATIONS. 



therefore require to be distributed through the intermediate degrees. 

 Example : Suppose the corrections to bo at 



32° 42° 51° 62° 72° 82° 02° 



_0-2 —0-2 —0-1 —01 —0-2 —0-3 —0-3 



they shoukl be distributed as follows : 



32° ) 47" ) 67° ) 77° ) 



to } — 0-2 to —0-1 to —0-2 and ^—0-3 



47 ) 67 ) 77 ) above ) 



From the readings of the dry- and wet-bulb thermometers can be 

 deduced the temperature of the dew-point, the elastic force of 

 aqueous vapour, and the relative humidity. Glaisher's ' Hygro- 

 metrical Tables ' '* are those in general use in this country for 

 making these deductions, and they should be in the possession of 

 the observer for reference. 



I have devised a table, f based on Glaisher's factors, by which 

 the dew-point can be quickly calculated at inspection fi-om the 

 readings of the dry- and wet-bulb thermometers (see Table V.). 

 It is intended only for such readings as are ordinarily observed in 

 this country, viz. between 30° and 79°. 



The arrangement of the Table is as follows : — The first column 

 on the left gives the reading of the dry-bulb thermometer for 

 every degree from 30° to 79°. The other columns give, for each 

 degree of difference between the readings of the dry- and wet-bulb 

 thermometers, the amount to be subtracted from the reading of the 

 ■wet-bulb thermometer to obtain the temperature of the dew-point. 

 The amounts for tenths of degrees can of course be at once obtained 

 by merely shifting the decimal point one place to the left. 



The following examples will show the manner of using the 

 Table : — 



(1). Suppose the reading of the dry-bulb thermometer ° 



to be 50-0 



And the reading of the wet-bulb thermometer to be 450 

 The difference is ... ... ... 5'0 



On looking at the Table, we find the amount to be subtracted 



from the reading of the wet-bulb thermometer is ... 5-3 



Therefore the dew-point is, 4 5° — 5° -3 397 



(2). Suppose the reading of the dry-bulb thermometer 



to be ... ... ... ... ... ... 55-5 



And the reading of the wet-bulb thermometer to be 48-3 

 The difference is ... ... ... 7*2 



On referring to the Table, we see the amount to be sub- 

 tracted for 7°-0=6°-7, and for 0°-2 = 0°-19, say 0°-2, giving 

 6°*9 as the total amount to be subtracted from the reading 

 of the wet-bulb thermometer. 

 Therefore the dew-point is, 48°-3 — 6°-9 41-4 



* ' Ilygronietrical Tables adapted to the Use of the Dry- and Wet-bulb 

 Thermometer.' By James Glaisher, F.R.S. Filth edition. London, 1869. 



t ' Table for facilitating the determination of the Dew-point from observations 

 of the Dry- and Wet-Bulb Thermometers.' Loudon, 1874. 



