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ROYAL SOCIETY OF CANADA 



However, in table No. 3, wherein comparisons between chemical 

 estimation and a good wet and dry bulb instrument are made, several 

 points stand out prominently. 



In most of the instances the chemical results are lower by about 



The regularity of these differences is striking; but it will also be 

 noticed that this only applies for moderately low degrees of humidity, 

 e.g., 25-40^, below that the differences become erratic. 



At higher degrees, the correspondence becomes closer and closer until 

 we reach the region of 70-100 per cent, when the results of both methods 

 of obsei-vation coincide fairly well. 



TABLE IIL 



In table No. 3, column (a) is the vapour pressure in inches, of the 

 water vapour actually present in the air at the time of observation; 

 ascertained by chemical hygrometer; column (b) is the relative humidity, 

 calculated from column (a). 



Column (c) is the direct reading by the hygrodeik and column (d) 

 is tlie relative humidity calculated from an ordinary wet and dry bulb 

 instrument by using Glaisher's tables. 



The wet and dry bulb instrument was simply subjected to the 

 ordinary air currents in the room, and therefore represents the instru- 

 ment as used under ordinary conditions. 



