122 THE ROYAL SOCIETY OF CANADA 



humidity, absolute humidity and temperature, x, y and z respectively 

 (remembering that y could equally well be chosen to represent the 

 aqueous vapour pressure to which the absolute humidity is propor- 

 tional), we see that we are dealing with three quantities x, y and z, of 

 which X is an explicit function of y and z, and where y and z may be 

 determined experimentally but where x has to be calculated either 

 from y and z, or from quantities which depend upon them. Under 

 these circumstances it is clear that good reason should be shown 

 before it is taken for granted that x and z should be considered as 

 standard quantities, leaving y for recalculation if required. As such a 

 course is, however, followed, it is certainly uselessly involved unless it 

 can be proved that x is of paramount importance compared to y. 

 In our case it can, therefore, be understood clearly that the term 

 relative humidity should not reasonably be adopted as a standard 

 quantity unless definite proof is forthcoming to show that advantages 

 accrue from such procedure. 



Such advantages should occur, in the classification and study of 

 humidity phenomena, in the method of expressing humidity conditions 

 for chemical and physical problems, and in the choice, for meteoro- 

 logical records, of the best physical quantities for indicating atmo- 

 spheric conditions. These advantages are not, however, apparent. 



In the classification and study of humidity phenomena, the term 

 appears to lead to confusion rather than to simplification. It is met 

 first as a source of difficulty in the question of student instruction — 

 the average student is always perplexed about humidity, and the 

 lecturer finds clarity of explanation difficult to achieve. Concentrat- 

 ing unduly on the relative humidity, the student must appreciate, for 

 example, how on the one hand with a constant amount of aqueous 

 vapour in the air, the relative humidity may vary from a very high 

 per cent out of doors to a very low per cent indoors,^ and how on the 

 other hand with varying conditions of both moisture content and 

 temperature, the relative humidity may under certain circumstances 

 remain stationary. Further, the simultaneous treatment of satura- 

 tion and vapour pressure with their respective variations, usually 

 increases the difficulty. The general result has been, not only that 

 elementary students have found the matter perplexing, but that many 

 writers and investigators have retained vague conceptions, and have 

 obscured the essential points of important problems by the unneces- 

 sary emphasis they have laid upon this secondary quantity. 



'Under the winter climatic conditions of Eastern Canada it is quite common to 

 find the indoor relative humidity over sixty per cent less than the outdoor relative 

 humidity, in spite of the fact that there is at that time usually a larger absolute 

 humidity inside. 



