210 



ROYAL SOCIETY OF CANADA 



results of the wet and dry bulb hygrometers and the exact chemical 

 estimations of the water vapour in the atmosphere at the same time: 



EELATIVE HUMIDITIES: 



Simultaneous Observations hy the Two. Methods. 



The first six observations were taken on different days at very irre- 

 gular intervals extending over six weeks. The wet and dry bulb 

 thermometers were suspended in the middle of tiie laboratory where only a 

 slight current of air obtained. The disparity in the results here are 

 extremely striking and from the few figures obtained tone cannot deduce 

 any corrections applicable to the wet and dry bulb instruments. Where 

 the humidity is about 70 to 80 per cent the results apparently are not 

 Very far from the accurate condition of the humidity, but with a fairly 

 still atmosphere and a low percentage of moisture the results of the wet 

 and dry bulb instrument varied tremendously, being out on an average 

 20 per cent. 



The last four observations, namely, Nos. 7, 8, 9, and 10, are inter- 

 esting being all taken on the same day, 7 and 8 taken in the morning at 

 a two-hour interval, the wet and dry bulb instrument being placed under 

 still conditions as above mentioned. Here again the discrepancy is 

 about 20 per cent as before. In ITos. 9 and 10 observations were taken 

 in a very marked draught of air, the instruments being placed in the 

 draughts from three large open windows and one would not be far short 

 of the mark by saying that the conditions were almost identical with 



