208 ROYAL SOCIETY uF CANADA 



On arriving in the laboratory on February 3rd, after a clear, cold 

 night, a small cheap indicating hygnometer of the spiral type, was ob- 

 served to be reading nearly zero humidity. This instrument had been 

 carefully calibrated over its entire scale some time previous and had been 

 then set correctly. It may be stated that this instrument was selected 

 from a lot of half a dozen sent to us on trial, all of which were found 

 entirely wrong, not only in reading but what was worse in range. The 

 reading may always be corrected easil}^, but the range is a much more 

 serious matter to adjust without injury to the delicate spiral. 



It was decided to check this low reading by means of a reliable in- 

 strument. The Eegnault hygrometer was accordingly used and a 

 telescope provided for (observing the appearance and disappearance of the 

 film of moisture on the silver bulb containing the ether. The dew point 

 was found to lie between 10.5° F. and 11. C^ F., and was clearly defined 

 between these limits. The maximum and minimum air temperature 

 was given for that date as + 11.5°F., and — 13.S°F. The relative 

 humidity calculated from the dew point was only 9 per cent, and showed 

 that the dryness of the air was very great indeed, and that the spiral 

 hygrometer was nearly correct. 



The four following days were cold and clear, as shown by the follow- 

 ing temperatures in Fahrenheit degrees: 



Everything was conducing to excessive dryness as was shown on the 

 morning of the 7th in the labioratory when a comparison was made of the 

 various hygrometers we possessed. 



The Eegnault hygrometer gave a dew point of 3.75°F. (limits of 

 appearance and disappearance of mist — hoar frost — 3.5° and 4°F.), 

 which is above the mean air temperature. This shows that the air was 

 dryer than the materials in the laboratory, some moisture being im- 

 parted to the air on account of this. 



The relative humidity calculated from this observation is 6.25 per 

 cent. The spiral hygrometer showed 5 per cent humiditn% but the in- 

 dications of the wet and dry bulb hygrometer of the stationary type were 

 interesting. The dry bulb registered 69 °F., and the wet bulb 57°F., 

 showing a difference of 12°F., or 6.4° C. This gives a relative humidity 

 of 45 per cent; this was at the same time as the other hygrometers gave 

 5 and 6.25 per cent respectively. 



