304 



Royal Society : — 



December 6. — Sir Benjamin Brodie, Bart., V.P., in the Chair. 



The following communication was read : — 



" On the Determination of the Dew-point by means of the Dry- 

 and Wet-bulb Thermometers." In a Letter of Lieut. Noble, R.N., 

 of Toronto, to Charles R. Weld, Esq. 



Toronto, September 10th, 1855. 



My dear Sir, — The residts of the accompanying table for com- 

 puting the dew-point from readings of the dry- and wet-bulb thermo- 

 meters, are, as I believe you know, derived from observations taken 

 here during last winter by Mr. Campbell and myself: — 



Table for computing the Dew-point from Readings of the Dry- and 

 Wet-Bulb Thermometers. 



These results will be obvious at a glance ; but a few remarks 

 upon the instruments employed, and upon the degree of reliance to 

 be placed upon them, may not be uninteresting. 



The dry- and wet-bulb thermometers (for which we were indebted 

 to the kindness of Prof. Cherriman, Director of the Magnetic Ob- 

 servatorj', Toronto) were made by Negretti and Zambra, and their 

 index errors were ascertained, above 3::° by Mr. Glaisher, and below 

 32° by ourselves, by comparison with a Kew standard. The divi- 

 sions upon these thermometers were too small to read 0°-l with 

 great accuracy ; and in discussing our observations at low tempera- 

 tures, we were in consequence obliged to reject such as would, with 



