470 



I have made a great number of experiments with my modification 

 of the condensing Hygrometer, for the purpose of contrasting the dew- 

 points observed by it with those determined by the wet bulb Thermo- 

 meter. The following Table contains a selection of them, many being 

 rejected on account of obvious mismanagement, mistakes, or doubts : — 



Table IY. 



1 GmpGr3.tu.rG 

 of 

 the Air. 



1 tlliptlut U.X V 



of 



Wet Bulb. 



Dew Point 

 calculated Co- 

 efficient 88. 



Dgw Point 



by 



Condenser. 



o 



o 



o 



o 



52-28 



455 



37-5 



37-76 



60-10 



55-5 



52-7 



52-12 



63-5 



57-5 



53-2 



53-2 



59-5 



52-5 



46-5 



46-5 



60-25 



55-5 



52-25 



52-0 



61 -2 



58 



56-1 



56-5 



66 



58 



52-36 



52 



63 



57-5 



55 



53 



66-5 



■ 57 



52 -38 



52-5 



64-5 



58 



53-56 



535 



62-5 



55-75 



50-75 



505 



57-75 



54-5 



52 



52-25 



64 



57-0 



52-15 



52-25 



60-5 



55 5 



51-8 



52-25 



59 



54 



50-1 



52-25 



57-5 



54-75 



53 1 



52-75 



60-25 



56 



53 



53 



63 



56-5 



51-75 



52 



51-5 



50-2 



49 



49-5 



52-5 



50-75 



49-3 



49-3 



52 



50-5 



49 3 



49-5 



51-5 



50-5 



49-6 



49-5 



60-75 



59-5 



42-8 



42 



The condensing Hygrometer, founded as it is on an universally 

 admitted principle, is no doubt, when carefully made, skilfully ma- 

 nipulated, and correctly observed, a reliable instrument for obtaining 

 accurate information of the hygrometric condition of the atmosphere. 

 The material employed as the indicator of atmospheric moisture by 

 Le Roy, Dalton, and Daniel! was glass, an hygroscopic substance 

 in its own nature, and used as such in the Hygrometer of Hoch- 

 heimer. But glass complicates, although in a very slight degree, 

 the evidence of the instrument, by bringing chemical affinity into 

 operation, and so far resisting evaporation, which, in this case, ought to 

 be the only agent concerned. Polished silver is a much more perfect 

 indicator than glass. It was first used half a century since by the 

 author of the article "Hygrometry," in the " Edinburgh Encyclopaedia," 

 and afterwards by Regnault and others. The advantages of Regnault's 



