000 NOTES TO BOOK X. 



with their liquids, determined by Dr. Faraday, as men- 

 tioned in Note (QA), are analogous to the elasticity of 

 steam here spoken of. 



(UA.) p. 578. As a happy application of the Atmo- 

 logical Laws which have been discovered, I may mention 

 the completion of the theory and use of the Wet-bulb Hy- 

 grometer ; an instrument in which, from the depression of 

 temperature produced by wetting the bulb of a thermo- 

 meter, we infer the further depression which would pro- 

 duce dew. Of this instrument the history is thus summed 

 up by Prof. Forbes : " Hutton invented the method ; 

 Leslie revived and extended it, giving probably the earliest, 

 though an imperfect, theory; Gay-Lussac, by his excel- 

 lent experiments and reasoning from them, completed the 

 theory, so far as perfectly dry air is concerned; Ivory 

 extended the theory ; which was reduced to practice by 

 Auguste and Bohnenberger, who determined the constant 

 with accuracy. English observers have done little more 

 than confirm the conclusions of our industrious Germanic 

 neighbours ; nevertheless the experiments of Apjohn and 

 Prinsep must ever be considered as conclusively settling 

 the value of the coefficient near the one extremity of the 

 scale, as those of Ksemtz have done for the other,' 1 (Se- 

 cond Report on Meteorology, p. 101.) 



Prof. Forbes's two Reports On the Recent Progress and 

 Present State of Meteorology, given among the Reports of 

 the British Association for 1832 and 1840, contain a com- 

 plete and luminous account of recent researches on this 

 subject. It may perhaps be asked why I have not given 

 Meteorology a place among the Inductive Sciences ; but 

 if the reader refers to these accounts, or any other ade- 

 quate view of the subject, he will see that Meteorology is 



