RATIO OF EVAPORATION TO HUMIDITY. 33>7 



Consequently the evaporation in air perfectly dry is to 

 the evaporation in air that contains Z cubic lines of water 

 in the cubic foot, at the same temperature X, in the ratio 

 X X 



Of (2-718) U ° 5 to (2,718) n '° 5 _ A. 



I have concluded from various experiments, that, by in- Formula for 

 creasing the linear factor of the formula of evaporation * ca,cu ? ati,1<; eva " 



° ' poration at any- 



one fifth, this formula would pretty accurately represent temperature 



the evaporation in air perfectly dry. If we make this eori J£ d Jj™ Jjj* ity 

 rection, and reduce to lines by multiplying by the propor- 

 tion Jj\j, confining ourselves to two decimal places, this 



X 



formula will become (A) . ; . . (272) ° (0-34 lines) 



X 



consequently f (272) — J (0-34 lines) is the 



formula, that gives the value of the evaporation, or low- 

 ering of the surface, of water expressed in lines, that takes 

 place in twenty-four hours in air at the temperature of X 

 degrees of De Luc's thermometer, and which contains Z 

 cubic lines of water in the cubic foot. The calculation of 

 the last formula is very simple; since it is sufficient, to de- 

 duct from the quantity calculated by the formula (A) the 

 quantity Z (0 03 of a line); to which is reduced the effect 

 of the humidity of the air. 



To facilitate the application of this formula, nothing is Desideratum. 

 requisite but a more convenient and speedy mode of deter- 

 mining the number of cubic lines of water diffused in a cubic 

 foot of air than that of drying this air by potash or quick- 

 lime, and then finding the increase in weight of the latter. 

 I have sought this, which would lead, as has been seen, to 

 the discovery of a true hygrometer ; but my endeavours have 

 not been more successful, than those of the celebrated natural 

 philosophers, who have paid attention to the same subject. 



The imperfection of these researches has been the reason 

 that I have so long deferred publishing them. I was still in 



* Journ. de Phys. vol. LXV, p. 452 : or Journ. vol. XXVlf, 

 p. 23. 



Vol. XXXII. Supplement. 2 A hope* 



