HYGROLOGT^ AND ITS CONNECTION WITH METEOROLOGY. 2^9 



February, 1797 : each of them began by producing extreme 

 dryness in the vessel, and proceeded by the evaporation of suc- 

 cessive grains of water ; observing afterward the changes pro- 

 duced on the %^ro7??e/er at the thi«e fix?d temperatures. In The vesse! re- 

 the course of these experiments I bad a proof, that the vessel mainedair- 

 ren;iained air-tight. For in order to ascertain the effects of the ^'^^^" 

 increase of water at the three temperatures, I consecrated many 

 days, even weeks, to the observation of each step, by repeating 

 it many times; which made both sets of experiments last near The expen- 

 6 months: however, 1 found no sensible difference in these "^ents many 

 observations from the first to the last day, with every quantity t'"'-" ^^P^^'^"*. 

 of water ; and in ending thera, I had an immediate proof, 

 which it would be too long- here to explain, that the aqueous 

 vapour, which had been produced in the vessels, had added its 

 expansibility to that of the air originally enclosed in it. 



20. This, I think, was a complete determination of the cor- Rules of hy. 

 respondence between the degrees of my hygrometer, and the duced fromdier 

 quantities of evaporated water in one cubic foot of air, at the exp.t;rimenu. 

 observed degrees oi heat. I then undertook to derive from 



these experiments general rules of /iyffrome^r^/. These deduc- 

 tions begin at p. 325, of the 2d vol. of the above-mentioned 

 work ; they are given in 13 successive, tables, of which I shall 

 only mention two. 



21. In tcible ii. are united the results of both experiments, 

 (which differ very little from each other), reduced to their 

 mean terms. Each set began at the point of extreme dryness in 

 the vessel ; a point where the hygrometer stood at in both. 

 At that point, no moisture being in the vessel, the change of 

 heat from 50 to 00 of Fahr. produced no change in the hygro- 

 meter. During both sets of experiments, the limits of the Limits of eva- 

 evaporation in the vessel were the same: 5 grains only oi water f "'^^^"."^05/ 

 could remain evaporated at the temperature of 50 ; 6 grains at ratures. 



that of 55, and 7 grains at 60. Beyond these quantities, at the 

 respective temperatures, a certain quantity of tt'a/cr was depo- 

 sited on the sides of the vessel in the form of dew j but when 

 tl^is effect took place at the temperature of 50, the dew was 

 dissipated when the heat of my room came to 55 ; and when 

 it happened at 55, it was dissipated when the heat in the room 

 arrived at 60. 



22. Thus therefore we have the natural limits of the quanti- 



ties 



