HYGROLOGY, AND ITS CONNECTION WITH METEOROLOGY. QQJ 



zvater in hii5 vessel : it certainly could not be very exact ; but 

 it v^7as sufficiently so, for the final and most important conclu- 

 sions of a first attempt of these experiments. However, these 

 objections had rendered the greatest number of experimental 

 philosophers inattentive to this great step concerning meteoro- 

 logy, so that it was almost forgotten. This was my first motive 

 for undertaking the same experiments with the precautions 

 above explained. 



15, I found this attempt much more dirficult than I had The experi- 

 expected ; for it cost me more than two years in useless trials, 



for obtaining, first, a vessel which would remain air-tight 

 during all the time that these experiments should require. At 

 last, however, I succeeded, and the experiments themselves 

 took me after\^ard more than one year. These experiments j^gjated ;„ ^ 

 are related in a work which I published at Paris, in 1803, French work, 

 under the title of Traite ilimentaire sur les Fluides expansibles : 

 but on account of the present circumstances of Europe, and 

 this work being in Frsnch, a few copies only are come to Eng- 

 land. This, Sir, makes me desirous to consign to your Journal 

 a short account of these experiments. 



16. My purpose was to ascertain what quantities of Object of the 

 evaporated water in a known \space of air corresponded to ^ 



each degree of my hygrometer; and I determined, that this 

 space should be one cubic Joot. My first success in overcoming 

 the difficulties was that of obtaining a vessel, which would vessel for ma- 

 remain air-tight during the whole course of these experiments, king themm, 

 I found, that no vessel could be rendered air-tight so long, 

 which had a large opening at the top 5 and that therefore this 

 opening should be only what was necessary to introduce the 

 instruments into it. I then procured a glass vessel, about 23 

 inches high, and 85 in diameter, the opening of which at the 

 top was only 2^ inches in diameter, I measured the capacity 

 of this vessel ; it was not quite one cubic foot ; but I ascer- 

 tained the difi:erences to which I was to proportionate the quan- 

 tities of evaporated water, so that they might be as ] grain in a 

 cubic font. 



17. Before that time, I had found a sure method of ascer- Method of as- 

 certaining the 

 laining the quantities of water successively evaporated m a ves- quantity of 



sel, without opening it: in order to prevent any exchange of ^^^^'^'■.^^^P°" 

 i-iii 11, rated in a ves- 



the internal with the external air, lest the latter should intro- sd with cer- 



duce tainty. 



