S^S KYGROLOGY, AND ITS CON2JECTION "WITH METBOROLOGY. 



duce some moisture with it. This method was to enclose equal 

 quantities of wafer in very thin and small glass lullles, with a 

 neck drawn to a very small point, easily sealed with the flame of 

 a taper ; and before this last operation, I determined the 

 quantity of zvater that each contained, by a beam which indi- 

 cated lOOOlh part of a grain. These glass bubbles were placed 

 in the upper part of the vessel on a circular stand, and I had, 

 outwards at the top, a mechanism for breaking them without 

 opening the vessel. This method I applied to ihe glass vessel 

 above mentioned, 



18. Such were the means which I employed for ascertaining 



the quantities of evaporated water in a cubic foot of air, acting 



Mr. tie Saus- on the enclosed hygrometer. But these experiments required 



that raSls not ^""^^^^ condition, which Mr. de Saussure had already intro- 



condensed by duced in them : because those natural philosophers, who attri- 



«<^»y' bated rain to the moisture in the atmosphere, bad supposed, 



that this moisture was condensated by cold. Mr. De Saussure 



had sufficiently proved, that it was not the case, by observing 



the effects of the changes of temperature on his enclosed 



hygrometer. I was therefore to introduce the same condition 



,^ in my experiment, and for this purpose I enclosed also in my 



TTiermometer ,; .,x^,,., , -ri r • 



enclosed in the vessel a tkermometer with Fahrenheit s scale. Lastly, as I in- 



Tessel. tended to make the same observatioris on every successive grain 



of evaporated water, which would take a \ery long time j 



Extreme mo?s- having previously found that extreme moisture was produced in 



ture produced j|^g vessel by a small number of grains of water ; and even 

 feya few grains •' ^ ' 



<of water to a that they could not undergo great changes in the degree of 

 cubic foot of Jieaty without some water being deposited in the sides of the 

 The experi- vessel : this obliged me, in order to obtain the same tempera- 

 ments confined tures in the observations of the effects of each successive grain 

 to spring and ^ , . i i i i 



autumn for ot evaporated water in the vessel, to make these experiments 



uniformity of only in the spring and the autumn j because, in these seasons, 

 'I could obtain naturally almost every day in my room the tem- 

 peratures of 50, 55, 60 of Fahrenheit, on which I fixed for all 

 these experiments. By this method I was sure, that the tem- 

 perature would be always the same in every part of the vessel 

 it being that of the air in the room. 

 Tv/o series of J 9- I made two series of these experiments ; one beginning 

 (experiments jn the autumn of 1795, and ending in January, 1796 j the 

 other beginning in the autumn of 1796^ and terminating in 



February, 



