Hygrometry, 25 
fidering the hygrofcopic phenomena of thofe fubftances, it ap- 
peared to me, that their changes of weight could not be pro- 
portional to the degrees of moijlure in the mediwn ; and that 
even the fenfe of the word moijlure applied to them was very 
difficult to determine (§ 14.). As for the fubftance of the 
hygrometer itfelf, I did not find any reafon to think, that its 
changes of weight could be more proportional to moijlure than 
its degrees of expanfon ; fince on thefe laft depended in part 
the quantity of water that could be admitted into its pores at 
each degree of moijlure in the air. 
39. Being thus difappointed in my firft fcheme, I thought 
of a more dired method, which was to ad on moijlure itfelf, 
by firft producing, in a glafs veflel containing an hygrofcope , as 
much drynefs as I could conceive poffible at that time, and 
then introducing into it fucceffive equal quantities of water , 
4 or which I had found a fure means without opening the vefleh 
But then again fome previous experiments deftroyed my confi- 
dence in that method; having found,— ift, That the evapo- 
rated water had a tendency to depofit itfelf againft the glafs 
by the fmalleft difference between the infide and outfide tem- 
peratures , even to the degree of becoming vifible on fome part 
of the veflel, long before I had any reafon to exped extreme 
moijlure. — 2d , That by the common temperature of my room, 
the hygrofcope in the veflel remained always at a confiderable 
diftance from its point of extreme moijlure , though the bottom 
of the veflel was covered with water ; and that it varied with 
the temperature ; which could not have happened if moijlure 
had been extreme . — 3d, That when I endeavoured to increafe 
moifure in the veflel by cooling it, I produced very often the 
contrary effed, at the fame time that a quantity of the diflemi- 
nated water gathered over the glafs. 
Vol. LXXXI. E 
40. As 
