Hygrometry . 3 r 
of thofe in length of the other hygrofcopes , having not had 
time to make the neceffary calculations, of which however I 
have the data . 
48. The neceffary time for a complete diffufion of the newly 
introduced moijlure in the veffel renders it impoflible to proceed, 
in that introdudion, by regular fteps. The method I ufe is, 
to obferve the motion of my ufual hygrometer , which is a Jlip of 
whalebone , and to remove the caufe of increafe of moiflure be- 
fore it has moved 5 degrees. In that manner the fteps of the 
increafing moiflure have been in general lefs than 5 degrees of 
that inftrument ; but, by interpolation, I have reduced them 
to what they would have been if the fame inftrument had 
been moved fucceffively 5 degrees. 
49. I have faid before, that when the maximum of evapora - 
tion is produced in a clofe veflel by a temperature fenfibly 
above the freezing point, there is no regularity to be expeded in 
any farther attempt to increafe moiflure ; the diffeminated 
water being then abundant, the fmalleft difference of tempe- 
rature between different parts of the apparatus makes it depofit 
itfelf on fome furface, and pafs from one to the other (§ 39.) ; 
which circumftance is alfo mentioned by Profeffor Picte t of 
Geneva, in his late work, EJfais de Phyfque . For that rea- 
fon, when the evaporated water in the veffel was near its maxi - 
mum, my laft operation was, to putin again the wet cloth, while 
I kept the temperature at 6o°, and to take it out when the indices 
of the beams were fixed. My ufual hygrometer was then at 
87°; and as it had ftill 13 degrees to move towards its point of 
extreme moiflure , and all the others in proportion of their known 
marches , I have added to the obferved increafes of weight in 
the JhavtngSy a quantity proportional to their former marches 
2 comparatively 
