C 41s ] 
abfolute capacity of the cup remained larger than it 
was before. 
28. To fatisfy myfelf about this, I got another 
wooden cylinder, which filled the capacity of the 
veffel in its prefent ftate. This I again put into the 
water, and left it there a fufficient time ; I then ex- 
pofed it to the air to be dried ; and after that found 
that the wooden cylinder filled it as before. Hence 
I concluded, that in the conftruCtion of my hygro- 
meter the ivory cup fhould be dipped for fome time 
in water, and afterwards dried, before it was ufed. 
29. Thus having cleared up my conjectures, as 
much as they could be, by thele preliminary experi- 
ments, and got fome infight into the proportions of 
the different parts of the machine, I proceeded to its 
conftruction, and finifhed it in the following manner: 
Drfcription of an Hygrometer. 
30. Tab. xvin. figure 1. fhews the feCtion of the 
inferior part of the inftrument, of its true length, in 
the direction of its axis. 
The firft part to be defcribed, being in fome mea- 
fure the foul of the hygrometer, is an ivory tube, 
aab , open at the end a a, and clofed at b . It is 
made of a piece of ivory, taken at the diftance of 
fome inches from the top of a pretty large elephant’s 
tooth, and likewife at the fame diftance from its fur- 
face, and from the canal which reaches to that point 
(68). This piece is to be bored exaCtly in the di- 
rection of its fibres ; this hole is to be very ftreight, 
and its dimenfions are 2 L lines in diameter, and two 
inches 8 lines in depth from a a to c. 
31. Prepare 
