Hygrometry . 421 
"bottom. The fteady part of the inftrument is reprefented by 
Jig. 4 . 5 it is partly an half tube, cut longitudinally through 
the axis, and having fidewife two vertical rows of large holes. 
A whole tube goes over that half one ; for which purpofe the 
piece a, a, is taken off by unferewing the female ferew b which 
belongs to the part d; this laft is a ifnall open tube, cut out- 
lide in ferew. The large external tube has alfo two vertical 
cows of holes, at fuch a diftance from one another, that, when 
one of them correfponds to one of the rows of the half tube, 
the other is in front. The two oppofite pofitions that tube can 
be brought to are in order that the inftrument may be placed 
either iide of a window, and each of thofe pofitions is deter- 
mined by one end of a cut at the bottom of the tube in a, fig . 
3. which then holds againft the fteady pin c, fig. 4. The rows 
of holes of the tube are to be turned towards the room, to 
prevent the rain from falling on the fi ip ; and the dial being 
inclofed in a box with a glafs in front, no rain can get into the 
inftrument. It muft alfo be fixed in a place not much expofed 
to the fun, or be fereened from it without preventing the circu- 
lation of the air. The communication of the flip with the 
external air through the rows of holes and the open bottom d$ 
Jig. 4. is fufficient for that clafs of obfervations. By the man- 
ner of its being hooked, it may be eafily taken off for carrying 
elfewhere ; and, if a quick obfervation is wanted, the tube alf® 
may eafily be taken off. 
I have the honour of prefen ting one of thofe inftruments t® 
the Royal Society ; and, as it is very defirable that fome hygro- 
meter be added to the other meteorological inftruments ufually 
obferved, I wifh this may deferve a place in their Obfervatory 
for that purpofe. 
rtsn&i 
