484 Proceedings of the Royal Irish Academy. 
Berzelius distinguished water into the three states of aqueous gas, 
aqueous vapour, and liquid water. When aqueous gas is cooled in the 
air, vapour is formed, which is water in its ultimate division ; but if 
cooled on the surface of a cold solid, it does not form vapour, but 
passes at once into liquid water. In the case of this hygrometer, 
aqueous gas is cooled on the gut line and becomes water. When the 
index stands at 0 (represented by a point) the gut line, having been 
exposed to the action of exsiccants, is supposed to be anhydrous. 
When the gut line begins to absorb, it begins to turn the index ; 
and when this has travelled ten times round, it has completed the hy- 
grometric range of the local atmosphere, and of the instrument. 
The length of gut line actually in operation, exclusive of the silk, 
w^hich gave 10 rounds of the index in my trials, was 3^ inches ; but 
the stem which holds it is adjustable to a greater or less length as may 
be necessary to produce 10 rounds. 
With regard to the working of this instrument, the following will 
give some idea, being the result of a trial of a new gut line in what 
may be called its natural state without any exsiccation. The hygrometer 
was covered with a glass cylinder, half of which was lined with wet 
blotting paper. If the gut-line had been previously exsiccated, it 
would have given eleven turns to the index, and a few degrees. 
1st 
roun 
id performed in 7j 
2nd 
JJ < 2 
3rd 
1 5 
8i 
8f 
4 th 
5th 
J ) 
6th 
11 
7th 
J } 
13 
8th 
18 
9 th 
J? 
27 
10th 
5 J 
61 
A similar hygrometer, being totally immersed in water, the index 
v/ent round eight times in five minutes, in times not very unequal. 
When the hygrometer is exposed to the natural dampness of the 
air, the first two or three, or perhaps four, or five revolutions of the 
index are scarcely different, in point of time, unless the atmosphere 
have meanwhile changed hygrometrically, which it so frequently does. 
Much will depend on the thinness of the gut line. Proper lengths 
from the same string may be preserved indefinitely in a glass tube of 
very small bore sealed with wax. A gut line, long in use, is easily re- 
moved and replaced, and may not require to be changed but after a 
long service; especially if the glass receiver be constantly kept on 
when the hygrometer is not in use. 
This hygrometer, when suddenly brought into the open air, after 
confinement in the house, although the index may immediately begin 
to move, does not at once truly show the state of the atmosphere, 
