1817.] and a new Hysrometer. . 321 
the bladder, and gradually force the mercury of the hygrometer to 
rise in the tube. When it has risen to within half an inch of the 
top, the screwing is to be discontinued. 
It is evident that by this contrivance the pressure is wholly thrown 
off the bladder, and that no degree of agitation can ever affect it. 
Another advantage is, that it gives a power of insulating the in- 
strument, and of only bringing it into action when necessary 3 by 
which means it will be preserved uninjured for any number of years 
even in water. 
1 do not find that, in the ordinary state of the atmosphere, the 
bladders are subject to any alteration in their properties. I have 
had some past me as hygrometers for above three years, and there 
is no perceptible change in their delicacy. But it is not proper that 
they should be allowed to remain for a length of time in water, as, 
like every other animal matter in such a situation, they are liable 
to decay. 
I do not consider it necessary here to enlarge on the uses and ap- 
plications of the hygrometer, as it is presumed that the greater 
number of persons interested in science are already fully acquainted 
with them. A permanent system of meteorology can only be 
founded on the multiplied observations of individuals on different 
parts of the earth. Theories which are built ona less solid founda- 
tion are soon overturned and forgotten; but every insulated fact 
will be carefully preserved as an additional step towards the forma- 
tion of that perfect system which will at last, from the accumulation 
of data, truly explain the nature of all atmospherical phenomena. 
In a future paper I will take an opportunity of detailing the 
result of experiments on the power of various absorbents, and other 
circumstances connected with hygrometry. 
These instruments have been constructed for me by Mr. Thomas 
Jones, of Charing Cross, who was originally employed by Sir H. 
Englefield to make his mountain barometer, and who still continues 
to make them, Mr. Jones has deservedly acquired much reputation 
for the accuracy of his works; and I am highly indebted to his skill 
and ingenuity in overcoming many practical difficulties in the for- 
mation of this barometer and hygrometer, and in bringing them to 
their present degree of perfection. 
— | 
Norre.—I may here remark, for correction, that in a former 
paper (vol. viii. p. 125) the word solubility has been printed for 
volatility, which alters the sense. It has escaped being noticed in 
the errata. 
Vor. IX. N° IV. Xx 
