On a Portable Hygrometer. 351 
Arr: XII.—On a Portable Hygrometer ; by A. A. Haves. 
By presenting. the meteorologist and chemist, with his beautiful 
and truly philosophical instrument, Mr. Daniell has left little chance 
' for improvement, so far as delicacy and accuracy of indication are 
concerned ; and were it less fragile, perhaps no other would be desired, 
by those who experiment on aqueous vapor. As it is in mountain- 
ous countries, or on the tops of mountains, that the results of experi- 
ments on aqueous vapor, are of most value; from the phenomena 
being presented in a more simple form, and divested in part, of the — 
attendant circumstances which modify them ; an instrument adapted 
to such purposes, should be as portable as is consistent with delicacy. 
The simple apparatus devised Mr. Dalton, and used in those decisive’ 
experiments, which have so intimately connected his name with the 
history of meteorological science, is sufficient to enable us to deter- 
mine the temperature of the aqueous vapor in the atmosphere, and 
by a reduction in the size, and a slight modification of form, an instrur 
ment is obtained, which is well fitted for general meteorological pur- 
poses. Instead of the cylindrical jar used by Mr. Dalton, I substi- 
tute a thin brass tube, the diameter of which, is one half greater than 
that of the cylindrical, or spherical bulb of the thermometer, which 
forms a part of the instrument; its length is one inch and a half; it 
is closed at one end, the other having a screw cut on the inside, to 
receive a screw cap and a rim, or projection below, to allow the disk 
of caoutchouc which precedes the cap, to be compressed, forming a 
convenient and efficient “stuffing box.” At that end of the tube 
which fits the cap, a narrow ferule of polished platina, or steel is sold- 
ered to the outside of the tube, and one half of its length from the- 
other end, is covered with soft cotton thread. The scale of the ther- 
mometer, graduated from 120° to —30°, terminates about one inch 
from the bulb. At this extremity, a screw cap, and disk of caout- 
chouc, both pierced for the tube of the thermometer, are firmly at- 
tached. When not in use, the tube is closed by a cork, and packs 
oh the case, by the side of the thermometer and phial for containing 
er. 
In all acrological experiments, the thermometer is used for deter- 
ming the temperature of the atmosphere, carefully avoiding those 
sources of error, which render this a delicate operation. For deter- 
mining the dew point, so much alcohol is put into the tube, as is ne- 
