FROM THE HIGHER ATMOSPHERE. 483 
and endeared to me by many pleasing associations. The re- 
sult of them has been the construction of a delicate instrument, 
which will be deemed, I hope, a valuable accession to meteo- 
rology, and indeed to physical science in general. From the 
term «aiéeioc, which, in reference to the atmosphere, signi- 
fies at once clear, dry and cold, I have appropriated the 
name of ithrioscope to this new combination of the py- 
roscope. The sensibility of the mstrument is very striking, 
for the liquor incessantly falls and rises in the stem with 
every passing cloud. Under a fine blue sky, it will some- 
times indicate a cold of 50 millesimal degrees; yet on other 
days, when the air seems equally bright, the effect is only 30°. 
The causes of these variations are not quite ascertained. The 
action is in general greatest under a clear and translucid at- 
mosphere. But particular winds, blowing at different altitudes, 
seem to modify the effect, and so may perhaps the transition. 
from summer to winter. 
There are three principal forms of the Athrioscope: 1. Erect: 
2. Sectoral ; 3. Pendant. 
1. Erect.—All the requisite conditions for measuring the at- 
mospheric impressions are attained, by adapting the pyroscope 
to the cavity of apolished metallic cup, of rather an oblong 
spheroidal shape, the axis having a vertical position, the lower 
focus being occupied by the sentient ball, while the section of a 
horizontal plane; at the upper focus, forms the orifice, (see 
fig. 3. Pl. XL.) The cup may be made of thin brass. or sil-. 
Very. either hammered or cast, and then; turned and polish-. 
ed on a lathe; the diameter being from two. to four inches, and’ 
the eccentricity of the elliptical figure varied. within. certain li- 
mits.according to circumstances. The most convenient propor- 
tion, however, is, that the eccentricity should be equal to half. 
the transverse axis, or that the focus should be placed at the 
3P2 third’ 
