352 
MISCELLANY. 
At 10 o'clock in the evening, the thermometer stood at — 29°. The 
sky was perfectly serene and clear. At half past 11, the thermometer 
had fallen to — 32°. At half past 3, (the 29th,) the thermometer was at 
— 38° ; the mercury in the phials of course still fluid. The atmosphere 
was remarkably transparent and perfectly calm. At half past 6, the 
thermometer stood at — 4C°. It soon rose one degree while we were 
bending over to examine it — the mercury in the phials still fluid. I now 
poured out a small quantity of the mercury into an excavation in a piece 
of charcoal. At } before 7, the thermometer was again at — 40° ; the 
mercury in the phials still fluid; but that on the charcoal was partially 
congealed. As I examined it with a slender stick, it exhibited the ap- 
pearance of a soft solid, separating into parts without running into globules; 
and the fragments were rough, and evidently crystalline. These appear- 
ances, however, continued only a short time ; but while I was examining 
it, being of course necessarily bent over it, the whole soon returned to a 
perfectly fluid state. At 7 o'clock, the thermometer was still as before at 
— 40°. The mercury in the phials was unchanged. That on the piece of 
charcoal exhibited the same appearances as at the last observation, only in 
a less marked degree, and it sooner became fluid. Soon after this, the sun 
rose, and of course the attempt was discontinued. 
To Prof. Silliman. — Bear Sir, — I send you above, the extract from 
my minutes of an observation of the effect of natural cold on mercury, on 
the Kenebeck. A few weeks later, having been supplied by the kindness 
of the late Mr. Vaughan with several excellent, thermometers of Trough- 
ton's manufacture, 1 attempted to ascertain how much effect was attributa- 
ble to the cooling of the surface by radiation, in a similar state of atmos- 
phere : and on one occasion found a difference of 18 degrees between a 
thermometer on charcoal on the ground, and another suspended freely in 
the air, 18 or 20 feet above it — one being 36°, the other 18° below zero. 
This was in a clear night, and subsequently when clouds appeared, the 
difference diminished, until at the commencement of snow the two instru- 
ments agreed. Yours very truly, 
E. Hall, Jr. 
Huston, Wednesday Evening, March 23, 183G. 
Amer. Jour. Sci. & Art. 
