whirled upon its axis, the centrifugal power will carry the heavier
fluid to the circumference, and the lighter will in consequence be found
round the axis. 3. There may be a place at some certain latitude between
the poles and the line on each side the equator, where the inflammable
supernatant atmosphere may end, owing to the greater centrifugal force
of the heavier aerial atmosphere. 4. Between the termination of the
aerial and the beginning of the gasseous atmosphere, the airs will
occasionally be intermixed, and thus become inflammable by the electric
spark; these circumstances will assist in explaining the phenomena of
fire-balls, northern lights, and of some variable winds, and long
continued rains.

Since the above note was first written, Mr. Volta I am informed has
applied the supposition of a supernatant atmosphere of inflammable air,
to explain some phenomena in meteorology. And Mr. Lavoisier has
announced his design to write on this subject. Traite de Chimie, Tom. I.
I am happy to find these opinions supported by such respectable
authority.]

[_And bend the twilight_. l. 126. The crepuscular atmosphere, or the
region where the light of the sun ceases to be refracted to us, is
estimated by philosophers to be between 40 and 50 miles high, at which
time the sun is about 18 degrees below the horizon; and the rarity of
the air is supposed to be from 4,000 to 10,000 times greater than at the
surface of the earth. Cotes's Hydrost. p. 123. The duration of twilight
differs in different seasons and in different latitudes; in England the
shortest twilight is about the beginning of October and of March; in
more northern latitudes, where the sun never sinks more than 18 degrees,
below the horizon, the twilight continues the whole night. The time of
its duration may also be occasionally affected by the varying height of