XXXVI
Owing to gravity the atmosphere will have a globular surface,
and owing to the mobility of its parts there will be higher waves
there than on the surface of an ocean. In consequence of gravi
ty and elasticity the density of air will increase towards the sur
face of the earth.
CHAPTER VI.
Pressure and Weight of the Air.
186-222.
§ 83. 1) Torricelli, a pupil of Galileo. proved not only
the pressure of air, but also the amount of this pressure. A
glass tube, closed at one end, is filled with mercury; the other
aperture being first closed with the thumb, we invert the tube
and place it vertically in a mercury trough. The mercury sinks
until it stands at a height of 30 inches. This shews, that the
atmosphere can support a column of mercury the height of which
is 30 inches. Since the weight of a column of mercury (30
inches high), the section of which is equal to a square inch, con
sists of 30 cubic inches, and as the weight of a cubic inch of
mercury is = 0.49 of a pound, the pressure of the atmosphere
on a square inch of surface is equal to 14.7 pounds, (15 pounds
in round numbers, which is called "one atmosphere").
Remark. Knowing the length of the earth's radius, it is not difficult
to calculate the weight of the whole mass of atmosphere surrounding
the earth.
§ 84. Construction of the Barometer (measure of the air's
weight). 186. What we have proved of atmospheric pressure
as holds true only at sea-level. Pascal found out, that the mer
cury in the the tube descends in proportion as We ascend in the
