Pascal’s treatise on the weight of the whole mass of air forms the
basis of the modern science of Pneumatics. In order to prove that the
mass of air presses by its weight on all the bodies which it surrounds,
and also that it is elastic and compressible, he carried a balloon,
half-filled with air, to the top of the Puy de Dome, a mountain about
500 toises above Clermont, in Auvergne. It gradually inflated itself
as it ascended, and when it reached the summit it was quite full,
and swollen as if fresh air had been blown into it; or, what is the
same thing, it swelled in proportion as the weight of the column of
air which pressed upon it was diminished. When again brought down it
became more and more flaccid, and when it reached the bottom it resumed
its original condition. In the nine chapters of which the treatise
consists, Pascal shows that all the phenomena and effects hitherto
ascribed to the horror of a vacuum arise from the weight of the mass
of air; and after explaining the variable pressure of the atmosphere
in different localities and in its different states, and the rise of
water in pumps, he calculates that the whole mass of air round our
globe weighs 8,983,889,440,000,000,000 French pounds.--_North-British
Review_, No. 2.
It seems probable, from many indications, that the greatest height at
which visible clouds _ever exist_ does not exceed ten miles; at which
height the density of the air is about an eighth part of what it is at
the level of the sea.--_Sir John Herschel._