00000236 |
Previous | 236 of 595 | Next |
|
small (250x250 max)
medium (500x500 max)
Large
Extra Large
large ( > 500x500)
Full Resolution
All (PDF)
|
WEIGHT OF THE AIR.
213
CHAPTER n.
WEIGHT OF THE AIR.—HEIGHT OF THE UPPER STRATA.—BAROMETRIC
MEASURES.
The weight of-the aerial particles, which makes itself felt in so terrible
a manner in hurricanes, is relatively very small, since a litre of air (nine-
tenths of a quart) taken at the surface of the ground, and at the temperature of zero, weighs 770 times less than a litre of water. But the atmospheric mass surrounding the globe is such that, if it were to be entirely
agglomerated in a single ball, it would weigh as much as a sphere of copper nearly sixty-three miles in diameter; that is, the twelve hundred
thousandth part of the mass of the earth.* The pressure exercised by
the atmosphere on a man of middle size is not less than fourteen or fifteen
tons; it is true, however, that this pressure, making itself felt at the same
time in all directions on our frame, is by that very fact neutralized.
We know that a column of air on any point whatever of the earth is
equivalent, on an average, to that of a column of water of thirty-two feet,
or to thirty inches of mercury; it is the knowledge of this fact that has
enabled us to construct the barometer.
Still, if we know the weight of the atmosphere, we can not yet s*ay in a
positive manner to what distance it rises in space. If the higher aerial
strata had the same density as those on the surface of the sea, the total
thickness of the air would not exceed five miles, and, consequently, the
highest mountains of the earth, the Gaourisankar, the Kinchinjunga, the
Dapsang, and many others, would raise their peaks into empty space
above the atmosphere. But it is not so; above the lower strata, compressed by the weight of all the superincumbent aerial mass, the particles
separate in proportion as the pressure diminishes, the air becomes rarer
and rarer in the heights of space, and ends by being completely lost, like
the thin fluid which composes the tail of comets. According to the calculations of Laplace, it is at more than 26,000 miles above the surface of
the earth that, in consequence of the increase of centrifugal force, and the
diminution of the weight, the aerial particles which may still be in space
must forcibly escape from the terrestrial orbit. Perhaps it is, in tact, in
these elevated regions at the very limits of the spheres of attraction of
the heavenly bodies, that the exchange of their gaseous particles takes
place. However that may be, it is at a height very inconsiderable in comparison with the extreme limit indicated by Laplace, that the atmosphere
ceases to be respirable by man. At the summit of Etna—that is to say,
at an elevation of two miles—we have nearly a third of the aerial mass
under our feet. At three miles and a half, a height above which a great
* Sir John Herschel, Meteorology, p. 16.
| Title | The ocean, atmosphere, and life |
| Creator | Reclus, Elisée |
| Publisher | Harper |
| Place of Publication | New York |
| Date | 1873 |
| Language | eng |
| Type | Books/Pamphlets |
| Title | 00000236 |
| Type | Books/Pamphlets |
| Transcript | WEIGHT OF THE AIR. 213 CHAPTER n. WEIGHT OF THE AIR.—HEIGHT OF THE UPPER STRATA.—BAROMETRIC MEASURES. The weight of-the aerial particles, which makes itself felt in so terrible a manner in hurricanes, is relatively very small, since a litre of air (nine- tenths of a quart) taken at the surface of the ground, and at the temperature of zero, weighs 770 times less than a litre of water. But the atmospheric mass surrounding the globe is such that, if it were to be entirely agglomerated in a single ball, it would weigh as much as a sphere of copper nearly sixty-three miles in diameter; that is, the twelve hundred thousandth part of the mass of the earth.* The pressure exercised by the atmosphere on a man of middle size is not less than fourteen or fifteen tons; it is true, however, that this pressure, making itself felt at the same time in all directions on our frame, is by that very fact neutralized. We know that a column of air on any point whatever of the earth is equivalent, on an average, to that of a column of water of thirty-two feet, or to thirty inches of mercury; it is the knowledge of this fact that has enabled us to construct the barometer. Still, if we know the weight of the atmosphere, we can not yet s*ay in a positive manner to what distance it rises in space. If the higher aerial strata had the same density as those on the surface of the sea, the total thickness of the air would not exceed five miles, and, consequently, the highest mountains of the earth, the Gaourisankar, the Kinchinjunga, the Dapsang, and many others, would raise their peaks into empty space above the atmosphere. But it is not so; above the lower strata, compressed by the weight of all the superincumbent aerial mass, the particles separate in proportion as the pressure diminishes, the air becomes rarer and rarer in the heights of space, and ends by being completely lost, like the thin fluid which composes the tail of comets. According to the calculations of Laplace, it is at more than 26,000 miles above the surface of the earth that, in consequence of the increase of centrifugal force, and the diminution of the weight, the aerial particles which may still be in space must forcibly escape from the terrestrial orbit. Perhaps it is, in tact, in these elevated regions at the very limits of the spheres of attraction of the heavenly bodies, that the exchange of their gaseous particles takes place. However that may be, it is at a height very inconsiderable in comparison with the extreme limit indicated by Laplace, that the atmosphere ceases to be respirable by man. At the summit of Etna—that is to say, at an elevation of two miles—we have nearly a third of the aerial mass under our feet. At three miles and a half, a height above which a great * Sir John Herschel, Meteorology, p. 16. |
|
|
|
|
|
|
| B |
|
| C |
|
| G |
|
| H |
|
| M |
|
| T |
|
| U |
|
| Y |
|
|
|
