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SPEED OF REVOLVING MASSES OF AIR. 257
CHAPTER X.
SPEED OF THE REVOLVING MASSES OP AIR.—SPEED OF THE CYCLONE.—
FALL OF THE BAROMETRIC COLUMN.—IRREGULARITIES OP THE WIND IN
THE PATH OF THE CYCLONE.
It is not yet known what degree of swiftness the masses of air carried
by the cyclones can attain, for it is in the upper regions of the atmosphere, where the medium only offers a feeble resistance to the aerial currents, that the storm-wind must have its greatest rapidity. And it does
not suffice to ascertain the progress of the particles of air immediately
at the level of the ground, or even slightly above it, to form an idea
of the speed at which the atmospheric mass carried by the hurricane
moves. In one of his ascents Mr. Coxwell made a journey of sixty-eight
miles in sixty minutes, while below him the instruments indicated a speed
of hardly fourteen miles in the same interval. Another time Mr. Glaisher
moved at fifteen miles per hour, while at the Greenwich observatory the
same sheet of air only advanced five hundred yards. How great, then, is
the speed of the cyclone at a certain height above the ground, when on
the earth, strewn with obstacles, it- progresses at the rate of fifty yards per
second, or one hundred miles per hour—four times the speed of our locomotives ! This fearful rapidity of the air at the surface of the ocean, and
the friction of the aerial particles which results, explains perfectly, as
Cicero remarked 2000 years ago, why the temperature of the water rises
during storms.*
As to the pressure exercised by the aerial current which moves with
such speed, it is truly formidable. In a memoir on the construction of
light-houses, Fresnel estimated the strongest pressure of the wind at six.
hundred and sixteen pounds per square yard, but it is very probable that
in a number of hurricanes this figure has been greatly surpassed. Not to
mention the effects produced by the great cyclones of the tropics, a number of cases have presented themselves in the temperate zone where the
pressure exercised by the wind on a space of little extent was much greater than meteorologists had foreseen. Thus, to cite but one example, the
storm ofthe 27th of February, 1860, coming from the west, and plunging
in the plain of Narbonne, by the strait where the canal and railroads of
the south pass, was violent enough to force off the rails and partially
overturn two trains, which it struck crossways, between the stations of
Salces and Rivesaltes. According to the engineer, Mathieu, who probably gives, it is true, too high an estimate, the pressure necessary to overturn certain carriages must have been nine hundred and fifty-two pounds
per square yard of surface.f
* De Natura Deorum—Zeitschrift fur Erdkunde, March, 1864.
t Eugene Elachat, Traversee des Alpes.
17
| Title | The ocean, atmosphere, and life |
| Creator | Reclus, Elisée |
| Publisher | Harper |
| Place of Publication | New York |
| Date | 1873 |
| Language | eng |
| Type | Books/Pamphlets |
| Title | 00000282 |
| Type | Books/Pamphlets |
| Transcript | SPEED OF REVOLVING MASSES OF AIR. 257 CHAPTER X. SPEED OF THE REVOLVING MASSES OP AIR.—SPEED OF THE CYCLONE.— FALL OF THE BAROMETRIC COLUMN.—IRREGULARITIES OP THE WIND IN THE PATH OF THE CYCLONE. It is not yet known what degree of swiftness the masses of air carried by the cyclones can attain, for it is in the upper regions of the atmosphere, where the medium only offers a feeble resistance to the aerial currents, that the storm-wind must have its greatest rapidity. And it does not suffice to ascertain the progress of the particles of air immediately at the level of the ground, or even slightly above it, to form an idea of the speed at which the atmospheric mass carried by the hurricane moves. In one of his ascents Mr. Coxwell made a journey of sixty-eight miles in sixty minutes, while below him the instruments indicated a speed of hardly fourteen miles in the same interval. Another time Mr. Glaisher moved at fifteen miles per hour, while at the Greenwich observatory the same sheet of air only advanced five hundred yards. How great, then, is the speed of the cyclone at a certain height above the ground, when on the earth, strewn with obstacles, it- progresses at the rate of fifty yards per second, or one hundred miles per hour—four times the speed of our locomotives ! This fearful rapidity of the air at the surface of the ocean, and the friction of the aerial particles which results, explains perfectly, as Cicero remarked 2000 years ago, why the temperature of the water rises during storms.* As to the pressure exercised by the aerial current which moves with such speed, it is truly formidable. In a memoir on the construction of light-houses, Fresnel estimated the strongest pressure of the wind at six. hundred and sixteen pounds per square yard, but it is very probable that in a number of hurricanes this figure has been greatly surpassed. Not to mention the effects produced by the great cyclones of the tropics, a number of cases have presented themselves in the temperate zone where the pressure exercised by the wind on a space of little extent was much greater than meteorologists had foreseen. Thus, to cite but one example, the storm ofthe 27th of February, 1860, coming from the west, and plunging in the plain of Narbonne, by the strait where the canal and railroads of the south pass, was violent enough to force off the rails and partially overturn two trains, which it struck crossways, between the stations of Salces and Rivesaltes. According to the engineer, Mathieu, who probably gives, it is true, too high an estimate, the pressure necessary to overturn certain carriages must have been nine hundred and fifty-two pounds per square yard of surface.f * De Natura Deorum—Zeitschrift fur Erdkunde, March, 1864. t Eugene Elachat, Traversee des Alpes. 17 |
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