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LAND AND SEA BREEZES. 241
on one side toward the shores of Italy, on the other toward the islands
and mountains of Istria and Dalmatia. During the night the coasts
that surround the waters ofthe Adriatic send back to the sea, as to a common centre, the fresh air which they have received; to the divergent currents ofthe day succeeds a wave of convergent breezes.
In the same way the mountains have their own system of breezes alternating with a regularity similar to that ofthe land and sea breeze on the
coasts of the ocean. In the day, especially in summer, when the summits
of the mountains are exposed to all the intensity of the solar rays, and receive a considerable quantity of heat which causes their temperature to
approach that ofthe valleys, the air reposing on the summits expands and
rises. At the same time, the air ofthe plains which lie at the foot ofthe
mountains is itself expanded in greater proportions, so that an ascending current is produced from the base to the summit of the peaks, in all
the valleys, and over all the escarpments. The atmospheric strata of the
plain move in the direction of the heights with all the more impetuosity
the more strongly heated the summits have been by the sun. In certain
valleys, especially those ofthe Stura, and other Alpine rivers, which water
the plains of Piedmont, the ascending wind has such force that the greater part of the trees are uniformly inclined toward the mountains. Pollen, remains of plants, insects and butterflies, are carried away bj the
current of air, and by their debris soil the whiteness of the snow. In the
night, phenomena of an opposite kind are produced, but with less intensity ; the highftmountains, whose summits rise far into the sky, lose their
heat by nocturnal radiation more rapidly than the valleys, the sheets of
air which surround them are chilled and descend again, in part toward
the plains from which they had ascended a few hours before. Thus an exchange between the two zones is established, an ebb and flow, a rising and
falling atmospheric tide, regulated in its intensity by the variations ofthe
temperature; and here Ave see again, as in the coast breezes, the rotatory
movement pointed out by Dove.
As an example of these breezes, called in the French Alps pontias, re-
bats, cdoups du vent, we may cite the three aerial currents which flow incessantly in the valleys of Savoy, unless the local system of atmospheric
currents be modified by tempests. These three streams of air are those
of Faucigny, Tarentaise, and Maurienne. The first traverses the valley of
the Arve from Geneva to Mont Blanc; the second moves in the valleys
of the Isere, and its tributary, the Doron; the third alternately ascends
and descends the valley ofthe Arc toward Mont Cenis and the pass of
Iseran. Ordinarily, the ascending wind commences toward ten o'clock in
the morning in the valleys of Savoy, and the descending current flows
back again toward the plains at nine o'clock in the evening. In certain
places, it is called matinie're, because it makes itself felt, most of all, before the rising ofthe sun. M. Fournet, who has for a long time studied
these phenomena of atmospheric tides, has ascertained that the passage,
from the ebb to the flow, is especially rapid m the narrow defiles, while
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 | 00000266 |
| Type | Books/Pamphlets |
| Transcript | LAND AND SEA BREEZES. 241 on one side toward the shores of Italy, on the other toward the islands and mountains of Istria and Dalmatia. During the night the coasts that surround the waters ofthe Adriatic send back to the sea, as to a common centre, the fresh air which they have received; to the divergent currents ofthe day succeeds a wave of convergent breezes. In the same way the mountains have their own system of breezes alternating with a regularity similar to that ofthe land and sea breeze on the coasts of the ocean. In the day, especially in summer, when the summits of the mountains are exposed to all the intensity of the solar rays, and receive a considerable quantity of heat which causes their temperature to approach that ofthe valleys, the air reposing on the summits expands and rises. At the same time, the air ofthe plains which lie at the foot ofthe mountains is itself expanded in greater proportions, so that an ascending current is produced from the base to the summit of the peaks, in all the valleys, and over all the escarpments. The atmospheric strata of the plain move in the direction of the heights with all the more impetuosity the more strongly heated the summits have been by the sun. In certain valleys, especially those ofthe Stura, and other Alpine rivers, which water the plains of Piedmont, the ascending wind has such force that the greater part of the trees are uniformly inclined toward the mountains. Pollen, remains of plants, insects and butterflies, are carried away bj the current of air, and by their debris soil the whiteness of the snow. In the night, phenomena of an opposite kind are produced, but with less intensity ; the highftmountains, whose summits rise far into the sky, lose their heat by nocturnal radiation more rapidly than the valleys, the sheets of air which surround them are chilled and descend again, in part toward the plains from which they had ascended a few hours before. Thus an exchange between the two zones is established, an ebb and flow, a rising and falling atmospheric tide, regulated in its intensity by the variations ofthe temperature; and here Ave see again, as in the coast breezes, the rotatory movement pointed out by Dove. As an example of these breezes, called in the French Alps pontias, re- bats, cdoups du vent, we may cite the three aerial currents which flow incessantly in the valleys of Savoy, unless the local system of atmospheric currents be modified by tempests. These three streams of air are those of Faucigny, Tarentaise, and Maurienne. The first traverses the valley of the Arve from Geneva to Mont Blanc; the second moves in the valleys of the Isere, and its tributary, the Doron; the third alternately ascends and descends the valley ofthe Arc toward Mont Cenis and the pass of Iseran. Ordinarily, the ascending wind commences toward ten o'clock in the morning in the valleys of Savoy, and the descending current flows back again toward the plains at nine o'clock in the evening. In certain places, it is called matinie're, because it makes itself felt, most of all, before the rising ofthe sun. M. Fournet, who has for a long time studied these phenomena of atmospheric tides, has ascertained that the passage, from the ebb to the flow, is especially rapid m the narrow defiles, while 16 |
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