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carefully corrected for the influence of the pressure of the water. Lenz deduced the important conclusion that there is at and under the equator a belt of water cooler than the water to the north and south of it, the existence of which is explained on the principle that there must be a flow of warm surface water from the equatorial regions toward either pole, and which must be accompanied by a corresponding flow toward the equator in the lower regions of the ocean, so that at the equator itself, where the two deepsea currents meet, cool water rises to the surface. This priuciple has been independently propounded by Dr. Carpenter to explain the cold band between the Gulf Stream and the United States coast, and justifies him in the statement that his own researches during the past ten years have but afforded a confirmation and elaboration of Leniz's doctrine of oceanic circulation.—12 A, X., 170.

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NEW GENERALIZATION IN OCEAN PHYSICS. A new generalization of much importance in reference to ocean physics bas lately been derived from the observations of the Challenger in the Malay Archipelago during her recent passage from Cape York to Hong-Kong. The seas visited, we are told, consist of a series of sunken lakes or basins, each surrounded and cut off from the neighboring seas by a shallower rim or border. There is a general oceanic circulation down to a depth equal to that of the border, and the temperature gradually decreases from the surface to this level. The entire mass below, however, having no communication with the outer water, and consequently no circulation, remains at nearly the same temperature as that flowing over the floor of the rim; or, in other words, the water coming along the floor of the ocean from the antarctic seas, which is found in all the deep open channels, can not obtain admission through or over the rim.

On this account the bottom temperature depends entirely upon the altitude of the encircling rim. Thus, in Torres Strait, with a depth of 2450 fathoms, and a rim reaching within 1300 fathoms of the surface, the body of water below that depth has a steady temperature of 35°. The Sulu Sea, which is 2550 fathoms deep, with a rim reaching within 400 fathoms of the surface, has a temperature to its bottom

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as high as 50°. The Molucca Passage, however, is open to the depth of 1200 fathoms, and the China Sea to that of 1500 fathoms.-12 A, Dec. 31, 1874, 174.

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INFLUENCE OF WINDS UPON THE TIDES. In the appendix to the recent volume of the report of the United States Coast Survey, Mr. Ferrel presents a revision of his discussion of the tides of Boston Harbor, in which, among other matters, he investigates the effect of winds and barometric pressure on the height of the tides. After comparing the actual observations with the ordinary formula for computing the heights of the tides, certain residuals remain, which may possibly be in part explained as due to the influence of the winds and the barometer, He shows that this influence varies very much in different parts of the world. Thus, at Boston, a rise of an inch in the barometer is followed by a fall of seven and one-third inches of water. At Brest, however, for the same change in pressure, the change in the water is fourteen and one-ninth inches, and at Liverpool eleven and one-tenth inches, while at London it is only seven inches, being even less than the value obtained for Boston. The direct effect of atmospheric pressure is probably to a large extent inextricably complicated with the influence of the winds. Mr. Ferrel suggests as an explanation that when the barometer is rising we usually have clearing weather on the New England coast, with westerly winds, which tend to lower the sea level; they consequently more than counteract the direct effects of inertia and friction. When the barometer is falling there are nsually east winds, or, at least, an absence of west winds, and the sea level at this time is a little above the mean level. Very strong winds change the sea level in Boston Harbor a foot or more, ten such cases occurring in the course of one year.-Report of the U. S. Coast Survey, 1871, 94.

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THE CHALLENGER OBSERVATIONS ON THE DEEP-SEA BOTTOM.

Professor Huxley, in a recent lecture at the Royal Institution upon the work of the Challenger expedition and its bearing upon geological problems, sums up the general results, in regard to the composition of the ocean bed, by showing that from the researches of Sabine, Ross, Penny, Ehren

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berg, Bailey, and others, it was then known that from deposits,
chiefly of the siliceous cases of plants of the lowest order,
the diatomaceæ, a “cap” of siliceous sand was being formed
at the northern, and another at the southern pole. It was
also proved that the grand areas of the general sea-bottom
of the Atlantic and Pacific oceans were similarly constituted
of a girdle of calcareous mud, of indefinite depth, formed by
a similar vein of discarded calcareous shells of animals of low
organization—the foraminifera. Now this white calcareous
matter of the foraminifera shells has been shown by the Chal-
lenger researches to be replaced, in certain deep oceanic val.
leys between Tristan d'Acunha and Kerguelen's Island, and
elsewhere, by a very fine red clay. In certain geological
deposits, of greater or less antiquity, beds of glauconite, or
green siliceous sand, exist, which are composed entirely of
the casts of ancient foraminifera formed of a green material,
which is a compound of silicate of iron and alumina. The
chemist of the Challenger having found that, from the decom-
position by weak acids of the calcareous shells dredged up
from the 18,000-feet depths, there is a residuum of one or two
per cent. of red marl, exactly like that dredged up from the
18,000-feet depths of the valleys referred to, the conclusion
is arrived at that the red mud is the accumulation of this
small percentage of clayey matter, resulting from the whole-
sale decomposition of the calcareous polythalamous shells.
The povelty of the Challenger discovery consists, therefore,
in the fact that clay deposits can also be assigned, like sili-
ceous and calcareous deposits, to the resultant débris of organ-
isms living at the surface of the sea. Supposing, therefore,
that the whole globe were immersed under an entire envel-
ope of water, deposits of all the materials of our stratified
geological rocks could be going on without the slightest as-
sistance from the degradation and wearing away of any actual
land surface at all; and these deposits, subjected in the or-
dinary natural course of events to ordinary processes and
actions, could be modified into gneiss, schists, slate, limestone,
and every variety of geologic rocks.—3 A, Jan. 6, 1875, 171.

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INFLUENCE OF FORESTS ON CLIMATE.

Claré, in the Revue des Deux Mondes, takes strong ground as to the exercise by forests of a very decided influence upon

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climate. In his article he remarks that forests have a chemical, physical, physiological, and mechanical action on the climate of a country. In regard to the physical action, while the foliage of woods allows much less rain-water to reach the ground than in unwooded land, this is more than compensated by the difference of evaporation in the two cases, that of the open fields being nearly five times as great as that of the woods. The melting of snow, too, is retarded by forests, thus causing a more gradual outflow of the water. Again, forests are obstacles to atmospheric movements. An air current meeting a wood is compressed and forced upward, so that it yields part of its moisture in the form of rain. Forests also protect crops against the winds; and it is an established fact that thunder-storms are less frequent and violent in wooded regions than in open countries, as the trees draw from the atmosphere the electricity it contains, which accumulates on regions that are bare. Forests, too, have a decisive action as regards the formation of hail, hailstorms occurring but rarely in a wooded region. A case has lately been noted where a violent hailstorm on approaching and crossing a forest ceased to produce hail, but resumed its formation on passing to the unwooded country beyond.-18 A, June 11, 324.

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NOTE ON THE VERTICAL DISTRIBUTION OF TEMPERATURE ON

THE OCEAN. Mr. Buchanan, chemist on board of the Challenger, writes that the effect of the changing seasons on the temperature of the sea-water seems to him not to have received sufficient attention. During the whole period of the heating of the water it has, from its increasing temperature, been steadily becoming lighter, so that the communication of heat to the water below by convection has been entirely suspended. It has, also, by evaporation, become denser than it was before at the same temperature. During the approach of winter, the superficial water having cooled, sinks through the warmer water below it, until it reaches the stratum having the same temperature as itself. Nor does it stop there, but continues to sink, owing to its density, carrying its temperature with it to the lower colder layers. The result is that we have during the winter a heating effect going on in the lower re

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gions, and during the summer a cooling effect; so that the
greater the yearly range of atmospheric temperature, the
greater the depth in the ocean to which its effect will be felt.
He thus explains the presence of the large body of compara-
tively warm water in the North Atlantic, the existence of
which has been usually ascribed to an assumed back-water
of the Gulf Stream. This warm water is, in fact, due to no
such extraneous cause, but is the actual effect of the condi-
tions of the climate at the surface, which effects become ap-
parent, because the water is free from the influence of oceanic
currents, and exposed to the effect of climate alone.- Pro-
ceedings of the Royal Society, 1875, p. 123.

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NAUTICAL METEOROLOGY,
Nautical meteorology has for its object the study of both
atmosphere and ocean in their relations to navigation, and
the utilization of our knowledge of the winds and currents,
the laws of tempests, etc., in order to accomplish the shortest
possible voyages between given points. The foundation of
This application of scientific study to the wants of navigation
was laid by Maury, and a recent work by Ploix and Caspari
seems to embody many of the recent improvements that have
been made. This work is intended as a guide to the mariner
in the use that he can make of the charts published by me-
teorologists. After giving a general descriptive account of
interesting phenomena, instruments, methods of observation,
and the general climatological features, the volume gives a
résumé of the oceanic routes recommended for the different
months of the year throughout the navigated oceans. For
instance, it insists especially upon the importance of attend-
ing to the point where the ship crosses the equator in passing
from one hemisphere into the other. Thus, in order to go
from Europe to either the Cape of Good Hope or to Cape
Horn, we should cross the equator at the same point; but,
varying with the seasons, we should pass either near the
African or near the Brazilian coasts, but never in the inter-
mediate region where the navigator is exposed to persistent
calms. Another interesting point is the navigation in high
southern latitudes, where we meet almost constantly west
winds. Thus, in order to go to Australia, we sail from Eu-
rope to the south of the Cape of Good Hope, but in order to

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