ART. X.-CRITICAL NOTICES.

The Physical Geography of the Sea. By M. F. MAURY, LL. D., Lieut. U. S. Navy. New York: Harper & Brothers. 1855.-The name of Lieut. Maury has become a household word among "those that go down to the sea in ships," and all who take any interest, theoretical or practical, in the great highway of nations. For years he has been studying the phenomena of the vast abyss of waves, and bringing new facts to light concerning the wonderful things of the ocean. Great circle sailing, and wind and current charts are familiarly associated with his name by every one who reads the daily newspapers, and the scientific world acknowledges great benefit from his labors.

At first, the sole design in the compilation of the "Wind and Current Charts was to improve navigation by the collation of a vast number of individual experiences. The result proved the correctness of their author's opinions; for, by their aid, the average passage to California was shortened one-fourth, and that from Australia to England, one-fifth. It is impossible to calculate the benefit resulting to commerce from the general adoption of the course recommended by Lieut. Maury. It was stated to the British Association, at its two last meetings, that if this system of research were extended to the Indian Ocean, it would save annually to British commerce, in those seas alone, one or two millions of dollars, and in all seas, ten millions.

But this result, brilliant as it is, did not satisfy the mind of the projector of this new system of investigation. Scientific facts of great value have resulted from it; many secrets having been wrenched from the mysterious sea. One of the first peculiarities observed in these charts, compiled from so many old log-books, was the cutting up of the ocean into what Lieut. M. calls "great turnpike-looking thoroughfares." There were roads to South America, to the Paciñc, to Australia, &c., and it was remarkable how very circuitous and irregular were some of these routes.

"Thus," says Lieut. Maury, "the great highway from the United States to the Cape of Good Hope, nearly crossed the Atlantic, it was discovered, three times. The other parts of the ocean by the wayside were blank, untraveled spaces. All the vessels that sailed went by one road and returned by the other. Now and then, there was a sort of a country cross-road, that was frequented by robbers and bad men, as

they passed on their voyage from Africa to the West Indies and back. But all the rest of the ocean on the wayside, and to the distance of hundreds of miles on either hand, was blank, and seemed as untraveled and as much out of the way of the haunts of civilized man as are the solitudes of the wilderness that lie broad off from the emigrants' trail to Oregon. Such was the old route."

A solution was, of course, sought for this very remarkable fact, and it was finally discovered that tradition had regulated these routes. The first navigators accidentally took a certain course, guided by winds and currents, and their successors, having received their sailing directions, religiously followed them. The navigation of the ocean was therefore regulated by a set of legends, handed down from one sailor to another, which spoke of necessary precautions and fearful perils now found to be purely imaginary.

The first charts which were published called attention to these untraveled spaces. Mariners were called upon to record their observations, and transmit them to the National Observatory at Washington, being promised, in return, new charts and sailing directions based upon this experience. The proposition was eagerly accepted, and brilliant discoveries have rewarded the skill and perseverance employed in the task of unfolding the mysteries of the ocean. The Government of the

United States, which had the signal good fortune of having struck out this new line of investigation, perceiving the important results likely to accrue to the science and navigation of the world from it, suggested the adoption of a uniform system of observations at sea, and invited a conference of the maritime powers for the purpose. This was held in Brussels, in the summer of 1853, and a plan was adopted, by which a regular series of observations could be conducted. Nothing is allowed to interrupt these studies, undertaken for the common benefit of all who use the sea. Even the fury of war has been commanded to spare the record which contains these precious facts.

The results already obtained, in the opinion of that veteran of science, Baron Humboldt, justify the establishment of a new department of science, which he proposes to call the Physical Geography of the Sea.

The work before us is an account of the actual state of this new science. It gives "a philosophical account of the winds and currents of the sea; of the circulation of the atmosphere and the ocean; of the temperature and depth of the sea; of the wonders that are hidden in its depths; and of the phenomena that display themselves at its surface—in short, of the economy of the sea and its adaptations, of its salts, its

waters, its climates, and its inhabitants, and of whatever there may of general interest in its commercial uses or industrial pursuits."

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Such is the task which the author sets himself, and he performs it in a highly creditable manner. The first subject discussed is the Gulf Stream. In considering the various theories of his origin, he pays particular attention to that of Dr. Franklin, who supposed that the tradewinds forced the ocean into the Caribbean Sea, banking up its water, and thus forming a head for the Gulf Stream. He shows, however, that the cold-water bed of this stream actually rises at the rate of ten inches to the mile; so that it runs up an inclined plane. Besides this, there is a polar current setting down from Baffin's Bay, between the Gulf Stream and the coast of the United States; and there are other streams making southwards, along the shores of the Eastern Continent. Bottles thrown into the ocean have drifted in such a manner as to show a manifest connection between these polar currents and the equatorial one, which we call the Gulf Stream. The great quantities of sea-weed, called the mar di sargosso, which occupies the middle of the Atlantic basin, is another indication of the existence of a circulation of water around the shores of this ocean. This would, of course, set aside the trade-wind theory, which receives another deadly blow from the calculated resistance to the current, which is that of several atmospheres, and of course could not be overcome by the pressure of one.

The initial point of these currents is to be found in the relative temperature of the tropics and the poles. The cold water at the poles being heavy, and the warm waves at the equator light, a system of currents must necessarily be established-one set running from the equator to the poles, the other from the poles to the equator. The initial velocity of the Gulf Stream is supposed to arise from the greater saltness and consequent increased density of these waters over that of the surrounding ocean. This difference is believed to arise from the difference between the evaporation from the one set of waters, and the precipitation of rain upon the other set. Thus, the waters of the Baltic and of the North Sea contain only half the quantity of salts common to sea-water generally, while those of the Gulf Stream are far salter than the mass of the ocean. Hence, by the natural tendency of water to an equilibrium, we should have a flow of this heavy liquid of the Caribbean Sea towards the lighter waters of these distant seas.

But there are other peculiarities about the Gulf Stream. Its current is roof-shaped, being higher in the middle than upon either edge; and yet the drift always takes place upon the outer edge of the stream, and

never upon the inner. When we take this in connection with another phenomenon, well known to engineers-viz: the tendency of cars to run off the track of a railroad running north and south, always on the righthand side, we have an explanation of this drift. It is due to the diurnal motion of the earth, which regulates the tendency of all floating matters, when not impelled by other stronger forces.

The whole Gulf Stream itself has a similar easting, setting finally due east, after it reaches the Banks of Newfoundland. These were formerly supposed to deflect it, but our author believes them to be an effect, and not a cause of the bending of the stream, since it is here that the icebergs, with their heavy ballast of northern gravel, are thawed by the warm waters of the gulf.

The cause of this course is to be sought in the physical forces already alluded to. Our author illustrates it by supposing that Ireland were visible from the Straits of Bennini, and a man were to aim at it with a cannon. He would then sight along the plane of a great circle, but the earth moving faster near the equator than it does towards the poles, the gun would move faster than the target, and the ball would strike ahead of the mark. It is just this course of a projectile that the Gulf Stream

assumes.

There are many other points of interest connected with the Gulf Stream to which our author calls our attention, but our space does not permit us to notice them at any length. The heating properties of this current have long been known. Lieut. Maury compares this system of oceanic currents to the hot water warming arrangements of modern houses. The torrid zone represents the furnace; the Mexican Gulf and the Caribbean Sea, the caldrons; and the Gulf Stream the conductingpipe. To this England owes its damp, moderate climate, and Ireland that verdure which has obtained for it the name of the Emerald Isle.

The most terrific storms occur along this current, and raise the most frightful seas. One of the disasters, consequent upon the turbulent weather of the Gulf Stream, will not soon be forgotten. The wreck of the San Francisco was surrounded with such incidents of suffering, anxiety, and heroic devotion, that the story thrills our hearts to this day as though told but yesterday. But that wreck possesses another interest, of a scientific character. Such was the excitement of public feeling, that Government dispatched two vessels in search of the missing steamer, and applied to the Observatory for information in regard to the point where search should be made. The position of the disabled ship at a certain time being known, the observations already made enabled

the gentlemen connected with that institution to declare her position at the period of search. Had the cutter been in time, her sailing directions would have brought her in sight of the ill-fated steamer. How striking is this illustration of the incalculable benefit likely to be derived from the series of observations carried on at the Observatory, especially when we remember that the barque Kilby lost sight of the wreck during the night, and could not tell where to look for her the next morning.

The atmosphere is next studied, and phenomena of the trade-winds carefully examined. Halley's theory is accepted as furnishing a key to the explanation of these constant winds; but it is considerably modified, in order to adapt it to our present wider range of observation. These winds are shown to be the aerial fountains of our great rivers. The circulation of the air is proved by the microscopic discoveries which Ehrenberg has been able to make in sea-dust. The minute organisms which are carried by the winds that come from Africa are not derived from that continent originally, but from South America; and, from the observed direction of the winds, they must have ascended first into the upper strata of the atmosphere, and then descended again, changing their course.

But we find ourselves already led on by our pleasant memories of this delightful volume far beyond the common limits of a critical notice. We must therefore reluctantly leave off, saying, only, that it is a book which is needed to fill a gap in science, that it is written in a most fascinating style, and abounds in new and valuable information, and, finally, that it deserves a place on the same shelf with the Cosmos and the Aspects of Nature.

Report of the Superintendent of the Coast Survey, showing the Progress of the Survey during the Year 1853. Washington: Robert Armstrong, Public Printer. 1854.-One of the most important and generally interesting operations now carried on by the Federal Government is the exploration of our coast. Proverbially one of the stormiest and most dangerous in the world, deservedly dreaded by the sailor as well as the passenger, and yet visited by a rich and extensive commerce, it becomes an imperative duty to ascertain its dangers, and, if possible, to provide against them. This is the main occupation of the Coast Survey Department, which has charge of the entire Pacific and Atlantic coast of the country. Its members are constantly engaged in taking soundings off various shores, exploring harbors, searching and deciding on