THE PHYSICAL GEOGRAPHY OF THE SEA AND ITS METEOROLOGY.

COMMANDER MAURY has long been known by the practical, useful and comprehensive character of his nautical compilations and original writings. Assiduously laboring for many years, aided by scientific professors as well as by experienced practical men, he has done ample justice to the confidence and liberality of the United States. Successive editions of his Sailing Directions and Charts, in number many thousands, have been widely and well distributed, gratuitously, among those who are responsible for life at sea-whose business is on the ocean. We were informed, at a meeting of the Royal Geographical Society, that more than seven hundred quarto volumes and four thousand large charts have been thus dispersed among sea captains and instructors in maritime affairs, besides others in Great Britain and Ireland; while a proportionate number has been distributed in Holland, France, Portugal, Spain and Italy, above and beyond the much larger supply similarly granted to every United States ship of war, and to every merchantman willing to coöperate in observing.

Not only has a great amount of available knowledge been thus circulated directly, but a spirit of observation, a habit of noting and comparing, has increased most advantageously during late years among officers at sea-indirectly consequent on the acquisition of such knowledge as it has been the object of Commander MAURY, as it was likewise of our own Admiral BEAUFORT, to collect, digest and diffuse. We refer especially to our late Admiralty Hydrographer, by whose sagacity, talent and perseverance all maritime nations have benefited very generally.

After thus rendering special service to the maritime world, the various publications that have issued from the National Observatory at Washington have been submitted, by its indefatigable superintendent, to a process of elaborate selection and condensation, out of which, with much new matter, has resulted the present well-printed, clearly-arranged and most interesting, as well as useful, octavo volume. A careful perusal has shown us the necessity of noticing a few weak points-for some such, of course, there are―lest inexperienced persons should be led into occasional difficulties, even by so admirable a general guide.

That a work essentially maritime should be heralded with the word Geography" has occasioned doubt—a feeling which has soon yielded, however, to the reflections that the term includes all the world's surface, the greater part of which is covered by sea-and that it has the sanction of HUMBOLDT and HERSCHEL. In the almost overwhelming aggregation of ideas suggested by even a superficial glance through the table of contents, it is hard to eliminate the most striking, and to comment on those alone, briefly, without digressing into a string of essays. In truth, it is a text-book for many a long discourse.

In the first chapter are explanations and illustrations of oceanic and atmospheric phenomena, as pleasant to read as worthy of their writersone being the lamented Dr. BUIST. But in treating of the tides, some reference to the later researches and views of WHEWELL and HERSCHEL is desirable. A perusal of the article, "Physical Geography," in the

present edition of the Encyclopædia Britannica, and reference to the consecutive essays on the tides, which have been so luminous to seamen, show that those authorities are indiposed to attribute tidal results in northern seas to the sole or principal effect of a great tide-wave generated in the expanse of the southern ocean. They advert to a westerly and returning movement in mass, depending on depth and width of water, the attractions of moon and sun, and the obstacles opposing a continuous westerly wave. Such an undulation was described long ago by HERSCHEL as "exceedingly broad and excessively flat." It has the least sensible effect near the middle of the ocean; but is evidenced by the impulse given near a shelving shore, or an estuary where the sea has a positive current, and, therefore, a momentum, additional to the merely local, and (unless opposed and broken) vertically circuitous motion of a pure undulation or wave of water.

Horizontal or lateral movements, occasioned by obstructions of continents, islands or shallows, to great tidal waves, may have far more effect, geologically and on climates, than has hitherto been noticed. There is an impulse in one direction, towards the west, after the attracting bodies -moon and sun-greater than the returning or equilibrating action towards the east; and this, continued incessantly, must cause a preponderance of oceanic movement westward. Do we not see the results in comparative heaping or forcing of water into the Gulf of Mexico, towards the Indian Archipelago and the east coast of Africa? And are there not currents setting from those regions northward or southward, if not both, and eastward again where impeded and circumscribed-such as the Gulf Stream, the Japanese current, the South Pacific, South Atlantic and Lagulhas currents? These currents, originated by consecutive tidal impulses, are doubtless strengthened and promoted by prevalent winds, especially the perennial and the monsoons.

The depths of ocean, their conditions and their temperatures become more and more subjects of interest as we gradually approximate towards accurate knowledge of them, and as our requirements oblige us to investigate their mysteries. Commander MAURY's pages on these recondite secrets are full of valuable ideas.

1

He had the satisfaction (during his too brief visit to London, a few days ago) of meeting those who had just brought living creatures from more than seven thousand feet below the sea, and of inspecting an ingenious device for ascertaining temperature at any depth, irrespective of pressure or condensation. It is on the principle of a metallic barometer, so far as having plates of metal that expand or contract according to temperature, their ends working a lever which ranges through a graduated arc, carrying, either way, passive indexes by which extreme temperatures are shown on similar arcs. The water has free access through this new apparatus. Excellent advice and sound opinions are given by our author respecting electric wires and their coverings. But he ascribes the perishing of their absurd iron armature to galvanic action alone, namely, that caused by sea-water, with the iron and copper of the wires. In many, if not in most instances, there is a rapid oxidation of the iron, wherever covered by water only, and not excluded by mud, or otherwise, from air, in the water, in addition to direct and destructive action of copper ore, or veins, cropping out at the bottom of the sea near land. Instances are on record of chain cables ruined, in a few weeks only, by overlying a rocky

patch of copper ore. Where a metallic defence against chafing is indispensable, as over rocks, in shallow water, copper only should be used.

The officer recently employed by France to examine and report on submarine telegraphy in general, has stated to his government that the best insulator is caoutchouc, and that a wire of large section is better than smaller wires. Experiments are in favor of india-rubber, as now applied, certainly; but is it probable that any vegetable substance will last long under water-especially sea-water-abounding in animal life and a variety of material ingredients? Some combination of vitreous, although rather ductile and flexible character, insulating and durable, may yet be devised by chemists and electricians.

Trials, only just concluded, with wires varying in their sectional area, have occasioned a hasty conclusion against other evidence of a different nature, that the "conductivity" of a small wire equals that of one larger in section.

In these experiments, while the smallest wire could transmit the charge without special impediment, it would go as fast and as far as in a wire of indefinitely large sectional area; but if the small wire were overcharged, or heated, to a degree diminishing "conductivity" while much increasing retardation, or what the French term "condensation," then a sensible difference would be discovered immediately. A man may walk along a narrow way as fast and as far as along a wide road, while he is not jostled, impeded or inconveniently squeezed. When lightning-the electric current from Nature's battery in the atmosphere-strikes the spindle of a HARRIS conductor fixed in a lofty mast, it is always carried down to the sea, not only without damaging any thing, (unless, perhaps, melting a few inches of the small spindle point,) but without displacing a particle of covering paint, or leaving a trace of its progress. Could this be so if the mysterious agent did not traverse the solid-and more readily-with less heat, and therefore without fusion, when finding ample metallic pathway?

To go further into this question-to show the fallacy of very prevalent ideas about "circuits," and to give a simple view of inductive action accordant with Prof. FARADAY's latest discoveries and investigations, would be misplaced here, however enticing. Indeed, it would be as futile as presumptuous to offer immature opinions, in addition to the few wellascertained facts.

In the second chapter a lance is aimed at the proof armor of a most redoubtable champion of philosophy and science. To understand the controversy, more than the following extracts should be read, especially arguments urged in support of an idea that comparative density, saltness and evaporation (their chief cause) are the principal, if not the only originators of oceanic currents on a great scale. Commander MAURY says:

"With the view of ascertaining the average number of days during the year that the N. E. trade-winds of the Atlantic operate upon the currents between 25° N. and the equator, log-books containing no less than 380,284 observations on the force and direction of the wind in that ocean were examined. The data thus afforded were carefully compared and discussed. The results show that within those latitudes, and on the average, the wind from the N. E. quadrant is in excess of the winds from the S. W. only 111 days out of the 365. During the rest of the year the S. W. counteract the effect of the N. E. winds upon the currents. Now, can

The

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the N. E. trades, by blowing for less than one-third of the time, cause the Gulf Stream to run all the time, and without varying its velocity either to their force or their prevalence? Sir JOHN HERSCHEL maintains that they can; that the trade-winds are the sole cause of the Gulf Stream; not, indeed, by causing a head of water' in the West Indian seas, but by rolling particles of water before them, somewhat as billiard balls are rolled over the table. He denies to evaporation, temperature, salts and sea-shells any effective influence whatever upon the circulation of the waters in the ocean. According to him, the winds are the supreme current-producing power in the sea. This theory would require all the currents of the sea to set with the winds, or, when deflected, to be deflected from the shore, as billiard balls are from the cushions of the table, making the littoral angles of incidence and reflection equal. Now, so far from this being the case, not ONE of the constant currents of the sea either makes such a rebound or sets with the winds. The Gulf Stream sets as it comes out of the Gulf of Mexico, and for hundreds of miles after it enters the Atlantic, against the trade-winds; for a part of the way it runs right in the wind's eye.' The Japan current, the Gulf Stream of the Pacific,' does the same. The Mozambique current runs to the south, against the S. E. trade-winds, and it changes not with the monsoons. ice-bearing currents of the north oppose the winds in their course. BOLDT's current has its genesis in the ex-tropical regions of the south, where the 'brave west winds' blow with almost, if not with quite the regularity of the trades, but with double their force. And this current, instead of setting to the S. E. before these winds, flows north in spite of them. These are the main and constant currents of the sea-the great arteries and jugulars through which its circulation is conducted. In every instance, and regardless of winds, those currents that are warm flow towards the poles, those that are cold set towards the equator. And this they do, not by the force of the winds, but in spite of them, and by the force of those very agencies that make the winds to blow. They flow thus by virtue of those efforts which the sea is continually making to restore that equilibrium to its waters which heat and cold, the forces of evaporation and the secretion of its inhabitants, are everlastingly destroying. If the winds makes the upper, what makes the under and counter currents? This question is of itself enough to impeach that supremacy of the winds upon the currents, which the renowned philosopher, with whom I am so unfortunate as to differ, travelled so far out of his way to vindicate. The 'bottles' also dispute, in their silent way, the 'supremacy of the winds' over the currents of the sea. The bottles that are thrown overboard to try currents are partly out of the water. The wind has influence upon them; yet of all those-and they are manythat have been thrown overboard in the trade-wind region of the North Atlantic, or in the Caribbean Sea, where the trade-winds blow, none have been found to drift with the wind; they all drift with the current, and nearly at right angles to the wind. That the winds do make currents in the sea no one will have the hardihood to deny; but currents that are born of the winds are as unstable as the winds; uncertain as to time, place and direction, they are sporadic and ephemeral."

Perhaps too much has been made of the very small differences between the specific gravity of the ocean in various regions. Assuming 1,000 parts (say grains) as the weight of one volume of pure distilled water, the

average weight of an equal volume, by measure, of ocean water, is 1,027 of such parts. Rarely, indeed, has it been found, at or near the surface, to exceed 1,030; but it diminishes at the surface first, after heavy rains, or within the influence of fresh-water rivers, (such as the Amazon, Orinoco, Mississippi, Congo, Ganges, Indus, Hoang-Ho, &c.,) and, in general, on soundings near land. It is very difficult to read the scale of a hydrometer accurately, when a ship has motion, and if very great care be not taken, an oily finger, or the adhesion of dust on so delicate a test instrument, may make a difference (as the late Mr. WELSH proved) of more than two divisions or parts of the scale, between 1,000 and 1,040.*

The chapters on climate and commerce, on the atmosphere, and on rains and rivers, are full to repletion of valuable remarks, the results of collecting in all directions before sifting and condensing. We could wish that more frequent reference had been made to authorities whose ideas, if not words, strike the mind in reading these well-filled pages. We have a reverential attachment to the works of early navigators, such as DAMPIER, COOK, LA PEROUSE and FLINDERS, and have been accustomed to prize the experience, inaccessible to many, we admit, of other seamen in this century. In quoting instances of excessive fall of rain, our excellent author has been misinformed on two material points, and has, of course, proportionally weakened the force of arguments based on those supposed facts. Speaking of the rain fall in Patagonia, he mentions nearly 150 inches in a year, quoting KING and FITZROY. On referring to "The Voyages of the Adventure and Beagle," we can find no such statement. No record of rain-fall was made by the Beagle's officersonly one by those of the Adventure, which was for two months only in Chiloe. The much lamented FOSTER, when in the Chanticleer, near Cape Horn, had a rain-gauge in St. Martin's Cove for rather more than a month of particularly bad weather, in the rainest season. Between Western and Eastern Patagonia we presume there must be great differences of climate in the same latitude, owing to the lofty Andes on the west, and prevalent westerly winds which blow over or round their snowy summits. The other instance, which it seems necessary to notice, is the presumed fall of about 600 inches of rain in a year in India. Examination of Col. SYKES' statements has shown, that during heavy rain, of a very rainy season, about 300 inches of rain fell. But the rest of the year was dry in that country. Prof. OLDHAM's facts, however, support Commander MAURY's statement of 600 inches in one year.

At the opening of his chapter on red fogs and sea breezes we read: "The inhabitants of the sea-shore in tropical countries wait every morning with impatience the coming of the sea breeze. It usually sets in about ten o'clock. Then the sultry heat of the oppressive morning is dissipated, and there is a delightful freshness in the air, which seems to give new life to all for their daily labors. About sunset there is again another calm. The sea breeze is now done, and in a short time the land breeze sets in. This alternation of the land and sea breeze-a wind from the sea by day and from the land by night—is so regular in inter-tropical

To avoid recurrence to this point, it may here be observed that, in pages 216 and 222, the percentages stated by the author, as bases of his argument, are those of the differences between the specific gravities; not those of the respective whole numbers themselves. The addition of a figure has given an undue importance to the matter.