The second division—hydrography, commences with charts of the ocean, and with charts of those wondrous, and still comparatively obscure, agencies, the eleven currents which intersect it in all quarters. Then follow charts of the Pacific and Indian Oceans, now forming such new and interesting objects to the navigator and the philanthropist. We then have maps of the tides and river systems.
The Indian Ocean, now scarcely more than beginning to be the subject of scientific inquiry, will probably assist us effectively in the discoveries of those most important agents, the winds. The monsoon and the typhoon of those seas exhibit characters apparently almost exclusive. To ascertain their general direction, and their especial limits, must be a great boon to the commerce which is now directing itself, with such renewed vigour, to those tempting regions. The lights which have been thrown on the use of the barometer, and on the rise and direction of the West Indian storms, have already given a species of guidance to this important investigation; and if the theory of the hurricane can never render its power harmless, it may, at least, make human precaution more vigilant, and, of course, more successful.
Those investigations are naturally followed by the third great division of the work—meteorology. The value of exact observations on wind and weather must have been felt from the beginning of the world; but, until our day, it was little more than the science of the shepherd, who foretold a high wind or a shower, generally when both had already come. The barometer and thermometer, though both well known, and both admirable, had done but little for a science, which, without exactness of practice and connexion of causes, is nothing.
Humboldt, by his attempt to trace lines of temperature on the map of the globe, first raised those scattered conceptions into the shape of a science. Yet Humboldt was not the original inventor of the inquiry into the mean temperatures. Meyer of Gottingen first threw the observations on this important and evasive subject into the well-known formula, which made the temperature depend on the square of the cosine of the latitude. Playfair followed, by including in his formula the elevation of the place and the season. The object of Humboldt was, to determine, by a series of curves on the earth's surface,the points at which—however the temperature differed from time to time—the average annually was the same. On this important subject we are now furnished with a map of striking detail and execution.
The late magnetic researches pursued round the globe may, at no remote period, establish a connexion between the revolution of the magnetic poles and the isothermal lines, as had been long since conjectured. But, as practical science advances, we shall probably see all the great agencies of nature combined,—if not all shown to be but the modifications of one.
The Hyetographic or rain chart of this volume gives a most complete and minute detail of a most important subject. It exhibits the rains of the globe, in their constant gradation from the equator to the pole, in their influence on the seasons, and in their degrees from the plains to the summit of the hills. A map is added, on the polarisation of the atmosphere—almost a new science—with an explanatory article by Sir David Brewster.
The fourth division is Natural History; itself divided into Phytology, Zoology, and Ethnography. This division abounds in maps, and in these departments they are obviously of the most necessary use. In the description of plants and animals, the pencil must speak, the tongue loses its faculty; a sketch, executed at the moment, will give a fuller explanation than any dexterity or copiousness of language can. We accordingly have here charts of all the geographical positions of the plants important to the food of man, and of the geographical distribution of plants on the surface of the globe.
The Zoological charts give the regions, the habitats, and the characters of all the diversities of animal life on the land—from the mammalia to the birds and reptiles.
The Ethnographical portion, or view of the general position and races of the European nations, commences with a fine map, by Kombst, exhibiting a view of all its varieties, with reference to birth, language, religion, and forms of government. Having thus glanced at the scientific contents of this noble volume, we propose to give some sketches of those portions of the globe which, within the last half century, have become the refuge or the property of the emigration from the British shores.
Australia, the fifth continent, is nearly as large as Europe. Divided by the tropic, it is capable of producing the chief plants of both the temperate and the tropical zones. Its principal geological feature is a mountain chain, which, extending through its whole length on its eastern coast, runs on the north into New Guinea, and on the south into Van Diemen's Land. From its immense size, (two thousand four hundred miles from east to west, and one thousand seven hundred from north to south,) and from the savage state of its native population, the exact nature of its central portion is yet only to be conjectured. But conjecture has been busy; and by some it is held, that the centre is a Mediterranean, from the direction of some of the rivers; by others, that it is a huge Sahara, from the hot winds which often blow towards the coast. But two late expeditions, sent from Sydney, have passed, without difficulty, the one as far as Torres Strait, and the other almost to the head of the Gulf of Carpentaria. It is true, that neither of those was towards the centre; but they had the wiser practical object, of ascertaining the nature of the country most important to the British settler—that great tract lying between the mountains of the cast coast and the sea. And that country they found to be fair and fertile, temperate and easily accessible. The whole expedition of Colonel Mitchel, the surveyor-general, has almost the air of romance. He describes the country, in the latter half of his advance to the north, as not only of remarkable richness, but of singularly picturesque beauty; the latter a quality of the most unusual order in Australia. To the customary complaint of want of water in the interior, Colonel Mitchel answers, that Australia, to remedy this defect, wants nothing but labour; that it has rivers which supply water in the rainy season sufficient for the use of the year; that the formation of the land everywhere suggests the idea of vast reservoirs; and that man has only to complete what nature has begun. The British settlements in the south and west will probably soon bring these resources into action.