as 26 and 27 in our little Map; the remarkable crater Manilius (24) lies only a little below the area represented; for telescopic search these features, previously recognized from their position relative to the M. Serenitatis and the Apennines, will always be sure guides. The cleft passing through Hyginus is the first described by B. and M. It is conspicuous enough to be seen in a good telescope with a power of 40, and under almost any illumination. Its commencement, from the N.E., is at a long, low hill, and here it appears almost as a flat valley, nearly 1 mile wide, but after a length of 9 miles it becomes narrowed to a breadth of 1300-1500 yards, with such steepness and depth that, in one instance, B. and M. distinctly perceived the delicate black line of shadow on one side running parallel with the brightly-illuminated opposite bank. In this part of its course, which is through level ground, it encounters four little craters, the second of which is 3200 yards, or nearly 2 miles across; the others 2000 to 2500 yards. After running about 50 miles it reaches the larger crater, Hyginus. But what happens to it there, and in its further progress, must be reserved to a future opportunity.

OCCULTATIONS.

Aug. 2nd, 22h. 34m. to 23h. 16m., or in common reckoning, 3rd, 10h. 34m. to 11h. 16m. A.M. the planet Mars. This obviously requires a large aperture and equatoreal mounting. -15th, e' Aquarii, 6 mag. 11h. 54m. to 12h. 52m.-16th, λ Aquarii, 4 mag. 7h. 50m. to 8h. 51m.

PHYSICAL GEOGRAPHY AS A POPULAR STUDY.*

AMONGST the newly-cultivated branches of science, Physical Geography is one of the most generally interesting, because its broad facts and reasonings are easily appreciated, and no expensive apparatus is necessary for its pursuit. It ought to form a prominent subject in any national system of education; and when it is absent, school-teaching in what is called geography," usually consists of little more than lists of latitudes and longitudes, courses of rivers, and positions of cities, separated from all associations that could give them the character of true knowledge. The simplest facts and problems of physical geography are eagerly apprehended by young children, when properly explained, while the complex considerations of terrestrial structure, and its influence upon temperature, climate, and civilization, tax the highest intellect, and furnish material for the profoundest thought.

During the last twenty years many excellent works on physical geography have been produced by various writers; but no one has appreciated more clearly than Professor Ansted the range of subjects that ought to be included, or the way in which they ought to be presented, so as to make the philosophy of the science intelligible as well as its facts. The advantage of a comprehensive scheme is very great, though it is necessarily associated with an unavoidable degree of incompleteness, when, as in the book before us, a variety of important matters are compressed within the limits of a few hundred pages.

mences.

Professor Ansted begins by considering "the Earth as a Planet," after which follows a chapter on "Physical Forces," succeeded by one on " the Succession of Rocks." These chapters are introductory, and it is in the second part that what is commonly understood as "Physical Geography" really comThe distribution of land occupies three chapters; water, including ice phenomena, four chapters; four more are devoted to air, including winds and climate; igneous phenomena are treated in two chapters; and the work concludes with expositions of the broad features of terrestrial life. Any one of these subjects might be easily expanded into a treatise the size of the whole book; but there is an obvious advantage in presenting them in an epitomized form, and in the order which the Professor has adopted.

"Physical Geography." By Professor D. T. Ansted, M.A., F.R.S., F.R.G.S., F.G S., Honorary Fellow of Kings College, London, and late Fellow of Jesus College, Cambridge, etc., etc. Wm. Allen & Co.

The size of the earth, its average density, the velocities of its diurnal rotation, and of its annual course, the size and weight of its satellite-these and similar facts belonging to astronomy, supply considerations which lie at the root of physical geography. We are continually, and, on the whole, equally affected by one class of astronomical facts, such as the recurrence of night and day, summer and winter, lunar action on the tides, and many others; while another class of astronomical facts relate to changes very slowly effected, and only producing important results after the lapse of long periods of time. We, or the people of any given generation, are of course most immediately influenced by the quickly-recurring changes; but, looking to the laws of succession and continuity, manifested throughout the operations of nature, it will be seen that our physical structure, our methods of life, and even our, habits of thought, are, to a certain and large extent, the results. of previous conditions of our planet, dating back even to its origin in the remote abysses of the past.

A very important consideration, well adduced by Professor Ansted, arises out of the astronomical fact that the eccentricity of the earth's orbit is the subject of secular changes. "When the eccentricity is greatest, the greatest distance of the sun from the earth may amount to 102,256,873 miles, and its nearest distance will then only be 87,503,039 miles, showing the very considerable difference of 14,753,834 miles, or more than one-seventh of the larger semi-diameter. This is a very important fact; for, as the amount of heat received from the sun varies as the square of the distance, it follows that the quantity of heat received in the former position, compared with that in the latter, will be as 19 to 26."

It will take twenty-four thousand years for the minimum of eccentricity to be reached, so that the change does not immediately concern the present inhabitants of the globe; but in past periods it may have materially affected the creatures then living upon it, and likewise produced modifications of form and climate, the influence of which has descended to our own times.

At present the earth comes nearest to the sun in winter; but "if, when the eccentricity is greatest, the case is reversed, the land of the northern hemisphere would be warmed only to the very minimum extent in winter, and heated to a maximum in summer, the difference would then equal one-fifth of the whole. There would then be far more extreme climates on the

earth than there are now." In his "Outlines of Astronomy," Sir John Herschel, commenting on speculations of this nature, observes that about four thousand years before the Christian era, the place of the perihelion must have coincided with the

vernal equinox (or have been situated in long. 0°), and in long. 90° about A.D. 1250. In A.D. 11700, he adds that "the extreme summer and winter of the southern hemisphere will be transferred to the northern." Such changes must have taken place thousands of times in geological eras, and may have partially accounted for those changes of climate which geology and paleontology show to have occurred.

Terrestrial climate is still more strongly affected by the disposition of masses of land and water, the height and direction of mountain-chains, the character of the soil, its being covered with trees or left bare, etc. Of the whole surface of the earth "only a fourth part, or about fifty-two millions of square miles, rises above the uniform level of the water and form land," and it is remarkable that a great part of this land "is grouped round one hemisphere, so that not more than one twentyseventh part has land opposed to it on the opposite hemisphere. Thus, if a person stationed vertically over Falmouth in England could see half the globe, he would see more than forty-nine out of the fifty-one millions of square miles of land, or about an equal surface of land and water. If, however, he were perched equally high above New Zealand, he would see ninetysix and a half millions of square miles of water, and less than two millions of square miles of land."

Any important change in the relative proportions and dispositions of land and water would materially modify the earth's climate. Supposing the quantity of each within a moderate number of miles from the surface to remain the same, but the shallow seas to be considerably deepened and at the same time narrowed, and the bulk of continuous continents very much augmented, there would be a diminution of evaporation, and an addition to excessive or continental climate. On the other hand, rendering deep seas shallower, and diminishing the area of land by a corresponding change in its level would produce opposite effects, and the violence of the alteration would depend partly on the average extent to which levels were modified, still more on the position of the high lands.

The laws which determine the relative disposition of land and water are very little known; and hence there is room for two opposite suppositions, according to one of which the present arrangement depends on permanent causes of very ancient date; and, according to the other, great changes may have taken place within comparatively moderate periods, and equally important alterations may still be going on, though their rate may be very slow. Professor Ansted refers to a speculation of Mr. James Yates, that the centre of gravity of the earth would not be coincident with the centre of magnitude without the protuberance of water on one side, and that the inequality of land

in the two hemispheres is permanent. We have not read the paper in which Mr. Yates put forward this ingenious speculation, but we doubt there being sufficient evidence to raise it above the level of a conjecture, and when we look to the action of aqueous, igneous, and aerial causes of modification, we are not disposed to attach very great importance to a difference of average specific gravity, if it exist, in the land of the two hemispheres, through a great metalliferous deposit in one, and a more cavernous texture in the other.

The great continental mass ranges from north-east to southeast, thus crossing the earth's diurnal motion from west to east, but what was the direction of former continents we do not know; it may at some periods have been widely different from what it is now.

Passing for the moment from the consideration of the disposition of land and water masses as affecting climate, and through that acting upon civilization, another important influence of such arrangements must be noticed, and that is the facility they afford, or the difficulties they oppose to, intercommunication and commerce. Hitherto lands much indented by seas and navigable rivers have had an enormous advantage in this respect over massive continents; and the advance of Europe, as compared with Asia, has, in no small degree, been occasioned by the extent and sinuosities of its coast lines. In Europe there is a mile of coast for every hundred and eightyseven square miles of surface; in Asia the proportion is one mile of coast to five hundred and twenty-eight square miles of surface; in Africa one to seven hundred and thirty-eight; in North America one to two hundred and sixty-six; in South America one to three hundred and thirty. But we now live in an epoch in which human invention modifies the value of these conditions, great continents are being traversed by railways, even before roads are constructed, and ultimately this may more than compensate for their deficiency in coast.

The physical characteristics of the different continents are peculiarly interesting:-" Europe is, on the whole, a hilly and mountainous country. Asia contains the loftiest mountain groups of the globe, and also vast plateaux. Africa has its lofty mountains and elevated plains. Deserts very little above the sea level accompany the plateaux; but are small in comparison. America, notwithstanding the important and lofty chains of the Andes and Rocky Mountains, is mostly characterized by its plains. The high lands are a fringe of plateaux, and the gigantic valleys, of which those of the Mississippi, the Amazons, and La Plata are examples, are low plains. Mountains, except in the great chain of the Andes, in Central America and on the west coast of the Andes, are subordinate,