elastic force burrowing "straight on end" like a mole under the ground, and, nine times out of ten, finding less resistance in its front than in any other direction; while, if such a ridge were subsequently to "cave," or drop in, it would leave no noticeable hollow. It seems more consistent with appearances to refer these clefts to the cracking and splitting, which would result from a contraction affecting the superficial more rapidly than the subjacent material. Such an explanation would not be without serious difficulties, from the very plastic condition of the surface which would be required, and the inconsistency of such a state with the sharpness and cleanness of earlier outbursts; still it may claim attention; but we are as yet too little advanced in the collection and comparison of facts to be able to form any very conclusive generalization. One thing is evident; that if we follow the example of Schmidt in including the Great Valley of the Alps in the catalogue, it is there that we shall find the most satisfactory test of our hypotheses, and that nothing can be admitted which fails to account. for the production of that colossal gorge.

At any rate, B. and M. consider it certain that with, perhaps, a few exceptions, these clefts belong to the latest epoch of the lunar formations. Assuming the identity of their origin with that of the long low ridges, we may remark that it does not appear how this idea can be made to harmonize with the aspect of these latter, which in so many cases look like channels of communication contemporaneous with the formation of the more important mountains and craters; but there seem to be instances in which the posterior date of the clefts is capable of proof; and one such will shortly be laid before us. Considering it as well established that their general epoch is comparatively a modern one, these observers do not wholly deny the possibility of such processes being still in operation; and they admit that their opinion to the contrary, however strong, rests only upon the experience of seven or eight years.

The inquiry-a very curious one has also been treated as an open question by a modern authority of great weight, Dr. J. F. J. Schmidt. This eminent astronomer has informed us, in his interesting memoir on the "Rills" of the Moon, that he has been occupied for twenty-five years in the study of lunar topography, during which he has made upwards of 1000 drawings and 3000 height-measures, without coming to any other conclusion than that no change of surface has recently taken place on any considerable scale; but that, as to the progressive multiplication of these minute clefts, he has by no means abandoned the idea of its possibility. He has succeeded in adding a great number to those already known; but this may

be readily accounted for, partly by his having made them more his especial study than B. and M. could do while occupied in a general selenography, and partly by the superior aperture of his telescope, and, still more, the charming purity of the Athenian sky, far transcending that of Berlin or even Rome. The value of his evidence may be understood from his principal instance, which relates to the region N.W. of Aristarchus (43). Here, 1862, May 10, with a power of 200 on his 8-in. dialyte (an instrument of inferior quality, from the decomposition of the glass), he detected no less than fifteen unknown clefts, some of considerable length and breadth, and not more difficult than many shown by Lohrmann and Mädler. He saw also, in the same neighbourhood, a group of new craters of no remarkable minuteness. Schr. had drawn this district six times; L. and M. must have done so eight or ten times, and under opposite illuminations. Schmidt himself had made twenty-one sketches and numberless observations, without perceiving these objects. On three evenings in 1836, M. drew the very spot, probably with the great 9-in. achromatic at Berlin; and while he inserted some smaller craters, omitted larger ones, as well as the clefts. In May, 1853, Schmidt had missed them all with the same instrument. All circumstances considered, if this is not wholly conclusive, we may look upon it as advancing a considerable way towards a conclusion. Schmidt's figure of this region gives high promise of the hitherto unpublished general Map of six (Paris) feet in diameter, which he is preparing solely from his own observations, and which we sincerely trust he may be permitted to complete. His catalogue of clefts gives 11 discovered by Schr., 75 by L., 55 by M., 6 by Kinan, and 278 by himself up to Feb. 1865425 in all; a number which his diligence has probably since considerably increased.*

It is

Having spent so much time in the general description of these curious objects, we must proceed to the complete and very instructive specimens referred to in the opening of our remarks; of which, and of the principal features of the neighbourhood, a diagram accompanies the present paper. copied from the Map of B. and M., omitting, however, a great accumulation of detail, and retaining only such features as serve our immediate purpose. The top coincides with the Lunar Equator. Agrippa and Godin will be easily identified

One of those ascribed to Schr., the grand cleft in the Alps, was really discovered by Bianchini. Gruithuisen detected many, but has in general given very defective identification. Two of his, at least, are I think omitted in this list; and two if not three more might have been added which I noticed on the floor of Atlas with Mr. Bird's 12-in. silvered glass reflector, 1865, Sept. 7. I have also seen a bent cleft in the interior of Furnerius with a 5-in. object glass.

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 bere 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.

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 commences. The 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 King s College, London, and late Fellow of Jesus College, Cambridge, etc., etc. Wm. Allen & Co.