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does not, however, refer to this) was not anacquainted with such appearances, having noticed them several times in craters (he especially mentions Copernicus, Theophilus, Zach, and Sacrobosco), where an ill-defined edge of brownish grey rendered the length of the shadow difficult of measurement, while other perfectly similar craters in the same neighbourhood were free from any such peculiarity. For an explanation he sees no need of having recourse to penumbra or atmosphere ; it might be sufficiently accounted for by a multitude of colossal blocks on the crest of the ring, whose narrow lines of shadow cast upon the opposite wall, with their intervening streaks of light, being separately undistinguishable by us, would produce the confused general impression of a diluted border. In this case, he refers to some terrestrial correspondences, such as the shadow of a row of close-set iron spikes on the top of a door or wall, seen from a suitable position and distance; or the shadow of a fringe of ice-ruins and rock-pinnacles falling on a snowy slope, which he once remarked in great beauty from the Wengern Alp; the edge of a mountain shadow, elsewhere sharp, becoming very indistinct when projected on the very obliquely slanting snows of the Silverhorn and Guggi glacier, the employment of a common eye-glass showed the cause to lie in the confused impression of many long, narrow, separate streaks of shade. (We may observe, by the way, that the eye for terrestrial scenery, evident in this great observer, qualifies him in a high degree for the analogical interpretation of the varied aspects of the Moon.)
But though this is a plausible elucidation, it may not be the true key to the mystery. To the objection that it would be difficult to account in this way for so broad a zone of duskiness as Schr. has represented, falling, too, upon a slope inclined in the wrong direction, it might be answered that his drawing was too rough to be trusted in minute details, and that he seems to have satisfied himself too easily upon the subject. But it is evident that more has yet to be explained, and that the point deserves study. Though there is no improbability in the idea that the summit of a ring should be crested with a row of natural battlements or pinnacles; yet these, if close enough to produce a confused half-tone in the part of the shadow cast by the ridge where it lies facing the sun, would in every other position overlap one another so much in perspective as to intercept too much light, and produce a full and defined shade. Here, therefore, a very powerful instrument would so far decide the question that an equal intensity of halftone along the whole border of the shadow would negative Schmidt's solution. And so would any want of periodical recurrence in the phenomenon-a point which seems to have
escaped attention. Of course, in any comparison of observations, a very close similarity of conditions would be required; but this being fulfilled, the non-appearance of the border would so distinctly point to some unexplained and possibly unsuspected cause, as to invest the inquiry with peculiar interest. Any observer making an especial study of the edges of the interior shadows of great craters might not regret the loss of time in the end.
The position of Eratosthenes is in the midst of landscapes of very contrasted characters–the level Sinus Æstuum, the towering Apennines, the vast extent of the Mare Imbrium, and a most remarkable honey.combed district which we shall find to the E. The line of the Apennines may be considered as continued through it in that direction by a broken range of hills, of which the extremity, of great steepness on every side, especially N.-the n of B. and M., attains according to them 4000ft. : Schr. had given it 250ft. more. Running S. from the E. side of the wall is a more considerable range, reaching near its beginning, according to Schr., 9500ft., and leading down to a large ring named Stadius by B. and M. when they failed in identifying, as has been mentioned, Riccioli's spot of that name. This, 43 miles in diameter, and therefore surpassing in that one respect its overpowering neighbour Eratosthenes, is a strange contrast to it in other ways, the embankment, on which they have figured two or three minute craters, being as a whole scarcely 130ft. high, the mere outline of a wall, so as to have escaped the attention of B. and M. for three years. face is not depressed, and the question may possibly suggest itself, Have we here all that remains visible of a great ring, whose height without and depth within have been subsequently reduced to these trifling proportions by a circumfusion and penetration of matter, once fluid or plastic, but now consolidated ? The inquiry is thrown out as a mere suggestion for examination and thought, with the sole addition that there are very many other parts of the lunar surface where such a suspicion might as naturally arise. B. and M. remark in its interior only some ridges and one small crater, probably less elevated even than the ring. Of this more hereafter. We next cross the curious district already alluded to, and to be described at a future time, to the magnificent Copernicus (30), one of the most imposing and best-developed specimens of its class. There are many its equals or superiors in size and depth in other parts of the Moon, but few more remarkable at once in themselves and their situation ; its structure is very perfect, and its insulated position, and the absence of any material foreshortening, exhibit it to especial advantage. The diameter of its colossal wall is about 56 miles. This wonderful rampart, which does
not deviate much from a circular form, bears a comparatively narrow crest, very brilliant, even to 8° and 90, in full illumination; under especially favourable conditions it appears like a string of pearls, and on one occasion B. and M. believed that they counted upwards of 50 of these probably very minute summits. The highest point on the W. attains 11,300ft., on the E. it is only about 300ft. lower, as measured from the depth below. Schr. had given 9,600ft. The whole breadth of the wall is considerable, and its structure is very complex; nowhere, perhaps, on the lunar surface is the terrace-form more obvious, though some of the ridges can hardly come under that designation, being divided by deep gorges from the central crest. This circumstance, and the serpentine form of some of them, had been noticed by Schr., and beautifully represented by Sir J. Herschel in his Outlines of Astronomy," where the portrait, though anonymous, may be easily recognized. Between the innumerable ridges which break up the inner slope on the N., Schr.'s 27ft. reflector showed him about 20 minute hills. He remarks that if the interior were inhabited by creatures like ourselves, their journeys would be attended with much difficulty; "but Omnipotence knows no bounds in the manifold organization of its creatures." There is a considerable central mass, consisting of six separate summits, of which two overtop the rest; the small one between them, discovered by Schr., could not be found by him upon a subsequent occasion, but appears in the drawing of H.
Schmidt, who considers this ring as combining all the characters of the class to which it belongs, will hardly be contradicted when he says that “ careful studies of this incomparably beautiful and magnificent image alone fully counterpoise those of a hundred other craters." On E. he found the inclination of the crest and some of the terraces amounting in places to 50° and even 60°—a fearfully rapid acclivity-which towards the foot sinks down to 10° and 2° ; and on this side he considered it about 12,500ft. high ; the W. peak is some 1000ft. loftier still, rising nearly 7000ft. above the convex terraces at its base, themselves ranging 6000ft. above the interior. The latter, he says, is probably concave; the two principal central hills attain, E. 2400ft., W. 2000ft. Even these must require a considerable climb, and command a magnificent view of the surrounding rampart, at a distance of twenty-eight miles on every side. The same observer remarks the absence of minute outbursts on and within the wall, and, also, the general raising of the ground for a long distance-no less than one hundred miles from E. to W., which may be detected when Copernicus lies 5° to 10° from the terminator-a very interesting fact, as showing the wide outspreading and probably deep
focus of the mighty force, which ultimately burst, at this spot, out beneath the open sky. We may observe, too, that this probably shows the condition of the surface at that time, neither so hard as to be inflexible under pressure from beneath, nor so plastic as to return to its original level when the eruption came to an end; or, perhaps, that the latter action continued so long that the upheaved area stiffened by degrees into its present form. The exterior height of the wall can hardly be measured with any certainty, the end of the shadow falling on this gradual and very irregular slope; Schmidt gives it, however, on E. about 4300ft. The central hills, it will be observed, lie far below the exterior surface; a fact the general prevalence of which upon the Moon had been already noticed by Mädler. A great part of this surrounding area was found by Schr. to be covered with an innumerable multitude of greyish ridges, especially S. and S.E., there being fewer N. and E., and scarcely any W. (a fact, we may observe, possibly connected with the greater height of the ring on that side, and if so, showing their posterior formation). These exhibited to him, though not as distinctly as the streams around Aristillus formerly described, a radiation from the centre. A portion of them has been represented by Herschel, and described as “evident indications of lava-currents streaming outwards in all directions.” To travellers from among ourselves, what could be more marvellous than the gradual ascent for some twenty miles among these colossal remains of the ancient fires, while every position of vantage showed us far ahead the abrupt and irregular edge of the crater towering up through many points of the horizon, and assuming as we neared it the most imposing dimensions; this once reached and climbed-a matter no doubt of severe and continued toil—what a display of creative power would burst upon the view; terrace beyond terrace beneath our feet, sloping rapidly down to an enormous amphitheatre as deep, perhaps, as the peak of Mont Blanc is raised above the valley of Chamouni, and encompassed by a circular cliff, the prolongation of our own standing-ground, the opposite side of which would be as distant from our eye as Oxford is from London! But to realize the process by which that gigantic caldron was formed, and the scene which it presented when it was in full action, whatever the nature of that action may have been, surpasses the liveliest human imagination. When at length we could withdraw our eyes from the gulf beneath us, filled perhaps in part with the blackest shade, and could survey the neighbourhood around us, we should find that it comprised much that elsewhere would be deemed of a higbly remarkable character; from the rapid rounding off of the lunar globe, the horizon becomes much more contracted than on the Earth, and the prospects are comparatively limited even from the loftiest summits; but this defect must be somewhat con pensated by the perfect clearness of the air, if so it may be termed, and in the present instance, our range of sight to the W. and N.W. might probably comprise the outline of a most peculiar district, already more than once adverted to, and with some yet untold peculiarities of Copernicus, to be described hereafter.
TRANSIT OF JUPITER'S SATELLITES.
Nov. 2nd. II. shadow in transit, 6h. 9m. to 9h. II. leaves disk, 6h. 28m.—7th. I. in transit, 5h. 42m. to 8h. 2m. I. shadow ditto, 7h. lm. to 9h. 20m.-8th. III, shadow leaves disk, Th. 36m.-9th. II. in transit, 6h. 8m. to 9h. 2m. II. shadow enters, 8h. 48m.-13th. IV. shadow leaves disk, 8h. - 14th. I. in transit, 7h. 36m. to 9h. 56m, I. shadow enters, 8h. 57m.—15th. 111. leaves disk, 6h. 15m. III. shadow enters, 8h. 3m.—16th. I. shadow leaves disk, 5h. 45m. II. enters, 8h. 44m.—21st. I. enters, 9h. 31m.-22nd. III. enters, 6h. 36m. -23rd. I. shadow in transit, 5h. 21m. to 7h. 40m. I. leaves disk, 6h. 20m.
OCCULTATIONS. Nov. 6th. Aquarii, 4 mag. 10h. 29m. to 11h. 38m.-78 A quarii, 6 mag. 11h. 56m. to 12h. 47m.-8th. 10 Ceti, 6 mag. 7h. 6m. to 8h. 21m.-12th. 48, Tauri, 6 mag. 1lh, 15m. to 12h.