« AnteriorContinuar »
was applied by him to the whole dark hill-country N. of the small crater now so called : and his first cleft commences there as a flat valley : he did not notice any of the minuter craters in its course, but places upon it, as interrupting it, the Hyginus of B. and M., of which he remarks, in a subsequent observation with the 27 f. reflector, that it has certainly no ring : at the same time he found that the W. end of the cleft, which he had previously carried right up to the wall of Agrippa, is lost about one diameter of that crater N. of it. The second cleft he brings, not out of B. and M.'s small crater, which he does not notice, but from a point further E., the end of his Hyginus ; and originally drew it as dividing a flat bright crater (his D), about half as large as Agrippa, which has on its S.W. side a smaller crater, q, and another flat, crater-like depression v, between q and the cleft. Of these objects q is the Silberschlag of B, and M., but D and v cannot be identified in their Map; the ridges, however, about their a, N.E. of Silberschlag, and those N. of that crater, in some states of illumination assume a ring-like aspect : a source of deception well known to lunar observers. Schr. also shows the crater which B. and M. place on the N. bank of the cleft; but in two separate designs he has made the cleft pass further S., about equidistant between this lesser crater and Silberschlag. From all this it will be seen how difficult it is to reconcile representations by different hands, or even to account for their discrepancy. Further W. Schr. places two mountains in the course of the cleft; the first of these, o, seems to be the a of B. and M.; the second, M, is their ß. What struck him greatly was, that he saw, 1794, Mar. 8, with a 7 f. Newtonjan, the ring of his D on both sides, and the mountains o and y, all split by the cleft: Sept. 1, with his 27 f. reflector he found the ring of D and the mountain u undivided (agreeing in this last with B. and M.). 1796, Feb. 15, was divided, with a four-inch Dollond: Mar. 15, with his 13 f. reflector, D had its ring incomplete and open on the N.E., where the cleft enters it; but the other side of the ring (namely, the very narrow gorge at a, B. and M.) was undivided, as well as the mountains o and u: 1798, July 19, he and Olbers, with the 13 f., both saw u undivided, and the latter noticed the slight bend in the cleft shown by B and M. a little W. of this spot. Schr. also found at the S. end of the chain of which u is the central portion, a mountain which he had never seen before, though the highest of all, casting a long spire of shadow while the rest had none, and measuring 3200 f. From this he was induced to infer former atmospheric obscuration; and he could not resist a very cautious suggestion, that the singular alternately open and closed aspect of the mountains above the cleft might point to some artificial
operation in utilizing a natural feature. The alteration is much more probably due in part to libration, exposing to the eye more or less, at different times, of a very narrow line of shade, and partly to the change of seasons on the moon, which, slight as it is, is sufficient, by varying a little the bearing of the sunrise, to cause the same edge of a cleft running E. and W. to be at one time illuminated, at another in shade.
We will now turn to Lohrmann, and hear what he has to say—premising that the date of his “Sections,” though earlier, did not differ much from that of B. and M. And here again we find discrepancy enough to be unpleasant. His first cleft, to begin with, is much more sharply bent at Hyginus than in our diagram: and though he agrees with B. and M. as to the wider commencement, and the four craters in its course before reaching Hyginus, yet it is remarkable, that while he makes the first and fourth very minute, he enlarges the two intermediate ones to two-thirds of the size of Hyginus, saying also in his text that there are two larger and two smaller deep cavities, which under favourable circumstances he has several times distinctly seen. One of these little craters, he adds, lies on the edge of Hyginus ; his drawing shows that it is additional to the other four. He remarks that Hyginus has no visible ring, and has drawn none round the two larger of the four craters. Another minute crater is drawn, but not described, just W. of Hyginus. He carries the end of the cleft as far as the site of B. and Mi's Agrippa b, stopping it against a chain of hills running up to the wall of the great crater.
The cleft of Ariadæus he begins (from E.) with a small crater, as B. and M., and has shown their two minute pits on either side of it, further W. He recognizes Schr.'s D as a flat crater, the ring of which is a mere bank on the N.: he shows traces of v, and like Schr. places the smaller crater opposite Silberschlag at some little distance from the N. bank. After several failures he found the mountain measured by Schr. He carries the cleft through everything in its course, expanding it a little at its W. end. It is less luminous, he says, than that of Hyginus, but still visible in Full. Of the cleft-system near Triesnecker he perceived nothing. Chacornac perfectly recognizes Schr.'s D and v, and makes the cleft divide a, but rot B, W. of Silberschlag. Schmidt has added considerably to the number of clefts in this district; but as the descriptions in his catalogue are very brief, and without designs, they are little more than memoranda, which will become fully intelligible, we trust, hereafter, by comparison with his promised lunar map:
As the present is our best opportunity of studying these
curious objects, I shall beg permission to add a few observations of my own; they are indeed of a very fragmentary character, but may perhaps be useful to those who are disposed to make out the whole detail of this interesting region, which, after all the attention given to it, is still but imperfectly known. My excellent 5. in. object-glass carried me, of course, considerably further than B. and M., and my 9} in. “With” speculum, would have made a much greater advance, but for the long continuance of unfavourable weather.
Beginning, as at first, at the widened extremity of the Hyginus cleft, where it lies like a long pool under a bank of some height on the left-hand, I find that in the middle of this part it sends out a narrow continuation towards the E., which having cut through a low dark mass of hills, is soon lost in the plain on the other side of them ; beyond this, at a short distance, its direction is carried on by the N. edge of a mountain mass, but I could not trace any cleft there. Less than half-way from this “pool” to Hyginus, an insulated hill stands close above it on the right, after passing which it becomes convex towards the W., and evidently broader, contracting, however, suddenly, and turning more to the left a little way before reaching Hyjinus. In this broader part, it would seem that the three first craters of B. and M. must be placed (including the two which L. has so exaggerated in size), and I might have detected them at this time in steadier air. Hyginus itself I have repeatedly seen without a wall, though possibly it might come out close to the terminator, where I have never observed it. Schin. doubts whether any actually ringless craters exist on the moon, but they are known on the earth, the “explosion-craters” of Humboldt; cavities surrounded by inconsiderable margins of ejected fragments only; such are the Maars of the Eifel, and several in Auvergne and Java. I have never seen the two bright lines crossing the floor, as described by B. and M. Once I detected one of them, corresponding with the S. edge of the cleft, very narrow, but obvious, and cut off by a narrow black space from the E. slope of the crater; but I have more. frequently seen the whole cleft entering the crater as a broader line of light. On one occasion, an indistinct uncertain shading led me to suspect that its level was somewhat depressed as it passed through the crater's edge, and I have never been able to trace it beyond the breadth of the floor, nor to ascertain how this white stripe comes to an end, though once I thought there was a slight shadow there. The two accompanying sketches, taken (1) 1861, April 18; (2) 1867, Feb. 7, will give some idea, though a very rough one, of the object. They show also the cavity which encroaches on the N. edge of Hyginus, and which has been given, though too small, by L., but omitted by B. and M.; it is about the diameter of the larger crater. The projecting cusp on the right-hand was on the latter occasion very luminous. The two small craters E. and W. of Hyginus are larger than as shown in L. or B. and M.: when sketched, the one was all bright, the other partially in shade. The bending of the cleft does not take place in Hyginus, as shown by L., but in or near the latter crater. I have no note of any other crater W. of Hyginus, but I carry the cleft further than B. and M., turning it, like L., with a bend more S. towards the site of Agrippa b, and then again bending it W. and carrying it on as a very minute line across the N. slope of Agrippa, at a considerable distance from the ring. B. and M. may have seen part of this as the long bank shown (but a little too far N.) in our diagram.
The second great cleft I have seen bordered in all its length, though less distinctly in the portion E. of Silberschlag, by a narrow faint shadow parallel to it on the S., as though on that side at least it had an elevated margin. * I have drawn it as commencing on the N. side of Ariadæus a. Three times it has appeared to me interrupted by the narrow ridge W. of B, which it divides in B. and M. I have never seen ß nor a divided by it; as to a on the other (E.) side of Silberschlag, I am less confident. I may have mistaken it for the ridge N. a little W. of Silberschlag, by which, like Schr., I have seen the cleft entirely intercepted. It has not appeared to me to pass close to the crater opposite Silberschlag as in B, and M., but at a little distance, as in Schr. and L., and the bend at this place is greatly exaggerated by B. and M. The semi-crater form of Schr.'s D I have plainly made out. A little E. of this spot it sends off a very distinct branch to the S.E., which apparently forms a communication with the W. end of the Hyginus cleft, somewhat N. of the point where the latter carries on a branch, already noticed, across the N. slope of Agrippa. I have no note of the small crater at the E. end of this cleft, but I have remarked a very faint narrow dark line continued on from near that spot still further E., towards the end of the Hyginus cleft.
These minutiæ may be of some interest as showing the multiplicity and intricacy of these cracks, and as aids to further study; but the most curious remains to be specified. 1861, April 17, 1 perceived that the part of the cleft between a and B
* With the great Northumberland Telescope, at Cambridge, aperture 11. in., Breen has seen both banks very plainly, alike in valley and mountain, and has noticed them stretching a short distance into the dark part of the diso.
berschlag, ny have their (E.sind never",
by two paranus was distin fact th
is double, or rather that in this space are comprised the ends of two clefts not in the same line, but running parallel for a short distance, as is shown in the accompanying very rough
sketch. The S. portion, though narrow, was very evident. As I have found this subsequently confirmed, I would venture to propose an addition to the nomencla
ture here, and to call the E. portion “the cleft of Silberschlag," as the W. is that of Ariadæus. How so apparent a feature should have escaped all previous observers, and even Schmidt himself, it is not easy to understand ; but it proves how much yet remains to be done for the topography of the Moon.
This becomes still more evident with great apertures and high powers, for which many peculiarities here are doubtless reserved. Such was especially my conviction in the use of Mr. Bird's noble 12 in. silvered mirror, 1865, Sept. 5. The illumination was then far too high, but some idea of the scene may be obtained from the fact that the bottom of the first cleft
W. of Hyginus was distinctly seen as a grey streak bordered by two parallel bright lines. This was interesting in another respect. The steep banks, as less directly enlightened, should have had a darker appearance, on optical grounds, than the included level space; their opposite aspect must have been due to local colour. On one occasion I thought, in using my 9} in. mirror, that the Silberschlag cleft passed over, not through, a considerable mountain; but the observation was too hasty, and should be repeated.
As to the region of Triesnecker, I have noted several additions. The angular point of meeting, and the minute crater on the slope beneath it, are both set too near the ring by B. and M., and that angle is really the common junction of four clefts ; one of which proceeds due S., I know not whether it may be Ś, ill-drawn in their map, or a line of communication with it; another runs as a continuation of ß up to the N.W. edge of the great ring: the cleft y, as Breen had previously found, is double, with overlapping ends, like those of the junction between Ariadæus and Silberschlag; and possibly this may be found to be a peculiarity of frequent occurrence. y appears, too, to lead directly towards the small crater near its N. end : while c, or e (both which letters are affixed in the map to the cleft pointing to the centre of Triesnecker-e has been accidentally misplaced in our diagram), probably passes W. of the little crater E. of Hyginus.
We leave now this curious region with the sincere hope that some of our readers may be induced to make it an object of patient research : a very little experience will show that no