Crater-chains of Copernicus.-To the details previously given, the following may be added.-1855, April 2. 3,7-inch achromatic; of ring of Copernicus enlightened. The row of craters casts a considerable external shadow (so 1866, April 23. 5-inch).-1861, April 18. 54-inch achromatic. "The W. portion which joins the ring of Stadius is on the terminator. It is evidently a low ridge, blown through in many places by a succession of little bowls, whose summits caught the sun in a wild, strange, confused manner, and exhibited two interrupted parallel lines of little, bright, irregularly-disposed specks.". 1862, Feb. 8. 5-inch achromatic. Copernicus its own breadth within the terminator. The region "wonderfully seen, and in much fuller detail than in B. and M. I seem to see through and beyond all their work. The N. extremity of the craterchain dies out in a faint narrow rill [cleft], otherwise than in B. and M. The S. and S.W. slope of Copernicus are thickly studded with very minute craters, omitted by them, but really forming an unbroken dotted continuation of the Crater-Region, as far as their Copernicus C [at the N.E. end of Riccioli's Rhaeticus], and as far as (? if not beyond) their double crater Copernicus A, towards Reinhold. Thus it is evident to sense that the whole crater-region is posterior to Copernicus."1862, April 8. 5-inch achromatic. Copernicus entered half its own breadth. "Very fine definition, tranquilly undulating, which would have defied photography, with cool but not severe N.E. gentle breeze-Copernicus a glorious sight; continuation of crater-chain most distinct all along S.W. slope." -1864, Dec. 8. 5-inch achromatic. Terminator through Heraclides (E. cape of Sinus Iridum, K). The row of minute craters ending with Stadius C (B. and M.) is confluent for a short distance, otherwise than they have figured it.—1865, Jan. 6 (see Stadius). The crater-chains "are very wonderful; they seem much more inosculating and rill-like than as given in B. and M., or than as I used to see them. Three or four craters N. of B. and M.'s C are evidently blown into one long trough."-1866, Feb. 23 (see Stadius). The crater-chain is 'exceedingly rough and irregular, but casting some shadow; enough to show that the rings of the little pits are of a fair proportional elevation. It is much like a mole-run, with holes in it. It leads straight on to the E. side of Stadius." The simile here employed would be naturally suggested by a residence in the country, where such objects frequently meet the eye. In the course of the following autumn I came across a “run” of this nature in a meadow, fifty-four or fifty-five yards in length, ending by inclosing an oval space. Without including two small side branches, I counted upwards of ninety larger or smaller mole-hills on this ridge, nowhere more than two

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yards, and often but a few inches, apart. To anyone familiar with lunar features, the resemblance in these cases is so striking, that it seems hardly possible at first to believe that it is a mere coincidence; but a little reflection will show that it can be nothing more. There can be no analogy between the operations of an intelligent and self-directing creature, burrowing intentionally just below the surface, and the mechanical working of a force which, obeying involuntarily the law of creation, is compelled of necessity to burst through and expend itself at once wherever the least resistance is offered. Schr., indeed, and B. and M. have spoken of the lateral working of elastic subterranean forces; but it is very difficult to conceive the modus operandi, especially in a case like the present, where the tunnelling is so superficial, and the vertical resistance can have been so slight; unfortunately, it seems equally difficult to suggest a less objectionable explanation. We are here, however, struck with at least one analogy, which is exemplified in innumerable situations and upon very varied scales in the Moon;-the great tendency pointed out by Sir C. Lyell in terrestrial volcanos "to shift their principal points of discharge."-1866, April 25. 5-inch achromatic. Terminator through E. wall of Gassendi (64). "Have not some of these pits become larger and deeper?"-an idea, however, which might arise from closer acquaintance. pointed out a similar illusion in the case of double stars, which seem to widen as we are familiarized with them, and among such minute details every precaution must be taken against involuntary deception. -1867, Nov. 18. 9-inch mirror. Terminator (in wane) close to Linné. "Crater-chains so evident at this distance from Terminator, that it is inconceivable how they should have been missed by Schr."

Copernicus. Of this glorious object I have, of course, many notices.-1862, April 8. 5-inch; Copernicus entered something more than half its breadth. "The outer E. slope of the ring showed a number of furrows radiating outwards, as though the interstices of lava-streams." These, as we have remarked on a former occasion, were discovered by Schr. (It may be added that, considering that these furrowings, of which he says he found scarcely any on the W. side, extend down to the immediate neighbourhood of the crater-chain; that the instrument employed was a powerful speculum of about 9 inches diameter; that the illumination must have been favourable; and that the observation bears every mark of care; it is very difficult to conceive how so curious an object could have escaped his earnest and careful gaze, had it been as fully developed, 1796, March 18, as it is now. A similar

Memoir on Etna, "Philosophical Transactions," 1858.

remark applies to his observation of 1797, Feb. 6, when he discovered, with a power of 288, the cleft already described on the N.E. side of the glacis, and when he says the terraces of the ring were so sharply defined that he felt as though he could climb them. Contrast this with the fact that, without any previous knowledge of its existence, and without any special attention to its site, I detected this object, 1832, April 9, with an aperture of 3-inches of an ill-corrected fluid achromatic, bearing a power somewhere about 100.)-1864, March 17. 5-inch; Copernicus entered more than its own breadth. "There are wonderful radiating streams, as of a continuous succession of blocks, or of lava cracked and roughened in cooling, extending to a long distance on every side. They are most visible in the present illumination through the E. semicircle-least distinct S.W. Through the W. semicircumference these streams seem to cover all the glacis even from the top of the wall; on the opposite shadowy side the terraces are so strongly marked that the radiations do not appear across them, though they cover the slope beneath. The S. half of the interior (or rather the S.E. quadrant, the S. W. being in shade) is all strewed with blocks-especially with 212 [a very keenly defining microscopic eye-piece]; the N. part is much smoother."-1864, March 18. 5-inch. Terminator just beyond Sin. Iridum, and touching W. wall of Gassendi. "The interior terraces are shown by their shadow to have a convex outline, from the foot of the highest wall to the floor, indicating, perhaps, that in settling down the upper part was the most fluid."

1864, Dec. 8, 5-in. Terminator through Heraclides. "A strange observation-definition marvellously sharp-I have very rarely seen it matched; but low clouds hanging around, and dissolving into rain so close over our heads, that when one of them was passing as a haze across the Moon, I found, by lengthening the focus, that a profusion of the minutest dark globules were streaming over the disc from the W. (somewhat like Messier's observation of the Sun), notwithstanding which the details, though pale from haze and a considerable amount of dew and rain on the object-glass, continued sharp, and the limb was fairly defined even when I tried a power (461 and Barlow lens reversed) which must have approached 700 or 800. Copernicus glorious, full of details, almost like Secchi [the engraving]. The S. half of the floor is very irregular; the unevennesses have more the aspect of streams flowing from the central cones than of single blocks. There is some, but a less degree of roughness in the N.W. quarter; I trace none in the N.E." [The particulars of this observation are given in full, as being instructive in

their own way. They show under what unexpected circumstances the greatest distinctness may be found; and that, therefore, no night should be condemned untried; and that it is extremely difficult for an inexperienced person to form, from a brief trial on celestial objects, an accurate opinion of the quality of any large instrument: small apertures are far less affected by atmospheric disturbance.]-1865, Mar. 6, 51-in. Central hill beginning to appear. "Copernicus very magnificent, covered with hillocks and roughnesses, which, under the present illumination, so extend over the terraces of the ring that the summit of the latter does not appear as though it rose clear above the external lava-streams, but as though they had flowed over it."-1866, Feb. 23, 54-in. "W. ring just beginning to come on terminator: marvellously rough glacis, but no distinct radiation.-1867, Dec. 5, 9-in. mirror. "It is very interesting to mark the contrast between the bright white illumination of the interior of the wall and its terraces on the E. and the colossal heaps of grey scoriæ, which look as if they had been rolled over the summit of the ring on every side, and remained piled one above another even to its summit; it being quite evident in this illumination that the wall has nowhere a distinct existence above them. The radiations, which are very clear, do not begin till a long way below." 2h. later, when the ring was distant a diameter from term., it is noted that the E. side, "at some little distance from its summit, casts a black shadow for a considerable length, giving the mistaken impression of a perpendicular cliff, or even overhanging edge, so that there must be a sudden increase of declivity at this part; the radiations are all below, and the upper part of the ring looks exactly as though it had been rolled over the lip of the crater, or forced by pressure out of the interior, subsequent to the formation of the radiated surface; the lava-currents, if they are such, and not streams of blocks or scoriæ, must have been in a more fluid condition than the wall, both as extending further, and over a more gentle slope. The internal terraces look as though they had resulted from the slipping back into the interior of matter which had failed to be projected over the lip." 12h. afterwards, "the black shadow is passing off, and there is a distinct impression that the ring proper is convex on the outside in a vertical section," as the terraces, at least W., had been found to be in the interior. "Above this there is a low, narrow, irregularly bent central crest or lip, of considerable steepness, which seems to divide the ring proper-i.e., the convex part without, and the terraces within, into nearly equal parts in point of horizontal extent." My powerful reflector exhibits with ease the curious vertical gullies which cut down for a short distance the inner

slope just above its junction with the floor; they are readily seen N. and S., but are most evident on the former side: landslips from above may probably explain them.-As to Full Moon markings, I find only the following: 1855, Aug. 27, "The appearance of the ring is encroached upon by a grey bay on S.S.W. side."-1855, Oct. 24 (a little before total eclipse), "While none of Tycho's streaks reach the foot of his wall, it is remarkable that Copernicus is penetrated even to the centre by several of his; two distinctly on the W. side, and one or two, not so well made out, on the N. The former look almost like a prolongation of the system of Kepler, as if Copernicus had pierced through, or been pierced through by it." (From some such observations, of which he has given no detail, Nichol assigned the chronological sequence, Copernicus, Aristarchus, Kepler. However this may be, it is not easy to interpret the development of a different shading, frequently taking the appearance of a definite patch or stain, among matter not only forced from beneath, but subjected to the most violent dislocation. If not due to original difference of material, it points to subsequent modification either from within or without. There seem reasons for doubting the former cause, as well-defined dark spots are occasionally met with where, as we suppose, the materials have been so dislocated that any original distinction could not have been so clearly maintained.)

The bare results of these rough studies might have been given in a briefer compass, but, in the original form, there may be some interest and some advantage to the inexperienced student. He may thus perceive what apparent variations may be produced by a slight difference in illumination, how unsafe are inferences from single observations, and how discrepancies are to be reconciled, if at all, by repeated examination. With a little more of the advantges of leisure, these memoranda might have been presented in a less fragmentary form, espe cially since the mirror now in my possession gives results far in advance of almost any hitherto published (and indeed the same might be said of smaller apertures of the same accurate workmanship). But even these may answer a good end by stimulating curiosity, and showing in what direction it may be suitably exercised.

it

Before finally quitting the neighbourhood of Copernicus, may be well to make some addition from the observations of B. and M. The next crater of any size S.S.W. of the mighty monarch of the district, is Gambart, a circle, 16 miles across, but neither high nor deep. In this direction lies a large insulated accumulation of short ridges, trending the same way, the highest lying in a line from Copernicus to that crater. They are more connected, but less elevated, on the W. of the