companion, 4800 ft. deep according to Schr., was discovered by him, as well as a curious cleft running E.S.E. from it for some distance, which he compared to the great valley in the Alps, from the way in which its sloping sides are studded with small irregular hills, as though an upheaved and hollow ridge had fallen in, leaving the firmer portions hanging on its declivities. In the Roman drawing, the end next the crater is feathered out into oblique lateral fissures.

But the more remarkable features here are the great lightstreaks which diverge from it in every direction. They form a less regular system of radiation than is to be found issuing from other centres, but still their relation to Copernicus as a departure point cannot be mistaken. Several of them connect this great crater with others in the neighbourhood which repeat the phænomenon, though on a smaller scale; in fact, but few large rings between the equator and 30° N. Lat. are wholly without them, and some exhibit them even beyond that limit. Near Copernicus they are merged in a bright but confused "nimbus," or glory, interrupted here and there by streaks and insulated patches of darkness, of which one is even found close to the wall. Further out they expand, and direct themselves partly in divergent, partly in parallel lines, to the neighbouring craters. Those pointing S. towards Reinhold (31) and Gambart (a crater between Reinhold and Sömmering-INT. OBS., xii. 218) are more feeble and ill-defined; they seem to indicate a fresh focus at Reinhold, but do not diverge from it again: those directed towards Schröter are more considerable, but do not reach the hill country; and here the aspect of the surface is rather that of dark streaks traversing brightness than the reverse. One such large dark streak passes from Copernicus A to Stadius, the S. quarter of which it includes, and then is lost. The darkest of these begin at a grey mountain marked , and extend S.W. for 40 miles: the inquiry of B. and M. whether one or other of the unascertained spots of Riccioli is to be recognized here, must appear singular after a slight comparison of the old maps, which leave no doubt of identification as to his Rhaeticus, though some regret at its not having been more accurately delineated in their great map. Towards Eratosthenes almost all the light is united in one mass, of which the brightness of the Sinus Estuum may be considered a continuation. Further N. begin some very prominent streaks, few less than five miles broad, one leading to Lambert (35), 14 miles; some, which seem to start in the plain itself, are crossed obliquely by others coming from Eratosthenes the reverse way. Towards N. they are narrower and much interrupted; they are larger and more intense N.E. A great divided streak passes from Mayer (32)-a large crater N.E. of

Copernicus, with a smaller one on its W. edge-to Euler (36); others pass through the Oceanus Procellarum to meet the narrow and not easily distinguishable streaks of Aristarchus (43), and run into a great spot of light between both. Others, shorter and less distinct in appearance and direction, are found S. of Mayer. On the side of Kepler (41) they are more clear and decided several, nearly parallel, run E. to that crater, and enter its "nimbus," thus uniting the two main streaksystems of the N. hemisphere. These details are so far worthy of record, as the suspicion of change in the reflective power of portions of the lunar surface, if not yet warranted, is not unreasonable. The streaks are of course best seen in Full Moon, very little of them being visible if the terminator has not passed Mayer in the increase, or reached Eratosthenes in the wane, and that little being masked by the opposite direction of the mountain ridges.

Copernicus and its nimbus can be clearly made out on the night-side before the First, not so readily after the Last Quarter.

We now come to a very singular region, more than once adverted to in our previous paper, and certainly in its own way one of the most remarkable in the Moon;-the Craterchains, as we may term them, between Copernicus and Eratosthenes. Here we find the greatest and strangest contrast to the neighbouring Sinus Estuum. There, craters are all but invisible, even after the strictest search: here they exist in such profusion that it is doubtful whether any really level surface intervenes. The sixty-one shown in the map, of which the greater part lie in a line between Pytheas (a moderatesized crater two-thirds of the way from Copernicus to Lambert) and Stadius, are probably not the half that are perceptible, but past delineation. They are not scattered at random through the plain, but lie behind one another in rows, in some places closely compressed, in others wider apart at nearly equal distances, and but few seem entirely insulated. Though the majority are very minute, and only a few exceed 1" in diameter, B. and M. cannot give them, like Gruithuisen, a width of only 500 (French) feet, but would estimate most of them at as many toises (3200 feet). The closely compressed rows, they observe, assume easily the aspect of a connected cleft; and, in fact, the two forms are nearly interchangeable; we only need imagine the absence of a common and usually very low partition, to convert the one into the other. At the N. end of the landscape, for the length of a lunar degree, there is such a cleft, with a distinct embankment on either side, and four of the smallest craters in its depth, with which the next three craters S. of it often seem to form a whole. At a distance of

20° at furthest from the terminator this crater-swarm becomes invisible, and the surface is then almost exactly similar in aspect to the Sinus Estuum itself.

The discovery of this very singular region is due to Gruithuisen, 1815. He has well described its aspect, and speaks of the rows of craters as forming in places hollow ways, or being connected by a large longitudinal furrow, while the separate craters had outlets E. and W., which, however, are not visible if the illumination is precisely in that direction. And then he goes on, in his own way, to refer to the especial fertility indicated by the darkness of the soil; and considers them, if not volcanos, the artificial dwellings of living beings; in another place indicating his own choice between the alternatives by asserting that there is not a trace of a volcano, ancient or modern, upon the Moon! all its cavities having been formed by the impact of masses falling from space-of which portions still protrude as central hills! They are mentioned again by Kunowsky, 1821, who says that he often distinctly recognized, in clefts, rows of crater-like eruptions. Lohrmann's Sections and letterpress unfortunately do not include this region his General Map indicates broad, low ridges, pierced with a moderate number of craters; but, though the first impression is not that of similarity to the Map of B. & M., a closer inspection shows that the objects represented must have been nearly the same. A corresponding view with that of Kunowsky is taken by Schmidt, who remarks that "everywhere a keen and unprejudiced course of observation will indicate that rills (clefts) are only crater-rows in a particular modification, as the innumerable transition-forms prove, and as Mädler first (?) pointed out." Little craters, he tells us, often lie in long lines, as if they had broken out of a crack, and he enumerates about 300 visible in the region now under discussion, many of which are contiguous, and frequently so confluent as to form ravines like regular clefts: their external height being, he thinks, very insignificant-somewhere between 150 and 600 feet.

Why these crater-chains were unnoticed by Schr. is a question which, though it seems to have been never asked, is deserving of an attempt at a reply. It so happens, indeed, that Eratosthenes and Copernicus were examined by him at different times, and represented in separate views; and that these miniature volcanos soon disappear after sunrise; and it may be admitted that he overlooked many small objects in various places. But, on the other hand, it must be borne in mind that his attention was evidently frequently directed to Copernicus; that the object, though fugitive, is in a very remarkable and conspicuous place, and is by no means collect

ively minute, and that it would be distinctly visible in instruments having not more than a tenth or twentieth part of the power of those employed by him. If, therefore, we were to infer that this manifold outburst had taken place some time at the beginning of the present century, our argument would not want plausibility. It can, however, be only advanced with hesitation, especially in the face of such an authority as Schmidt, who asserted (previous to the much controverted discovery as to Linné) that no single region of the Moon had been sufficiently investigated, even with only a 5-ft. refractor, to admit of a satisfactory solution of the inquiry, whether eruptive action is still in progress. This, he then thoughta few years may probably show how far correctly-would require a special delineation and measurement of small areas little affected by libration, carried on for years with the most powerful instruments, and, if possible, under a sky such as the North of Europe does not afford.

It may, at any rate, be admitted that Selenography is not as yet sufficiently advanced to admit of our rejecting as wholly unserviceable any observations made with ordinary care and knowledge of the subject; and selection can only be practised among an accumulation of materials such as we do not hitherto possess. It is on this ground that I venture to bring forward a few extracts from my own note-books, which may be of some use for the purpose of comparison, or as awakening the curiosity or directing the attention of those who may be commencing lunar inquiries. We shall include the Mare Vaporum and Eratosthenes with our present position, in a very desultory and incomplete study of some of the aspects of this region.

"1831. April 20. Near Eratosthenes. The level plains and singular dusky tracts S. and S.W. of this crater, when carefully viewed, exhibited a peculiar stripy appearance, extremely like that of a cloudy sky; and the effect was quite that of local colour, not unequal surface, since the streaks made only an angle of 10° or 15° with the line of the cusps." The instrument employed was an ill-corrected fluid achromatic, on Barlow's principle, with an aperture of three inches, and power

about 100.

1855, Oct. 18. The terminator passing through the Sinus Estuum, this curious effect was again observed with a good 3-inch object-glass, as though a brushfull of dark but not evenly-mixed grey colour had been swept over the surface towards E. by S.-The following night, when of the ring of Copernicus was enlightened beyond the terminator, it was very evident and more extensive-" a vaporous or smoky appearance, drawn in stripes or thin parallel bands over most of the surface included between Manilius and Copernicus; its N. limit

being bounded by a line joining the centres of Manilius and Eratosthenes, its S. extending as far as Schröter (of B. and M.). The direction is about E. by S., and the streaks are parallel, and show no tendency to converge to Copernicus.”—Oct. 20. The dark streakiness was "more intermixed with light stripes, which seem to be the streaks of Copernicus; in fact, the appearance, judging from to-night, may be due to the graduallyincreasing visibility of those streaks coming up into sight with the higher illumination, through a smoky, brownish-grey surface. As observed last night, these streaks in the S. part of the surface in question do not point to the centre of Copernicus." Oct. 22, 4d. 2h. after First Quarter. "Dark streakiness seems now, in a very changed aspect, with great preponderance of light, to show an admixture in its S. portion of the streams of Kepler with those of Copernicus; the former seeming to pass by the S. side of the ring of Copernicus, and, of course, to be subsequently parallel to its streams. There is an evident crossing and interference of the two systems, as if they had not been contemporaneous, but the one had burst through the other." 1855, Dec. 29, 2d. 4h. before Last Quarter. Mare Vaporum: "the streakiness not remarkable, as in the increasing Moon."

1855, Oct. 19 (as before). Dark tracts near Sinus Estuum. The equatorial region is "strikingly marked by three undefined spots of a brownish-grey of considerable extent, having a smoky aspect. The first is the slope of the Apennines S. of Huygens, especially where it borders the Sinus Estuum by a gentle and slightly-elevated circular sweep; the second is apparently a rough surface of no great height, extending from I (B. and M.) N. of Schröter to the E. side of that crater; the third is a mass of low hillocks beneath the S.W. foot of Copernicus. Besides these, and divided from the second by a lighter surface, is a small dark tract, consisting, I believe, of two portions, and so represented by B. and M., N. of r (above)." These spots are all fairly traceable in the great map. 1867, Nov. 7. 9-inch silvered reflector; terminator a little beyond Gassendi (64). The three dark spots of 1855, Oct. 19, very fairly made out, though illumination very much more advanced: the third seems to be the Rhaeticus of Riccioli, very distinct and dark; but if the dark spot divided by a light streak S.W. of Copernicus in B. and M. is meant for this, as it appears, it is not well laid down; too small, and too far N. The "small dark tract of two portions" appears of a more complex form: the W., which is a pretty regular ellipse in B. and M. is now divided in half by a narrow brighter streak pointing S.W.-the E. is deeply indented from N.E. in the same direction by a broader and more obvious stream.