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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, 5-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, 51-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." 18h. 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 migh; have been presented in a less fragmentary form, especially 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.
Before finally quitting the neighbourhood of Copernicus, it 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 centre of that line, where they form a nearly equilateral triangle, with one angle N. The N.W. side of this area is bordered by a long dark valley, extending S.W. 37 miles, and dividing it from a system of small parallel chains, whose highest summit, %, attains about 2600 feet. This mountain, already mentioned in p. 371 of our last number, must be looked for just S.S.W. of the little but conspicuous crater c, the only one at once S.W. of Copernicus and S.E. of Stadius ; it must also stand very near the N.E. end of the bright streak which divides Rhæticus in the Full Moon (p. 216, antea). Of the parallel ridges they say, "these mountains are very dark, and here, in the Full Moon, a large blackish spot shows itself,” in which they are unconsciously describing the W. part of their vainly-sought Rhæticus of Riccioli, the other portion seeming to be the “ long dark valley” just described. There appears little doubt that in this parallelism may be found the
rampart-work” of Gruithuisen, the regular arrangement of which would probably repay a search ; at the other end of the streak dividing Rhæticus, and consequently near the S.W. angle of their hill-triangle to the E. of it, they place a little summit e. They remark that while the dark mountains continue so in full illumination, the triangle is brighter, 30 to 31° of light, and e has “exclusively a brilliancy of 7°, which it does not lose even in the neighbourhood of the terminator, an anomaly which is so much the more remarkable because it otherwise is not distinguished, either through form or elevation, from the rest, several of which overtop it.”
I regret that I did not notice this curious passage in time to compare it with the existing state of reflective power, but I have no recollection of such a spot when I was identifying Rhæticus, the notices of which are strangely scattered about in B. & M., and it must be left as an interesting subject of research for some of our readers.
E. of Gambart is a bright (8°) and conspicuous little crater A.
Reinhold (our 31) is a crater 31 miles in diameter, with strong terraces and a central hill at the N. end of a little ridge. The W. side of the ring is 9400ft., the E. 7000ft. above the interior. Schr. gives the former measure 8700ft., and makes the external height of the E. wall 1900ft. A mountain-ridge connects it with Copernicus, bending, as it were, round both the rings.
N.E. of Copernicus, we find a lofty tract which B. and M. call Mt. Carpathus, extending with its dependencies from E. to W.280 miles. It includes Gay Lussac, a double crater already described in our p. 370: the smaller basin A is deeper, steeper, and brighter than its broader, and apparently more
ancient neighbour ; a relation frequently obtaining in these configurations. Close S.E. of it our guides notice a dark spot in the Full Moon ; an exemplification of our recent remarks. The ring of Gay Lussac is interrupted by a minute crater close to the companion-crater A; and they point out a curious arrangement here: three pairs of objects-A and this little pit-two summits (a) close together on the N.W. slope of the ring—and two others (B) on the E., make up respectively two equilateral triangles, with sides parallel and very close together, whose common centre coincides with that of Gay Lussac itself.
The cleft proceeding from it has already passed under our review. The mountains E. are confused in arrangement, with no central axis ; and are penetrated by valleys usually as luminous as the heights. Measurement is difficult from the way in which the shadows fall. One high promontory reaches 6300ft. Towards the E. extremity lies a considerable crater, Tobias Mayer, 22 miles in diameter. A summit of its W. ring rises 9700ft. above the cavity. Schr. pointed out that in consequence of its position on the mountain's flank, its E. side was much lower-he gave it but 2700ft. (short measure). It has a central hill, which from local colour appears large in Full Moon. S.E. of this the map shows a very minute crater in the depth; rather an unusual position. W. of the ring lies a conspicuous sub-crater, as it might perhaps be termed, Mayer a. The extremity of the mountains N.E. of Mayer rises to 4000ft.--Milichius, a small bright (89) crater lies in a curiously-shaded region of the M. Imbrium (I), nearly S. of Mayer and E. of Copernicus. S.S.E. of this is another similar crater, Hortensius, very remarkable for its isolation, and the luminosity surrounding it, almost like a miniature streak-system. In a position forming a right-angled triangle with the two last objects—the right angle being towards Copernicus—is a spot containing within the compass of less than 30 miles eight parallel ridges running nearly N. and S., and all pretty nearly of similar length and elevation.
Another step S.W. brings us from Hortensius to Reinhold again, and completes the circuit of a region where so much is seen, and so little is understood, of the wonderful works of God.
TRANSITS OF JUPITER'S SATELLITES.
Jan. 1st. I. egress, 5h. 11m.-Ditto shadow, 6h. 16m.5th. II, shadow ingress, 5h. 50m. II. egress, 6h. 34m.8th. I. shadow ingress, 5h. 53m. I. egress, 7h. 12m.12th. II. ingress, bh. 29m.—15th. I. ingress, 6h. 54m.24th. I. egress, 5h. 45m.-Ditto shadow, 6h. 31m.-30th. II. shadow egress, 5h. 45m.-31st. I. shadow ingress, 6h. 8m.
Jan. 6th. 48 Tauri, 6 mag. 9h. 20m. to 10h. 24m. „ Tauri, 4 mag. 11h. 28m. to 12h. 33m.—30th. f Piscium, 6 mag. 9h, 56m. to 10h. 26m.
OUR FRESH-WATER PLANARIÆ.
BY W. HOUGHTON, M.A., F.L.S.
(With a Plate.) ANYBODY who has occasionally gathered water-cress, or searched amongst aquatic weeds for objects for the aquarium, must be acquainted with certain small black or brown creatures, of an oblong form when at rest, soft, smooth, and flat, and about five lines in length and one and a half broad. These are two species, or, it may be, two varieties only, of Planarian worms. Probably the collector of objects for the aquarium sees in these animated black blotches very little to attract his attention, and he throws them aside; or if curiosity tempts him to bottle a few specimens for examination, he finds that he is able to make out very little of their structure, and sees scarcely anything to interesť him in their habits; and certainly when we compare these fresh-water Planarice with other rare and exquisite forms of animal life, such a Cristatella, Fredericella or Plumatella amongst our fresh-water Polyzoa, or a Meliccrta or a Stephanoceros amongst the Rotatoria, these little black dabs have small claims to beauty; nevertheless the large white species, Planaria lactea, with the pink arborescent ramifications of its digestive system, is by no means devoid of beauty, whilst the commoner black or brown kinds present many points of interest to the naturalist, both in their habits and anatomy. The Planariæ, as their name imperts, are of a flattened form ; the under surface of some of the species bears some resemblance to the foot of a gastropodous mollusc. In many parts of their organization the Planariæ resemble the Flukes which inhabit the liver and other viscera of various animals, especially ruminants; but none of the Planario are internal parasites, nor do they, like tho Flukes, undergo a metamorphosis. They inhabit fresh and salt water, and are to be found on the leaves and stems of aquatic plants, and amongst the roots of the Laminario, between tide marks. On the present occasion I shall confine my remarks to the fresh-water species, of which a great number have been described as occurring in France by Dugès who has published two very interesting memoirs on these animals.* In this country also,
* See “ Annales des Sciences Naturelles," Tom. xv, and Tom. xxi.