The photographic news

• Bandzählung: 35.1891
• Erscheinungsdatum: 1891
• Sprache: Englisch
• Signatur: F 135
• Vorlage: Hochschule für Grafik und Buchkunst Leipzig
• Digitalisat: Hochschule für Grafik und Buchkunst Leipzig
• Digitalisat: SLUB Dresden
• Rechtehinweis: Public Domain Mark 1.0
• URN: urn:nbn:de:bsz:14-db-id1780948042-189100009
• PURL: http://digital.slub-dresden.de/id1780948042-18910000
• OAI: oai:de:slub-dresden:db:id-1780948042-18910000
• Sammlungen: LDP: Historische Bestände der Hochschule für Grafik und Buchkunst Leipzig
• Sammlungen: Fotografie
• Strukturtyp: Band

• Digitalisat: SLUB Dresden
• Strukturtyp: Ausgabe

July 10, 1891.] THE PHOTOGRAPHIC NEWS. 495 the monograph of the formation which is being prepared under the auspices of the Association. The floor, in addition to the many craterlets and saucer shaped depressions and low ridges visible thereon, is tra versed by a system of light markings and associated light spots, even more remarkable than those discovered in Plato, Fracastorius, and Archimedes. Between January 1881, and August 1883, Mr. A. Williams recorded at least eighty-five of these faint, light streaks, which objects will, of course, receive the close attention of the section, with a view to confirm his observations. The hexagonal shape of the border of Ptolemaus is far from being a solitary instance of the tendency to a six-sided figure among the larger class of walled and ring plains. The same pecu liarity may be noted in the case of Copernicus, and in many other of the so-called rings, large and small. The explanation of this, and also of the fact that arrangement of the mountains and highlands of which it is made up have, in many places, no apparent relation whatever to the contour of the floor (a structural condition also not con fined by any means to Ptolemaus), may be left to the ingenuity of the framers of hypotheses. In describing the eastern wall, Mr. Eiger referred to a remarkable gap in it, where, for a distance of three or four miles, there is no barrier at all between the floor and the outside country. In conclusion, he contended for the importance of the observer acquiring a correct appreciation of the actual size of the formation he studies, so as not to under rate the true significance of details. He also urged the members of the section not to attempt to draw more of Ptolemaus, or any other formation, than they can reason ably hope to finish during the course of three or four hours’ observation, and to devote themselves to a limited area, or their work would not possess any great seleno graphical value. Mr. Green then gave a paper on “The Lunar Seas,” which was also illustrated by means of the lantern. lie said : On examining a map or photograph of the moon it will be evident that these seas follow a definite order of arrangement, the smaller being near the limb, and the larger nearer the centre of the disc. There is not a single instance of these dark areas extending to the limb, and although large craters may be found there, and larger still are revealed by libration, they are not filled with dark matter like the seas. It should also be observed that, even when the dark formations come very near the limb, as on the north-east, there is still an unbroken line of bright surface beyond them, so that we have no reason to expect that similar blotches exist on the side turned from the earth. The brighter portions of the lunar sur face are separated most definitely from the seas by being higher, more detailed, and to a great extent covered with crater-like forms. The seas, on the contrary, are lower, comparatively smooth, and craters few and far between. The question then arises, which of these two so widely diversified surfaces is the older ? It has been supposed by some that the seas represent the more ancient state of our satellite, and that the crater-covered surface has encroached on them ; yet this cannot be the case, for the shapes of the seas would then have been that of the spaces left between invading circular forms ; but this is not the case ; the seas tend greatly to circles, and press forward into the crater-covered surface with a fairly even line, broken occasionally by the remains of partly destroyed craters. Mr. Green illustrated this point by drawings of Fracastorius, the ruins of the north wall of which, he pointed out, could be seen under favourable circum stances, and of Doppelmeyer, Gassendi, and the Sinus Iridium. He also showed how the base of the Apennines appeared to be fringed by great massesof dbris, which seemed to have fallen from their summits. He then resumed : Thus far we have found that the lunar seas are comparatively a recent formation, that they increase in size from the limb towards the centre, and that, in all probability, they exist only on the side which is turned towards the earth. These circumstances point conclusively to some terrestrial influence in their formation, and for such influence we shall not have long to seek, as it will be found readily in the power of gravity and its tidal disturbances. Time was, doubtless, when the moon had an axial rotation, and when, in consequence of a semi-fluid state, the attraction of the earth raised upon her surface a considerable tidal projection. This wave, by friction and other retarding causes, eventually reduced the rotation, till at last the moon presented the most heavy side towards the earth, and her rotation as a free movement ceased to exist. Then came the formation of the seas. The still liquid interior, in obedience to the powerful attraction of the earth, welled up through every crack and opening, choosing, of course, the weakest places, and, spreading on the sur face, reduced it again to the semi-fluid condition, where now it is to be seen in the various forms of these lunar seas. It need not be supposed that these irruptions rose to a higher level than the older cratered-covered surface; but that the heated mass cut its way into the general sur face which it undermined, and gradually reduced the fallen portions. An example of this may be seen on the eastern edge of the Apennines, near Archimedes. The possibility of this remelting process is evident from the frequent cutting of one crater form into another, por tions of the older crater being thoroughly destroyed by the contact. Mr. Alex. J. G. Adams said : The idea that, owing to tidal action by the earth, lunar seas exist upon the side facing us only, was not quite clear to him. Were we to assume a single tide alone ? The effect of gravitation was the production of two tides in a line with the dis turbing body, and he thought this state would apply to the moon. Moreover, while in no way detracting from the general hypothesis, and while fully allowing for clean ness at the disc edge, the probability of double tide carried with it the idea of seas upon either side of the moon. The point of tidal lag had been touched upon and deserved further remark. Our tidal effects were always in rear of causation, and in some cases there appeared to be a har monic give and take, as exampled by the fact that, whereas the spring tides lagged more and more each spring luna tion, the neaps gained, insomuch as to produce occasional overlapping. In the case of the moon, however, it was probable, owing to coincidence in her periods of orbital and rotative motions, that her tidal lag would be compara tively fixed, and seemingly just such as to produce decrease of sea upon her western limb. Croydon Microscopical and Natural History Club (Photographic Section).—On July 4th a large assortment of negatives and prints was exhibited by members, taken dur ing the recent excursions. The half-day excursion to Erith and Greenhithe for July 25th has been altered to Kingston-on- Thames ; trains from Clapham Junction 2-15 and 255 p.m. ; Waterloo, 2*5 and 2'40 p.m.