144. 



KNOWLEDGE. 



[JnNE';i, 1897. 



whatever may have been the composition of the ocean 

 ■which once washed it, or however that ocean may have 

 disappeared. 



Of the two great headlands which form the horns of the 

 bow, the more westerly, Cape Laplace, is considerably the 

 higher, reaching as it does an elevation of nine thousand 

 feet. Cape Heraclides, the more easterly, is also a bold 

 headland, bnt not quite half the height of its companion 

 sentinel. The profile of the cape and the adjacent details 

 have received a good deal of attention, not only on account 

 of their really striking appearance, but also from their 

 fancied resemblance to a female figure — Cape Heraclides 

 being the '• Moon Maiden." 



The region of our chart is one which opens to us not a 

 few perplexing questions. First of all, whence comes the 

 astonishing brilliancy of Aristarchus ? Were the whole 

 moon of the same brightness, one might accept with but 

 httle question the ingenious theory which Mr. S. E. Peal 

 has urged with such fertility of argument and persistency 

 of endeavour. But the average albedo of the lunar surface 

 falls so far below that of snow, its brightness per unit of 

 surface is so distinctly less than that of the poles of Mars, 

 that it appears impossible to accept Mr. Peal's representa- 

 tion of the moon as a world which has donned the white 

 garb of a universal and eternal winter. 



Aristarchus, indeed, might from its brightness lay some 

 claim to be considered a snow-capped mountain, but it 

 possesses absolutely no features of height and position 

 which should make it a more favourable object for snow 

 deposit than its near neighbour Herodotus. Its walls are 

 by no means specially lofty, nor is it situated near the 

 poles, its latitude being only twenty-three degrees. If we 

 take account of the suggestion that has been made, that 

 the dark tones of the mnria are due to the deposit formed 

 by the age-long accumulation of meteoric dust, then, 

 again, Aristarchus presents us with a riddle, for it is well 

 towards the eastern side of the moon, which will naturally 

 receive the greatest supply of meteoric fragments, and 

 should, therefore, be darker than similar formations further 

 to the west. The suggestion, however, assumes — I think, 

 without warrant — that meteorites falling on the moon would 

 be as dark (that is, have as dull a surface) as those which 

 reach the ground here. The slag-covered meteorites with 

 which we are familiar here have passed through our dense 

 atmosphere, and been subjected to an intensity of frictional 

 heat altogether unlike anything which their brethren en- 

 counter ere they strike the lunar soil. 



There is another suggestion which must account, to some 

 extent, for the varieties of tint and brightness of the moon's 

 surface. This we may briefly express by the term "weather- 

 ing," for lunar weathering there must be, though of a 

 very different kind from terrestrial. The alternation of 

 exposure for fourteen days to the direct rays of the sun, 

 with the exposure for a similar period to the cold of space, 

 must set up a continual disintegration of the surface, and the 

 particles thus separated will, as Mr. Davison has pointed 

 out (Knowledge, Vol. XIX., p. 278), tend to "creep" 

 downwards in all cases where they are resting on a slope. 

 We may look upon it, then, that the greater brightness of 

 the mountains than of the grey plains is due partly to the 

 fact that the surface of the former consists largely of 

 material pretty recently exposed — a point to which Mr. 

 Peal has drawn attention [Journal of the Britis/i Astrono- 

 mical Association, Vol. VII., p. 7) ; but this theory does not 

 help us with Aristarchus, where we find the floor as bright 

 as the central peak or the rampart. 



We are forced, I think, then, to suppose that Aristarchus 

 owes its brilliancy partly to the actual materials of which 

 it is composed, and partly to its being of such recent 



formation that weathering ha3 not yet produced any visible 

 deposit upon the floor. 



It may be worth while in this connection to draw 

 attention to one of the minor markings of our plate. 

 Nearly in the centre of that portion of the Oceanus 

 Procellarum which comes within our photograph is a 

 bright spot which marks the place of the little ring-plain, 

 Bessarion. The northern part of the spot shows us a very 

 distinct crater, Bessarion E, surrounded by a bright, 

 glittering surface — a type of formation specially classified 

 by Miidler as "light- surrounded craters, "and distinguishing 

 the region of the moon near this meridian, and for some 

 degrees on both aides of the equator. If we may extend 

 the analogy of the conclusion which we have already 

 reached in the case of Aristarchus, these, too, may be of 

 recent origin, and their neighbourhood to Aristarchus may 

 be an indication that we have here the region of the moon 

 latest subject to violent change. 



The Sinus Iridum leads us to reflections of a very 

 different character. Noting the frequency along the borders 

 ofsomeof the "seas" of walled plains and ring-plains which 

 have been attacked or broken down on their seaward side — 

 such as Fracastorius, Julius Cresar, and many others — some 

 observers have suggested that the Sinus Iridum is but a 

 larger instance of the same character. Were its circle 

 complete it would about equal Clavius, Schickard, or 

 Grimaldi, so that its dimensions would not be excessive. 

 It would then bear to the Mare Imbrium much the same 

 relation that Fracastorius does to the Mare Nectaris. An 

 examination, however, of the highlands that bound it, 

 scarcely, I think, supports this view. They do not appear 

 to form part of a once circular wall, the half of which is 

 now lost ; nor is it quite conceivable that a rampart of such 

 magnificence as the other semicircle must have been in 

 order to correspond, could have sunk into the Mare 

 Imbrium and left no sign. It seems far more reasonable 

 to suppose that in the Iris Highlands, and in the bold 

 contour of the Sinus Iridum, we have preserved to us 

 features of the primeval structure of the lunar surface. 



DAY VIEWS OF VENUS. 



By P. M. Ry\'ES. 



FEW people know how easy it ia to see Venus in the 

 day with the naked eye. It has been said that 

 Venus is visible in daylight once in eight years 

 only, but I can aflirm, from my own observations, 

 that this supposition is an incorrect one. 

 Observations of Venus in the daytime were made at a 

 very early date. The following are a few instances : — ■ 

 A.D. 398, 984, 1008, 1014, 1077, 1280, 1360, 1715, and 

 1750. 



Arago relates that General Buonaparte, upon repairing 

 to Luxemburg, when the Directory were about to give him 

 a ff'te, was " very much surprised to find the crowd 

 assembled in the Rue de Touracour pay more attention to 

 a region of the heavens situated above the palace than to 

 his person or the brilliant staff that accompanied him. 

 He inquired the cause, and learned that these curious 

 persons were observing with astonishment, although it 

 was noon, a star, which they supposed to be that of the 

 conqueror of Italy — an allusion to which the illustrious 

 general did not seem indifferent when he himself, with his 

 piercing eyes, remarked the radiant body." The star in 

 question was no other than Venus. 



At the beginning of March Venus was in a very favour- 

 able position for observation, and was distinctly visible in 

 the day. 



