210 



KNOWLEDGE. 



[November 1, 1893. 



moon as we see it iu the daylight reflects less than one- 

 sixth of the light which falls upon it, for the crescent or 

 gihbous moon which is seen in the daytime is never as 

 white as the full moon, because, except when the moon is 

 opposite to the sun, we, in looking from the earth, see 

 some part of the black shadows thrown by the lunar 

 mountains, and the admixture of dark shadows tends to 

 dull the general whiteness of the lunar surface. 



It needs only a very cursory glance at the moon to see 

 that it is not all equally white. The rustic and the child, 

 without any optical aid, see dark patches on its surface, in 

 which they recognize the features of a laughing face, or, 

 with the aid of a little imagination, detect the figure of an 

 old man carrying a bundle of sticks. As seen with an 

 opera glass or telescope, the difference in brightness of 

 difierent parts of the moon's face becomes much more 

 noticeable. It is immediately recognized that the lunar 

 plains are, as a general rule, much darker than the moun- 

 tainous regions and high ground, and that the moon's 

 limb or smooth outer edge is whiter than the rest of the 

 lunar disc ; but at the moon's limb only mountain-tops 

 are visible, the valleys and low-lying land being hidden 

 by intervening hills. We thus learn that on the moon 

 the mountain-tops are whiter than the low-lying land, and 

 from terrestrial analogies we conclude that this is more 

 probably duo to some white substance covering the high 

 ground than to a difference between the tint of the soil of 

 which the lunar plains are composed and the rocks of 

 which the mountains are built. 



We may, I think, venture to speak of the lunar moun- 

 tains as being composed of rock, for many of them have 

 very steep sides ; and if they were composed of sand, or 

 any very friable rock, we should 

 not expect to find the lofty pre- 

 cipices which are recognizable 

 in many parts of the moon. 

 See, for example, the 

 north-eastern flank of ^"' '' 

 the lunar Apennines 

 (Fig. 2) and the steep 

 conical hills which 

 rife from the Mare Im- 

 brium, such as Piton 

 to the east of Cassini 

 (Fig. 5), and Pico 

 and the Tenerifle ^'g- l- 



Mountains to the south-oast of Plato (Fig. i\ 



On tlie earth our hard rocks are either of volcanic origin 

 or. if of aqueous or aerial origin, their hardness indicates 



that they 

 have been 

 buried and 

 have un- 

 dergone 

 cha nges 

 due to 

 pressure 

 and heat, or the infiltra- 

 tion of water carrying 

 soluble substances ft'om 

 one particle to another 

 and cementing them 

 together. 



The forms of the 

 lunar mountains pre- 

 sent in many cases a striking resemblance 

 to the forms of terrestrial mountains of 

 volcanic origin, but there are some lunar 

 mountain chains and ridges which seem rather to suggest 



KiruliMts 



Via. 2.— The 

 I.iiiiar Apennines. 



the crumpling of horizontal strata. See, for example, the 

 Riphsean Mountains (Fig. 3), shown 

 in the photographic plates in the 

 September number, and the ridges 

 to the south of Archimedes, well 

 shown in the plates in this number, 

 as well as the curious stag's horn 

 form, called the Kirch Mountains, 

 to the north of Archimedes and to 

 the east of Aristillus (see Fig. 1). 



But there are no long mountain 

 chains trending north and south 

 upon the moon as on the earth ; 

 and if we may accept the theory 

 which attributes the northerly and 

 southerly trend of the chief lines 

 of crumpling of terrestrial strata to 

 the directive influence of the tidal 

 stress, it would follow that the lunar features we now 

 see have come into existence since the epoch when 



Fici. y. 



Eiphienn Mountiiins. 



Mt. Blanc. 



Pico. 



Great 

 Cleft. 



Teneriife 

 Mts. 



Lixnar All 



Fig. 4. 



Plato. 



the moon's period of rotation about her axis came into 

 coincidence with her period of revolution about the earth ; 

 for before that epoch the tide which swept round the moon 



Tbeffitetus. 



Kirch Crater. 



Piazzi Smyth. 



Lunar Alps. Pitun. 



must have been much larger and more effective in in- 

 fluencing the direction of the ridges of crumpling on the 

 moon than the terrestrial tide now is upon the earth, 

 not only because the earth has more than eighty-one times 

 the mass of the moon, but also because the moon was then 

 probably nearer to the earth than it i.s at present. 



Leaving out of account 

 the great lunar mountain 

 chains which surround the 

 JIare Imbrium, and which 

 seem to be the dilapidated 

 relics of a vast crater 

 ring that once surrounded 

 the plain, it is worthy of 



Kudoxus. 



AriRtoteles. 



Godin. 



KiG. I). 



remark that the small lunar 

 mountain chains and ridges, 

 A^niTa. ^jj ^jjg maria above referred 

 to, have a north and south 

 trend. In addition to the 

 Riphajan Mountains, the Kirch 

 Mountains, and the ranges of hills to the south of Archi- 

 medes, I would refer the reader to the ridges shown in the 



inc.. 



