276 



KNOWLEDGE. 



[December 1, 1899. 



plain Bullialdus, with its three satellites A, B.and C, all 

 with bold unbroken ramparts, and all with their floors 

 many hundreds of feet below the level of the jnare. 



With the reservation then of Bullialdus and its satellites 

 it appears clear that generally speaking the great rings 

 preceded the " seas " in order of time. The six rings 

 mentioned above, Hippalus, Lee, Doppelmayer, Capuanus, 

 Kies, and Lubiniezky, are amongst the relics of the earlier 

 moon. 



Dealing with the maria next, the succession of ridges on 

 the Mare Humorum point out clearly what has happened 

 there. The lines which these follow, however sinuous in 

 detail, are manifestly circular and concentric in general 

 type, and the crevasses which cut through Hippalus, and 

 the country beyond, seem to carry on the same curves on 

 a wider radius. It is scarcely possible to avoid the con- 

 clusion arrived at by Messrs. Loewy and Puiseux that the 

 ridges and crevasses have a common origin. 



It appears, then, that the basin now constituting the 

 Mare Humorum has taken its present form by a series of 



VVurJelbauer 



MARE 

 ® © 

 N U B01 U M 





O^s^lvji 



Pketcli Map of Hijijiiilns and it? surroundings. 



subsidences. Each subsidence was marked at its circum- 

 ference by a crevasse, or fault, roughly circular in shape, 

 and those crevasses which were formed earliest nearest the 

 centre, and which surrounded the deepest subsidences, gave 

 egress to the liquid or viscid matter of the interior, which 

 welled up through them, filling up the crevasses, and 

 forming ridges upon them. These outflows would naturally 

 become less and less the further the crevasse was from the 

 centre of the subsidence, and the less the depth to which 

 the sinking at the crevasse had taken place, until at length 

 a distance is reached at which no filling up of the crevasse 

 takes place. 



The crevasses, or " rills," then, are more recent than the 

 " seas " as they are than the rings. That the rills are 

 more recent than the rings is clearly shown by Hippalus 

 itself, a deep crevasse cutting completely through it. 



But the rills are not the most recent formation of all. 

 As mentioned above, a bright crater, Campanus A, occupies 

 the centre of the photograph. This crater stands right 

 upon a rill, and completely interrupts it ; and a more 

 conspicuous crater, Agatharcides A, interrupts it further 

 north. Nelson, indeed, considers that it can be traced, 

 greatly narrowed across both craters, but the photograph 

 does not seem to bear this out. 



The relation between the rills and the mountain masses 

 is less clear. Neison describes this rill, and the one 



immediately to the east of it, as commencing at a small 

 crater, Campanus g, east of Campanus. On the photo- 

 graph, the influence of the rill can be traced quite 

 unmistakably to the east of the crater, amongst the broken 

 highlands which border the south of Mare Humorum, 

 almost to the walls of Vitello. These highlands, therefore, 

 are also earUer than the rills. 



Another instance of a late ring-plain is seen in Ramsden, 

 the peculiarly distinct ring-plain on the floor of the Sinus 

 Epidemiarum. Three well-marked rills, in the form of a 

 capital N, are clearly seen on the photograph to the north 

 of the ring, and two of these are very distinctly prolonged 

 beyond the ring to the south. Ramsden, therefore, like 

 Campanus A , may be looked upon as one of the younger 

 formations of the district. 



The finest rill of the entire region can be traced on the 

 photograph, but, from the illumination, is less evident 

 than the rills of Hippalus. This is the great Capuanus 

 rill, if'. It starts from the most easterly of the three 

 great spurs thrown out from the north-east rampart of 

 Capuanus, and strikes nearly due west in a right line, 

 cutting through the mountain range connecting Cichus 

 and Mercator, and extending to the wall of Hesiodus, a 

 course of two hundred miles. 



The great depth of the floors of Bullialdus and its 

 satellites below the level of the mare would seem to show 

 that they were formed later than the grey plain itself. If 

 this be so, it may be inferred that the Mare Nubium was 

 an older formation than the Mare Humorum, since the 

 former had been completed whilst the internal forces were 

 still powerful enough to give rise to so fine a ring as 

 Bullialdus, on so much larger a scale than the little craters 

 marking the ridges of the Mare Humorum and studding 

 its lowest basins. And an attentive study of the district 

 immediately around Hippalus, which separates the two 

 " seas," wiU, I think, confirm this view. 



Two other lines of structure shown in the plate may be 

 alluded to. The first is the well-marked tendency to 

 aUgnment in a S.W. and N.E. direction. The line through 

 Cichus, Mercator, Campanus, and Hippalus, and carried on 

 to Gassendi, the south wall of which is just seen on the 

 edge of the photograph, seems fundamental to the whole 

 region. It is plainly seen in Capuanus, both in the spurs 

 projecting from the rampart outward, the markings on the 

 floor, and the clefts through the wall. It characterises 

 the general trend of the mountains east of the Sinus 

 Epidemiarum, and bordering the Mare Humorum. It 

 probably indicates the lines upon which the earliest lunar 

 configurations were based. 



Next in time, probably, come the great rings, so many 

 of which are ranged on these fundamental S.W. and N.E. 

 lines. Then come the subsidences which created the 

 grey plains — that of the Nubium, probably considerably 

 earlier than the Humorum. On these plains we find the 

 lines of ridges and crevasses, the innermost indicating 

 where the earlier sinkings took place. These were followed 

 by the formation of ring-plains and craters along the lines 

 of fault, and in other weak regions of the crust. Lastly, 

 we find the white streaks — those in the present plate are 

 for the most part of the system with Tycho for its centre 

 — passing over all the preceding formations indifl'erently. 

 ♦ 



%ttttvs. 



[The Editors do not hold themselTeB responsible for the opinions or 

 statements of correspondents.] 



IS THE STELLAR UNIVERSE FINITE? 

 To the Editors of Knowledge. 

 Sirs, — I fear Mr. Burns will draw down on his devoted 



