September 5, 1895] 



NATURE 



439 



"V PHOTOGRAPHS OF THE MOON TAKEN 

 AT THE PARIS OBSERVATORY. 



QUITE recently some negatives of photographs of the 

 ,^^ Moon, taken at the Paris Observatory by MM. 

 Lcfwy and P. I'uiseux, were exhibited at tlic Academy 

 of Sciences. 



The negatives have been carefully studied, enlarge- 

 ments made, and specimens sent to all the principal 

 scientific societies interested in them. These enlarged 

 copies arc of great help in the study of the Moon, and 

 ha\e been the means of making clearer many uncertain 

 l)oints, for they allow every detail to be seen without j 

 difficult)'. Their chief adxantage, however, lies in the 

 great expanse of surface which they embrace ; many 

 facts, hard to discover on the smaller negatives, have 

 now been ascertained. 



In their communication made to the Academy, MM. 

 Lrewy and Puiscux gave an account of the results they 

 have obtained in studying these photographs. Some of 

 them are of great interest. 



Considering, first, the Moon's surface, they note that its 

 markings arc of a less varied type than those of the 

 earth, and its prominences are chiefly of a circular shape. 

 By the way in which the Moon reflects, it is thought that j 

 its crust is of solid matter, similar to \olcanic rocks. 

 This agrees perfectly with Laplace's hypothesis, in which 

 he states that the Moon was thrown off from the earth ; 

 when the latter was in a nebulous state. The Moon's ' 

 mean density scarcely surpasses that of the crust of the - 

 earth ; its materials, judging exclusively from the exterior 

 crust, are of a more uniform chemical composition. 

 But although we might trace its history from the time in 

 which it was thrown off from the earth, it is clear that all 

 the facts rest on a verj- uncertain basis ; it is scarcely 

 ]jrobable that the Moon had the same appearance then 

 it has now ; it is only when the masses had become to 

 a certain extent solid, that the surface-markings could 

 have been formed which are now to be seen. .-\ very 

 long period must have elapsed between the nebulous 

 state of the .Moon and its present fi.ved condition, the 

 jjrocess commencing, no doubt, by the union of the 

 particles of scoria;. Owing, however, to currents arising 

 from various sources, ruptures must often have taken 

 place, causing lines to be left on the parts which were 

 not quite solid. 



The various lines, which can be followed on the 

 photographs, may be c|uite easily described. They are 

 valleys between huge mountains. One of the largest is 

 the valley of the .\lps, to the west of Plato ; another one 

 between Herschel and Hipparchus, between Bode and 

 Ukert ; and one to the south-west of Rheita. It would 

 be absurd to imagine them anything like the terrestrial 

 valleys ; they are almost perfectly straight, do not branch 

 off at all, and keep the same width almost the whole 

 length. There is no sign of what has become of the 

 materials out of them, and when minutely examined, they 

 appear to have flat bottoms ; this fact seems to prove 

 that they were once filled with some liquid which has 

 dried up. .\s before stated, their origin is most probably 

 due to currents, which must necessarily have developed 

 in the mass of the moon when still fluid. These valleys 

 are grouped about in various parts, and run parallel 

 chiefly, especially near the equator, but they also go in 

 other directions. There is nothing to show that the 

 direction has remained the same. 



So long as the revolution and rotation of the Moon 

 were not performed in the same time, the tides must 

 have produced very considerable change of level, which 

 would hinder the crust from becoming solid. The scoria, 

 therefore, would gr.idually form itself into larger and 

 larger islands, which, however, might often have got 

 broken up owing to constant collisions. Still gradually 

 gaining in thickness, they eventually constituted the 



NO. 1349, VOL. 52] 



oldest part of the Moon, and at their expense the circular 

 formations were formed which we now see. After a time 

 banks of scoriic of great length covered the Moon, leaving 

 only narrow passages for circulation. Continual collisions 

 destroyed the projecting parts, which facilitated the 

 ultimate joining of the islands. 



The fluid masses of a body like the Moon take part in 

 the general circulation, but naturally have their tides 

 under the influence of gravity. The combination of 

 these two movements produces irregular rates in the 

 floating masses, which more or less always impede their 

 displacement. This irregular rate causes renewed 

 collisions and rectilinear formations differing in direction 

 from the first. After such various forces had been brought 

 into play, it is not astonishing that the marks left are 

 not absolutely regular and symmetrical. The parallel 

 lines indicate the existence of similarly directed currents 

 at the time the superficial solidification was going on. 

 The lines running in different directions, indicate changes 

 in the direction of those currents. 



Let us now consider the result of a huge boulder of 

 crust getting detached and falling. If falling on a slope, 

 it would naturally slip down, and in the matter, not yet 

 solid, form, as it were, a path ; thus ultimately a valley 

 would be made. This explanation applies itself more 

 especially to the valley of the Alps, because of its very 

 precise shape. If, therefore, these valleys are imperfect 

 joinings of ancient ruptures, they must form, on the hard 

 crust, lines of less resistance. The lines of craters are 

 now easily explained, also the various holes in the 

 furrows, which- may be looked upon as explosion outlets. 



If, on the other hand, they date from superficial solidi- 

 fication, their presence must have influenced the sub- 

 sequent formations. Admitting that, under a part of the 

 crust already thick, a diminution of pressure is produced, 

 capable of producing a cavity, these changes might be 

 brought about by the gradual cooling of the Moon, or by 

 the movements of the interior tides. The cavities might 

 take almost a circular form if the crust were homo- 

 geneous, having for the centre the point where the 

 pressure was at a minimum. But if there arc other 

 ruptures and lines, they would probably form the boundary 

 to the cavity. \\'e notice that the polygon form is most 

 frequent after the circular ; in many cases, also, the 

 furrows form tangents to the circles. 



MM. Lcewy and Puiseux remark, finally, that it is not 

 for them to say which of the hypotheses is correct ; they 

 merely wish to call attention to the immense help 

 the enlarged negatives may prove themselves to be. 

 Eventually, no doubt, they will be the means of making a 

 map, which may show us that the surface structure of the 

 Moon is very similar to our own. 



We imagine that not every one will agree with all the 

 opinions above expressed by MM. Locwy and Puiseux, 

 but it is clear that several important questions have been 

 raised by the magnificent photographs we owe to their 

 skill and industrv. 



UNSCIENTIFIC EXCAVATIONS IN EGYPT. 



PROF. DR. G. SCHWEIXFURTH has recently 

 written a most interesting letter to the editor of 

 Die Zeitschrift fiir Aegyplisclie Sprachc. According 

 to him, the time has arrived when a limit ought to 

 be put to the energy of Egyptian excavators. Within 

 the last few years there has been such a tremendous 

 collecting of antiquities, that it has seemed to be 

 the desire to leave nothing whatever for the next genera- 

 tion to discover. Our near descendants will, in all prob- 

 ability, not thank us for our want of patience ; it may have 

 totally difterent methods of research, and may bring 

 opinions forward we have not dreamt of If this be the 

 case we shall, most probably, be blamed for having dis- 



