278 



KNOWLEDGE. 



[Decembeb 1, 1896. 



biology and luorpliology of the iiivcrtebratee would do well to send 

 for IV lopv of this cntiilogue of scientific books and monogniphs. 



In the Quarlvrlii Inti-nin/ioiinl Journal of Min'osropy mid Xn/iira! 

 Scienre (Octobei', lM!t6) is to bo found a sliort paper upon " The 

 British Hvdmchuida- " — Oonus VI., Diiihidontus — b_v Charles i). 

 Soar. Tlio drawings ai'e i ci'v good, but the descrijitions are very 

 meagre eonsicU'ring tlie literature which haa been published upon the 

 genus by various uiicroseopical societies. 



In the Oliserrer (Portland, Comi.) for September there ai'e several 

 very intere.stini articles ; one, on " First Steps in the Si udv of Fishes," 

 by Dr. K. VV. Sliur.Odl (Wasliiugton), is illu-trnted by a'|>latc giving 

 twenty-three types of Ih.s and forms of fishes. It is fidl of suggestion 

 to the young ichthyologist. Tliosc who are desirous of studying the 

 habits of the trapdoor spiders will iiiul an article on " The C'tcuzia 

 Californica," by F. K. (iray, who is evidently a practical observer. 



The Jottinal nf r/iifsiral C/ieiiiixliy (October, ISOOI. Edited by 

 Wilder I). Bancroft and Joseph Vl. Trevor, of CoriU'U I'ldversity. 

 This is the first mnnher of what promises to be an important addition 

 to chemical literature when the magazine is settled into woi'king 

 order. There are three highly technical articles in this number — 

 one, on irrcviu'sible cells, by A. E. Taylor, giving ten tables of 

 valuations of the electromotive forces of the cells in the various 

 chemical solutions descrilicd in the text; the second article is a 

 translation of Prof. F. \V aid's (Austria) manuscript on " Chennstry 

 and its Laws"; and a paper on "Ternary Mixtures" by W. J). 

 Bancroft. 



Those iTiterested in the rise and ]irogress of mining cities will find 

 an illustrated pajier on " Nevada Sil\-er," by Charles H. Shinu, in 

 the October number of A/jple/on'.i Popular Srieiire Mon/li/i/, It 

 describes the finding of the gold and silver, and how " Old Pancake " 

 (JI. T. P. Comstock) "bluffed the good-natured discoverers into 

 taking himself and Manny Penrotl as equal partners." The history 

 of the men who discovered the mines first is graphically described. 

 Tlie lawsuits cost one-fifth of the products of the mines (five million 

 dollars) durini; IHliO to 1865. The pitched battles, forts, and the 

 armed men drilling, all find a place in the history of this famous 

 comer of Utah. 



A POSSIBLE CAUSE OF CHANGE ON THE 

 MOON'S SURFACE. 



By Chakles Davison, Sc.i)., F.G.S. 



IN spite of the fruitless search of many years, astro- 

 nomers have not yet apparently given up hope of 

 discovering changes on the moon's surface. And the 

 hope does not seem to be altogether without founda- 

 tion. In the great changes of temperature which 

 take place on the moon, changes which are untempered by 

 any atmosphere such as we possess, there resides a cause 

 capable perhaps of producing effects that may in time 

 become perceptible to our telesco^jes. 



The suggestion that such may be the case is due, I 

 believe, to Messrs. Nasmyth and Carpenter. Paring the 

 Ion" lunar day, they remark, the surface attains a tempera- 

 ture of about 500^ F., and during the equally long lunar 

 night one of about - 250° F. " Such a severe range of heat 

 can hardly be without effect upon some of the component 

 materials of the lunar surface. If there be any such 

 materials as the vitreous lavas that are found about our 

 volcanoes — such as obsidian, for instance — they are doubt- 

 less cracked and siilintered by these extreme transitions of 

 temperature ; and this comparatively rapid succession of 

 changes continued through long ages would, we may sup- 

 pose, result in a disintegration of some parts of the 

 surface, and at length somewhat modify the selenographic 

 contour." On the other hand, " it is possible," they add, 

 " that the surface matter is mainly composed of more 

 crystalline and porous lavas, and these might withstand the 

 fierce extremes like the ' fire-brick ' of mundane manu- 

 facture, to which in molecular structure they may be 

 considered comparable. Lavas as a rule are (upon the 

 earth) of this unvitreous nature, and if they are of like 

 constitution on the moon, there will be little reason to 

 suspect changes from the cause we are considering. ' They 



think it conceivable, however, " that the alleged changes in 

 the crater Linnr may have boon caused by a filling of the 

 crater by some such crumbling action as wo are here 

 contemplating.''* 



In making this suggestion, Nasmyth and Carpenter are 

 appealing to no imaginary agency. Several instances 

 might be given of the splintering of terrestrial rocks by 

 more or less sudden cooling. It will be sufficient to men- 

 tion one case, observed by Livingstone in the valley of the 

 Gova, a river iiowing into Lake Nyassa. " Several of the 

 mountain-sides in this cotintry," he says, " are remarkably 

 steep, and the loose blocks on them sharp and angular, 

 without a trace of weathering. For a time we considered 

 the angularity of the loose fragments as evidence that the 

 continent was of comparatively recent formation, but we 

 afterwards found the operation actually going on by which 

 the boulders are split into these sharp fragments. The 

 rocks are heated by the torrid sun during the day to such an 

 extent that one is sometimes startled on sitting down on 

 them after dusk to find them quite too hot for the fiesh, 

 protected by only thin trousers, to bear. The thermometer 

 placed on them rises to 137° in the sun. These heated 

 surfaces, cooling from without by the evening air, contract 

 more externally than within, and the unyielding interior 

 forces off the outer parts to a distance of one or two feet. 

 Let anyone in a rocky place observe the fragments that 

 have been thus shot off, and he will find in the vicinity 

 pieces from a few ounces to one or two hundred pounds in 

 weight, which exactly fit the new surface of the original 

 block ; and he may hear in the evenings among the hills, 

 where soimd travels readily, the ringing echo of the report, 

 which the natives ascribe to Mchesi or evil spirits, and the 

 more enlightened to these natural causes." I 



If changes of temperature can produce such effects on 

 the earth, they must act still more powerfully on the moon. 

 There, especially on the mountain-sides, large areas are 

 suililinli/ exposed to, or withdrawn from, the action of the 

 sun's rays. Moreover, the range of temperature, as we 

 have seen, is enormously greater. Thus, if the rocks which 

 compose the lunar mountains resemble even approximately 

 those which are found itpon the earth, there must evidently 

 be much fracturing and splintering ; level or inclined sur- 

 faces must in places be covered with loose fragments of 

 rock, while against the steeper hillsides slopes of loose 

 rocks, or "screes," must be piled up. 



It appears to me that these screes, if they exist and are 

 perceptible, are the regions where signs of change should be 

 especially looked for. As fresh fragments fall down from 

 the crags above, the slopes of the screes increase until they 

 attain, or nearly attain, their maximum inclination. The 

 surface blocks are then in a highly unstable condition, 

 and every newly-fallen rock showers down numbers of 

 others all round it before it finally comes to rest. 



Thus, if screes are found at all upon the moon, they will 

 continually increase in size until they mask the parent 

 cliff. So far as we know, there is little to check their 

 rate of growth, except that growtli itself, which gradually 

 lessens the area from which new blocks are to be derived. 

 The blocks themselves may splinter still further until the 

 spaces between them are filled up with small fragments 

 and dust, and this may perhaps retard their movement ; 

 but there can be no vegetation to find a root in this soil 

 and so bind the surface stones together. 



While changes of temperature furnish the materials of 

 screes, and gravity rearranges them, these two agencies in 

 concert are capable of producing a further movement of 



*" The Moon: considered as a Planet, a World, and a Satellite," 

 1883, pp 172-171. 



t "'The Zambesi and its Tributarie>, " pp. 4Ui, tll3. 



