Jan., 1905.] 



KNOWLEDGE & SCIENTIFIC NEWS. 



13 



ASTRONOMICAL. 



Professor Sha-ler's CompaLrison of the 

 Fea.tures of the Earth and the Moon. 



In \'olume XXXIV. of the " Smithsonian Contributions to 

 Knowledge," Professor Shaler, of Harvard University, 

 treats of the lunar features from the point of view of a 

 geologist. He divides them into the broad classes of Maria, 

 vulcanoids (in which apt term he includes all cup-lil;e forma- 

 tions from the greatest ring plains to the smallest crater bed), 

 reliefs (mountains or ridges), v.alleys and rills, and rays. He 

 discusses and rejects the hypothesis that all or an}' of the vul- 

 canoids were originated by meteor falls. Were such the cause 

 the bolide would not only have been itself vaporised by the 

 heat of collision, but the surface round, for many times its 

 diameter, would have been melted, and the lava so formed 

 would have been extremely fluid and more than sufficient to 

 fill up the pit caused by the entrance of the bolide. Neither 

 have we evidence on the earth of such numerous and great 

 meteor falls as would be necessary to account for the great 

 number of lunar craters. Though the lunar vents indicate 

 some process of eruption it is evident that this cannot be iden- 

 tical with that on the earth. Terrestrial volcanoes are due — 

 at least mainly — to water buried by aqueous sedimentation, 

 and such occluded water, or its dissociated gases, we cannot 

 admit upon the moon. Professor Shaler suggests some kind 

 of boihng, such as will take place in any fluid mass which is 

 heated below and cooled on the surface (as in molten iron), 

 where substances in the vaporous state, though they exist, are 

 not present in sufficient quantities greatly to affect the move- 

 ment, or there is a, circulation mainly impelled by the escape 

 of imprisoned vapours. 



* * * 



But the Maria are attributed by Professor Shaler to the fall 

 of great bolides, though many of the arguments, which caused 

 him to reject this as the origin of the vulcanoids, hold good. 

 Besides the Maria are arranged in such symmetrical fashion, 

 almost exclusively in the moon's northern hemisphere, that it 

 seems impossible to consider them as owing their origin to such 

 haphazard casualties as a meteor fall. Professor Shaler con- 

 siders that the low ridges which extend for many miles across 

 the Maria are more nearly analogous to terrestrial mountain 

 chains than the rugged reliefs which are usually called moun- 

 tains on the moon. The light rays, he considers, owe their 

 hue and brightness under a high sun to a crystalline deposit 

 which reflects sunlight chiefly when vertical. This is almost 

 proved by their shining also under earthshine, and the bright 

 patches are probably of the same nature. 



The problems raised are numerous, and Professor Shaler 

 states several in a manner that may help to their solution. As 

 regards the vexed question of change on the moon, he strongly 

 decides against the possibility of present volcanic action. If 

 Linne has changed he attributes it to the creeping action 

 caused by the great changes of temperature, assisted perhaps 

 by a blow from a chance meteor. As to the presence of 

 organic life, he points out that there is none at all on terres- 

 trial mountain peaks above 30,000 feet, where the earth's 

 atmosphere is but one-third its density at the surface. 

 Organic life has failed to adapt itself here to the conditions, 

 much less could it originate. How then can we conceive of 

 it on the moon ? 



♦ • * 



For one problem he can suggest no solution. If meteoric 

 dust falls on the moon in the same proportion as on the earth 



— and we have no reason to suppose otherwise— and during 

 past time in as groat quantities as now — and we have no reason 

 to suppose that it was less — how is it that the moon, unpro- 

 tected by any atmosphere, has preserved its clean reliefs and 

 its varied hues, and has not had all masked under a uniform 

 veil ? Especially how i? it that the bright rays — differing 

 widely in the date of their origins — which seem but stains on 

 the surface, are still bright, and the older rays no less bright 

 than the later? 



Return of Tempel's Second Periodica.1 

 Comet. 



Three short-period comets belonging to the Jupiter family 

 were discovered by Herr Tempel. Of these the one discovered 

 in 1 87 J has the shortest period, and was due to return to 

 perihelion this year. It was re-detected by M. Javelle with the 

 30-inch refractor of the Nice Observatory on November 30, 

 though it was of the most extreme faintness, and set within 

 three hours after the Sun. It appears to have been seen only 

 on two nights, but the observations show a most gratifying 

 precision in M. Coniel's ephemeris; the error being only four 

 seconds of time in R.A, and four seconds of arc in declination. 

 But for M. Javelle's two observations the comet would prol)al)ly 

 not have been seen at this return at all. Its previous appear- 

 ances were in the years 1S73, 1878, 1894 and 1899 ; the returns 

 of 1883 and 1889 having been unobserved. 



Discovery of a Ne'w Comet. 



A new comet, aliout the nth magnitude in brightness, was 

 discovered on December 17 by M. Giacobini, of the Nice 

 Observatory, just on the borders of the two constellations of 

 Hercules and Corona Borealis. It was a morning object, 

 moving in a north-easterly direction. It will not become at 

 all a conspicuous object, as the following elements show : — 



T = i905 Jan. 3d., 2814, Berlin M.T. 



«= 75° 9'-S] 



il= 225 1-2 J- 1904-0 



1 = 103 273 J 



log q= 0-27173 

 The inclination being very great and the motion retrograde, 

 it is exceedingly unlikely that the comet is a periodic one. 

 Its perihelion distance is large, lying much outside the orbit 

 of Mars. 



* * * 



The Grea-t R-ed Spot of Jupiter. 



In Astronomischc Nachrichtcn, No. 3983, there are two in- 

 teresting notes on Jupiter's great red spot, by the e.xperienced 

 observers, Mr. A. Stanley Williams and Mr. W. F. Denning. 

 The two notes are all the more interestinginthatthey seem to 

 indicate very different results. Mr. Stanley Williams gives the 

 value for the relative period of the spot as gh. 55m. 41-523. in 

 1903 from 4S5 observations, as compared with gh. 55m. 3g-6bs. 

 in 1902, and writes : " This is a remarkable increase from the 

 value obtained in the preceding year. The changes during 

 the past five vears have, in fact, been very considerable. . . 

 Such large and comparatively sudden changes are particularly 

 interesting in the case of an object like the red spot, since in 

 conjunction with its unchanged aspect they appear to indi- 

 cate, firstly, the relatively great rigidity or solidity (using this 

 word in a comparative sense) of the spot itself, and secondly 

 the mobility of the material surrounding it, and in which it 

 appears to float. There was no noticeable change either in 

 shape or appearance last year, though, owing to the higher 

 altitude of the planet the spot was a comparatively easy 

 object, and its outline could be distinguished without difliculty. 

 There may, however, have been a slight real increase of 

 plainness." • • j 



Mr. Denning, on the other hand, finds for the rotation period 

 during the last seven months, gh. 55m. 38-6S., which, he writes, 

 " is shorter than any period it has exhibited since 1883. In 

 1883 it was gh. 55m. 38-2s., and in 1884 gh. 55m. 3g-os. The 

 spot is now very faint. Its variable motion in recent years has 

 been very curious, and it will be highly interesting to watch 

 this object during ensuing months, and trace out any further 

 changes in velocity." 



