April 13, 1883.] 



• KNOWLEDGE 



225 



in the sky. Let us assume that we are employing a power 

 o£ 160. Well, this shows us the moon as she would 

 appear to the naked eye, were she only 1468 miles from 

 the surface of the earth — a pretty long distance truly ; but 

 •when we consider that Mont Bliinc is discernaUle, hy un- 

 assisted \ision, from Lyons, 100 miles off, throuc;h all the 

 thickness of the intervening terrestrial atmospheric vapour, 

 we shall gain some notion of what this represents in the 

 case of the airless moon, with her brilliant lights and iiiky 

 shadows. A power of l?•^0 will bring her seemingly within 

 939 miles of us : but no useful purpose will be attained by 

 the employment of such magnification (for Selenographical 

 purposes) with a 3-in telescope. In our subsequent 

 sketches I GO is the highest power that we shall use. The 

 nature and character of the objects it will reveal will be- 

 come apparent in the description of them which will follow. 



J\rl)ifU)5. 



POPULAR ASTRONOMY.* 



Bv Eicu.\Kii A. Proctor. 



1AM glad to see that this excellent treatise on astronomy 

 has reached a second edition in England. Of its success 

 in America it is unnecessary to speak. The present edition 

 has in several important respects been Virought up to date. 

 Among those may be specially mentioned : (1) Dr. H. 

 Draper's investigations on the existence of oxygen in the 

 sun (but why are they not mentioned in the index ?), of 

 which Professor Newcomb has formed an opinion very 

 different from that cold, half-dissenting view which rival 

 workers in this country have expressed ; (2) Janssen's 

 conclusions from his solar photographs (again the index 

 makes no mention of the added subject) ; (3) Professor 

 Langley's investigations on the solar spectrum (omitted 

 from index) ; (4) preliminary results from the late transit 

 of "Venus, and other recent methods of determining the 

 sun's distance ; and (•")) recent developments in cometary 

 astronomy. 



I have already reviewed the first edition of this im- 

 portant work at considerable length in these pages, so 

 that it is not necessary for me now to say that I regard it 

 as a most valualile contribution to the literature of astro- 

 nomy. Albeit one cannot but recognise that Professor 

 Newcomb is more at home with mathematics than with 

 composition, better as a coraputor than a theovizer, and a 

 little disposed to overlook the difficulties which ordinary 

 readers find when technicalities are employed. 



It is a little remarkaV)le that a professional astronomer, 

 well versed in optical and physical laws, should err on the 

 side of over-boldness in theorising. Yet Professor New- 

 comb seems to do so. Take, for instance, the following 

 passage in reference to the Saturnian ring system : — "The 

 question arises whether the comparative darkness of some 

 portions of the bright ring may not be due to the paucity 

 of the particles, which allow the dark background of the 

 sky to be seen through." (We can tell what Professor 

 Newcomb means, but it is not precisely what he says — viz., 

 that, according to this view, we can see through the dark 

 background of the sky !) "Tliis question cannot be posi- 

 tively answered until further observations have been made ; 

 but the preponderance of evidence favours the view that 

 the entire bright ring is opaque, and that the dark 



•"Popular Astronomy." By Simon. Newcomb, LL.D., of the 

 Tfaval Observatory, Washington. Second London edition. (Messrs. 

 Macmillan & Co., London.) 



shading is due entirely to a darker colour of that part of 

 the ring. Indeed, for anything we certainly know, 

 the whole ring may be continuous and opaque, 

 the darker shade of some parts arising solely from the 

 particles being there black in colour." Now, in the first 

 place, it is a demonstrated fact that the rings are not 

 continuous. No one who has studied the researches of 

 Clerk Maxwell and Benjamin Pt-irce can for a moment 

 question this. And in the second, wliile the theory which 

 accounts for the darkness of certain zones of the ring by 

 sparsity of distribution of matter along these zones is 

 natural and probable, the theory that certain sets of dark 

 bodies have collected into these zones, while the light- 

 coloured bodies have collected into others, is extravagant 

 to a degree. When gravity begins to act as a colour-sifter, 

 by influencing dark bodies and light bodies in different 

 ways, we can accept such ideas ; but not before. 



Here, again, is a statement singularly inexact from a 

 man with Professor Newcomb's knowledge of optics. 

 Speaking of the atmosphere of Venus in transit, he says, 

 " It would not be possible to see any indications of an at- 

 mosphere under such circumstances, for the reason that 

 the light passing through its denser portions would be 

 refracted entirely out of its course, so as not to reach an 

 observer on the earth at all. ' It would be just as reason- 

 able to say, " As regards the theory that we see the sun, 

 after he has set geometrically, because of the refractive 

 power of our air, it is, in fact, impossible to see him at all 

 under such circumstances, for the reason that the light 

 passing through the denser portions of our air is refracted 

 entirely out of its course, so as not to reach the observer 

 on earth at all." Precisely as we see the sun by means of 

 rays which did 7io( set out towards the observer, but were 

 refracted towards him, those which set out towards him 

 not reaching him at all, so, while rays from the sun towards 

 Venus, and beyond her towards an observer on earth, fail 

 to reach the observer, being deflected by the refractive 

 power of her atmosphere, rays from other parts of the sun, 

 which but for her air would not have reached the observer 

 on earth, come to him and in fact give him those indica- 

 tions of an atmosphere which Professor Newcomb says it 

 would be impossible to detect. 



Other such mistakes remain uncorrected in the second 

 English edition, and to some degree diminish the value of 

 what otherwise would be (for the ground it covers) one of 

 the most trustworthy astronomical works in existence. I 

 note also the way in which the " stereo-plates " have been 

 joined, evidence of anxiety to avoid expense in " resetting." 

 But the treatise is one which every student of astronomy 

 should read, and passages relating to suVijects which Pro- 

 fessor Newcomb has made specially his own are adniirabile. 



The English editor, if such there is, or the reader for 

 press, should have corrected in this edition the render- 

 ing of Georijiuin Sidus as " the Star of the Georges," 

 which would correspond to Gcorgiornm Sldn.s — not that it 

 matters much, as the silly name has long since followed 

 other similar absurdities to the limbo of forgotten things. 



TO YOUNG MEN.* 



Tiinnron false delicacy, many lads and youths are left to 

 fall into trouble, and not a few have their prospects of 

 healthy and happy life absolutely ruined. The knowledge 

 kept from them by those whose duty it is to impart it 

 wisely, and with proper explanation of its vital importance, 

 they learn (too many of them) from foolish talk and to 



* " A Physician's Sermon to Young Men." By Dr. William Pratt • 

 (Balliere, Tindall, &, Cox, London.) 



