108 



KNOWLEDGE. 



[May, 1903. 



although I consider their objections to be rather weak, and 

 with one exception not much to the point, tliey are yet of 

 great use to me, as showing me where my argument needs 

 streugtheuiug or where I am likely to be misunderstood. 



In a volume I am now preparing I hope to be able to 

 present my views in a more complete and more convincing 

 manner. 



Broadstone, Dorset, Alfred R. Wallace. 



April 8th, 1903. 



TO THE EDITORS OF KNOWLEDGE. 



Sirs, — Dr. A. R. Wallace's biological investigations 

 have been elevated and illuminated, throughout their long 

 course, by liis strong appreciation of the incomparable 

 moral dignity of Man. And this, too, is the inspiring 

 thought of his recent article in the Fortnighlly Review. 

 It rises beyond discussion ; welcome assent is the only fit 

 attitude of mind towards it. But the profound significance 

 of human life would be no whit impaired by assigning to 

 the scene of its expansion an eccentric position in the 

 universe; and a central position, as Mr. Maunder has 

 shown in Knowledge, and Prof. Turner in the Fortnightlq 

 Review, can belong only momentarily to a moving body. 

 Nor can it reasonably be supposed that the conditions of 

 vitality deteriorate with remoteness from the centre. In 

 the actual throng of the Milky Way, indeed, a peopled 

 planet might be exposed to perils from " furious driving," 

 or subtler obstructions to traffic. Within its ambit, 

 liowever, there is " room and verge enough " for the 

 unimpeded travelling of many millions of globes, freighted 

 though they may be with superhuman destinies. 



But has the universe a centre? In other words, is it of 

 limited dimensions ? Dr. Wallace avers that it is. His 

 arguments are, nevertheless, contravened by the high 

 astronomical authorities just referred to. The all- 

 pervading illumination of the sky-ground, which should 

 attest the shining of infinitely niuuerous suns, would be 

 prevented, they agree in considering, by the intercepting 

 action of an equally infinite number of dark bodies. 

 These, however, cannot be supposed to screen off gravita- 

 tioiud influences ; they should, on the contrary, reinforce 

 them. Hence, every body in space would be acted on by 

 infinite forces, soliciting it to move in every direction at 

 one and the same time. Cosmical paralysis would result ; 

 the " constellated Sims'' would stand stock still; unless 

 we make the hazardous assumption that a finite attraction, 

 super-added to an infinite sum of attractions, might avail to 

 determine velocity. That is to say, neighbouring stars 

 might exert effective pulls upon each other irrespectively 

 of the equilibrating pull of a measureless universe. 



There is, however, little profit in dwelling upon this 

 baffiing aspect of the question ; clearer evidence is before 

 our eyes. Everywhere in the heaveas structural relations 

 are manifest. Architectural design is traceable in them ; 

 they have parts fitted in together to form a vast yet 

 limited whole. The Galaxy has shape and boundaries, 

 and we h-ive no assured kuowleige of anything lying 

 outside those boundaries. It seems, then, a gratuitous 

 exercise of the imagination to conjure up abysses stored 

 with stars, energetic and effete, one set cutting off the 

 radiations of the other. 



Undeniably, Ur. Wallace's contention that our earth is 

 unique as being the abode of intelligent life corresponds, 

 in a measure, with the recent trend of astronomical 

 research. The conditions indispensable to organic" 

 existence which he has admirably defined are perceived, 

 more and more plainly, not to be present on any of our 

 sister-planets with the possible exception of Mars. More- 

 over, a large proportion of the stars have been ascertaine d 



to form systems unfavourably circumstanced for the 

 accommodation of globes approaching the terrestrial 

 model. Boundless variety, it is true, prevails throughout 

 the sidereal scheme; and this variety may only afford scope 

 for the display of the contriving power of Infinite Wisdom 

 in smoothing away apparent obstacles to life, and so 

 vitalising the seeming deserts of the universe. 



Agnes M. Clerke. 



TO THE EDITORS OF KNOWLEDGE. 



Sirs, — With reference to Dr. Wallace's article on this 

 subject in the Fortnighlly Review for March, 1903, 1 should 

 like to make a few remarks. 



As it is at present impossible to fix the exact limits of 

 the visible universe we cannot determine where its 

 centre may lie, and although the sun and solar system 

 apparently lie near the centre of the Milky Way, it does 

 not follow that we are really at or near that centre. 

 Indeed, there is evidence to show that we are perceptibly 

 nearer to one side of the Milky Way than to the opposite 

 side. Sir John Herschel was of opinion that the southern 

 portion of the Milky Way near the Southern Cross is 

 nearer to us than the northern part. Professor Newcomb 

 considers that we are probably nearer to the boundary of 

 the visible universe which lies in the direction of Sagittarius 

 and Scorpio, and he thinks that we may possibly be so 

 much nearer this particular region that we may soon be 

 able to detect proper motions among the fainter stars in 

 this direction. 



Considering the sun's motion through spice as recti- 

 linear, I pointed out ten years ago (" The Visible Universe," 

 p 197) that at some period back in geologic.il times the 

 sun was probably among the stars of the Mil';y Way. 

 The solar " apex." or point towards which the sun is 

 movintf, is, according to Prof. Kaptevn, in about 

 R.A. 27:i°-6, North De.lination 29° 5, and "he thinks that 

 " the most probable value that can at present he adopted" 

 for the sun's velocity is IS'4.5 kilometres, or 1146 miles a 

 second. With this velocity, the sun's annual motion would 

 be about 360 millions of miles (or nearly four times the 

 radius of the earth's orbit). Hence the distance traversed 

 in, say, 200,000 years woidd be 72 billions of miles. As 

 the distance of Sirius from the sun may be taken as 

 50 billions of miles (parallax 0""37), the solar motion 

 carried back would place the sun far beyond the distance 

 of Sirius 200,000 years ago. If we go back in geological 

 times, .say 5 millions of years, we find the sun at a distance 

 of 1800 billions of miles from its present position in space. 

 This would represent the distance of a star with a 

 parallax of about 0"01, or about 326 years' journey for 

 light. Removed to this distance the sun would be reduced 

 in brightness to a star of the 10th magnitude. It follows, 

 therefore, that if the sun is moving m a straight line it 

 must have been close to the position of 10th magnitude 

 stars (if of the same size and brightness) some 5 millions 

 of years ago. Going further back in geological time we 

 should find the sun among the stars of the Milky Way. 

 Prom the apparent connection of bright and faint stars in 

 the Gala.\y, Easton tliinks that the faint stars of the Milky 

 Way are at a distance which does not greatly exceed that of 

 stars of the 9th and loth magnitude {Astrophysical Journal, 

 March, 1895). 



It is of course possible, and indeed probable, that the 

 sun is not moving in a straight line, but in some gigantic 

 orbit round a centre of force. Recent researches seem to 

 show that the centre of the Milky Way probably lies in a 

 direction south of Cassiopeia's Chair, and a little south of 

 the Milky Way (about R.A. 24h.), the sun and solar system 

 lying to the south of the galactic centre, and a little to the 



