December, 1903.] 



KNOWLEDGE 



269 



discovery tended to reverse the Coperuica,n view of the 

 earth, if we miij use that expression, and to restore the 

 Ptolemaic, that our solar system, in which this earth is by 

 far the most favoured planet, was the central system of 

 the entire sidereal universe; central not merely as to 

 position in space, Ijut in fundamental importance. " We 

 ourselves are " the " sole and sufficient result," the " ade- 

 quate reason why such an universe should have been called 

 into existence." And " nowhere else than near the central 

 position in the universe which we occupy could that result 

 have been attained." 



These are strong and far-reaching expressions, and 

 oblige us to interpret Dr. Wallace's description of the sun 

 as occupying the centre of the sidereal universe with a 

 greater rigidity than he cared to admit. But we must 

 bear in mind that the whole point, to demonstrate which he 

 has directed his energies, is this : that there neither is, nor 

 can be, any other inhabited world beside our own. "We 

 ourselves are the sole and sufficient " cause why the 

 universe has " been called into existence." And in his first 

 paper the one physical condition upon which he relied to 

 establish the improbability of life arising elsewhere than 

 here, was the position of our sun in the centre of a cluster 

 of suns, and that cluster situated, not only precisely in 

 the plane of the Galaxy, but also centrally in that plane. 

 If tliere was another sun that was nearer to that centre 

 than we were, or even substantially as near, his argument, 

 such as it was, was vitiated in its essential condition. No 

 expression, therefore, however rigid and precise, could 

 have so ine.xorably bound him down to the idea that our 

 system was exactly and pennanently central, as the 

 exigencies of his argument did. This was a position 

 which it was not possible for astronomers to allow to pass 

 unchallenged. It was not warranted by the course of 

 astronomical discovery, and if it should be widely accepted, 

 it would tend to hamper our progress in the future. The 

 immense problem of the true form and structure of the 

 sidereal system — a problem in which a pi'ogress has been 

 made of late years, which Dr. Wallace has either overlooked 

 or ignored — will only yield, so far as its solution is possible, 

 very slowly and gradually to patient, painful and con- 

 tinuous research. But if we are to assume at the outset 

 that we occupy the exact centre of that universe, and 

 invest that assumption with a C[uasi-theological authority, 

 we shall have conjured ourselves back some three centuries 

 or more into the position held by those who resisted and 

 oppressed Galileo, and free enquiry into the greatest of 

 physical problems will have come to an end. 



The criticism offered by astronomers has had a good 

 effect upon Dr. Wallace's book. It has induced him to 

 give up the attempt to establish the unique character of 

 our sun on the lines of a supposed central position. In 

 his article in the FoHn'ujhlly Review tor September he 

 withdrew most of the advantages which he had suggested 

 might accrue to our system from that position. In his 

 book he gives up the position itself. He no longer plants 

 the sun in the centre of the hypothetical solar cluster, but 

 near its circumference (p. 304). He no longer places the sun 

 in the exact geometrical centre of the Milky Way, but about 

 one-twelfth of the diameter of the ring to one side (p. 162). 

 He admits implicitly that many other stars are as well or 

 perhaps better situated, and suggests that the advantage 

 of the central position which they all thus share is 

 that, being far within the circuit of the Milky Way, they 

 may possibly lie ])rotected by it from certain supposed 

 emanations. Now, just as it was necessary to lodge a 

 protest when Dr. Wallace claimed for the sun a central 

 position that was absolutely unique, so now there can be 

 as little hesitation iu declaring that ho lias at last read 

 rightly his authorities — Sir John Herschel, Sir Norman 



Lockyer, and others. It is true in this very loose sense 

 that the sun is central in the central plane of the Milky 

 Way. It was most emphatically not true in the sense iu 

 which Dr. Wallace first used it. 



The differentiation between our sun and other stars is 

 now sought to be brought about iu a much more legitimate 

 way. He gives just prominence to Mr. Herbert Spencer's 

 remarkable essay on the nebular hypothesis. It is true 

 that the trend of more recent discovery has tended to 

 weaken rather than support Sjieneer's argument. He 

 could not write to-day " scarcely any nebulae lie near the 

 Galactic circle," but still the immense probability remains 

 that the vast majority of all the celestial objects which we 

 see are members of but a single structure. Whether we 

 are acquainted with any aliens, and, if so, what proportion 

 they form of the entire celestial host, we are not at present 

 able to decide. Broadly speaking, stars, nebulae and 

 Galaxy, may reasonably be regarded as portions of one 

 and the same building. 



His next step is to point out that stars differ in their 

 spectra; consequently our sun is marked off from all stars 

 not of its own type. Further, even amongst stars of the 

 solar type, there may be points of difference, and Dr. Wallace 

 lays great stress on the discovery of spectroscopic binaries, 

 already numerous, and quotes Prof. Campbell who believes 

 that " the star that is not a spectroscopic binary will prove 

 to be the rare exception." For both these statements 

 Dr. Wallace has full and ample authority. Nay, more, it 

 is highly probable that we need not stop here, but that, as 

 our knowledge increases, we may find that no two stars 

 are exactly alike, that each has some characteristic special 

 to itself, some mark of individuality. But the inference 

 which Dr. Wallace would draw is certainly unwarrantable, 

 that all these differences necessarily imply unsuitability 

 for life-bearing planets. On the contrary, since he accepts 

 Sir Norman Lockyer's view that spectrum type means 

 simply the factors of time and temperature, we are, on this 

 hypothesis, in a position to assert with confidence that 

 solar stars have existed in a stable condition, like our own 

 sun, for a sufficient length of time for intelligent life to 

 have developed somewhere within their attendant system. 

 To reason otherwise is to beg nakedly the very question 

 which it is desired to prove. And in effect this is all that 

 his present argument comes to. Though it is a great im- 

 provement on the original argument, yet when the crucial 

 step has io be taken from the ascertained facts to the 

 wished-for conclusion, it amounts simply to assuming the 

 very tlii'ug that has to be proved. 



Tins is the point where the great argument of the book 

 fails. In other )Kirts it is much more successful. In 

 chapters X., XL, XII., and XIII.. where Dr. Wallace is 

 dealing with the " Essential Characters of a living 

 Organism," with " Essential life Conditions," and with 

 " The Earth in its Relation to Life," he is treating 

 of subjects upon which we have direct experimental 

 knowledge, and mauy of which he has made largely his 

 own. Here it is possible to follow him with much of both 

 admiration and assent. And iu chapter XIV.. in which he 

 claims to prove that "The Earth is the only habitable Planet 

 of the Solar System,'' applying the lessons which he has 

 drawn iu the four preceding chapters, his argument is a 

 strong one. Astronomers who have suffered much of late 

 from having such absurdities fathered on them as the 

 theory that the " canals " on Mars are evidence of the 

 presence there of skilled engineers, and that the white 

 spots occasionally seen on its terminator are the signals 

 by which they are endeavouring to communicate with us, 

 will welcome the clearness with which he has treated this 

 part of his subject. I am personally exceedingly glad to 

 see that Dr. Wallace argues that we have no re;U reason 



