256 



KNOW^LEDGE ♦ 



[September 1, 1887. 



sun-work, at the sun's present rate of emission of heat. The 

 late Sir e'harles Lyell, wlio carefully examined CroU's in- 

 vestigations, was satisfied that this estimate probably fell 

 short of the truth rather than exceeded it. 



But if there is one result which comes out clearly from 

 modern physical inquiries, it is that the sun's emission of 

 light and heat are due almost wholly to his gravitating 

 power, to the miglit by which he has been drawn and is 

 drawing in towards his centre the material now forming his 

 globe. Some little extra energy may arise from the drawing 

 in of matter external to his globe ; but it can be but very 

 little compared with that due to the mass already within 

 the solar globe as we see it, and the contraction which this 

 mass has still to undergo. Now, the force of contraction, 

 if it is supposed to have acted to draw in matter originally 

 at exceedingly great distances, until the whole mass has 

 been brought within the compass of the sun's present globe, 

 throughout which it is uniformly or nearly uniformly 

 strewn, could not have corresponded to more than about 

 20,000,000 years' emission of heat and light at the sun's 

 present rate of working. This would only correspond to 

 about one-fifth part of the amount of work which— judging 

 from the earth's crust— the sun has actually done. 



How are we to explain the apparent discrepancy between 

 the evidence given by the earth and that given by the sun 1 

 Very easily, according to Dr. C'roll, though for my own part 

 I find his explanation very difficult to accept. He thinks 

 that a part, and a very large part, of the sun's heat may have 

 been derived from the motion of masses originally non- 

 luminous, rushing with enormous velocities through space. 

 He says, quite truly, that if we are asked whence they 

 derived those velocities, we are in reality no more called 

 upon to reply than we should be if we were asked whence 

 they derived their substance. But he seems to me to over- 

 look the enormous improbability of collisions occurring 

 between masses thus travelUng about through inter-stellar 

 space. To conceive that the stars we see, either with the 

 unaided eye or the telescope, were originally formed by 

 the conflict of bodies originally rushing darkling through 

 space, is to conceive something as unlikely as that the bullets 

 fired by two widely-scattered bodies of opposing skirmishers 

 .should" be constantly encountering in mid-air — or rather, 

 it is to suppose what would be far more unlikely. 



Moreover, whatever heat might be generated by such 

 collisions, were they possible in the requii-ed number, would 

 be dissipated quickly, and long before any attendant orb 

 like the earth could possibly have begun to be the abode of 

 life. 



It seems to me, then, that we are driven to a very 

 different explanation— this, namely, that the process of 

 contraction has gone on much farther than it seems to have 

 done, and that consequently much more of the sun's work 

 has already been accomplished than had been supposed. 

 According to this view, the sun's real globe is very much 

 smaller than the globe we see. 



The knowledge thus obtained about the sun's interior has 

 been derived from the crust of the earth. 



But .so soon as we have thus been led to recognise the 

 remoteness of what we call the sun's surface (that is, the 

 solar surface we see) from the real sui-foce, other evidence 

 towards the same view begins to prasent itself. Thus the 

 marvellous motion of the solar spots, by which it has been 

 shown that the equatorial zone of the sun gains one entire 

 revolution in eight on the zone of spots farthest removed 

 from the equator, would be impossible were the surface we 

 see anywhere near the real suiface. We are absolutely com- 

 pelled by this amazing freedom of motion in the solar photo- 

 sphere to admit that in aU probability the real globe of the 

 sun is very much smaller than the globe we seem to see. 



limited by the surface which happens to have that degree of 

 brightness which prevents us alike from seeing below except 

 where spots exist, or from seeing outer layers, except during 

 the time of solar eclipse. 



There is another proof of the condition of the sun's 

 interior, which is more recondite and difficult. Professor 

 G. H. Darwin (a son of the late Charles Darwin) has shown, 

 by mathematical computations of the most convincing kind, 

 that if the sun's visible globe were of anything like uniform 

 density throughout there would be recognisable compression 

 at the solar poles. Now, all the most careful observations 

 of the sun agree in showing that if such compression exists 

 at all, it is so slight as not to be discernible with the best 

 telescopes yet made. It follows that the sun's globe must 

 be greatly condensed towards the centre. 



It is interesting to note that if the view to which we 

 have been led is correct — and it is difficult to see how it can 

 be otherwise — the sun has passed through a greater portion 

 of his career as a light emitting, heat-radiating, and conse- 

 quently life-supporting orb, than has been supposed. In 

 point of fact, the difference is so great as proliably to reduce 

 by more than three-fourths the estimate science makes of 

 the length of time during which the sun will continue to 

 supply adequately the heat and life necessary for our earth 

 and the other worlds circling around him. Albeit, there is 

 no reason to suppose that for many millions of years yet to 

 come the supply will run short. Moreover, man is ex- 

 hausting the life supplies of the earth herself at such a rate 

 that what we now regard as civilised life upon the earth 

 must die out millions of years before the solar emission of 

 light and heat will probably be appreciably reduced. 



This point, the wild waste of the earth's life stores, which, 

 millions of years in accumulating, will be exhausted in a 

 few thousand j'ears at the outside, if the present ever- 

 growing rate of consumption continue, will be considered 

 next month. 



«@ £( t p. 



Most men, in looking back over their lives, recognise 

 events which have seemed exceptionally lucky and others 

 which have appeared the reverse. The whole bearing of 

 my little treatise, " Chance and Luck," shows that I am no 

 believer in luck which may be counted on ; or, therefore, in 

 luck worth considering at all. But there have been times 

 when I have been speciallv fortunate. For example, that 

 just when I had been scolded for holding persistently the 

 solar theory of the corona, photography should come in and 

 confirm all I had maintained, was singularly fortunate : for 

 everyone understood t/iat argument. So, when I had main- 

 tained the theory that nebulre are parts of our galaxy, I 

 could not hope that a new star would be seen to die out 

 into a gaseous nebula (in Cygnus), that another new star 

 would appear in the famous star-cloud in Andromeda, and 

 that a new nebula would be detected by photography in the 

 midst of the Pleiades, and clinging so manifestly to one of 

 the stars there as to leave no doubt that the nebula really 

 lies in the midst of the cluster. Yet, again, I was very 

 lucky in that just when the Astronomer-Eoyal, admitting 

 the exactness of all my calculations in regard to the recent 

 transits of Venus, explained lustOy that the stations I sug- 

 gested could not be occupied, and, therefore, would not, 

 American and other astronomers proclaimed that those 

 stations could be occupied, and should be, and proved their 

 case and mine by occupying them forthwith, and making 

 excellent observations. 



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