ASTRONOMY.

Taranaki Daily News, Volume XLVII, Issue 8068, 26 March 1906, Page 4

ASTRONOMY.

Profcsor li. 11. Darn in delivered ill Grand part of his presidential o the l.'ritish Association at .Johannes itirg last month. Ue began by dealin, ,ith the evolution uf the community ii ho Stato or Commonwealth, and pasaei n to evolution throughout the externa Diverse. Ho explained the theory hich ho believed contained essentia laments of truth, which points to th rigin of the sun and planets from gra Hill accretions of meteoric stones, am eferred in detail to the celebrated nobu ar hypothesis of Kant and Laplace rho traced the origin of the solar sys em to a nebula or cloud or rarified ga ongregated round a central coudousa ion which was ultimately to form th ;un. Vnder the influence of rotntioi he nebula, which had come to a,ssurn :he form of a lens, became so flattens ;<hat a ring of matter detached itsell ind each ring formed a subordinat aebula. But, said Professor Darwin ['hough the telescope seems to confiri ;ha general correctness of Laplace's hj pothesis, it is hardly too much to sa, that every stage presents to us soni impossibility. He then went on to sketc .he evolution of a rotating liquid plane like the earth, and dealt with toe ir fluenoe of tidal oscillations. Let us consid'3i\ he said, the motio. of the earth and moon revolving i company round the 6tm, on the sup position that the friction of the tie'e iu the earth is the only effective ea-ia of change. We are, in fact, to discus a -working model of the system analo gous to those of which I have so oft*] spoken before; and it must suffice i set forth the result in its main outliii as referring only to the past. If w take the "day," regarding it as a perio of varied length, to mean the tiin occupied by a single rotation of th earth on its axis; and the "month, likewise variable in absolute longth, t mean the time occupied by the moo: in a single revolution round the earth the number of days in .the mouth ex presses tho speed of the earth's rotatioi relatively to the n)ie«l of the moon' revolution. Now iu our retrospect hot day and month are found coulinuousl; shortening; but as on the whole th mouth shortens much more quickly thai the day. the number of days in th month also falls. We may, then, ask .1 once —What, is the initial stage towhic the gradual transformation points'' say that, on following tho argument t its cud, the system may be traced bac to a time when the day and the mont wore identical in length, and were hot. only about four or iivo of our presen hours. Tho identity of day and monl moans that tho moon was always oppc site to the samo side of the earth; thu at the beginning tho earth always pre seitted tho samo face to tho iucoh, jus as tho moon flow always shows the sam face to us. jloieovor, when the mont was oidy some four or Aye of our pre sent hours in length, tlie moon mus have been only a few thousand mile from tho earth's surface—a great con trast with the present distance 0 210,000 miles. It might well be argue* front this conclusion alone that th moon is separated from tho earth mor or less as 3, single portion of matter a a time immediately antecedent to th initial stage to whieh s]ie has been trac ed. But there exists a yet more weight; argument favourable to this view, fo it appears that the initial stage is on. in whlG-h the stability of tho species 0 motion is tottering, so that the systen presents the characteristic of a trail sitional form, which wfi have seen li denote a change of type OJ' species in : previous case. Iu discussing tho trans formations of a liquid planet we saw th tendency of the single mass to divid. into two portions, and now we 6eem t< reach a similar crisis from the opposit. end, when in retrospect we trace bad the system to two masses of unequa sizes in close proximity wi'h one an other. - Tho argument almost carrie conviction with it. uUt I have necessar ily been compelled to pass over varioii doubtful points. Our ideas are blank as to the tint requisite for tho evolution either ac cording to Laplace's nebular hypothesi for the_ moteontic theory. All we e.f assert is that they domain! pnormou intervals of time as estimated in years If at every moment since the birth 0 the moon tidal friction had always beei at work in such a way as to produce tin greatest possible effect, then we sliouk find that 60.0Q0.000 years would he con sumed in this portion of evolutionary history. Tlie true period must bo niucJ greater, and it does not seem unreasonable to suppose that 500 to 1000 million years may have elapsed since the birth of the moon. Such an estimate would not seem extravagant to geologists who have, in various ways, made exceedingly rough determinations of geological periods. As far as my knowledge goes I slioull say that pure geology points to some period intermediate between SO and 1000 millions of years, the upper limit being more doubtful' than the lower. Thus far we do not find anything which Tenders tho tidal theory of evolution untenable. Since the mass of the sun is known, tho total amount of the lioat generated in it, in whatever modo it was formed, can be estimated with a considerable amount of precision. The heat received at the earth from tho sun can also lio measured with some accuracy, and hence it is a mere matter of calculation to determine how much heat the sun sonus out in a year. The total heat which Kin have been generated in the sun lividcd by tho annual output gives a jnotient of about 20,000,000. Hence it seemed to lie imperatively necessary ,hat tho wliolo history of tho solar sysx>m should be comprised within somo !0,000.000 yearns. This argument, which s duo to KelmhoUz, appeared to be absolutely crushing, and for the last <lO vsu-s tlie physicists havo been aocuscmed to tell tho geologists that they mist moderate their claims. But for ny.sel? I have always bolieved that the I'ologists were, more nearly correct than he physicists, notwithstanding tlie fact hat appearances were so strongly gainst them.

Kadium is perhaps millions of times' more powerful than dynamite. Tims it 'h cstiinaioil Uian an ounce of radium .vould contain enough power to raise 10 1)00 tons a mile above the oartlis .m-faco. Anot.ln.M- way of slating the ;ame estimate is:—Tlio energy needed to tow a ship of 12,001) ton.-s a distance I of (iODU sea miles at 15 knots is contained in 2i» oz. of vadium. The Saxon probably burns 5000 or 0000 tons of eaal I on a voyage of approximately the same | length. Other lines of argument tend |in The sumo direction. Now we know I i hat the earth contains radio-active materials, and it is safe to assume that it forms 'in some degree a sample of the materials of the solar system; hence, it is almost certain that the sun is radio- ' iotivo also. This branch of science is as yet but in its infancy, but we already see how unsafe it as to dogmatise on ' ho potentialities of matter. It appears, hen, that the physical argument i* not aisceptiblo of a greater degree of cer.aiuty than that of geologists, and the scale of geological t.mo ram"us '" j-reat measure unknown. I have now >uded my discussion of the solar system, ind must pass on to the wider fields of I

the stellar universe. A celestial photograph looks at first ike a dark sh/et of paper splashed with whitewash, hut further examination jhows that there is method in the arrangement of the white spots. Thus there is order of some sort in the hcav-

mis, and, although no reason can be as signed for the observed arrangement in any particular ea.se, yet it is possible to obta'n general ideas as to the succession of events in stellar evolution. Besides the stars there are numerous sbreaks, wisps and agglomerations of nebulosity, whoso light wo know to emanate'from gas. Spots of intense! tight are observed in lc>« brilliant regions; clusters of stars are sometimes .imbedded in nebulosity, while in othoi rasas each individual star of a cluster stands out clear by itself. These and other observations force tin us the conviction that the wispy clouds represent tho earliest, si ago of development, the more condensed nebulae a later stage, and the stars themselves the last stage. Thin view is in agi-eement with the nebular hypot!|eisis of Laplace, and wo may fairly conjecture that chains and lines of stars represent pre-existing streaks of nebulosity.