RIDDLE OF THE UNIVERSE.

New Zealand Times, Volume XXVII, Issue 5737, 4 November 1905, Page 10

RIDDLE OF THE UNIVERSE.

HOW THE SUN, MOON AND STABS WEBB FORMED.

Professor G. H. Darwin delivered the second part of his presidential address, to the British Association at Johannesburg last month. He began by dealing with the evolution of the community in the State or Commonwealth, and passed on to evolution throughout the external universe. He explained, the theory, which he believed contained essential elements of truth, which points to the origin of the sun and planets from gradual accretions of meteoric stones, and referred in detail to the celebrated nebular hypothesis of Kant and Laplace, who traced the origin of the solar system to a nebula or cloud of ratified gas congregated round a central condensation which was ultimately to form the sun. Under the influence of rotation the nebula, which had come-to assume the form of a lens, became so flattened that a ring of matter detached itself, and each ring formed a subordinate nebula. But, said Professor Darwin, though the telescope seems to confirm the general correctness of Laplace’s hypothesis, it is hardly too much to say that every stage presents to us some impossibility. He then went on to sketch the evolution of a rotating liquid planet like the, earth, and, dealt with the influence of tidal oscillations. Let ns consider, he said, the motion of the earth and moon revolving in company round the sun, on the supposition that tha friction of the tides in the earth is the only effective cause of change. We are, in fact, to discuss a working model of the system analogous to tiiose of which I have so often spoken before; and it must suffice to set forth the result in it© main outline a© referring only to the past. If we take the "day,” regarding it as a period of vanod length, to mean the time occupied by a single rotation of the earth on its axis; and tho “month/* likewise variable in absolute length, to mean the time occupied by the moon in a single revolution round the earth, the number of day sin the month expresses the speed of the earth’s rotation relatively to the speed of the moon’s revolution. Now m our retrospect both day and month are found continuously shortening: but as on the whole the month shortens much more quickly than the day, the number of days in the month also falls. We may, then, ask at once—What ia the initial stage to which the gradual transformation points ? I say that, on following the argument to its end, the system may be traced back to a time when the day and the month were identical in length, and were both only about four or five of our present hours. The identity of day and month moans that the moon was always opposite to the same side of the earth; thus at the beginning the earth always presented the same face to the moon, just as the moon now always shows the* same face to us. Moreover, when the month was only some four or five of our present hours in length. t)»e moon must have been only a few thousand miles from the earth’s surface—a great contrast with the present distance of 210,000 miles. It might well be argued from this conclusion alone that the moon separated from the earth more or less as a single portion of matter at a time immediately antecedent to the initial stage to which she has been traced, But there exists a yet more weighty argument favourable to this view, for it appears that the initial stage ia one in which the stability of the species of motion is tottering, so that the system presents the characteristic of a transitional form, which we have seen to denote a change of type or species in a previous case. In discussing the transformations of a liquid planet we saw the tendency of the single mass to divide into two portions, and now wo seem to reach a similar crisis from the opposite end, when in retrospect we trace back the, system to two masses of unequal sizes in close proximity with one another. The argument almost carries conviction with it, but I have necessarily been compelled to pass over various doubtful points.

Our ideas are blank as to the time requisite for the evolution either according to Laplace’s nebular hypothesis or the meteoritic theory. All we can assert is that they demand enormous intervals of time as estimated in years. If at every moment since the birth of the moon tidal friction had always been at work in such a way as to produce the greatest pose hie effect, then we should find that 60.000,000 years would be consumed in this portion of evolutionary history. The true period must be much greater, and it does hot seem unreasonable to suppose that 500 +o 1000 million years may have elapsed since the birth of the moon. Such an estimate v.oiua not eeem extravagant .o geologists w,,0 Lave, in various w'ays, mad 3 exceed ngly rough determinations of geological per•ods 4.6 far as my knowledge goes I should say that pure geology points to some period intermediate between 50 and 1000 millions of years, the upper limit being more doubtful than the lower. Thus far wo do not find anything which

renders the tidal theory of evolution nn, tenable. Since the mass of the sun is known, th* total amount of the heat generated in it; in whatever mode it was formed, can be estimated with a considerable amount of precision. The heat received at the earth from the eun can also be measured with some accuracy, and hence it is, & mere matter of calculation to determine how much heat the sun sends out in a year. The total heat which can have been generated in the sun divided by tbe annual output gives a quotient of about 20,000,000. Hence it seemed to be imperatively necessary that the whole history of the solar system should be comprised wiUiin some, 20,000,000 year*. This argument, which is duo to Holm* holtz, appeared to be absolutely crush, ing, and for the last forty years tbe physicits have been accustomed to tell the geologists that they must moderate their claims. But for myself I have always believed that the geologists were more nearly, correct than the notwithstanding the. fact that, appearaJU ces were so strongly against them. Eadinm is perhaps millions of timet) more powerful than dynamite. Thus it ia estimated that an ounce of radium would contain enough power to raise 10,000 tons a mile above the earth’s sms face. Another way of stating the same estimate is:—The energy needed to tow a ship of 12,000 tons a distance of 6000 sea miles at fifteen knots is contained jn 220 zof radium. The Saxon probably burna 5000 or 6000 tons of coal on a voyage of approximately the same length. Other lines of argument tend in thesams direction. Now we know that tho earth contains radio-active materials, and it is safe to assume that it forms in some do. gr©B a ©ample of the materials of tha solar system; henoo it ia almost certain that the sun is radio-active also. This branch of science is os yet but in its infancy, but we already see how unsafe it is to dogmatise on the potentialities of matter. It appears, then, that tha physical argument is not, susceptible of a greater degree of certainty than that of geologists, and the scale of geological time remains in great measure unknown, I have now ended my discussion of tha solar system, and must pass on to tha wider fields of the stellar universe. A celestial photograph looks at firsfi like a dark sheet of paper splashed with white-wash, bnt further examination shows that there is method in the arrangement of the white spots. - Thua there is order of some sort in tho heavens, and, although no reason can be assigned for the observed arrangement in any par. ticular case, yet it is possible to obtain general ideas aa to the succession of ov» enta in stellar evolution. Besides the stars there are numerous streaks, wisps and agglomerations of nebulosity, whose light we know to emanate from gaa. Spots of intenser light are observed in leas brilliant regions; clusters of star* are sometimes embedded in nebulosity, while in other oases each individual star of a cluster stands out clear by itself. These and other observations force on uft the conviction that the wispy clouds represent the earliest stage of develop, ment, the more condensed nebulae a latel stage, and the stars themselves the lost stage. This view is in agreement with thei nebular hypothesis of Laplace, and we may fairly conjecture that chains and lines of stars represent pre-existing streaks of nebulosity. Wo have seen that it ia possible tw trace the solar system back to a primitive nebula with some degree of confidence, and that there is reason to believe that the stars in general have originated in the same manner. But such primitive nebulae stand in as much need of explanation as their stellar offspring. Thus, even if we grant the exact truth of thee* theories the advance towards an explanation of" the universe remains miserably slight. Man is bnt a microscopic being relatively to astronomical space, and h* lives on a puny planet circling round «. star of inferior rank. Does it not, then, seem as futile to imagine that he can discover the origin and tendency of the universe aa to expect a housefly to instruct us as to the theory of the motions of the planets? And yet, as long aa he shall last, he will pursue his search, and will no doubt discover many wonderful things which are still hidden. We may indeed be amazed at all that man ha» been able to find out, hut the immeasurable magnitude of the undiscovered will throughout all time remain to hum bln his pride. Our children’s children will atil! be gazing and marvelling at tha starry heavens, but the riddle will never he read.