RIDDLE OF THE UNIVERSE.

New Zealand Mail, Issue 1756, 1 November 1905, Page 2

RIDDLE OF THE UNIVERSE.

HOW THE SUN, MOON AND STALLS WERE! 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 rarified gasl congregated round a central condensation which was ultimately to form the sun. Under the influence of rotation the nebula, which had come to assur © the form of a lens, became so flattened that a ring of matter detached itse’ and each ring formed a subordinate! tv-bma. But, said P'rofessor Darwin, thou i n 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 ©ome 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 us consider, he said, the motion of the earth and moon revolving in company round the sun, on the supposition that the 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 those of which I have so often spoken before; and it must suffice to set forth the result in it© main outline as referring only to the past. If we take the “day,” regarding it as a period of varied length, to mean the time occupied by a single rotation of the earth on its axis; and the '“month,” likewise variable in absolute length, to mean the time occupied by the moon in a single revolution round the earth, the number of days in the month expresses the speed of the earth’© rotation relatively to the speed of the moon’s revolution. Now in 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 ©ay 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 means 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 hour© in lengthy the moon must have been only a few thousand mile© from the earth’s 'surface—a'great contrast with the present distance of 24.0,000 miles. It might well be argued from this conclusion alone that the moon separated from the earth more or less a© 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 appear© that th© initial stage is 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 we seem to reach a. similar crisis from the opposite end, when'" in retrospect we trace back the system to two masse© 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 possible 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 not seem unreasonable to suppose that 500 to 1000 million years may have elapsed since the birth of th© moon. Such an estimate would not seem extravagant to geologists who have, in various ways, made exceedingly rough determination© of geological periods. As 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 we do not find anything which renders the tidal theory of evolution untenable.

Since the mass) of the sun is known, the 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 sun can also be measured with some accuracy, and hence it is a 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 the 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 within some 20,000,000 years. This argument, which is due to Helmholtz, appeared to be absolutely crushing, and for the last forty years the 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 physicists,

notwithstanding the fact that appearances were so strongly against’them.

Radium is perhaps million© of times more powerful than dynamite. Thu© it is estimated that an ounce of radium, would contain enough power to raise 10,000 tons a mile above the earth’s surface. Another way of stating the same estimate i©:—The energy needed to tow a ship of 12JKK) tons a distance of 6000 ©ea miles at fifteen knots i© contained in 220 zof radium. The Saxon probably burn© 5000 or 6000 tons of coal on a voyage of approximately the same length. Other lines of argument tend in the same direction. Now we know that the earth contains radio-active materials, and it is safe to assume that it forms in some degree a ©ample of the materials of the solar system; hence it is almost certain that the sun__is radio-active also. This branch of science is as yet but in its infancy, but we already see how unsafe it is to dogmatise on the potentialities of matter. It appears, then, that the physical argument i© not susceptible of a greater degree of certainty than that of geologists, and the scale of geological time remaips in great measure unknown. I have now ended my disexissdon of the solar system, and must pass on to the wider fields of the stellar universe. A celestial photograph looks at first like a dark sheet of paper splashed with white-wash, but further examination shows that there is method in the arrangement of the white spots. Thus there is order of some sort in the heavens, and, although no reason can be assigned for the observed arrangement in any particular case, yet it is possible to obtain general ideas as to the succession of events in stellar evolution. Besides the star© there are numerous v streaks, wisps ■and agglomerations of nebulosity, whose light we know to emanate from gas. ’Spots of intenser light are observed in less brilliant regions; clusters of stars are sometimes embedded in nebulosity, while in other cases each individual star of a cluster stands out clear by itself. These and other observations force on us the conviction that the wispy clouds represent the earliest stage of development, the more condensed nebulae a later stage, and the stars themselves the last stage. This view is in agreement with the nebular hypothesis of Laplace, and we may fairly conjecture that chains and lines of stars represent pre-existing streaks of nebulosity.

We have seen that it is possible to 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 ©ame manner. But such primitive nebulae stand in a© much need of explanation as their stellar offspring. Thus, even" if we grant the exact truth of these theories, the advance towards an explanation of the universe remains miserably slight. Man is but a microscopic being relatively to astronomical space, and he lives on a- puny planet circling round a star of inferior rank. Does it not, then, seem as futile to imagine that he can discover the origin and tendency of the universe as to expect a housefly to instruct us as to the theory of the motions of the planets? And yet, a© long as 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, but the immeasurable magnitude of the undiscovered will throughout all time remain to humble his pride. Our children’s children will still be gazing and marvelling at the ©tarry heavens, but the riddle will never be read.