THE SPEED OF STARS.

Oamaru Mail, Volume XXXIX, Issue 10957, 23 December 1911, Page 3 (Supplement)

THE SPEED OF STARS.

When some wondering admirer asked Newton how he made his great discoveries, the peerless philosopher replied: "Bv intending my mind." Hosts of people can attest -on*., or their own experience the efficacy of this formula as applied '. to everyday affairs. And bevond question maiiy great discoverers' have attained success by thus searching persistently along predetermined lines. Charles Darwin, for example, 'gathered the immense mass of evidence that enabled him to convince the world of the truth of the evolution hypothesis, by accumulating year after year facts insupport of a preconceived hvpothesis. Moreover, this greatest of naturalists made* the explicit and oftquotod assertion that the formulating of hypotheses, to be tested by Tacts, is not only a prime duty of the searcher after knowledge, but the method of all I others mast likely to bring him expeditiously to the goal of truth. ! Charles Darwin's son. Sir George Darwin, who has so fully justified the expectations based on his heritage, but whose work has carried him into quite different fields from those that chiefly claimed his father, publicly voiced the same sentiment in a presidential address before Section A of the British Association for the Advancement of Science.

Sir George's most important scientific work ha? had to do with the mathematical investigation of the motions of the bodies of the solar system. In particular, he made an epochal investigation of tidal action, which led to the formulation of his famous theory that tne moon owes its origin to tidal action on the earth when that body was still in a plastic state: in other words, that the moon was thrown off from the whirl-

ing globe, somewhat as splotches of mud are thrown from the revolving wliscl of a carriage. But I mention this interesting theoryonly in passing. The point I wish to emphasise is that Sir George Darwin, in the address above referred to, argues for the Newtonian method of "intending" the mind in a definite direction: believing that by the selection of particular classes of facts in support of a preconceived theory, the experimenter is more likely to arrive at an important goal than if he merely notes, more or less at random, tho implication of a wide variety of facts. But now comes Professor H. H. Turner, of Oxford, speaking as President at- the recent meeting of the Section of Mathematics and Astronomy of the British Association to challange the validity of this time-honored and hign-ly-accredited method. To speak quite accurately. Professor Turner does not, perhaps, wish to be understood as altogether discrediting the method of discovery by following a single trail, so to speak; but he does take up the cudgels very vigorously in support of the idea that liighly important results may be attained in the field of science through the mere pursuit of facts that in the beginning* may seem to lead hither and yon, with no goal in sight. Perhaps the most interesting of the numerous illustrations brought- forward by Professor Turner in support of his contention has to do with a highly important discovery recently made byProfessor W. W. Campbell, Director of the Lick Observatory. Professor Campbell is an expert in the use of the spectroscope, that exquisitely del-cate apparatus with which the astronomer gains weird insight into the chemical composition and phys-'cal activities of stars and nebula? unthinkably far away. This instrument supplied him with the data on which his new generalisation is based. The data have been ten years in the recording. They consist essentially of almost endless numbers of observations of the line of slight variation of moving stare.

It should, perhaps, lw explained that the spectroscope lcveals the motion of a star through shift in the normal position of the 4 so-called "Fraunhofer lines"

in the spectrum,—those tell-tale transverse bands in the miniature rainbow into which the prism or the diffractiongrating disperses a beam of white light. When the beam of light comes from a stationary object, these "Fraunhofer

lines"—each series of which is dependent upon the presence of a particular chemical—occupy a definite position in the spectrum. But if the luminous object is approaching the obseiver. the lines are shifted from the normal position in one direction : if it is receding they are shifted in the opposite direction. By measuring the amount of sh'ft. the actual speed of progression of the luminous object can be accurately estimated.

The luminous object in question may he a star so distant from the earth that the light coming from it a* the unvarying speed of about 185.000 miles petsecond, has required many years to reach us. That make- 1:0 difference. All distances are alike In the spectroscope. i'riifessur Campbell's investigation,

then, consisted in accurately recording the slight variations of as many stars as possible, it being expressly stated that iu so doing the observer was contenting himself with piling up facts that had no recognised bearing on- any preconceived theory whatever. He was not trying to piovo anything; nor had he the slightest notion as to whither, if anywhere in particular, these researches might lead. But when, after years of painstaking fact-gathering, he finally thought it time to tabulate his observations, he found that the large numbers of stars observed, when tested by thsir speed, tended to fall into intere&-ting and suggestive groups. There were some complications and seeming inconsistencies, as there_ usually are when the human observation of complex facts is in question, but, viewing the data as a whole, this highly interesting and utterly unexpected generalisation seemed to stand forth: "The older a star is, the faster it moves."

It had been known that there is greatvariation in the speed of stars. Our sun. for example, with its planetary attendants, is moving through space at the rate of amount 12 miles a second: whereas there are stars that are observed to move upwards of 200 miles a second. But hitherto there had been nothing to suggest that the difference in speed was in any wise related to the age of the stellar body. Therefore Professor Campbell's observations came as a complete surprise to the astronomical world. In the observer's own words: "That stellar velocities should be functions of spectral types (i.e. should vary with the chemical composition of the. star) Is one of the most surprising results of recent studios in stellar motions, for we naturally think of all matter as equally old gravitational!? - . Why should not the materials comprising a nebula or a Class B (bright "helium") star have been acted on as long and as effectively as the Class M (dull red) star?" The rigidly scientific cast of Professor Campbell's mind prevents him from attempting to givo a decisive and final answer to this question. But, on the other hand, it does not prevent him from suggesting a scientific interpreta- ' tion; only he is careful to avoid all appearance of dogmatism,—wen going to the length of putting his explanations in the form of questions. Let me again quote his words: "The established fact of increasing stellar velocities with increasing ages, suggests the questions: Are stellar materials in -the ante-stellar state subjected to Newton's law of gravitation? Do these materials exist in forms so finely divided that repulsion under radiation pressure more or less closely balances attraction? Does gravity become effective only, after the processes of combination are well under

Thus does Professor Campbell advance his theory.

Notwithstanding the interrogative form iu which this explanation is put forward, we. are perhaps fully justified in assuming that' Professor Campbell's question-marks are only the shield —I had almost said subterfuge—with which an ultra-scientific mind often tends to protect itself against the charge of hasty .generalisation. In point of fact, the explanation outlined in his questions seenis not only valid, but is perhaps the only plausible explanation that could be suggested consistently with our present knowledge.' Yet to any reader who has-not kept closely in touch with recent advances in physical science, the explanation must .seem altogether startling. Ever since Newton propounded his thesis that every particle of matter in the universe attracts every other particle with a force inversely as the mutual distances between the-particles and directly "as the product of their masses, this 'iaw," which seemed to explain all the motions"of the planets and stars no Jess than the fall of bodies

at the earth's surface, has been the very corner-stone of physical science. Vet Professor Campbell suggests that there is a stage of stellar development at which matter seems not to he subject to this law.

But lest the uninitiated suppose that this suggestion is.altogether anarchistic, let me hasten to add that ProfessoK. Campbell does not mean to imply quite what his words seem to suggest. Hi does not for a moment suppose that there was over a time when Newton's law-of gravitation was not operative; he means only that there may be conditions under which its action is overcome by more powerful antagonistic forces.

When you throw a. pebble into the air you momentarily annul the power of gravitation over that stone. But oven, while the pebble is flying straight upward, in seeming defiance of gravity, it is being acted on just as definitely and just as vigorously by the gravitation pull as before;' only the force of propulsion given by your arm-thrust masks and for the moment overbalances that persistent downward pull. And so it is, according to Professor Campbell's suggested hypothesis, with the materials that make up the nebulous mass, which, according to the best modern notions of the astronomer, constitutes the first stage of star-develop-ment. The reader who has not viewed nebula; through a. telescope has doubtless seen photographs of these interesting bodies. It will be recalled, therefore that a nebula seems to be made up of very fine particles of matter. Professor Campbell suggests that these particles are so subject to "radiation pressure" that there tendency to gravitate towards other bodies is for the moment overcome, as in the case of the stone that is thrown in the air.

Now, "radiation pressure," being interpreted, means the pressure of those waves in the universal ether of which sunlight furnishes the most familiar example. Striking evidence of which lias only quite recently been revealed to the physicist—is furnished by the tail of a comet, which, according to the most recent and most generally accepted explanation, consists simply of fine particles of matter driven off "from the body of the comet (itself a more or less nebulous mass) by the '.radiation pressure" of sunlight. The familiar observation that the tail of the comet always points away from the sun gives obvious support to this hypothesis. Professor Campbell's * suggestion, then, amounts to this: That a nebula consists wholly or in part of finely divided particles of matter that are thrust hither and yon in seeming defiance of the laws of gravitation by the light pressure of the myriads of incandescent stars. In due course, however, the fine particles of matter become aggregated —say through "collision—and thus become too large for the light waves to act on them effectively—for be it understood, "radiation pressure" can oppose gravitation effectively only whe'i acting on very minute particles; just as a breath of wind may scatter grains of sand, but cannot dislodge pebbles. So when the nebulous particles have sufficiently aggregated, they begin to fall together, under the- influence of gravitation, presently becoming so concentrated as to form the more or less solid body that we call a star. Thenceforth this body, undergoing a series of internal transformations that cause the astronomer to label it a star of class B, F, K, etc., must move in response to the aggregate gravitation rn;ll of the centre of the universe, and as time goes on it will gather speed in its,fall, just as a body dropped from a height gathers speed in falling toward the earth's surface. The older the star, then, the greater its momentum —which brings us hack to the matter of Professor Campbell's observations. Should the reader's imagination loarl him to ask whether there is any limit to the utimate speed attainable, the answer would seem to be that, sooner or later, the flying star will come into collision with some other flying star; when the two bodies, but the mutual impact, will be reduced once more to the original nebulous state. Their speed will then bo retarded, their action of flight altered, their particles momentarily dissipated: and their cycle of world-development will thus end.in ;l new beginning. This imagined culmination, it should he explained, is not to be directlyinferied from Professor Campbell's observations : but it is a conclusion warranted by other lines of astronomical research, to which the new studies .if star-speeds lends additional support.