IS GRAVITATION A PUSH OR A PULL?

Oamaru Mail, Volume XXXIX, Issue 10760, 6 May 1911, Page 3 (Supplement)

IS GRAVITATION A PUSH OR A PULL?

It is a curious fact that the commonest and most universal fact of nature is the hardest to explain—so hard, indeed, that none of the attempts to explain it is really plausible. Gravitation, so far as"we know, is universal —the most distant stars attract each other and so do the grains of dust that lie near each other on the pavement. It is this'very universality that makes gravitation hard to explain; we cannot get away from it or outside it to observe it or experiment upon it. Nothing will screen it off; the earth attracts a stone through a mountainous mass a mile thick, as powerfully as if the mountain wer6 not there. Another curious fact .is that while we usually tliink- of the eaftli as pulling down ' a stone to itself, theories of gravitation have always explained it as a push—when a stone falls, tliey say, something around' it is pushing it, and the earth is really exerting no power at all; it only serves as a screen to stop off the action of the push from the opposite direction. Le Sage, the first philosopher to try to explain gravity rationally considered that the push was given by tiny atoms —"ultramundane corpuscles," he called them —flying about in all directions. The latest theories suppose the push to be given by waves in the ether. The most up-to-date of all these theories, though it is hardly more plausible than the others,' derives support from the recent investigations which show that lightwaves exert a push on objects against which they strike. Its author is Charles F. Brush, of Cleveland, and his "Kinetic Theory of Gravitation" is described by him in Science (New York, March 10th). Says Mr Brush : "Gravitation is often described as a feeble force; and so v it is, from one point of view. It is difficult to measure, or even to detect, attraction be- j tween two small bodies. But when the bodies are of planetary size the aggregate attraction of their molecules is enormous. It is easy to calculate that the attraction between the earth and the moon, which is just sufficient to retain the latter in its orbit, would, if replaced by a steel cable, require that the cable be about 500 miles in diameter in order to withstand the strain. Between the earth and sun, the cable would have to be nearly as large in diameter as the earth; and attraction between the components of some double stars is millions of times greater than between the earth and sun. So tremendous a phenomenon as gravitation, a phenomenon compared with which all others seem trivial, must have a mighty origin. ...-■' "Whence comes the energy acquired by a falling body? Certainly it 'was not inherent in the body before the fall, as evidenced by/the fact that during unimpeded fall ruone of the physical or chemical attributes of the body| aside from the acquired motion, changes in the slightest degree. - . "Let us imagine a pound-weight of iron, for instance, raised from the sur- I face of the earth to a point near the moon, in a line joining the centres of the two bodies, the point so chosen that the opposing attraction. of the earth arid the moon shall exactly balance each other, leaying orbital motion out of consideration. "On the surface of the earth the pound-weight had some so-called 'potential energy of position' because it was capable of falling into a pit; but in | its new position near the moon, this , potential/energy not only has not been augmented, hut has disappeared entirely; the pound-weight, left free to move, reinains stationary. And yet we must have expended, more than 20,000,000 foot-pounds of energy hi overcoming the attraction of the earth and lifting the weight to its new position. . . In lifting the weight, this large amount of energy has disappeared utterly. We cannot believe that the whole or any part of Jit . has. been . annihilated ; it must, iju. some ; form, b& resident some'where.;i?l'- tftiik no -.one will contend that this energy is resident, in any form, in the cold, motionless poundweight. It believe it was absorbed by, and is now resident in, the ether through which the weight was raised. Conversely, if this be true, a falling body must acquire its eiiergy from- the ether through which it falis. . . "This view of-, gravitation implies that the ether is endowed with, very great intrinsic energy, in some-form. . I .believe that .kinetic eiiergy (motion-energy) of, the ether is- the;.fundamental cause oj" gravitation.; and that -a gravitating :body plays ;a secondary role.only, in disturbing the normally -uniform; distribution, .if the ether's energy." . : This eiiergy in the . ether is in the > forml -of nwaves,: -.on Mr Brush's hypot thesis; - .'vast.'in aggregate energy, eternal; in persistence,r withbut-finite source or destination/ propagated in straight lines in every direction." The condition of the - universe .thus resembles that of the interior of "a heated; furnace, where heat' waves are similarly propagated. ; This "vast resource, of energy" is filled by the degradation of all sorts of ordinary waves —light, heat, and so on, just as "wind ripples on the surface of water . . continually degenerate in wave-frequency until they are absorbed into and become a part of the mighty swell of the ocean." Evidently these waves must penetrate solid bodies freely. The things against which they really "push" are the ult'.mato atoms themselves; otherwise a tint disc would neigh more in a horizontal position than it would edgewise. The difficulty of accounting for this ease of penetration rarely bothers gravitation-theorists and it apparently has no terrors for Mr Bruse. He says of it:—

•'The ••thrr waves eonconvxl ill gravitation can not, however,. be like lightwaves . . . . because light-waves

neat bodies on which they fall; and their pressure is almost "wholly superficial, it .iocs not reach molecules much below the surface, and hence bears little relation to. mats. But let us substitute for the short and feeble waves of light, pn-.verful waves, still of the radiant kind, but of such great length ar.fl slow frequency that,,its before explained, they do not excite the molecular vibrations which we appreciate as heat, and hence arc not absorbed by matter; they pass freely through all bodies, bathing the interior molecules as effectually as those on the surface. "Under these conditions each molecule

or atom or-unit of a gravitating'body Mill have its own spherical shadow or field of influence, and the gravitatiye force acting on the body will' vary directly with the sum of its units, i.ev, with its mass." Iu closing, Mr Brush notes that if his ether .wave push-theory of gravitationis true it ought to'; be possible to; test it in some way. He says - "Provided the waves aro of one principal frequency, or even of several, we may find something, doubtless of mol& nniar magnitude only, which will cecillate in unison with them eo that resonance can occasionally he established and a riiiiiulative effect obtained sufficient to vno.irifest itself as heat In. scsicßliig .l'or some natural phenomenon of Tiiis'nature, I thought of the thermal condition .of the upper. atmosphere as a DOasiblc case. . . . I ha\'o done

r.iiich experimental work on theso-lines during the past year, but, nowithstanding refinement of method and manipulation, the results have thus far'been unsatisfactory. The work is still m progress, however," and investigation-of other phenomena is contemplated ''