WHAT IS GRAVITY?

Oamaru Mail, Volume XXXIX, Issue 12258, 8 June 1914, Page 8

WHAT IS GRAVITY?

That doubt still shrouds the most common mid universal fact of the material world—the attraction of matter by matter —is doubtless to "be reckoned tin: chief reproach of science. In an article in Harper's Magazine (New York) Sir Oliver Lodge sums up some of the chief attenvpts to account for gravitation. Curiously, nearly all of these depend on the assumption of some property, not in the matter which manifests the phenomenon, but in the space around it. The older philosophers were content to say that matter gravitates because it attracts and is ■attracted by'all other matter —which reminds one of the explanation of Moliere's physician—"opium puts one to sleep, because it has a sleepifying property.;'" But the corpuscles, vibrations, and tensions with which the modern explainers fill space «re not much more satisfactory. Says Sir Oliver:— "Attempts'to explain or discover the cause of gravitation have been numerous, ,Ynd, while most of them are worthless, a few are ingenious- and some important. "The best known is that of Le Sage, of Geneva, published in 1818, wherein gravity is supposed to he explained by a' bombardment of extravagantly minute corpuscles rushing through space and battering masses to-gether.

"It may seem strange that such a hypothesis can possibly account for the •apparent attraction of bodies; but it does, Tip to ia. certain point. It gives the law of inverse square and corresponds with' other facts, but the difficulty is to show that- the force would be proportioned to the mass of the body and independent of its state of aggregation. Indeed, on this theory it would seem plausible that a flat body exposed edgeways.to the stream".'.should, be differentiy affected from one exposing its full face; ,so that a plate on.its edge might be expected.to'. weight.less than when-it'lies" flat—a. thing .never yet observed,. iior'- -likely:, to b£'observed, however precisely the weighing'' is done. ■•"'■•

"It is just .tlie :; waj' in which" screening: has to bo worked out which'constitutes the weak, point of this theory.. Bodies must screen orie Another to some extent in order to be beaten together by the bombardment of their exposed sides; but on the other hand, bodies must screen one another very little', else other bodies in their neighborhood or between them would not be.acted on, for they would be* in a- gravity shadow. . ". . . This is' a fundamental difficulty, only s partially surmounted by the admitted extreme, porosity of matter to small enough .corpuscles ; and: it seems fatal' to eyery modification of Le Sage's theory." To show how seriously the difficulty of explaining gravity has been felt by natural philosophers, and to what strange lengths they have been prepared to go in order to get a clue, Sir Oliver instances Lord Kelvin's theory, wherein he showed that if material bodies were immersed in ah ocean of incompressible fluid, which fluid they kept on generating and. emitting at a. steady rate dependent on their mass, the surplus constantly flowing off .to infinity; or, conversely, if they always absorbing and annihilating a. similar fluid which was continually being supplied from infinity for their consumption—theny in either case they would be attracted precisely as the law of gravity requires; whereas if one body generated and another absorbed the fluid, they would repel one another. This is an interesting mathematical curiosity, but Sir Oliver does not consider that creation and annihilation of fluid is a legitimate physical conception. He goes on:— "Another attempt which has attracted a good deal o'f attention, and which is, on the face of it," more plausible; seeks to explain gravitation by waves in a medium. Robert Hooke, living in the Newtonian period, initiated this idea, because he found that bodies floating on the surface of water were gradually drawn toward a wavecentre of disturbance. Many experimenters have noticed that a tuningfork in vibration can attract pieces of paper. Lord Kelvin has investigated this also and has shown generally that wherever the motion of'a fluid is greatest there the pressure is least. . . . In illustration of this action it will be found that blowing vigorously with the mouth quite close to a flat piece of paper tends to lift or attract the paper or make it adhere to the mouth. Blow, ihg through a tube ending in a flat disc, ■ something like a stethoscope, shows' the effect much better. Any one who protrudes the lips and tries to blow away a piece of paper held lightly against them will fail, until the distance is allowed to become great ejiough for the impetus of the wind to overcome the diminished pressure. There is a vibratory theory of gravitation extant, therefore; mnd it is sometimes illustrated experimentally by small hollow chambers, like elastic capsules, immersed in water and kept rapidly alternating pump. "But to me it appears that vibration is not a. sufficiently fundamental and unalterable property of matter to constitute a likely explanation of so extraordinarily fixed and permanent an effect as gravitation;. that must surely depend on something constitutional and deeply imbedded in the very existence of the ultimate unit of matter. "So we are driven back to the idea of a tension in the ether, set up at the moment when an electron came into existence! But how an electron can be' bxought into existence, or what an electron is, we do not know, though we may not always remain ignorant, Newton himself, however, perceived that such a, tension—if it could be deduced as an inseparable consequence of matter, or if its existence could be otherwise demonstrated —would do what was wanted.

'The problem is .just as biting now . . ."■ and perhaps its difficulty J is intensified rather than alleviated by | the enormously stronger electric attractions and repulsions which are nonknown to occur between electrons and between electrically charged atoms—the latter being the forces of chemical affinity. For between the smallest material units the electric attraction is, so to speak, infinitely stronger than any gravitation attraction; we. are not really sure that electrons gravitate at all, 'Their gravitation, if jt exists—as I think it probably dpes—must be the merest residues, some irreducible minimum which characterises all without regard to sign. ''lt is singular that there is no known gravitational repulsion, that it is all attraction: that there is not a principle of ' levity ' as well as a principle of 'gravity'! Some have surmised that in the course of ages all the matter which repelled our kind has absented itself and'gone- into tlia uttermost parts of infinity. But surely some might i have been mechanically entangled or entrapped for our edification. Most likely, however, no such general repulsion exists. Electrical repulsion exists, of course—an electrostatic force depending on the first power of electrostatin charge, and therefore depending on the sign of that charge—but in addition to this large etfect there may be a. minute residue or 'surplus depending on some even power of the charge, a residue excessively, hopelessly minute.

ne ciin recKon mat tue gravita tionnl force between two electrons, a any distance apart, is to their electrica attraction or repulsion at tlie same dis tance in the ratio of 1 to 1,000,000. 01,10,000.000. the numbers of cipliers .ir the denominator of this, fraction beinc fifteen. Yet if such mi almost in" finitesimal but unalterable uniform constant residue of stress .should ever be shown to be produced in the ether by the very existence of the singularity, in it which we call an electron—or whatever the unit of matter may turn out to be —then the whole business of astronomy can be worked, and the gigantic forces between sun and planets will be accounted for. For electrical foroes. howeveii relatively erlormous, cancel out in the aggregate because they are of opposite sign; but the ridiculously small gravitational residue goes on piling itself up—nothing interfering with it or diminishing any part oflit—until the mutual force of planetary gravitational attraction becomes millions of millions of tons."