Law of gravitation

“ Now the whole structure of science would be hopelessly undermined had not scientific men come to have the fullest confidence in the invariability of certain of these sequences of events. Let us, for example, take the familiar and fundamental observation that any unsupported object, having what we term weight, invariably falls directly towards the centre of the earth. We express this fact in terms of a so-called law of gravitation, and every one, consciously or unconsciously, gives full deference to this law. ”

“ The gravitational theory, which emerges out of the general theory of relativity, is, in contradistinction to the Newtonian theory, built up, not upon an elementary law of the gravitational forces, but upon an elementary law of the motion of a body in the gravitational field. ”

“ It is a known consequence of the Newtonian law of gravitation, that the increase of attraction by diminution of distance is so small that two massive bodies, when they touch [157] each other, attract each other so much the less the smaller they are ”

“ Such is the law of universal gravitation. Now, the question is, why do either the attractions of masses, or those of their component particles, follow this law of the inverse square of the distance rather than any other? When the distance becomes one, two, and three, why should not the force also become one, two, and three?—or if it must be weaker at points more remote from the attracting body, why should it not be one, a half, a third? ”

“ Turning from the heavens to the earth, and ignoring such primitive observations as that of the distinction between land and water, we may note that there was one great scientific law which must have forced itself upon the attention of primitive man. This is the law of universal terrestrial gravitation. The word gravitation suggests the name of Newton, and it may excite surprise to hear a knowledge of gravitation ascribed to men who preceded that philosopher by, say, twenty-five or fifty thousand years. ”

“ I am well convinced that since the law governing the intensity of universal gravitation is similar to that for light, the thought will have occurred to many physicists that an ethereal substance moving in rectilinear paths may be the cause of gravitation, and that they may have applied to it whatever of skill in the mathematics they have possessed. ”

“ "It is never a question of BELIEF; the only scientific attitude one can take on any subject is whether it is TRUE. The law of gravitation worked as efficiently before Newton as after him. The cosmos would be fairly chaotic if its laws could not operate without the sanction of human belief. ”

“ This brought about the strange view that inertial and gravitational phenomena, which are probably not less intimately connected with one another than electric and magnetic phenomena, have nothing to do with one another. The phenomenon of inertia is placed at the base of classical mechanics as the fundamental property of matter, whereas gravitation is only, as it were, introduced by Newton's law as one of the many possible forces of nature. The remarkable fact of the equality of the inertial and gravitational mass of bodies only appears as an accidental coincidence. ”

“ Conceive the synthesis of both, and you have matter as a fluxional antecedent, which, in the very act of formation, passes into body by its gravity, and yet in all bodies it still remains as their mass, which, being exclusively calculable under the law of gravitation, gives rise, as we before observed, to the science of statics, most improperly called celestial mechanics. ”

“ The most serious objection against the Newtonian law as an exact law was that it had become ambiguous. The law refers to the product of the masses of the two bodies; but the mass depends on the velocity—a fact unknown in Newton's day. Are we to take the variable mass, or the mass reduced to rest? ”

“ Now we have a problem. We can deduce often from one part of physics, like the Law of Gravitation, a principle which turns out to be much more valid than the derivation. This does not happen in mathematics; theorems do not come out in places where they are not supposed to be. ”

“ It is thus natural that we should start building up the new theory from this point. The new law of motion must be a differential law, which, in the first place, describes the motion of a point-mass under the influence of both inertia and gravity, and which, secondly, always preserves the same form, irrespective of the system of co-ordinates to which it be referred, so that no system of co-ordinates [Pg 45] enjoys a preference to any other. ”

“ He thinks that this alone will explain why the sidereal system does not collapse toward its common center of gravity. "According to the theory of gravity I have proposed, although the ordinary law may be exact through the solar system and far beyond, there must be distances at which the condition that the excursions of the vibrating particles of the aether are large compared to the dimensions of the atoms ceases to be fulfilled. In that case the attraction changes to repulsion." ”

“ As a fact of daily observation, motion is a variable function, and like heat, color, form, or density, is not conserved.
When a stone is thrown upward therefore, it loses tension, because this Ms been found empirically to be the inflexible law of distance-ratio for the gravitative force, and for no other human reason. It gains in potential energy by the ascent because there has been a corresponding expenditure of kinetic energy in effecting the ascent ”