Aether and Gravitation

by William George Hooper

Let S represent the sun, and A and B the orbit of the earth round the sun; C E D part of Jupiter's orbit round the sun; while D E F represents the orbit of Jupiter's satellite. When the earth, Jupiter, and the satellite are in a straight line with each other, the satellite suffers an eclipse through passing into the shadow thrown by Jupiter. Now Roemer found that there was a difference in the time of the eclipse when the earth was at B, that is, when it was nearest to Jupiter, and when it was at A, which is that part of the earth's orbit furthest away from Jupiter. That difference was accounted for by the fact, that when the earth was at A the light had to travel further from Jupiter than when the earth was nearest to Jupiter, that is at point B. Thus, when the earth was nearest to Jupiter, the light had a shorter journey to travel than when it was furthest from Jupiter. The difference, he found, was about 16 minutes, and he reasoned that this difference was caused by the light having to cross the earth's orbit from B to A, in its longer journey, than when it only had to reach the earth at B. The mean distance of the earth from the sun, that is, the radius of the earth's orbit, is about 92-1/2 million miles, so that the diameter of the earth's orbit is about 185,000,000 miles, and if it takes about 16 minutes for light to traverse this distance, we find that light has a velocity, according to Roemer, of 192,500 miles per second. The result, however, arrived at by Roemer was not generally accepted at that time, and it was not till 1728 that Bradley discovered what is known as the Aberration of Light, and from that discovery proved that light was not transmitted instantaneously through space, but that it was transmitted with finite velocity; and that that velocity corresponded fairly well with the velocity given by Roemer. Bradley, in his astronomical observations, noticed that some of the fixed stars, so called, did not appear to be really fixed, but that they described small circles in the heavens each year. This fact greatly perplexed him, until at last he hit upon the true solution by taking into account the motion of the earth in its orbit, together with the fact that light had a finite velocity. This result showed that the light from the stars travelled with the same velocity as that which travelled from Jupiter's satellites. The Aberration of Light, as his discovery was termed, may be illustrated in the following way--Suppose that you are standing still, and that it is raining, the rain descending vertically on the umbrella that you hold up to cover you. As soon as you begin to walk, the rain-drops will apparently begin to slant, and if the walk is changed into a run, the greater apparently will be the slanting direction that the rain-drops take. In the same way, the rays of light from a star would fall vertically upon the earth if it were motionless, but as the earth is moving through space with varying velocity, it gives to the rays of light a slanting direction. By calculating the speed of the earth, and ascertaining the exact slanting direction of the rays, the velocity of light may be ascertained. This Bradley did, and showed that it coincided almost with the result arrived at by Roemer. Various other means have been adapted to test the results arrived at by these two astronomers. Fizeau, in 1849, was able to measure the velocity of light by using, not planetary or stellar distances, but by simply using distances in the city of Paris; while Foucault, in 1860, devised a method of measuring the velocity of light in air or any other medium. The results arrived at by these men leave no doubt as to the exact speed of light, which may now be reckoned to have a velocity of 186,000 miles, or 300,000,000 metres per second. Notwithstanding this great speed at which light travels, the nearest stars are so far off that their light takes about 3-1/2 years to reach the earth, while scientists tell us that some of the most distant stars are so remote, that their light takes thousands of years to reach our earth, travelling at the rate of 186,000 miles per second. From considerations like these we get a dim conception of the almost illimitable extent of the universe. Now let us try to understand what this rate of motion really means. We have to remember that light is caused by wave motions in the Aether, so that we have here a wave motion which is travelling through the Aether at the enormous rate already quoted. Light takes about 8-1/2 minutes to travel from the sun to the earth, a distance of 92,000,000 miles. Our fastest trains do not travel 80 miles an hour, and if a train left the sun and continued its journey through space at that rate, it would take over 130 years before it reached our earth, while the light would perform the journey in 8-1/2 minutes. We have some idea of the velocity of a train travelling at 80 miles an hour; what, however, must be the velocity of a wave motion which travels 22,500 times as fast? In [Art. 56] we have seen that all energy is the energy of motion, and therefore wherever we get motion of any kind or sort, there we must have energy accompanying it, or the power to do work. We have here, then, a source of energy in the aetherial waves known as light waves, with their enormous velocity which is almost inconceivable and illimitable. What must be the energy which exists in space due to the wave motion of the Aether? We have to remember on this point that we are no longer dealing with a frictionless medium, but that we are dealing with matter, only in a far more rarefied and far more elastic form than ordinary matter, but nevertheless matter just as air is considered matter, and, being matter, its very motion imparts to the light waves a power and a force which make them capable of doing work. The kind of work done will be considered later on, when we deal with the dynamical value of light. That we do not feel the power and energy of the light waves is due to the well-known fact that their power is broken by the activity of the atmospheric particles, each of which, in their myriads, is ever moving with great velocity, and therefore bombard the light waves, as they endeavour to strike the earth. Thus the aetherial light waves are broken up and shattered, and fall to the earth not with their full energy or power, but in a blended form, or with that reflected energy which we call light. If they were to come unbroken and unchecked upon us, and on the earth, in the same way that they apparently do upon our satellite the moon, we doubtless should experience very different effects of their energy and power due to their enormous velocity.

Art. 77. Dynamical Value of Light.--We have already learned ([Art. 68]) that heat possesses a dynamical value, such value being measured by Joule, and its equivalent in foot-pounds being exactly ascertained. We have further seen ([Art. 69], on the identity of light and heat), that the same aetherial waves which produce heat are also concerned in the production of light. If, therefore, the aetherial waves which give rise to heat possess a dynamical action and equivalent, it follows that light must also possess a dynamical action and equivalent, and such action should be capable of being expressed in terms of foot-pounds. Clerk Maxwell has recorded the exact dynamical equivalent of light. On this matter he writes:[14] “If in strong sunlight the energy of light which falls upon a square foot is 83.4 foot-pounds per second, the mean energy of one cubic foot of sunlight is about .0,000,000,882 of a foot-pound, and the mean pressure on a square foot is .0,000,000,882 of a pound weight.” We have here then the exact dynamical equivalent, according to Maxwell, of a cubic foot of sunlight near the earth's surface, and of the pressure exerted by light on a body with which it comes into contact.

Again, Lord Kelvin[15] has measured the exact dynamical equivalent of a cubic mile of sunlight, both near the surface of the sun and then near the surface of the earth, and in a note adds that the relation of the two values is as 46,000 to 1. So that if the dynamical value of a cubic mile of sunlight near the earth's surface be represented by unity, then the value of a cubic mile of sunlight near the sun's surface would be 46,000 times greater, while he further adds that it would take 4140 horse-power every minute, as the amount of work required to generate the energy existing in a cubic kilometre of light near the sun, a kilometre being equal to about 1093 yards.

Professor Challis[16] stated in 1872 that “Light is to be ranked with the physical forces, and its dynamical action is equally to be ascribed to the pressure of the Aether.” Now I want to put this question to the reader: If light possesses this dynamical action, that is, if it possesses a motive or driving power, what must be the exact effect of the dynamical action of the light waves from the sun upon all the planets and meteors that revolve round it? We know that the sun is 324,000 times the mass of our earth, and that it has a diameter of about 856,000 miles and a circumference of over two million and a half miles. What, therefore, must be the energy of the aetherial light waves that it speeds on their way through space on every side? Stokes,[17] in regard to the mechanical energy of Light, states that “the amount of energy poured forth into space corresponds in round numbers to 12,000 horse-power per square foot,” and that every square foot of the sun's surface supplies energy at the above rate. The number of feet in the sun's surface can be approximately determined. Roughly, there are 2,284,000,000 square miles of surface on the sun's huge form, and there are 27,878,400 square feet in a mile. By multiplying these two numbers we can ascertain the exact number of square feet on the surface of the sun. If, therefore, every square foot possesses a mechanical value equal to 12,000 horse-power, what must be the mechanical equivalent of the sun's radiation of light that it pours forth into space?

I want to call the attention of the reader to another fact, and that is, that light always proceeds in straight lines from the sun ([Art. 76]), and therefore if there be any mechanical action in light at all, that action must be one which is always directed from the sun in straight lines. Now experience universally teaches us, that if a body is pushed, and pushed with such a force as has been indicated, then that body not only moves, but moves in the direction that the supposed horses would push. I have already shown ([Art. 76]) that the path of light is that of a straight line corresponding to the path of the attractive force of gravity; therefore these horses must ever push in a direction from the sun along the same path that the sun's attractive power takes. In other words, the mechanical action of these supposed horses will be a repulsive one, that repulsion being due to the dynamical action of the light waves upon the body that they come into contact with. If this is correct, then not only is heat a repulsive motion, as stated in [Art. 63], but light is equally the possessor of a repulsive motion, because its action is ever directed from the sun. We might continue to follow the supposed horses as they continued their course through space, and we should find that their energy decreased inversely as the square of the distance, partly because the further they proceeded into space the larger the area would be they would have to cover, and therefore their energy would be decreased proportionately.

Professor Stokes, in the same work[18] already referred to, in continuation of the same idea, states: “At the distance of the earth the energy received would correspond to about one horse-power for every square of 5 feet, on that side of the earth's surface facing the sun, supposing the rays to fall perpendicularly.” That being so, we can exactly calculate in horse-power the energy received from light on that side of the earth facing the sun, at its distance of 92,000,000 miles. The area of the earth's surface is, roughly, 200,000,000 × 5280 square feet, and if the energy received is equal to one horse-power for every 5 square feet, then the amount of energy received by the earth on that side facing the sun would be equal to 200,000,000 × 5280 × 1/2 × 1/5 horse-power. This power, it must be remembered, is ever directed away from the sun, and upon that side of the planet that faces the solar orb. So that we have virtually a repulsive force ever directed against the earth, estimated by Professor Stokes to be equal to the estimated horse-power.

This assumption of the repulsive power of light brings the phenomena of light into harmony with that of heat, because we have already seen ([Art. 63]) that heat is essentially a repulsive motion, as indicated by Davy, Rumford and others; and, as heat and light both have a common origin, then light should possess a repulsive power also.

As further proof of this statement, let me again quote from Clerk Maxwell. In the quotation already given in this Art. we have seen that the pressure of sunlight on a square foot is equal to 83.4 lb. He adds the following words to those already quoted: “A flat body exposed to sunlight would experience this pressure on its illuminated side only, and would therefore be repelled from the side on which the light falls.”

Now if more conclusive proof of the correctness of the argument I am advancing were required, I do not think it could be given from any greater authority than that just quoted. Coming from the pen of one of the most brilliant scientists that the past century has known, I venture to think the opinion will be received with that due weight which it demands.