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see that every one of the luminous bodies, without exception, moved in lines which converged in one point in the heavens : none of them started from that point; but their paths, when traced backwards, met in it like rays in a focus, and the manner of their fall showed that they descended from it in nearly parallel straight lines towards the earth.
By far the most extraordinary part of the whole phenomenon is, that this radiant point was observed to remain stationary near the star y Leonis for more than two hours and a half, which proved the source of the meteoric shower to be altogether independent of the earth's rotation, and its parallax showed it to be far above the atmosphere.
As a body could not be actually at rest in that position, the group or nebula must either have been moving round the earth or the sun. Had it been moving about the earth, the course of the meteors would have been tangential to its surface; whereas they fell almost perpendicularly, so that the earth in its annual revolution must have met with the group. The bodies or the parts of the nebula that were nearest must have been attracted towards the earth by its gravity, and, as they were estimated to move at the rate of fourteen miles in a second, they must have taken fire on entering our atmosphere, and been consumed in their passage through it.
As all the circumstances of the phenomena were similar on the same day and during the same hours in 1832, and as extraordinary flights of shooting stars were seen at many places both in Europe and America on the 13th of November, 1834, 1835, and 1836, tending also from a fixed point in the constellation Leo, it has been conjectured, with much apparent probability, that this nebula or group of bodies performs its revolution round the sun in a period of about 182 days, in an elliptical orbit, whose major axis is 119 millions of miles; and that its aphelion distance, where it comes in contact with the earth's atmosphere, is about 95 millions of miles, or nearly the same with the mean distance of the earth from the sun. This body must have met with disturbances after 1799, which prevented it from encountering the earth for 32 years, and it may again deviate from its path from the same cause.
It is now well ascertained that great showers of shooting stars occur also on the 12th of August, whose point of divergence is
B Camelopardali, so that the earth's atmosphere comes into contact with a zone of these small bodies twice in the year. By a systematic series of observations, MM. Benzenberg and Brand have clearly made out that the heights at which the falling stars appear and vanish vary from 16 miles to 140, and their velocities from 18 to 36 miles in a second, velocities so great as certainly to indicate a planetary revolution round the sun. As shooting stars are seen almost every night when the sky is 'clear, Sir John Lubbock has thought it probable that some of these bodies may have come so near, that the attraction of the earth has overcome that of the sun, and caused them to revolve as satellites round it. Should that be the case, they might shine by the reflected light of the sun, and suddenly cease to be visible on entering the earth's shadow. The splitting of the falling stars like a rocket, and the trains of light, may be accounted for by supposing the stars to graze the surface of the shadow before being eclipsed; and the disappearance would be more or less rapid according to the breadth of the penumbra traversed. The calculations of M. Petit, Director of the Observatory of Toulouse, not only render probable the existence of small satellites, but tend to establish the identity of a body revolving round the earth in three hours and twenty minutes, at a distance of 5000 miles above its surface. It is evident that in this case the same satellite would be seen very often, and a very few would be sufficient to account for their nightly appearance. It is possible, however, that some shooting stars may belong to one class, and some to the other, since one group may be revolving about the sun, and another round the earth. In the case of a satellite shooting star, geometry furnishes the means of ascertaining its exact distance from the spectator, or from the centre of the earth, if the time and place of its disappearance be known with regard to the neighbouring stars. Since the falling stars are consumed in the atmosphere, their masses must be small, but it is possible that occasionally one may be large enough to arrive at the surface of the earth as an aërolite.
Diffusion of Matter through Space - Gravitation
plicity of its Laws
- Its Velocity SimGravitation independent of the Magnitude and Distances of the Bodies Not impeded by the intervention of any Substance Its Intensity invariable - General Laws-Recapitulation and Conclusion.
THE known quantity of
matter bears a very small proportion to the immensity of space. Large as the bodies are, the distances which separate them are immeasurably greater; but, as design is manifest in every part of creation, it is probable that, if the various systems in the universe had been nearer to one another, their mutual disturbances would have been inconsistent with the harmony and stability of the whole. It is clear that space is not pervaded by atmospheric air of such density as that we breathe, since its resistance would long ere this have arrested the motion of the planets: it certainly is not a void, but replete with a medium possibly in itself electric or magnetic, but at all events capable of transmitting light, heat, magnetism, gravity, and probably influences of which we can form no idea.
Whatever the laws may be that obtain in the more distant regions of creation, we are assured that one alone regulates the motions, not only of our own system, but also of the binary systems of the fixed stars; and, as general laws form the ultimate object of philosophical research, we cannot conclude these remarks without considering the nature of gravitation—that extraordinary power whose effects we have been endeavouring to trace through some of their mazes. It was at one time imagined that the acceleration in the moon's mean motion was occasioned by the successive transmission of the gravitating force. It has been proved that, in order to produce this effect, its velocity must be about fifty millions of times greater than that of light, which flies at the rate of 192,000 miles in a second. Its action, even at the distance of the sun, may therefore be regarded as instantaneous; yet, remote as the fixed stars are, the solar gravitation
must have some influence on the nearest of them, as, for example, a Centauri, which is only 20,602 times the radius of the earth's orbit from the sun, while La Place has computed that the solar gravitation extends a hundred millions of times farther than the semidiameter of the terrestrial orbit. Possibly the star dust in the Milky Way may be beyond, or on the verge of, that enormous limit; yet it is very unlikely that either the sun, or any of the stars which form the great cluster to which we belong, should be unconnected bodies.
The curves in which the celestial bodies move by the force of gravitation are only lines of the second order. The attraction of spheroids, according to any other law of force than that of gravitation, would be much more complicated; and, as it is easy to prove that matter might have been moved according to an infinite variety of laws, it may be concluded that gravitation must have been selected by Divine Wisdom out of an infinity of others, as being the most simple, and that which gives the greatest stability to the celestial motions.
It is a singular result of the simplicity of the laws of nature, which admit only of the observation and comparison of ratios, that the gravitation and theory of the motions of the celestial bodies are independent of their absolute magnitudes and distances. Consequently, if all the bodies of the solar system, their mutual distances, and their velocities, were to diminish proportionally, they would describe curves in all respects similar to those in which they now move; and the system might be successively reduced to the smallest sensible dimensions, and still exhibit the same appearances.
The action of the gravitating force is not impeded by the intervention even of the densest substances. If the attraction of the sun for the centre of the earth, and of the hemisphere diametrically opposite to him, were diminished by a difficulty in penetrating the interposed matter, the tides would be more obviously affected. Its attraction is the same also, whatever the substances of the celestial bodies may be; for, if the action of the sun upon the earth differed by a millionth part from his action upon the moon, the difference would occasion a periodical variation in the moon's parallax, whose maximum would be the of a second, and also a variation in her longitude amounting to several seconds -a supposition proved to be impossible by the agreement of
theory with observation. Thus all matter is pervious to gravitation, and is equally attracted by it.
Gravitation is a feeble force, vastly inferior to electric action, chemical affinity, and cohesion; yet, as far as human knowledge extends, the intensity of gravitation has never varied within the limits of the solar system; nor does even analogy lead us to expect that it should: on the contrary, there is every reason to be assured that the great laws of the universe are immutable, like their Author. Nor can we suppose the structure of the globe alone to be exempt from the universal fiat of general laws, though ages may pass before the changes it has undergone, or that are now in progress, can be referred to existing causes with the same certainty with which the motions of the planets, and all their periodic and secular variations, are referable to the law of gravitation. The traces of extreme antiquity perpetually occurring to the geologist give that information, as to the origin of things, in vain looked for in the other parts of the universe. They date the beginning of time with regard to our system, since there is ground to believe that the formation of the earth was contemporaneous with that of the rest of the planets; but they show that creation is the work of Him with whom "a thousand years are as one day, and one day as a thousand years."
In the work now brought to a conclusion, it has been necessary to select from the whole circle of the sciences a few of the most obvious of those proximate links which connect them together, and to pass over innumerable cases both of evident and occult alliance. Any one branch traced through its ramifications would alone have occupied a volume; it is hoped, nevertheless, that the view here given will suffice to show the extent to which a consideration of the reciprocal influence of even a few of these subjects may ultimately lead. It thus appears that the theory of dynamics, founded upon terrestrial phenomena, is indispensable for acquiring a knowledge of the revolutions of the celestial bodies and their reciprocal influences. The motions of the satellites are affected by the forms of their primaries, and the figures of the planets themselves depend upon their rotations. The symmetry of their internal structure proves the stability of these rotatory motions, and the immutability of the length of the day, which furnishes an invariable standard of time; and the actual size of the terrestrial spheroid affords the means of ascer