Aether and Gravitation Part 32

This conception of the origin and development of a comet will also account, and that on a logical and philosophical basis, for another fact which is a.s.sociated with cometary phenomena. I refer to the fact of the expulsion of gaseous matter out of the head of a comet as it nears the sun, which expulsion will be dealt with in the article on "Parts of a Comet."

Another problem that might be solved by this conception of a comet lies in the question, as to whether comets s.h.i.+ne by their own light?

If comets are really formed of condensed Aether, as I believe them to be, then, as light is due to a periodic wave motion of the Aether, as soon as the Aether (of which the comets' tails, for example, were formed) was made to vibrate with that rapidity sufficient to produce light waves in the surrounding Aether, the tails would then s.h.i.+ne by their own light, in exactly the same way that any other body emits light waves, as soon as its aetherial vibrations reach the rapidity necessary to produce the waves of light, which vibrations would lie between 2000 to 8000 billions per second.

The number of the comets that exist in the solar system cannot be ascertained with any degree of accuracy, but the total probably extends into millions. They are of all sizes, from those which possess diameters of several miles, to those extending over thousands of miles. They also possess...o...b..ts, with which we will now deal.

ART. 112. _Orbits of Comets._--As has already been pointed out, comets perform their journey round the sun, not only in the plane of the ecliptic, but also at all angles relatively to that plane. In this respect they differ from the orbits of planets and satellites, which perform their journey in orbits situated wholly in the plane of the ecliptic (Art. 109).

There is another important difference between the orbits of the comets and those of the planets. In the case of the latter the orbit is that of an ellipse, while in the case of the comet the orbit may be either that of a parabola or a hyperbola, which may be looked upon as elongated ellipses open at one end. There are, however, some comets whose orbits are perfectly elliptical, and whose return may be calculated with a fair amount of accuracy.

These are known either as Short Period Comets, as represented by Faye's Comet, Encke's and De Vico's; or Long Period Comets, as represented by the comets of 1811, 1844, and 1858. In the case of all these, as their return to our solar system can be determined, it follows that they must revolve around the sun in some sort of a closed orbit, probably that of an exceedingly elongated ellipse.

There are, however, other comets which appear once, or it may be several times only, and then disappear out of the solar system for ever. Now the question arises, as to whether the orbits of the comets which are so variable can be explained by the motions of the Aether which we have already ascribed to it? We have seen (Art. 109) how it is possible to account physically for the plane of the ecliptic from the motions of the Aether, and how it is that all the planets move within that plane, but here we have a phenomenon of a different kind, as observation distinctly teaches us that the comets do not move in, or keep within the plane of the ecliptic, but gravitate round the sun at all angles to that plane.

In order for us, therefore, to be able to account, and that on a philosophical basis, for this fact, we must revert to our conception of the sun in its relation to the solar system. In Art. 88 we learned that the sun was an electro-magnet possessing its electro-magnetic field, and generating electro-magnetic waves which were radiated forth from it on every side. From Art. 89 we learn that an electro-magnetic body possesses lines of force, and that these lines of force take various directions as they are generated by the body, as proved by Faraday's ill.u.s.trations. Further, a moving electro-magnet, as the sun for example, carries its lines of force with it, as proved by Maxwell.

Now these lines of force extend not only east and west, but also north and south, as depicted in Fig. 29.

Hitherto we have only dealt with the lines of force proceeding from the sun equatorially, which lines form the plane of the ecliptic. We have, now, to take into consideration those lines which extend out into s.p.a.ce, north and south of that plane. These are not so curved as the others, but are more inclined to be straight, or less curved, as they are really parts of large curves which extend much further outwards into s.p.a.ce.

The orbits of the Short or Long Period Comets can be explained by the fact that they perform their journey more or less in the plane of the ecliptic, though in some cases at a much greater angle than that of any of the planets. Provided, however, they remain within the influence of the electro-magnetic field of the sun, there is then a physical explanation as to their orbital motion round the sun, in a similar way to the orbital motion of the planets, though at greater angles to the plane of the ecliptic.

For we have to remember, that wherever the electro-magnetic waves of the sun's electro-magnetic field extend, there we have also the rotation of that field round its central body, though with a continually decreasing intensity, as already pointed out. Wherever, therefore, we get rotatory Aether currents, due to the rotation of the electro-magnetic field, there we get the conditions which would enable any kind of gaseous or material body to be circulated round the sun. The case, however, of comets which do not return has to be viewed from a different standpoint.

Here it seems to me we are dealing with ma.s.ses of condensed Aether that come within the inductive influence of the electro-magnetic waves of the sun, as that body moves through s.p.a.ce with its velocity of about 500,000 miles per day. We have to conceive of this condensed Aether situated north and south of the plane of the ecliptic, and situated probably millions of miles away. As the sun moves onward in its journey through s.p.a.ce, carrying its electro-magnetic field with it, then, by the inductive action of the sun, the comet would be attracted by that body, and so would be gradually drawn towards it.

Under this inductive influence it would rush towards the sun, until, approaching very close to it, it would be repelled by the electro-magnetic waves or centrifugal force of that body, and be hurled again by their repulsive energy far far away into s.p.a.ce to the north or south of the plane of the ecliptic. As it was moving away from the syn, north or south of the ecliptic, the sun would be moving onwards through s.p.a.ce in the plane of the ecliptic, which would practically be at right angles to the motion of the comet, so that by the time the comet had receded far into the depths of s.p.a.ce, the sun with its electro-magnetic field would have moved on also in a direction at right angles to the comet's motion.

The effect of the sun's...o...b..tal motion would be, that it would be unable to again exert sufficient inductive power upon the comet to bring it within its inductive influence once more. For example, suppose there is a ma.s.s of Aether condensing at point _A_ in interstellar s.p.a.ce situated some millions of miles north of the plane of the ecliptic, which is represented by the straight lines _B_ _C_. The sun is moving in the direction towards the part of s.p.a.ce represented by point _B_. We will suppose that when the sun is near point _C_ the ma.s.s of Aether at point _A_ is too far away to be appreciably influenced by the inductive action of the sun. But as the sun moves towards point _F_, then the condensed Aether, which practically forms the body of the comet, will come within its influence and be drawn towards the sun, at an angle to the plane of the ecliptic.

[Ill.u.s.tration: Fig: 30.]

By the time the body of the comet has reached the sun, it will have acquired a momentum which enables it to rush past the sun, and then it will be repelled by the electro-magnetic waves in the direction of _F_ _G_, which is still at an angle to the plane of the ecliptic; but its motion, combined with the repulsive power of the electro-magnetic waves, is carrying it outside the sphere and influence of the sun's electro-magnetic field. At the same time the sun is proceeding onwards through s.p.a.ce, leaving the comet far behind, so that by the time the comet has reached the confines of the solar system, it has either pa.s.sed under the influence of another star, or has become further condensed to form a meteor, which begins to circle around the largest and nearest body. I do not a.s.sert that this hypothesis is strictly correct, but it seems to me that only on some such hypothesis can the appearance and apparent loss of irregular comets be explained.

ART. 113. _Short Period Comets and Long Period Comets._--We have seen in the previous article, that some Comets revolve round the sun in closed orbits of exceeding great eccentricity, and the return of these may be calculated with certainty. There are about two dozen comets which revolve around the sun, and which return at intervals lying between three years and 76 years.

This cla.s.s of comets may be divided into two kinds, which are known as Short Period Comets and Long Period Comets respectively. The following table gives a list of the chief of the Short Period Comets, together with some particulars relating to time of revolution, etc.:--

COMETS. PERIOD OF PERIHELION APHELION REVOLUTION. DISTANCE. DISTANCE.

Encke's ... 3-1/4 years. 32,000,000 miles. 387,000,000 miles.

De Vico's ... 5-1/2 " 110,000,000 " 475,000,000 "

Biela's ... 6-1/2 " 82,000,000 " 585,000,000 "

D'Arrest's ... 6-1/2 "

Faye's ... 7-1/2 " 192,000,000 " 603,000,000 "

Halley's ... 76-3/4 " 56,000,000 " 3,200,000,000 "

Encke's Comet was discovered by Professor Encke of Berlin, and named after him. It revolves in an ellipse of great eccentricity, as proved by the fact that when nearest to the sun, it is inside Mercury's...o...b..t, but when furthest away from the sun, it pa.s.ses beyond the orbit of Mars, reaching almost to the orbit of Jupiter. One of the most remarkable facts about this comet is, that it has done more to establish the existence of that resisting medium around the sun, whose existence we have demonstrated, than any other comet. Encke found on its periodical return that its mean distance was gradually getting less, and in order to account for this, he supposed that it was due to the existence of a resisting medium which enveloped the sun, and extended some distance into s.p.a.ce.

This conclusion has been supported in recent years by Von Asten, a German mathematician, who has supported the theory of a resisting medium. On this point Herschel writes in his _Outlines of Astronomy_, Art. 577: "This is evidently the effect which would be produced by a resistance experienced by the comet from a very rare aetherial medium pervading the regions in which it moves; for such resistance, by diminis.h.i.+ng its actual velocity, would diminish its centrifugal force.

Accordingly, this is the solution proposed by Encke, and at present generally received."

So that we have in Encke's Comet another proof of the existence of that aetherial medium, which is not frictionless, but has the power to oppose any body which moves through it, when that body moves in an opposite direction to its own motions.

Another Short Period Comet worthy of notice is that of Biela, named after M. Biela, its discoverer. This comet had a period of six and a half years, and reappeared at several successive intervals until about the year 1845, when it seems to have been broken or split up into two parts.

In December 1845 the comet divided into two parts, which travelled parallel to each other for a long distance. During this separation, very singular changes were observed to be taking place in both the original comet and its offshoot.

Both had a nucleus, and both had tails, which were parallel to each other. The comets continued to travel together until the 15th March 1846, when the new comet began to fade away, until, on the 24th March, the old comet only was visible, while in April both had disappeared entirely. A similar phenomenon was again observed at its next pa.s.sage in 1852, but since then Biela's Comet has entirely disappeared. It is suggested by astronomers, that the comet has become condensed, and broken up, forming a shoal of meteors.

Support is lent to this theory by the fact that in November 1872, when the earth was pa.s.sing through s.p.a.ce and had arrived at that part of its...o...b..t which intercepted the orbit of Biela's Comet, instead of the comet being seen, the earth came into contact with a swarm of meteors, and this is accepted as evidence that Biela's Comet was condensed far away in the colder regions of interplanetary s.p.a.ce into a more solid form of matter, known as meteors. One of the more famous of the short period cla.s.s of comets is that known as Halley's Comet, which has a period of about 76 years. This comet has been seen in its return journey to the sun about 25 times. It was named after its discoverer, Edmund Halley. He was led to identify this comet with that of 1531 and 1607, and thus to conclude that it had a period of 75 or 76 years. He therefore predicted its reappearance in 1759. As the year approached, its arrival was eagerly looked for, to see if the prediction would be verified.

It was thought, however, by a certain astronomer named Clairaut, that the larger planets, as Saturn and Jupiter, might interfere with its...o...b..tal motions, and after careful calculations a difference of 618 days was allowed, which brought its antic.i.p.ated reappearance down to April 1759. It actually reappeared in March of that year. Its next reappearance was fixed to take place about November 1835. The comet became visible on 5th August 1835, and continued to be seen till April 1836, when it again disappeared.

As the reappearance of the comet was calculated by the application of the Newtonian Law of Gravitation, such a result only gave added confirmation to the application of that law to cometary bodies.

Of the Long Period Comets there are several known. That of 1858 has a period, it is thought, of 2000 years. The 1811 comet has a period of 3000 years, while that of 1844 has a period of over 10,000 years. All these comets move in orbits of such great size that their return is improbable. One of the characteristic features about Long Period Comets is their great brilliancy and size.

The 1858 comet, known as Donati's Comet, was first seen by that astronomer at Florence in June. It was invisible, however, to the naked eye, as it only appeared through the telescope like a faint cloud of light, gradually getting brighter and brighter. Toward the end of August it began to show signs of developing a tail, and became visible to the eye on August 29th. During September and October it greatly increased in size and brilliancy, and was plainly visible in the western heavens.

After October 10th it was only visible in the southern hemisphere, gradually decreasing in brightness. It was seen till March 1859, when it disappeared, and will probably not return till the year 3858, as its period of revolution is about 2000 years.

Donati's Comet pa.s.sed between the earth and many stars, which could be seen very distinctly through its tail. One of the stars was Arcturus, and, though some of the densest parts of the comet pa.s.sed over it, yet the star could be seen all the time, thus conclusively proving that the head and tail of a comet are only composed of gaseous matter, probably condensed Aether, as suggested in Art. 111.

ART. 114. _Parts of a Comet._--A comet may be divided into three parts: 1st, Nucleus; 2nd, Head or Coma; and 3rd, Tail.

The nucleus is the central part of the head or coma, and is generally the brightest part of the whole comet. On the theory that a comet is due to the condensation of Aether, the nucleus would represent the first act in the process of condensation, as there would have to be some centre of condensation, and that centre would be represented by the nucleus.

Further, the process of condensation would a.s.sume a spherical form, as the conception of our aetherial atom is that of a sphere or an oblate spheroid. As the process of condensation went on, the layers that would be produced would form a kind of envelope around the point of condensation, with the result that the nucleus would ultimately consist of a large ma.s.s of gaseous matter, made up of layer upon layer of condensed Aether around some central point, which formed the nucleus.

This hypothesis agrees with observed phenomena, because, when we deal with the tails of comets, we shall see that the tail is simply formed by the reverse process to that of condensation, as in the case of cometary tails the gaseous envelopes so formed will be thrown off (either through heat generated by friction, or by the increased heat as the comet nears the sun), which are then repelled away from the sun by the centrifugal force. Herschel,[41] referring to the nucleus, states, paragraph 559: "An atmosphere free to expand in all directions would envelop the nucleus spherically," while in his Reflection on Halley's Comet, he states, Art. 570, "1st, That the matter of the nucleus of a comet is powerfully excited and dilated into a vaporous state by the action of the sun's rays, escaping in streams and jets at those points of its surface which oppose the least resistance. 2nd, That the process chiefly takes place in that portion of the nucleus which is turned towards the sun, the vapour escaping in that direction. 3rd, That when so emitted, it is prevented from proceeding in the direction originally impressed upon it, by some force directed _from_ the sun, drifting it back and carrying it out to vast distances behind the nucleus forming the tail."

When we come to deal with the question of the formation of the tail, we shall find that every reflection made by Herschel is satisfactorily fulfilled by the conception of a gravitating and condensing Aether.

Before considering the tail, however, we will deal with the head or coma.

The head or coma is that part of the comet which exists round the nucleus. It is less bright than the nucleus, and oftentimes appears as a shadowy ma.s.s of light. Herschel, in his 4th Reflection, states that "a considerable part of the vapour actually produced remains in the neighbourhood of the nucleus forming the head or coma." So that the head of a comet is simply the vaporised part of the nucleus which is produced by the increased heat of the sun, in the same way that water would be vaporised by the addition of heat, the vapour in that case being thrown off in the form of steam.

This formation of the head is but a continuation of the reversal of the process of condensation, which originally gave existence to the ma.s.s of matter termed the comet. The diameter of this head or coma often extends to thousands of miles. The head of the 1811 comet was 540,000 miles in diameter, while that of the 1843 was 112,000 miles. As the nucleus is formed of a series of envelopes, so the head also consists of a series of envelopes.

The comet of 1858 constantly threw off these envelopes, which were first expelled _towards_ the sun, and then repelled away _from_ the sun, forming the tail. The matter forming the head and the nucleus is perfectly transparent, as stars have been seen through the matter which forms those parts. Herschel,[42] paragraph 558, states "that whenever powerful telescopes have been turned on these bodies, they have not failed to dispel the illusion which attributes solidity to that more condensed part of the head which appears to the naked eye, though it is true that in some a very minute stellar point has been seen indicating the existence of a stellar body."

_Tails._--The tail of a comet is that part which flows from the head, and is afterwards repelled by the repulsive power of the sun into s.p.a.ce.

We shall deal with this repulsive power, whose existence we have already demonstrated, and the part which it plays in the formation of a comet's tail, in the next article. The tail of a comet is oftentimes considered to be the comet itself, rather than a part of the same, but as the tail is the most distinctive feature of a comet, and is the part most visible to the naked eye, there has arisen the popular but mistaken idea of ident.i.ty between the tail and the comet itself.

Tails are of all kinds. There are some which are short, while others are long. Then we have comets with single tails, or double, and in some cases even multiple tails. Occasionally comets appear which have no tails at all. The comet of 1744 had six tails, which spread out in the shape of a large fan.

One of the most remarkable features of tails is their abnormal length, which oftentimes reaches into millions of miles. The comet of 1843 had a tail 112,000,000 miles long. Another feature about the tails of comets is that they are always directed _away_ from the sun. Up to the present I believe no satisfactory explanation has been given of this fact, but with the conception of the rotating Aether as given in Art. 94, we shall for the first time be able to give a satisfactory physical explanation of that phenomenon. In addition to this, the formation of cometary tails of all shapes receives a physical explanation, when taken into account with the fact that the sun is an electro-magnet, possessing its electro-magnetic field, and its lines of force, as described in Art. 88.