Art. 111. Comets. What are Comets?--In addition to the planets and asteroids which revolve around the sun, there are also other bodies termed Comets, which revolve round the solar orb.

Unlike the planets, however, they do not all keep to the plane of the ecliptic, but approach to, and recede from the sun at all angles to that plane, as well as in that plane itself. Comets are supposed to be huge masses of gaseous matter, in a more or less condensed condition. That they are not composed of absolutely solid matter is proved by the fact that it is possible to see the stars through the gaseous matter of which they are composed.

How the gaseous matter of which these comets are formed is originated, or how it is formed in solar or stellar space, has, I believe, up to the present never been explained, and indeed, with the idea of a frictionless Aether, I fail to see how any physical explanation of the origin and development of a comet can be satisfactorily given. With the conception of the Aether, however, that is put forward in this work, viz. that Aether is matter in its most rarefied and attenuated form, which can be condensed into a gaseous condition, with such a conception of the universal aetherial medium, the origin and development of gaseous matter from this Aether becomes a physical possibility.

Lord Kelvin, in the Philosophical Magazine, July 1902, on the “Clustering of Gravitational Matter in any part of the Universe,” has already suggested the possibility of the condensation of the Aether, but with the old idea of a frictionless Aether, that is, an Aether which does not possess mass, such a hypothesis is improbable. Because, if the Aether becomes condensed at all, it must be condensed into gaseous and solid matter, and all experiments and observation teach us that both these forms of matter possess mass and weight.

Therefore, if the frictionless Aether, which possesses no mass and weight, is to be condensed into gaseous or solid matter, there must come a period in the process of condensation when it must pass out of the condition of possessing no mass and no weight, into the condition of possessing mass and weight, which assumption is altogether opposed to those Rules of Philosophy based upon experiment and observation.

Aether can only pass into a gaseous or solid condition, in which condition it will possess mass and weight, on the assumption that in the aetherial condition it possesses the same properties, only in a modified form, which it possesses after the process of condensation has taken place. In a similar way that air can pass out of its gaseous condition into a liquid condition, or any gas can pass out of its gaseous into a liquid condition, so Aether, on the conception as given in Chapter IV., can pass out of its aetherial and rarefied condition into that form of matter which is known as gaseous. We shall deal with this aspect of Aether more fully when we come to deal with the Nebular Hypothesis, as the same principle underlies that hypothesis as underlies the origin and development of comets.

Thus, comets may be formed at any time in interstellar space out of the Aether that exists there, provided the conditions of its formation are to be found there. Then, as they are gradually formed, they would, like any other bodies, come more directly under the influence of any large bodies, as the sun, and be attracted by them.

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 associated 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 shine 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 shine 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 orbits, 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 illustrations. 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 space, 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 space.

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 masses of condensed Aether that come within the inductive influence of the electro-magnetic waves of the sun, as that body moves through space 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 space, 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 space 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 space 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 space, 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 orbital 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 mass of Aether condensing at point A in interstellar space 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 space represented by point B. We will suppose that when the sun is near point C the mass 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.

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 space, leaving the comet far behind, so that by the time the comet has reached the confines of the solar system, it has either passed 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 assert 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 class 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.:--

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 orbit, but when furthest away from the sun, it passes 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 space.

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 diminishing 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 passage 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 passing through space and had arrived at that part of its orbit 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 space into a more solid form of matter, known as meteors. One of the more famous of the short period class 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 orbital motions, and after careful calculations a difference of 618 days was allowed, which brought its anticipated 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 passed 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 passed 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 assume 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 mass 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,[40] 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 mass 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 mass 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,[41] 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 space. 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 identity 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.

Art. 115. Centrifugal Force and Comets' Tails.--In order to account for the existence of the tails of comets, various repulsive forces have been introduced from time to time into the solar system, so that the phenomena of cometary tails might be satisfactorily accounted for.

It has been felt by every astronomer that some repulsive force, which had its origin in the sun, was absolutely necessary to explain the existence of the tails, and as no real force could be demonstrated to exist, recourse had to be made to repulsive forces of a more or less hypothetical nature. The necessity of this repulsive force is nowhere more plainly indicated than by Sir J. Herschel in his Lectures on Scientific Subjects, where, dealing with the phenomena of comets' tails, he writes: “They have furnished us with a proof, amounting to demonstration, of the existence of a repulsive force directed from the sun, as well as that great and general attractive force which keeps planets in their orbits.”

In the same work, referring to the comet of 1680, he writes: “This comet was perhaps the most magnificent ever seen. It appeared from November 1680 to March 1681. In its approach to the sun it was not very bright, but began to throw out its tail when about as far from the sun as the earth. It passed its perihelion on December 8th, and when nearest to the sun was only about 1/10 part of the sun's diameter from the surface. No wonder it gave evidence of violent excitement, coming from the cold region outside planetary space. Already, when arrived even in our temperate regions, it began to show signs of internal activity. The head had begun to develop and the tail to elongate, till the comet was for a time lost sight of. No human eye beheld the wondrous spectacle which it must have offered on December 8th. Only four days afterwards, however, it was seen again, and the tail, whose direction was reversed, and which observe could not possibly be the same tail, its tail had already lengthened out to the extent of about 90 millions of miles, so that it must have been shot out with immense force in a direction from the sun.”

The reader will have observed it took from November 10th to December 8th, or 28 days, to fall to the sun for the same distance, and that with all the velocity it had on November 10th to start with. Herschel sums up the matter thus: “Beyond a doubt, the widest and most interesting prospect of future discovery which their study (comets' tails) holds to us, is, that distinction between gravitating and levitating matter, that positive and unrefutable demonstration of the existence in nature of a repulsive force co-extensive with, but enormously more powerful than the attractive force we call gravity, which the phenomena of their tails afford.”

Thus the philosophic mind of Herschel saw in the existence of cometary tails, the irrefutable evidence of the existence of a repulsive force, not of a hypothetical character, but as real as the existence of gravity itself. Various attempts have been made to define that repulsive force which was thus demanded, and the same force has been ascribed by scientists to the repulsion due to heat, to light, and also to electricity.

Several French scientists have suggested that the repulsive force was due to the heat of the sun. M. Roche was one of those who stated that the phenomena of cometary tails was due to the repulsive power of heat, which found its origin in the heat of the sun. M. Faye, another French scientist, states that the repulsive force had its origin in the heat of the sun. By a series of experiments he demonstrated that there was a repulsive power in all heat waves, which gave his theory that experimental support that any theory must possess to make it permanent.

Now in Art. 63 it was shown that heat does possess a repulsive power, but that that power is rather due to the electro-magnetic Aether whose vibrations produce the heat waves, than to the repulsion of heat; so that, indirectly, the assumption of both these French scientists, that the repulsive power of heat gave rise to the tails of comets, is correct. Then again it has been suggested that the repulsive power is produced by the pressure of the light waves. Professor Lebedew suggested this after he had experimentally proved that light waves did possess a repulsive power (Annalen der Physik, November 1901). It can easily be seen, as pointed out in Art. 70, that, inasmuch as light is due to the vibrations of the Aether, they too possess this repulsive power, and therefore Professor Lebedew's suggestion as to the nature of the repulsive power is correct, as the real centrifugal force is really due to an aetherial pressure.

Whether, therefore, we consider it from the standpoint of heat, or light or electricity, it ultimately resolves itself into the same aetherial medium which is at once the common source of all these forces. Again, it has been suggested that the repulsive power is electrical or electro-magnetic, and this view is receiving more support than either of the others from modern scientists.

Herschel suggested that the repulsive power was electrical, while Bredichin has worked out a very careful theory as to the effect of electrical repulsion upon different elements that are found in the comets' tails, with a view to explain the different shapes of the tails. But whether the force is looked at from the standpoint of heat, light or electricity, it ultimately resolves itself into the motions of the Aether, which gives rise by its different vibrations and motions to all the three forms of energy referred to.

When we also take into account the fact that Aether is gravitative, and therefore denser nearer to the sun than further away, and that it is also rotating round the central body the sun (Art. 91), then we have at once every condition necessary to explain all the various kinds of cometary tails, and also for the remarkable fact that the tail is always turned away from the sun, which is simply due to the effect of the rotating Aether with its outflowing electro-magnetic waves upon the gaseous matter of the comet. Thus from the phenomena of comets' tails, we have again arrived at the conclusion of the existence of that centrifugal force, whose origin and continuity are to be found in the electro-magnetic Aether which surrounds the sun, and which by its electro-magnetic waves gives rise to pressure on all bodies upon which they fall.Art. 116. Formation of Tails.--With the conception of the formation of the comet advanced in Art. 111, viz. that it is nothing more or less than Aether in a state of condensation, and remembering the explanation given of the parts of the comet, as the nucleus, and head or coma, we are now in a position to give a philosophical account of the formation of the tails of comets, which will satisfactorily fulfil all the Rules of Philosophy. In addition to the facts already referred to in the previous articles of this chapter, we must also recall our conception of the Aether as given in Chapter IV., remembering that it gets denser nearer the sun, and that it is not frictionless; therefore, when a body is urged through it, friction is produced, and heat is generated.

We must also remember that the Aether is rotating round the sun as that body proceeds through space. We have, therefore, to picture the condensed mass of Aether situated out in the cold interstellar space, gradually coming under the influence of the sun, as that body rushes on its journey through space with a velocity of 500,000 miles per hour.

Slowly, but surely, the mass of condensed Aether begins to respond to the attractive power of the sun, and to move through space towards the sun. So long as it is moving towards the sun, it is encountering and having to overcome the resistance of the Aether.

At first this resistance is very feeble, owing to the decreased density of the Aether, but as it proceeds on its journey it is constantly passing into denser parts of the aetherial electro-magnetic field around the sun. The result is, that as the resistance is increased, so there is greater friction between the matter of the comet and the atomic Aether in space, and, in consequence, heat is generated.

In addition to the generated heat, the comet is all the while passing into regions of greater intensity of heat. In both cases, the effect is only manifested on that side of the comet which is approaching the sun; for, if there be any friction at all, it will only be on that half of the comet which encounters the Aether, so to speak, while the same part will receive the added heat, as the distance between the comet and the sun is decreased. As can readily be seen therefore, this added heat acts only upon the half of the comet which is advancing, and which faces the sun, and as the effect of heat is always to vaporise, so the effect on the nucleus of the comet is to vaporise the condensed aetherial matter, and this vaporised aetherial matter is thrown off in layers which are partly spherical in form, the layers always being expelled in the first instance towards the sun, on account of that centrifugal motion which has its birth in the nucleus of the comet.

This explanation fully establishes and confirms the first and second Reflections of Herschel as given in Art. 114, and, moreover, is itself established by the very phenomena which comets present in their approach to the sun. As soon, however, as the vaporised matter is expelled from the nucleus towards the sun, it is met by the centrifugal motion of the electro-magnetic Aether which proceeds from the sun, and this pressure of the aetherial waves on the advancing comet acts as a repelling power, literally repelling the vaporised matter from the sun, and thus giving rise to the existence of its tail.

This explanation fully confirms the third Reflection of Herschel referred to in Art. 114, and is itself also confirmed by actual observation. During all this time, however, the comet has been approaching the sun with a decreased velocity, for its velocity has been minimised by the resistance it has had to overcome in its approach to the sun. As soon, however, as it reaches the sun, it is whirled round that body by the rotating Aether medium, as the intensity of its rotation is greatest nearest the sun, with a velocity which often exceeds thousands of miles per hour.

Having passed its perihelion, in view of the physical existence of our centrifugal motion, let us now ask ourselves what ought to happen to the comet? Previous to its perihelion, the comet's motion and the centrifugal motion due to the pressure of the Aether were in opposition, but after passing the perihelion, the comet's motion and the centrifugal motion will be acting conjointly, with the result that the motion of the comet would be accelerated. Now this is exactly what observation teaches us does happen in regard to comets, when they have passed their perihelion passage.

As Herschel pointed out with reference to the comet of 1680 (Art. 114), it took 28 days to fall to the sun, but only took four days to cover the same distance, after it had passed the sun and rounded the perihelion. So that we have here, as Herschel stated, an irrefutable evidence of the existence of the repulsive power whose existence we have demonstrated.

Again, there is another fact which has to be taken into consideration in regard to the tails of comets. Observation teaches us that their tails are invariably turned from the sun, though why they always are so turned away is an unsolved problem, apart from some real or hypothetical repulsive power. We have, however, to further remember that the electro-magnetic Aether around the sun is ever rotating with that body, and carrying with it in its rotation all associated planets and meteors.

This rotation of the Aether plays a most important part in the phenomena stated. Whether the comet is approaching the sun, or receding from the sun, it is still subject to the influence of this rotatory Aether medium. The result will be that the lighter particles of the vaporised matter will be acted upon more powerfully than the heavier parts, so that even when the comet is receding from the sun, after it has passed the perihelion, the lighter parts which go to form the tail will be more under the influence of the repelling Aether waves than the heavier parts, as the nucleus, as suggested by Bredichin.

Thus the natural result will be that the tail will still be directed away from the sun even when it is receding from that body. Gradually, however, as the comet recedes, it passes out of the denser Aether, where the intensity of motion and vibration are greatest, to those slower parts of the sun's aetherial field where they are less intense.

The effect of this is soon made manifest on the tail and head of the comet. The process which took place as it approached the sun is now exactly reversed, as it is now passing out of a denser into a more rarefied medium, where its motions and vibrations are less intense. The tail, therefore, appears to be drawn back to the head, while the head will itself gradually contract into the nucleus, as it recedes further and further into space. If the comet be situated within the plane, or nearly the plane of the ecliptic, then it is possible for it to return again, and go through the same process, unless it is captured on its outward journey by some of the large outer planets, as Jupiter. If, however, their planes do not coincide with the plane of the ecliptic, then it is very possible that they will not reappear again, but pass on to some other stellar system. Thus we can explain on a strictly philosophical basis one of the most interesting, and yet one of the most mysterious phenomena associated with our solar system, from the simple yet truly philosophical assumption that Aether is matter, in conjunction with all that that assumption logically involves.