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 ofF 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 hisOutlines 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 addedconfirmation 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 inArt. 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 formedby 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 directedfromthe 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 expelledtowardsthe sun, and then repelled awayfromthe sun, forming the tail. The matter forming the head and the nucleus is perfectly transparent, as stars have been seenthrough 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 directedawayfrom 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 inArt. 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 inArt. 88.
[40]Outlines of Astronomy.
[40]Outlines of Astronomy.
[41]Outlines of Astronomy.
[41]Outlines of Astronomy.
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 repulsiveforces of a more or less hypothetical nature. The necessity of this repulsive force is nowhere more plainly indicated than by Sir J. Herschel in hisLectures 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. Onlyfour daysafterwards, 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 directionfromthe 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 thatthe 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 inArt. 63it 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 inArt. 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 theelectro-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 inArt. 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 ChapterIV., 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 arepartly spherical in form, the layers always being expelled in the first instancetowardsthe 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 inArt. 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 proceedsfrom 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 inArt. 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 thesamedistance, 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 turnedfromthe 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.
Art. 117.The Starry World.--In addition to the planets and comets that are found in the heavens, there are other bodies, countless in their number, which we know as stars. Who has not looked up into the heavens on some clear night, and noticed how the vault of heaven was spangled over with points of light, each point representing a huge sun that exists in far-off space? For it must be remembered that every star is a sun, which, reasoning by analogy, is the centre of a stellar system, just in the same way that our sun is the centre of our solar system. Like our sun, all stars shine by their own light, and the quality of that brilliancy decides the magnitude of the star, the magnitude being indicative of the relative brilliancy of a star rather than its size. So that stars are divided into groups according to their magnitude, the magnitudes ranging from the first to the sixteenth, and even beyond. Those of the first magnitude are more brilliant than those of the second, those of the second more brilliant than those of the third, each magnitude decreasing in relative brilliancy as the number which indicates the magnitude increases. There are about sixteen different degrees of magnitude, in which are classified the millions of stars that exist in infinite space, but only stars up to the sixth magnitude are visible to the naked eye, the telescope revealing those which lie beyond. The total number of stars visible to the naked eye are about 6000, half of which are visible in each hemisphere.
About 20 stars comprise the group of the first magnitude, which include all the brightest stars visible, as Sirius, Canopus, Alpha, Arcturus, Rigel, and Capella.
Those of the second magnitude number about 65, and include the brighter stars to be found in the constellation known as the Great Bear. Stars of the third magnitude number about 200, of the fourth magnitude about 400, of the fifth magnitude 1100, and of the sixth magnitude about 3200.
With the aid of the telescope about 13,000 stars of the seventh magnitude are revealed to us, and 40,000 of the eighth magnitude, while of the ninth magnitude over 140,000 are revealed by the telescope. Asthe power of the telescope is increased, so the number revealed is increased also, until by the time we have reached stars of the fourteenth magnitude, at least 20,000,000 are revealed to us.
If we look into the heavens on a clear moonlight night, we shall further see that here and there are groups of stars clustered together. These clusters are termed constellations, and are named after some object which the arrangement of the stars seemed to suggest. Thus every one is familiar with that constellation known as the Great Bear, or the “Plough,” so called because of its resemblance to a plough.
The brightest stars of each constellation are named after the letters of the Greek alphabet, the brightest being called Alpha, the next in brilliancy Beta, and so on, right through the Greek alphabet. For example, the seven stars in the Great Bear are known as Alpha, Beta, Gamma, Delta, Epsilon, Zeta, and Eta.
The constellations are grouped into two divisions, known as the Northern and Southern constellations respectively.
The visible Northern constellations are 25 in number, and include the following well-known groups--
The visible Southern constellations are 18 in number, and include such groups as--
Variable Stars.--Not only are the stars of different magnitudes, but the brilliancy of some of them changes from time to time. This class of stars is known as variable stars, and has received the attention of modern astronomers for many years, in order that the cause of their variation might, if possible, be ascertained. The periods of variation differ in length, ranging from a number of days to 60 or 70 years.
One of the most interesting of variable stars is that known as Omicron Ceti, whose period of change is about 331 days. Its brilliancy variesfrom one of the second magnitude to one of the tenth.
Beta Persei is another well-known variable star. This star shines as one of the second magnitude for 2 days and 13 hours, and then suddenly loses its light, and in less than 4 hours becomes a star of the fourth magnitude. Its brilliancy then increases again, and in a similar time it regains its former brilliancy.
The conclusion that has been arrived at in regard to the cause of the variation of these stars is, that in each case the diminution of light is due to the existence of dark bodies, probably planets, which revolve round the central star.
This hypothesis was confirmed by Professor Vogel about 1889 by means of spectroscopic results.
Another interesting fact about stars is that they shine with various colours. The colours of stars are as various as the colours of the rainbow, and range through the whole spectrum, of red, orange, yellow, green, blue, indigo, violet, and white. What is more remarkable is the fact that the colours of the stars seem to change through great periods of time. If we turn to ancient records we learn that Sirius was red then, but is now green, while Capella was also red, but is now pale blue.
Double and Multiple Stars.--Many stars when looked at through powerful telescopes are found to be double, triple, quadruple, and even multiple, although when looked at by the naked eye, they seem to be single in appearance.
An example of a double star is to be found in the constellation of Lyra. A moderate telescope reveals this as a double star, while a still more powerful telescope reveals the strange fact that each apparently single star which forms the double is itself double, so that we have in this constellation a system of four stars, in which each pair revolves round a point situated between them.
Several thousand double stars are known altogether, while the motions of several hundreds of them have been detected with powerful telescopes. Some of the double stars are as follows--Zeta Hercules, Eta Coronae Borealis, Gamma Coronae Borealis, Beta Cygni, Alpha Centauri.
The colours of some of the double stars are very beautiful. Some are yellow and blue; others, yellow and purple, while others are orange and green. Some of the double stars are only optical doubles, that is to say, they apparently seem close together, while as a matter of fact they are immense distances from each other, the apparent doubleness being due to the fact that they are more or less in the same line of vision. Real double stars, where the component stars are situated close together,are known as physical doubles, to distinguish them from the optical doubles.
Binary Stars.--Another class of double stars are known as Binary Stars. This class of stars is composed of two stars which revolve around each other in regular orbits, and are among some of the most interesting objects in the heavens. About 1000 Binary stars are known altogether. Their motions, however, are very slow, and only in a comparatively few cases have the dimensions of their orbits been ascertained. Some of the Binary stars are Zeta Hercules, which has a period of about 36 years; Eta Coronae Borealis, which has a period of 43 years; while the brightest star, Sirius, is also a Binary star, with a period of about 50 years.
The Milky Way.--The Milky Way is the name given to that band of light which stretches across the sky at night-time, and forms a zone or belt that completely circles the celestial sphere.
This belt of light has maintained from the earliest ages the same relative position among the stars, and, when resolved by powerful telescopes, is found to consist entirely of stars scattered by millions across the expanse of the heavens.
The whole zone or belt is composed of nothing but stars, whose average magnitude, according to Herschel, is about the tenth.
Stars of all magnitudes are, however, found in this zone.
Of the brightest stars, about twelve are found in this region, while the majority of stars of the second, third, and fourth magnitudes are also found in or near it.
The great majority of star clusters are also found along the course of the Milky Way, while many of the irresolvable nebulae seem to congregate near the poles of this starry region.
The Milky Way is divided in one part of its course by a stream of stars, which seems to branch off as a separate stream, thus dividing it into two parts.
All these facts seem to point to the conclusion that the stars of the universe, instead of being scattered about haphazard in the space, form a ring or layer, of which the thickness is very small compared with its length and breadth.
Our own solar system, according to Herschel, occupies a place somewhere about the middle of the thickness of the zone, and near the point where it divides into two parts.
Recent observations go to show that there is a tendency of the sun's apex to drift along the edge of the Milky Way, and this drift seems to point to a plane of motion of the sun, nearly coinciding with the plane of the Milky Way.
Art. 118.Stars and Kepler's Laws.--We have learned in a previouschapter that the sun is the centre of a system which comprises a retinue of planets, with their attendant satellites, together with a number of asteroids or minor planets, with the addition of meteors and comets to complete the system.
Now if the sun is a star, then, according to our First and Second Rules of Philosophy, every star ought also to be the centre of a stellar system and the centre of two aetherial motions, that is, the Centrifugal and Centripetal forces, due to the pressures and tensions of the Aether medium. Further, every stellar system would be composed of exactly similar bodies to those which compose our solar system, as planets with their attendant satellites, together with meteors and comets; the whole of the stellar planets being bound to the central body by the combination of the two aetherial motions, and kept revolving round the central star by the rotating electro-magnetic Aether currents.
Such a hypothesis is entirely philosophical, as it is simple in conception, and fully agrees with our experience in relation to the only star of which we have any complete knowledge.
It is unthinkable to conceive of a star existing in so-called space, and constantly radiating out its light and heat for no purpose at all. All Nature teaches us that there is not a single thing in existence but what has a definite purpose, and a definite place to fill in the universe. Even the aetherial atoms, which form the foundation stones of the universe, have their own purpose to fulfil in the glorious scheme of the Universe conceived by the Eternal Infinite; and to suppose that a star has no purpose to fulfil, no task to perform, is to suppose something altogether opposed to the teaching of all Philosophy. Why even man, with his finite wisdom, would not be so foolish, so unwise, as to make a star, and set it in the firmament of heaven for no purpose at all! Are we therefore to suppose that the Divine Creator of all things possesses less wisdom than the creatures which He Himself hath made? Such an assumption would be a reflection not only on the wisdom of an All Wise Being, but would also be a reflection on our own ideas of philosophical reasoning.
Therefore the conclusion that we are compelled to come to, in relation to the millions of stars that exist in interstellar space, is that every star is the centre of a stellar system, and the centre of two aetherial motions due to the pressures and tensions of the electro-magnetic Aether; while rotating round each star are the ever-circulating electro-magnetic Aether currents, which form the medium by which all the stellar planets with their attendant satellites are ever made to revolve around that central body which supplies them with their light and heat. Some such conclusion as this Sir John Herschel arrived at, for in hisTreatise of Astronomy, Art. 592, he writes: “Now for what purpose are we to suppose such magnificent bodies scattered through the abyss ofspace? Surely not to illuminate our nights, which an additional moon of the 1/1000 part of our own moon would do much better. He must have studied astronomy to little purpose who can suppose man to be the only object of the Creator's care, or who does not see in the vast and wonderful apparatus around us, provisions for other races of animated beings. The stars, doubtless, are themselves suns, and may perhaps each in its sphere be the presiding centre around which other planets or bodies may be circulating.”
Further, with reference to the stability of each of these stellar systems, it is essential that the existence of a physical centrifugal force should be recognized, in order that the unity and harmony of the spheres should be maintained.
Professor Challis points this out very conclusively in thePhil. Mag. of 1859, where, writing on this point, he states: “It may also be remarked, that if the Law of Gravity be absolute, there is no security for the stability of a system of stars, whether the system be a Milky Way or a nebulous cluster. For, however small the mutual attraction between the constituent bodies may be, in the course of ages it must produce a general movement towards the centre or densest region. But the form of the Milky Way and of certain nebulae seems to present an utter contradiction to any such tendency.” With the conception, however, of a physical centrifugal force or motion due to the pressure of a physical medium, the stability of even the Milky Way may be physically conceived and understood.
Again, when we consider the sun as a star, we find that it has two motions of its own, one of rotation on an axis, and the other of translation in an orbit, such rotation being due to the fact that it is a magnet and has ever circulating round it electro-magnetic Aether currents (Art. 91). By inference, therefore, we arrive at the fact that every star is a magnet, as suggested by Professor Schuster, and possesses rotation on an axis, such rotation being due to exactly the same cause as produces the rotation of any other planetary or solar body (Art. 92). Not only has each star a rotation on its axis, but it must also possess translational motion in an orbit, and that orbital motion must be due to exactly a similar cause as that which produces the orbital motion of the sun. Are there any indications given by astronomical observations which lead us to the conclusion that stars do possess such orbital motions? The answer is unanimously in the affirmative; for, although all the stars and the constellations retain apparently the same relative position to each other, yet they are all in motion. The actual translational motion of the stars is termed proper motion, and has been calculated with more or less success in relationto many of the stars nearest to us. There are other motions of the stars known as apparent motions, which are easily noted by any observer. These apparent motions are due to the rotation of the earth on its axis, and its orbital motion round the sun.
Nothing is more certain, however, than that careful astronomical observations have revealed the fact that stars have actual orbital motions of their own through space. In many cases the orbital velocity has been approximately ascertained.
Halley discovered proper motions of certain stars as far back as 1715, when he found out, by comparing different observations, that Sirius, Arcturus, and Aldebaran had moved during the period which had elapsed since the respective observations were taken.
More recent observations tend to confirm the fact that stars have indeed proper motions, due to their actual translation through space. It has been ascertained, for example, that Arcturus is travelling at least 54 miles per second.
The proper motion of the stars, however, only gives us an indication of their relative motion through so-called space. It does not tell us whether the star is apparently receding from the earth, or approaching it.
Dr. Vogel has ascertained by a special system of photography in relation to the spectra of stars, that Rigel has a velocity away from the earth of nearly 39 miles per sec., Aldebaran of 30 miles per sec., and Capella of 15 miles per sec., while the Pole star is apparently approaching the earth at a rate of nearly 16 miles per sec.
Now if all the stars move through space with varying velocities, as spectroscopic and telescopic observations seem to suggest, the question naturally confronts us as to what is the particular kind of orbit which each star completes? Is the orbit that of an ellipse, or a circle, or a parabola?
That it must have some kind of orbit is obvious from the proper motions exhibited by the several stars. We have already learned fromArts. 107and108that the sun possesses an orbit, which orbit fulfils the first and second of Kepler's Laws.
If therefore the sun, as representing all stars, is subject to Kepler's Laws, then, according to our Second Rule of Philosophy by which we base our hypotheses on our experience, we are compelled to come to the conclusion that every star which possesses any motion at all through space must also be subject to Kepler's Laws, and therefore must each possess a controlling centre around which they severally revolve. Kepler himself was of the opinion that the stars were subject to the laws which go by his name, and this view of the subject was also accepted by Sir William Herschel.
Thus from philosophical considerations we affirm that each star, while it is itself the centre of a starry system, is also dependent upon and associated with some other body, to which it is held bound by the electro-magnetic Aether, and around which it is made to revolve by the circulating electro-magnetic currents associated with that central body. So that by philosophical reasoning we are led to view the whole of the innumerable stars that flood interstellar space, not as so many individual and isolated units, that have no relation to each other, but rather as parts of one great system, which in its entirety may form in its ultimate unity one harmonious whole, a universe.
As we come to consider star clusters and nebulae, we shall see how this idea of unity seems to be manifested throughout all celestial phenomena.
Art. 119.Aether and Nebulae.--In addition to the host of stars that flood the infinite space, there are other celestial bodies that meet the gaze of the astronomer as the telescope is turned upon the heavens.
These bodies, which are glowing masses of gaseous matter, are termed Nebulae. The word Nebulae signifies a cloud, but they are not clouds in the same sense as we apply that term to masses of vapour that exist in our own atmosphere. Sir Wm. Herschel did more towards the discovery of nebulae than perhaps any other astronomer, either before his time or since. His labours in the direction were completed and enlarged by his son, Sir John Herschel, who surveyed the Southern heavens in a way that had never been accomplished before.
The result of the combined labours of the two Herschels has placed information of the nebulae at our disposal which is invaluable. Several thousands of different nebulae are now known to us, and as the telescope is improved and its powers increased, fresh nebulae are being added to the number. Like stars, nebulae vary not only in size, but also in colour, shape, and even in the materials of which they are composed. They also vary in brightness, the light from some being much fainter than the light from others.
It has been estimated by Huggins that the light received from a nebula will not exceed the light of a sperm candle looked at from a distance of a quarter of a mile. It is thought by some astronomers that the light received from a nebula is indicative of the stage of development to which it has arrived. Where the light is faint, the nebulae are in their first stages of formation, and where it is brighter it is indicative of a more advanced stage of development. Thus nebulae may consist of nebulous matter in various stages of condensation, but they are not yet in that condition which corresponds to the condition supposed to existin our sun.
Nearly all the nebulae lie outside the Milky Way, so that it would seem as if in ages past all the nebulae that had ever existed in this starry zone had passed out of their nebulous condition and been further condensed into suns or stars, as they are called. Astronomical observations teach us that there are very few nebulae indeed to be seen in this starry highway, the part of the heavens which are richest in them lying far beyond the confines of this zone. For many years certain aggregations of luminous points in the heavens were supposed to be nebulae, but by the aid of more powerful telescopes they have now been resolved into clusters of stars. One of these clusters is the cluster in Hercules, while another is the great nebula of Orion. In the case of the former, situated in the constellation of Hercules, we find a great number of very small points of light grouped together in a more or less globular form. When looked at through a small telescope, this object looks like a nebula, but looked at through Lord Rosse's, or some other great telescope, it becomes at once resolved into an immense number of separate points of light, each one representing a star, there being between one and two thousand altogether in this constellation.
Clusters of stars are usually globular in form, though some are irregular in outline. The latter are generally rich in stars, with a less condensation of stars towards the centre. Sir Wm. Herschel considered the irregular clusters as being in a less advanced stage of condensation, as he was of the opinion that all groups ultimately tended to clusters which were globular in form. Before dealing with the different kinds of true nebulae we will now consider the question as to “What are Nebulae?”
Art. 120.What are Nebulae?--The question which presents itself to the mind of all astronomers when they have viewed the wondrous nebulae that exist in far-off space is, “What are Nebulae?” This question is so closely identified with the question as to “What is Matter?” that the solution of the one will give us the key to the solution of the other. It is now generally admitted, that nebulae are composed of a glowing mass of gaseous matter, that gaseous matter being partly composed of the gas Hydrogen. Dr. Huggins in 1864 first made the discovery of the existence of Hydrogen in certain nebulae by means of the spectroscope, which distinctly revealed certain lines that proved the existence of Hydrogen in the nebulae.
In the spectra of some of the nebulae, that of 31 Andromeda, for example, there are no dark lines shown, but only a continuous band of bright light, which would seem to indicate that there was no glowing gaseous matter in that nebula at all. But accepting the fact that thenebulae are composed of glowing gaseous matter, the problem confronts us as to where this gaseous matter comes from.
If, as spectrum analysis seems to teach us, there are nebulae in various stages of formation, there must be a period in their history of development when they had an origin. What, then, is the origin of a nebula, and what the physical explanation of that origin? From optical phenomena we learn that all space is not empty, but filled with the Aether which is universal (Art. 42). What is the relation, then, of this glowing nebulous matter to this universal Aether? If it be suggested that there is no relation, then we are in the unphilosophical position of having to admit, either that the nebulous matter of which the nebulae are composed never had any origin, or that it had its origin in some unknown and still undiscovered medium which exists in space. But both of these hypotheses are unphilosophical, as the former is contrary to all experience, while the latter is opposed to that simplicity of conception by which we only postulate one medium, the Aether, to fill all space.
Thus we are led to the conclusion, that the gaseous matter, be it hydrogen or nitrogen, must have some relation to the electro-magnetic Aether that is so universal in its extent. Already this relationship has been dealt with by one who has done more for the development of aetherial physics than any other scientist. Lord Kelvin, in his paper “On the Clustering of Gravitational Matter in any part of the Universe,”[42]has solved this relationship, though in so doing he has had to depart somewhat from the idea of an incompressible Aether. In that paper he writes as follows: “If we consider Aether to be matter, we postulate that it has rigidity enough for the vibrations of light, but we have no right to say that it is absolutely incompressible. We must admit that sufficiently great pressure could condense the Aether in a given space, allowing the Aether in the surrounding space to come in towards the ideal shrinking surface.” In another part of the paper, dealing with the same question, he writes: “In regions where the density was greater than in neighbouring regions, the density would become greater still; in places of less density, the density would become less, and large regions would quickly become void or nearly void of atoms. These large void regions would extend so as to completely surround regions of greater density.” He then points out, that as soon as this density becomes something like the density of the atmosphere, then collisions would take place between the particles, and continues: “Each collision would give rise to a train of waves in the Aether. These waves wouldcarry away energy, spreading it out through the void Aether of infinite space. The loss of energy thus taken away from the atoms would reduce large condensing clusters to the conditions of a gas in equilibrium under the influence of its own gravity, rotating like our sun or moving at moderate speed as in spiral nebulae. Gravitational condensation would at first produce rise of temperature, followed later by cooling, ultimately freezing, giving solid bodies, collision between which would produce meteoric stones such as we see them.”
Here then we have a definitive relationship between Aether and nebulae given to us from one of the keenest intellects of the present time, but in order for that relationship to become strictly philosophical, the conception of the Aether as advanced in this work must be accepted. For with the present conception of a frictionless Aether, such a hypothesis is altogether untenable, because it supposes something that is contrary to all experience and observation.
On the basis of a condensing frictionless Aether into any kind of solid body, be it nebula, meteor, sun or star, we have to suppose that it is possible for a medium (the Aether, which is outside the Law of Gravitation according to the present theory) to be condensed into a body, that is, a nebula or meteor which is subject to the Law of Gravitation; and the question arises, at what point in the history of its condensation does this frictionless Aether pass out of the condition of having no weight, to the condition when it has weight; or, in other words, from the condition when it is outside the Law of Gravitation, to the condition when it comes under the Law of Gravitation?
No satisfactory solution can possibly be offered to such a problem. Therefore one of two results must follow, either that the Aether is not frictionless, but possesses weight; or, that the condensation of the Aether is not possible. With the theory of Aether presented in this work, the whole question receives a simple and philosophical solution. As Aether is matter, it is therefore atomic; and being atomic, it is subject to the Law of Gravitation; and therefore, possessing mass and weight, it can readily pass into other forms of matter, and with such a conception Lord Kelvin's hypothesis becomes not only possible but probable. So that it is exceedingly probable that nebulae are nothing more nor less than condensed Aether, the same as comets were suggested to be condensed Aether. It may be asserted that such a hypothesis lacks that experimental evidence which is so necessary for its establishment, but I hope to show in the last chapter that Faraday has given the world that very experimental evidence which will place this hypothesis upon a firm and solid foundation, and enable it to pass out of the region ofthe hypothetical into the region of fact and experiment.
According to our hypothesis, therefore, nebulae are simply condensations of the electro-magnetic Aether that exists in interstellar space, and the various spectra of the different nebulae indicate the stage of development to which the process has arrived. Where the spectra are bright, and continuous, and free from any dark lines, there we have simply the Aether in its very first stage of condensation; and where we have the dark lines appearing, such lines indicate a more advanced stage to which the process has arrived.