[Footnote 41: _Outlines of Astronomy._]
[Footnote 42: _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 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 pa.s.sed 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 s.p.a.ce. 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 a.s.sumption 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 s.p.a.ce. We have, therefore, to picture the condensed ma.s.s of Aether situated out in the cold interstellar s.p.a.ce, gradually coming under the influence of the sun, as that body rushes on its journey through s.p.a.ce with a velocity of 500,000 miles per hour.
Slowly, but surely, the ma.s.s of condensed Aether begins to respond to the attractive power of the sun, and to move through s.p.a.ce 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 pa.s.sing 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 s.p.a.ce, and, in consequence, heat is generated.
In addition to the generated heat, the comet is all the while pa.s.sing 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 pa.s.sed 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 pa.s.sing 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 pa.s.sed their perihelion pa.s.sage.
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 pa.s.sed 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 a.s.sociated 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 pa.s.sed 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 pa.s.ses 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 pa.s.sing 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 s.p.a.ce. 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 pa.s.s 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 a.s.sociated with our solar system, from the simple yet truly philosophical a.s.sumption that Aether is matter, in conjunction with all that that a.s.sumption logically involves.
CHAPTER XIII
AETHER AND STARS AND NEBULAE
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 s.p.a.ce? For it must be remembered that every star is a sun, which, reasoning by a.n.a.logy, 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 cla.s.sified the millions of stars that exist in infinite s.p.a.ce, 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. As the 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 cl.u.s.tered together. These cl.u.s.ters 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--
Ursa Major The Great Bear.
Ursa Minor The Little Bear.
Draco The Dragon.
Hercules Hercules.
Cygnus The Swan.
Lyra The Lyre.
The visible Southern constellations are 18 in number, and include such groups as--
Cetus The Whale.
Orion Orion.
Canis Major The Great Dog.
Canis Minor The Little Dog.
Corona Australis The Southern Crown.
Crux Australis The Southern Cross.
_Variable Stars._--Not only are the stars of different magnitudes, but the brilliancy of some of them changes from time to time. This cla.s.s 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 varies from 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.