I will refer the reader to an extract taken out of Outlines of Astronomy, by Herschel (Art. 894), so that we may see what his conception of the zodiacal light was, and we will see how far his explanation is in conformity with our hypothesis of an atomic, gravitating and rotatory Aether medium.
He writes: "We shall conclude this chapter by the mention of two phenomena, which to me indicate the existence of some slight degree of nebulosity about the sun itself, and even to place it in the list of nebulous stars. The first is that called the Zodiacal Light, which may be seen any very clear evening soon after sunset, about the months of March, April and May, as a cone or lenticularly-shaped light extending from the horizon obliquely upwards, and following generally the course of the ecliptic, or rather that of the sun's equator. The apparent angular distance of its vertex from the sun varies, according to circumstances, from 40 deg. to 90 deg., and the breadth of its base perpendicular to its axis from 8 deg. to 30 deg. It is extremely faint and ill-defined, at least in this climate, though better seen in tropical regions, but cannot be mistaken for any atmospheric meteor or aurora borealis. It is manifestly in the nature of a lenticularly-formed envelope surrounding the sun, and extending beyond the orbits of Mercury and Venus, and nearly, perhaps quite, attaining that of the earth, since its vertex has been seen fully 90 deg. from the sun's place in a great circle. It may be conjectured to be no other than the denser part of that medium which we have some reason to believe resists the motions of comets; loaded perhaps with the actual materials of the tails of millions of those bodies of which they have been stripped in their successive perihelion passage. If its particles have inertia, they must necessarily stand with respect to the sun in the relation of separate and independent minute planets, each having its own orbit, plane of motion, and periodic time."
Let me call the reader's special attention to one or two statements of Herschel's given in this extract, in order to see how these statements harmonize with the view of the Aether submitted in this work. In the first place he states its shape is that of a lenticularly-formed envelope surrounding the sun, and extending beyond the orbits of Mercury and Venus, and probably to our earth. This harmonizes with the shape of the aetherial envelope as given in Art. 70. Then Herschel states it may be the denser part of that medium which we have reason to believe resists the motions of comets. That is exactly what it is, though Herschel failed to show why it should be the denser part of the Aether, as we have seen is the case, on account of its being gravitative. I will also prove later on, that Herschel was right with regard to the resistance of the motion of comets through it. Then he refers to its particles probably possessing inertia, as though he had anticipated the atomicity of the Aether, and assuming that atomicity, he was compelled to postulate inertia also as we have done in Art. 48.
Lastly, he points out that each separate particle must have its own plane of motion, its own orbit, and its periodic time. Now this view fully coincides with that laid down in this article, where we have learned that the rotating Aether has its own plane of motion, that plane being the Plane of the Ecliptic, and as every particle or atom has its allotted place in the rotating Aether, then, as Herschel points out, the particle must have its own orbit, and plane of motion, and also its own periodic time. If, therefore, we had desired fuller confirmation of this atomic gravitating Aether, we could not have wished for more conclusive proof than that given by one of the greatest philosophical astronomers of the last century. We shall see later that Herschel also had a clearer view of cometary phenomena, and of the forces which played a part in those phenomena, than any of his contemporaries, when we deal with the origin and motions of all comets. Thus from Herschel we learn that the zodiacal light is caused by the atomic, gravitating, and rotatory Aether as that aetherial medium revolves round the sun, while at the same time every atom of the medium is itself in a state of rotation on its axis, as it performs its journey in its own orbit and in its own plane of motion.
ART. 110. Centripetal Force.—We have now to consider what is the physical cause of that part of the compound Law of Gravitation known as the Centripetal Force. As we have already learned (Art. 10), this force is really none other than the Attractive Force of Gravitation, in that its mode of operation always acts towards the centre of the attracting body, and hence was called by Newton the Centripetal Force.
The centripetal force is, however, the exact counterpart and complement of the centrifugal force, in the same way that the latter is the exact counterpart of the former, as we have already learned that the centrifugal force operates along the same path, and that it is subject to the same law of proportion, being equal to the product of the masses of a body (Art. 85), and further, that its intensity is inversely as the square of the distance (Arts. 66, 74 and 84).
We have, however, discovered that the physical cause of the centrifugal force is due to the pressure of the electro-magnetic Aether (Art. 96). If, therefore, the physical cause of that law which is the complement and counterpart of Gravitation Attraction is to be found, and alone found, in the pressure and motions of the electro-magnetic Aether, then it is only logical and reasonable to infer that the physical cause of the Attraction of Gravitation is to be found in the same electro-magnetic Aether. That the Attraction of Gravitation is to be found in this medium is now an accepted hypothesis among scientists. Because, unless the physical cause of Gravitation Attraction is to be found in this electro-magnetic Aether, then, in order to account for that attraction, we should have to postulate the existence of another medium in space, in lieu of the Aether, which would be to the centripetal force what the Aether is to the centrifugal force. This would be distinctly unphilosophical, as it would be a violation of the first two rules of our philosophy, in that it would not be simple in its conception, and that such a hypothesis would imply the existence of two media which would occupy the same planetary and interstellar space at one and the same time, and this is a violation of all experience in its widest form.
Therefore the physical cause of Gravitation must be sought for in the same medium which gives the physical cause of the companion force, and that medium is the electro-magnetic Aether. Professor Preston in his Theory of Light is of this opinion. In Art. 327 he writes: "To account for the propagation of heat and light, that is, of radiant energy, we have postulated the existence of a medium filling all space. But the transference of the energy of radiant heat and light is not the only evidence we have in favour of the existence of an Aether. Electric, magnetic and electro-magnetic phenomena and Gravitation itself point in the same direction."
Professor Lodge, in his Modern Views of Electricity, is even more explicit in his statement of the case. On page 338 he states: "Gravitation is explainable by differences of pressure in the medium (i. e. the Aether) caused by some action between it and matter not yet understood." Further, Newton himself suggested that the physical cause of Gravitation Attraction was to be found in that aetherial medium which pervaded all space.
If, therefore, we attempt to explain the physical cause of Gravitation Attraction by the tensions of the universal Aether, we shall not only be dealing with the subject from a philosophical standpoint, but we shall solve the problem in that direction in which Professors Preston and Lodge and other scientists have suggested we are to seek for the solution. Professor Curry, in his Theory of Electricity and Magnetism, page 406, states: "If we regard the luminiferous Aether, as defined by Von Helmholtz's equations, as the given medium or transmitter of so-called gravitating action, we are then able on the one hand to interpret its longitudinal oscillations as gravitational waves propagated through space with the given enormous velocity, and on the other hand, to form some conception of the mysterious force of Gravitation itself, for we can then conceive it as a medium stress arising from a certain type of Aether oscillations, its longitudinal ones, that pervade entire space."
Now in order for us to lead up to the physical cause of the centripetal force, we must recall some of the facts already given with regard to planetary and solar space. Thus we have learned that the sun is an electro-magnet possessing its own magnetic field, with its lines of force (Art. 88). We have also learned that all the planets are electro-magnets, each possessing its own field with its lines of force (Art. 91).
We have further seen that the cause of all this electro-magnetism is due to the fact that electric currents are continually circulating round each body, and by their conjoint action with the magnets there are produced the electro-magnetic fields that are associated with each body in the solar system. From this hypothesis we arrived at the conclusion, that wherever there was Aether, there we found electricity, because of the electro-magnetic basis which Aether possesses. This result is fully confirmed by Maxwell's electro-magnetic theory of light (Art. 78), which has been so fully experimentally demonstrated by Hertz. Indeed, in the minds of several scientists there is a growing conviction that Aether and Electricity are possibly one and the same substance.
Professor Lodge, in the work already referred to, in relation to this hypothesis, writes in the preface to that book: "Crudely, one may say that as heat is a form of energy, so electricity is a form of Aether, or a mode of aetherial manifestation." And again: "A rough and crude statement adapted for popular use is that Electricity and Aether are identical. But that is not all that has to be said, for there are two opposite kinds of electricities, and there are not two Aethers. But there may be two aspects of one Aether, just as there are two sides to a sheet of paper."
As, therefore, we learn that Aether has an electro-magnetic basis, and that electricity is a mode of aetherial manifestation, we have therefore to consider one of the most fundamental laws of electricity, and note its application to solar and planetary space.
It is one of the fundamental laws of electricity, that equal and opposite quantities of electricity are always generated at one and the same time. Faraday's well-known ice-pail experiment proved this. It is an absolute impossibility for one kind of electricity to be generated without an equal quantity of the opposite kind being produced, although it is not strictly correct to use the term generated or produced in relation to electricity, as electricity cannot really be produced by any process whatever.
Another way of stating this law is, that the total induced charge on any body is always equal and opposite to the inducing charge. So that if we look upon the sun as an electrified body (Art. 80) surrounded by the aetherial envelopes or shells, then we can conceive of the inductive action of the sun upon any planet as taking place along the tubes of force in the Aether, which tubes are sections of the spherical envelopes that surround it. But this inductive action implies the existence of the very law already enunciated, viz. that equal and opposite quantities are always generated at one and the same time, and before that law can become operative in relation to the Aether, it must be postulated that the Aether possesses a dual character, that is, it possesses a positive and negative electrical basis.
This view of the Aether has already been developed by Dr. Larmor in his Electron Basis of the Aether, as in that hypothesis he postulates both positive and negative electrons. In his Aether and Matter he writes, page 3: "It assumes that the mass of each sub-atom is proportional to the absolute number of electrons, positive and negative, that it carries, and that the effective interatomic forces are entirely or mainly electric." Further, Professor Lodge on this point writes: "We now proceed a step further and analyze the Aether into two constituents, two equal opposite constituents, each endowed with inertia and each connected to the Aether by elastic ties. The two constituents are called positive and negative electricity respectively, and of these two electricities we imagine the Aether to be composed." Again, later on, p. 349 of the same work, he adds: "Is Aether electricity then? I do not say so, but that they are connected there can be no doubt. What I have to suggest is, that positive, and negative electricity together may make up the Aether."
Now, accepting this as correct, and I will prove that it is correct later on, from experiments performed by Faraday, we can see how the inductive action of the sun may be transmitted through space, and how that inductive action will effect any body in its electrical field, such inductive action always taking place through the polarization of the atomic Aether, and taking the form of an attractive power which is exerted towards the centre of the attracting body.
Further, this inductive action will be subject to the same laws of electricity as the centrifugal force is, which is the repulsive power due to the pressure of the Aether. Therefore the inductive action of the sun upon any body will, according to the laws of electricity, act inversely as the square of the distance (Art. 84), and will be directly as the product of the charges on the two attracting bodies, which we have seen according to Art. 85 is equal to the product of their masses. Not only will this inductive action apply to the sun, but it will equally apply to all planets, satellites and stars that exist in the heavens, each of these bodies according to Art. 80 being an electrified body possessing its electric field and lines of force radiating out into space.
Thus we arrive at the conclusion, that each body in the solar system is not only the centre of a centrifugal force due to the pressure of the electro-magnetic Aether, but that it is also the centre of an attractive force due to the existence of the positive and negative elements of the Aether, and of their attractive power for each other.
This attractive power is also subject to exactly the same laws that the centrifugal force is subject to in regard to intensity, proportion, and the direction which it takes. So that we have now two centripetal forces existing in space, which exactly correspond with each other, viz. Gravitation Attraction and the attraction due to Electrical Induction. The cause of one, however, is known, being due to the inductive influence of the various electrified bodies that exist in space, which inductive influence can be traced through the whole of the atomic Aether that exists between the two bodies, whereas the cause of the centripetal force or Gravitation Attraction is unknown. According to the Rules of Philosophy, therefore, it will be much simpler if we replace our Gravitation Attraction, whose cause is unknown, by the inductive power of the various bodies, the physical cause of which lies in the electro-magnetic Aether, or the dielectric as Faraday called it. In other words, we are compelled to come to the conclusion that the centripetal force, or Gravitation Attraction so called, is an electrical phenomenon, which finds its physical cause in the same universal Aether that the centrifugal force does.
Unless this view of the attraction of Gravitation is accepted, we should have two forces operating between all bodies, both operating at exactly the same time, in exactly the same direction, and with exactly the same intensity, and this phenomenon according to Newton would be unphilosophical. In Art. 4 we learn that Newton in the first rule states that "Nature is simple, and does not abound in superfluous causes of things." And again: "In the nature of Philosophy nothing is done in vain; and by means of many things, it is done in vain when it can be done by fewer." Here then we have apparently two forces which act in the same molecular or planetary or interstellar space, at one and the same time. Therefore if this be true, Nature does abound in a superfluous cause, because we have two forces in existence where one will suffice, and one of them therefore exists in vain. So that it will be philosophical if we do away with one of the causes, and replace the two causes by only one. Now which shall be done away with—the electrical attraction which is due to a physical medium, the electro-magnetic Aether, or the Gravitation Attraction, that is caused by some virtue of a body of which we have no knowledge, which is transmitted through space in a way that we cannot understand, and acts upon distant bodies in a manner altogether outside our usual experience and observation? There can only be one answer. If either of the two forces has to be done away with, it must be the mysterious, intangible, unphilosophical attraction of Gravitation, which must be replaced by the philosophical and known attraction of electricity, which can be traced to a physical medium, the electro-magnetic Aether that joins atom to atom, molecule to molecule, satellite to planet, planet to sun, and sun to star, and so gives unity to the universe of worlds. From philosophical considerations, therefore, we are compelled to come to the conclusion that the attraction of gravity and electrical attraction are one and the same.
Faraday arrived at this conclusion and performed certain experiments to confirm that conclusion, but he was unable to experimentally prove the truth. It does not follow, however, that because he failed to experimentally establish the connection, therefore the conclusion is wrong. In his Experimental Researches he writes, par. 2705, "On the possible relation of gravity to electricity":—"First of all, a body which was to be allowed to fall, was surrounded by a helix, and then its effect in falling sought for." This experiment Faraday states produced negative results (par. 2706). "A solid cylinder of copper was introduced into the helix, and carefully fastened to it, and this compound arrangement was allowed to fall." "The result of this experiment may be classified as doubtful. It gave very minute, but remarkable indications of a current in the galvanometer, and the probability of these being related to gravity appeared the greater, when it was found, in raising the helix or core, similar indications of contrary currents appeared." In par. 2717 Faraday thus sums up: "Here end my trials for the present. The results are negative. They do not shake my strong feeling of the existence of a relation between gravity and electricity, though they give no proof that such a relation exists." Here then we have expressed the strong conviction of the relation that undoubtedly exists between gravity and electricity by one of the greatest scientists that has ever lived, and I believe that it is a fact that he was engaged upon experiments to prove his conviction about the time of his death.
We will now endeavour to trace the action of the Law of Gravitation in its compound working, in its application to the atomic Aether that fills all space, and by its gravitating property surrounds all bodies situated in that space. We are dealing no longer with a frictionless medium, which is incapable of accepting and transmitting motion of any kind or sort, but we are now dealing with a medium composed of atoms, which can give rise to pressures and tensions, or repulsions and attractions from any one part of space to another.
If we can prove that an atomic Aether can give rise to these pressures and tensions from one body to another, and those pressures and tensions harmonize with, and satisfactorily account for, the phenomena sought to be explained, then we shall have succeeded in making our philosophy agree with our experience, and such a result as action at a distance will for ever disappear from the mental conception of all men, as it has long disappeared from the pages of philosophical and scientific works, though that disappearance was not accompanied with a satisfactory solution of the problem.
Let us, therefore, consider these pressures and tensions, or so-called repulsions and attractions that exist in this electro-magnetic Aether from the atomic standpoint, and by so doing try to realize how it is that one body, as the sun, acts upon another body, as the earth, through the intervening medium, the Aether. We can either consider it from the material standpoint, that is, by considering the Aether as matter, pure and simple, or by viewing it from the electrical standpoint, which may be considered from Clerk Maxwell's physical conception of an electric field. We will briefly consider it from the latter standpoint. Our conception of an aetherial atom was that of a spherical vortex atom possessing polarity and rotation on an axis. We must, however, make the distinction between the two kinds of aetherial atoms that Clerk Maxwell first indicated in his paper on Physical Lines of Force, Phil. Mag., 1861, and that Dr. Larmor has worked out in his Aether and Matter from the electron standpoint, viz. that the Aether is composed of positive and negative electrons. Or we can accept Professor Lodge's theory, that Aether is made up of positive and negative electricity. We are compelled to accept the hypothesis of two kinds of aetherial or electrical atoms, whatever they may be called, in view of the teaching of electricity, that positive and negative electricity are always to be found in association, and in combination, wherever electricity exists. We have proved that electricity is to be found throughout the realm of space (Art. 78); therefore in all planetary and stellar regions electricity is present. Thus it exists in the so-called space between the sun and planets, and between the planets and satellites, forming around them all spherical shells, that become less and less dense as they recede from the central body. Now it is by the action of these positive and negative electrical atoms, that the attraction of one body is transmitted across space from the sun to the earth, or from the earth to the sun, or from the earth to Jupiter, or from Jupiter to any of the planets, the action always taking place along the line joining the centres of gravity of the bodies, i. e. the radius vector, and with a force equal to the quantities of electricity in association with those bodies (Art. 85), and with an intensity that always acts inversely as the square of the distance. Thus the inductive action of any sun, planet or satellite, or any other planet or satellite, can be mentally traced from atom to atom, across the intervening space, that is filled with the atomic Aether, between any two attracting bodies. So that, if the sun attracts the earth, it attracts it by and through the motions and properties of the electro-magnetic Aether that is made up of positive and negative electricity, and that attraction, being produced by a physical medium which is as real and tangible as air or water, is brought into harmony with our experience and observation, as no body pushes or pulls another body, be it what it may, unless both bodies are joined together by some medium which transmits the push or the pull. Professor Lodge, in his Modern Views of Electricity, has illustrated from an electrical standpoint how the pressure and tension in any electrical field may be transmitted from particle to particle, or atom to atom. He supposes that a positive atom of electricity rotates in one direction while a negative atom rotates in the opposite direction. In any electric field these atoms are so associated with each other, that when one atom revolves, it makes the other to revolve in the opposite direction, with the result, that the spin or rotation is transmitted through the medium at a speed dependent upon the density of the medium.
For fuller details of the description I must refer the reader to the work already referred to. What I wish to call the reader's attention to is, that the tension and pressure in this field is not transmitted across a vacuum, in some unknown way, but is transmitted solely by a physical medium. The action is direct, and is produced, and alone produced, continued, and perpetuated by a physical medium which is composed of atoms of negative and positive electricity. So that if one body A acts upon another body B, it acts upon B solely and entirely by the action of the atoms which form the magnetic lines of force, and the equipotential surfaces around the electrified body, and that action can be traced mentally step by step across the intervening space that may exist between the two bodies. It is in an exactly similar manner, that the Attraction of Gravitation, which we conceive to be the same as electrical attraction, is transmitted from body to body in the atomic, molecular, planetary or stellar world. In each and every case, the pressure and tensions, which are inseparably connected, are transmitted by the atoms of the electro-magnetic Aether, that is, by the positive and negative atoms of electricity of which, according to Professor Lodge and Dr. Larmor, the Aether is composed. So that, if the sun acts on the earth, by the centrifugal force, it acts on it solely through and by the pressures which are originated in the atomic Aether by the central body. If the sun attracts the earth, by the centripetal force, that action can also be traced to the tensions that are originated among the atoms of the electro-magnetic Aether. There is nothing mysterious about the phenomenon in either case, as by accepting this view of an atomic Aether with its dual character of positive and negative electricity, the action may be traced mentally from point to point across the so-called intervening space that exists between any two bodies. In each and every case, wherever the centripetal or centrifugal force acts, the action is direct, because it is caused by a physical medium, which physical medium is in direct contact with each body acted upon, and also fills the space between those bodies. With this view of the centripetal force of Gravitation, our Philosophy is made to agree definitely with our experience, which teaches us beyond contradiction, that no body moves, unless it is either pushed or pulled by a physical medium. Unless this view of the centripetal force is accepted, we shall have to stumble on in darkness as to the physical cause of the centripetal force, and mentally accept the unphilosophical proposition, that a body can act on another in a way that we cannot understand, and by means which lie outside our experience and observation, and this hypothesis, as Newton and Herschel pointed out, is distinctly an unphilosophical proposition.
[Footnote 40: Modern Views of Electricity, p. 221.]
AETHER AND COMETS
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.:—
COMETS. PERIOD OF PERIHELION APHELION REVOLUTION. DISTANCE. DISTANCE.
Encke's ... 3-1/4 years. 32,000,000 miles. 387,000,000 miles. De Vico's ... 5-1/2 " 110,000,000 " 475,000,000 " Biela's ... 6-1/2 " 82,000,000 " 585,000,000 " D'Arrest's ... 6-1/2 " Faye's ... 7-1/2 " 192,000,000 " 603,000,000 " Halley's ... 76-3/4 " 56,000,000 " 3,200,000,000 "
Encke's Comet was discovered by Professor Encke of Berlin, and named after him. It revolves in an ellipse of great eccentricity, as proved by the fact that when nearest to the sun, it is inside Mercury's 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, 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, 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.
[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 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.
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 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. 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 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—
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 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 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.
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 previous chapter 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 his Treatise of Astronomy, Art. 592, he writes: "Now for what purpose are we to suppose such magnificent bodies scattered through the abyss of space? 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 the Phil. 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 relation to 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 from Arts. 107 and 108 that 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 exist in 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 the nebulae are composed of glowing gaseous matter, the problem confronts us as to where this gaseous matter comes from.