If, as spectrum a.n.a.lysis seems to teach us, there are nebulae in various stages of formation, there must be a period in their history of development when they had an origin. What, then, is the origin of a nebula, and what the physical explanation of that origin? From optical phenomena we learn that all s.p.a.ce is not empty, but filled with the Aether which is universal (Art. 42). What is the relation, then, of this glowing nebulous matter to this universal Aether? If it be suggested that there is no relation, then we are in the unphilosophical position of having to admit, either that the nebulous matter of which the nebulae are composed never had any origin, or that it had its origin in some unknown and still undiscovered medium which exists in s.p.a.ce. But both of these hypotheses are unphilosophical, as the former is contrary to all experience, while the latter is opposed to that simplicity of conception by which we only postulate one medium, the Aether, to fill all s.p.a.ce.
Thus we are led to the conclusion, that the gaseous matter, be it hydrogen or nitrogen, must have some relation to the electro-magnetic Aether that is so universal in its extent. Already this relationship has been dealt with by one who has done more for the development of aetherial physics than any other scientist. Lord Kelvin, in his paper "On the Cl.u.s.tering of Gravitational Matter in any part of the Universe,"[43] has solved this relationship, though in so doing he has had to depart somewhat from the idea of an incompressible Aether. In that paper he writes as follows: "If we consider Aether to be matter, we postulate that it has rigidity enough for the vibrations of light, but we have no right to say that it is absolutely incompressible. We must admit that sufficiently great pressure could condense the Aether in a given s.p.a.ce, allowing the Aether in the surrounding s.p.a.ce to come in towards the ideal shrinking surface." In another part of the paper, dealing with the same question, he writes: "In regions where the density was greater than in neighbouring regions, the density would become greater still; in places of less density, the density would become less, and large regions would quickly become void or nearly void of atoms.
These large void regions would extend so as to completely surround regions of greater density." He then points out, that as soon as this density becomes something like the density of the atmosphere, then collisions would take place between the particles, and continues: "Each collision would give rise to a train of waves in the Aether. These waves would carry away energy, spreading it out through the void Aether of infinite s.p.a.ce. The loss of energy thus taken away from the atoms would reduce large condensing cl.u.s.ters to the conditions of a gas in equilibrium under the influence of its own gravity, rotating like our sun or moving at moderate speed as in spiral nebulae. Gravitational condensation would at first produce rise of temperature, followed later by cooling, ultimately freezing, giving solid bodies, collision between which would produce meteoric stones such as we see them."
Here then we have a definitive relationship between Aether and nebulae given to us from one of the keenest intellects of the present time, but in order for that relationship to become strictly philosophical, the conception of the Aether as advanced in this work must be accepted. For with the present conception of a frictionless Aether, such a hypothesis is altogether untenable, because it supposes something that is contrary to all experience and observation.
On the basis of a condensing frictionless Aether into any kind of solid body, be it nebula, meteor, sun or star, we have to suppose that it is possible for a medium (the Aether, which is outside the Law of Gravitation according to the present theory) to be condensed into a body, that is, a nebula or meteor which is subject to the Law of Gravitation; and the question arises, at what point in the history of its condensation does this frictionless Aether pa.s.s out of the condition of having no weight, to the condition when it has weight; or, in other words, from the condition when it is outside the Law of Gravitation, to the condition when it comes under the Law of Gravitation?
No satisfactory solution can possibly be offered to such a problem.
Therefore one of two results must follow, either that the Aether is not frictionless, but possesses weight; or, that the condensation of the Aether is not possible. With the theory of Aether presented in this work, the whole question receives a simple and philosophical solution.
As Aether is matter, it is therefore atomic; and being atomic, it is subject to the Law of Gravitation; and therefore, possessing ma.s.s and weight, it can readily pa.s.s into other forms of matter, and with such a conception Lord Kelvin"s hypothesis becomes not only possible but probable. So that it is exceedingly probable that nebulae are nothing more nor less than condensed Aether, the same as comets were suggested to be condensed Aether. It may be a.s.serted that such a hypothesis lacks that experimental evidence which is so necessary for its establishment, but I hope to show in the last chapter that Faraday has given the world that very experimental evidence which will place this hypothesis upon a firm and solid foundation, and enable it to pa.s.s out of the region of the hypothetical into the region of fact and experiment.
According to our hypothesis, therefore, nebulae are simply condensations of the electro-magnetic Aether that exists in interstellar s.p.a.ce, and the various spectra of the different nebulae indicate the stage of development to which the process has arrived. Where the spectra are bright, and continuous, and free from any dark lines, there we have simply the Aether in its very first stage of condensation; and where we have the dark lines appearing, such lines indicate a more advanced stage to which the process has arrived.
[Footnote 43: _Philosophical Magazine_, July 1902.]
ART. 121. _Nebular Hypothesis._--The Nebular Hypothesis was first introduced by Kant in his work on the _History of the Earth and Theory of the Heavens_.
In that work he attempted to explain the origin of the universe on purely mechanical lines. Laplace, a French mathematician, about the same time came to similar conclusions as Kant had done, and published his views in his work on _Exposition du Systeme du Monde_, and later on in his more famous work the _Mecanique Celeste_.
A feature common to both these theories rested in the fact, that they supposed that all material bodies which exist in the universe once existed in a nebulous condition, and that they were formed out of this nebulous matter. Further, that this nebulous matter gradually condensed, and as it condensed, a rotational motion was imparted to them, which rotation quickened as the condensation was continued.
Then, as the rotation was accelerated, portions were flung off by the centrifugal force, and these portions of nebulous matter gradually condensed, forming the various planets of the system. As these condensed, they, in their turn, parted with some of their nebulous matter through the repulsive energy of the centrifugal force, and these secondary parts gave origin to the various satellites that exist round the planets.
Now, while the general principle involved in the nebular hypothesis is true, yet the conception according to Laplace is not verified by fact, as we learn that Ura.n.u.s and Neptune are still in a state of self-luminosity, while their density is the smallest of all the planets.
From this we should infer that the two outermost planets are the youngest planets of our solar system, but according to Laplace"s theory, they ought to be the oldest, as they would have been flung off first by the parent body as it rotated; and therefore, being flung off first, should be in a more advanced stage of development than any of the inner planets. M. Faye has suggested a remedy for this defect in the theory.
He supposes that the nebulous matter out of which the planets were formed, was not flung off by the central body the sun, but that each planet was formed at different centres of condensation within the nebular ma.s.s that existed in s.p.a.ce. This would, undoubtedly, meet the difficulty already referred to, and solves the problem as to how the various planets were formed at different distances in s.p.a.ce.
Further, such a solution is in perfect harmony with all the Rules of Philosophy. It is much more simple to conceive of Aether condensing at various points in what originally was the solar nebula, than it is to conceive of Aether condensing and shrinking towards one central point, and yet while condensing and shrinking, portions were flung off into s.p.a.ce which would form the planet. A greater objection has to be met, when we come to deal with the origin of all the meteors and minor planets that exist in their numbers in the solar system. In relation to their origin, it is much easier to conceive of portions of the Aether condensing at different centres of condensation, than to suppose that each portion of aetherial matter that originally formed the meteor, or asteroid, was flung off as a separate portion from the central body.
With the conception of an atomic and gravitating Aether, the Nebular Hypothesis, therefore, for the first time is placed upon a sound and philosophical basis, because the condensation of Aether, which is matter and possesses ma.s.s, admits of the origin of other matter from it which also possesses ma.s.s, together with other properties, as elasticity, density, compressibility and inertia.
When there is added to the atomic Aether the conception of a rotatory aetherial atom, as was indicated in Art. 44, we have at once a source from whence the rotation of the whole ma.s.s may be derived. Thus, as the condensation continued, and the nucleus or central part of the body was gradually formed, the rotation would be accelerated, because of the inherent energy which would exist in the condensed part. Further, as the condensation continued, the body so formed would be more or less spherical in form, as the conception of our aetherial atom was spherical, and when we conceive of the primary point of condensation, we have to think of a large number of spherical atoms coming together; and, as all the motions of the Aether which give rise to light, heat, electricity and magnetism, and which now include gravitation, are spherical in their operations, so their effect upon any condensing Aether would take a spherical form. Thus such bodies as nebulae, comets, asteroids, satellites, planets and suns should possess bodies more or less of a spherical form, subject to certain qualifying conditions, as rotation and orbital velocity, and this is in harmony with observation and experience. For we shall find that even in the case of nebulae, we have globular, ring or annular nebulae, and elliptic nebulae, while in the case of comets, the nuclei and coma are more or less spherical.
Further, it is a familiar fact that the shape of all asteroids, satellites, planets, and even the sun is spherical or that of an oblate spheroid, which latter is simply due to its rotational velocity on its axis.
Thus the principle involved in the nebular hypothesis receives its confirmation in the atomic and gravitating Aether, and with certain modifications of the different hypotheses advanced, is capable of uniting all those hypotheses that have ever been put forth in this direction into one perfect and harmonious whole.
Again, the condensation of the Aether, composed as it is of its atoms, ever in a state of rotation, does away with the Primitive impulse which was objected to in Art. 9. For in that article it was shown that the conception of a primitive impulse as conceived by Newton was unphilosophical, in that its conception was not simple, and failed to satisfactorily account for observed phenomena. With the hypothesis, however, of a rotatory aetherial atom, we have at once those conditions which at any time, in the history of the universe, may give rise to those conditions by which a body may be set rotating not only on its axis, but also revolving around some central body, as the process of condensation is continued.
So that in the primordial and universal electro-magnetic Aether that exists in all s.p.a.ce, we get those conditions which will not only give rise to the phenomena of light, heat, magnetism and electricity, but also those properties, qualities and motions by which are produced, maintained and perpetuated, the various bodies that exist in the Aether, which is at once the physical source and cause of the bodies.
ART. 122. _Kinds of Nebulae._--Nebulae may be cla.s.sified into the following groups--
1. Irregular Nebulae.
2. Ring and Elliptical Nebulae.
3. Spiral or Whirlpool Nebulae.
4. Planetary Nebulae.
_Irregular Nebulae._--Of this cla.s.s the most conspicuous are those in the constellations of Orion and Andromeda. So clearly defined are they, that they are oftentimes seen by the naked eye on a clear night, and are often mistaken for comets.
The great nebula in Orion is one of the most noticeable objects in the heavens. It is noted for its size and brilliancy, and also for the successful observation which it has been subjected to from time to time.
This large nebula is situated in that part of Orion which is occupied by several stars known as the Sword Handle. These multiple stars are known by the name of Theta. Around these multiple stars is to be seen the nebula, as though the multiple stars really were enveloped by the nebula extending for a great distance out into s.p.a.ce. It is of a faint bluish colour, with the central parts possessing the greatest brilliancy. The suggestion arises in our mind as to whether the nebulae are in any ways indicative of the presence of the electro-magnetic aetherial field that each star undoubtedly possesses. We learned in Art. 88 that the sun is an electro-magnet, and that it possesses its electro-magnetic field. We have also seen in Art. 109 that the zodiacal light, which is to be observed in connection with our solar system, is really indicative of the presence of that electro-magnetic field, as it rotates round the central body. Now, if an observer were situated out in s.p.a.ce, where the nebula of Orion is situated, and could look at our system with telescopes equally as powerful as those we possess, would not our sun present an equally nebulous light to them because of the presence of its electro-magnetic field?
Conversely, if every star possesses an electro-magnetic aetherial field, as they undoubtedly do, then it seems only reasonable to infer that that electro-magnetic field possesses a nebulosity which corresponds with our zodiacal light. The fact that the spectra of the nebulae are continuous, revealing no dark lines, seems to indicate the purity of some of the nebulae, and that therefore they are free from all known elements.
So that spectroscopic results seem to confirm this hypothesis, as the pure Aether that would surround every star, or multiples of stars, would certainly not reveal any dark lines by means of the spectroscope. Such a hypothesis, as to the real nature of a nebula, is entirely in harmony with the theory of the Aether presented in Chapter IV., because being gravitative it will surround each star or multiples of stars, and therefore be denser nearest to those stars, and being atomic, there will be a certain amount of nebulosity manifested by the denser parts of the medium, as is the case in our own solar system.
_Ring or Elliptical Nebulae._--These forms of nebulae are so named from their ring-shaped appearance, sometimes being known as Annular Nebulae.
The elliptical nebulae are usually cla.s.sed with them, as they are supposed to be similar kinds of nebulae looked at edgeways. The best known of this cla.s.s is that found in the constellation of Lyra, and known as 57M, which is the number of the star in Messier"s catalogue of stars. It is small but well-defined, so that it looks more like a flat oval solid ring than a nebula.
The central part is not entirely dark, but is filled up with a hazy light. Another annular nebula is that situated to the south-west of Lambda Scorpii. Sir J. Herschel[44] writes of it thus: "It is a delicate but well-defined annulus. The field is crowded with stars, two of which are nebulae. A beautiful delicate ring of a faint ghost-like appearance, about 40" in diameter, in a field of about 150 stars, of 11 and 12 magnitude and under."
Of the elliptical nebulae the best known is the one in the constellation of Andromeda, which goes by the name of 31M. It is visible on a clear night, and can be seen by the naked eye as a hazy light. There are several other elliptical nebulae, lying to the north-west of this great nebula.
_Planetary Nebulae._--The planetary nebulae represent a number of minute objects visible in the heavens. They look like globes of a bluish-coloured gas and are sometimes mistaken for small stars. Sir J.
Herschel writes about them as follows: "Planetary nebulae are very extraordinary objects. They have, as their name implies, a resemblance to planets, presenting discs, round or slightly oval, some being quite sharply defined, terminating in others a little hazy or softened at the border. They are comparatively rare objects, not more than 25 having been observed, and of these nearly three-quarters are in the southern hemisphere. Their disc is circular or slightly elliptic, with sharp, clear, and well-defined outline, having exactly the appearance of a planet with the exception only of its colour, which is full blue, varying somewhat upon green. M. Arago has surmised that they may possibly be envelopes shining by reflected light from a solar body placed in their centre, invisible to us because of its excessive distance."
The suggestion which arises to our mind in view of the atomic and gravitating Aether is, that the planetary nebulae are exactly what their names imply, that is, nebulous matter around planets. We have already learned that each satellite and planet possesses an electro-magnetic field, which field takes more or less the shape of a spherical form, so that if there are planets existing in the far-off systems in s.p.a.ce, as we are compelled to believe that there are, then they too would possess an electro-magnetic field, which would be composed of spherical envelopes surrounding the several planets. These planets would shine by reflected light, as suggested by M. Arago.
The possession by the planet of the nebulous matter, which we have already suggested is composed of the denser parts of the Aether around the planet, would give to the planet a nebulous appearance which would satisfactorily account for the term already given. They would indeed be what Sir John Herschel suggested they were, viz, planetary nebulae.
_Spiral Nebulae._--The Spiral, or Whirlpool Nebulae, are remarkable objects, and were first discovered by Lord Rosse with his six-foot telescope. One of the best examples of the spiral nebulae is that known as 51M. Small telescopes show this as two cl.u.s.ters, one of them being surrounded by a ring, at a distance, which is divided into two parts.
Lord Rosse, however, found it to be really a spiral nebula, the ring running into a series of spiral coils of nebulous matter, the outlying parts being connected with the main part by curved bands.
Huggins has found that the spectrum of this nebula is not gaseous. Other examples of this cla.s.s are 99M and 33M. What these spiral or whirlpool nebulae are, is unknown, but, on the hypothesis of a condensing and gravitating Aether which is in a state of rotation, the spiral nebulae can be easily pictured. For, as the condensation goes on, rotation will set in, and if we can picture such a phenomenon taking place in a plane which is at right angles to the line of vision, then we should have a full view of a nebula which would present a spiral form. Indeed, there is no phenomenon in connection with nebulae that cannot be physically explained by a condensing, gravitating and rotatory Aether; and as Aether is universal, the same properties will apply to it in distant s.p.a.ce as they do in the solar system; and apart from a gravitating and rotatory electro-magnetic Aether, the phenomena of our own solar system cannot be physically conceived or explained.
Therefore, if such an Aether can explain the phenomena a.s.sociated with our own system, it ought also to explain, and that to the fullest extent, all phenomena incidental to and a.s.sociated with the innumerable systems that flood the universe at large.
[Footnote 44: _Outlines of Astronomy._]
CHAPTER XIV
UNITY OF UNIVERSE
ART. 123. _The Universe._--In the preceding chapters we have endeavoured to deal with some of the princ.i.p.al phenomena that help to give a mechanical conception to the entire Universe.
It now remains for us to show, in this last chapter, how, underlying all the physical structure of the Universe, there is one fundamental and primordial medium, in which all the forms of matter and motion find their ultimate unity.
The Universe literally means one ultimate whole, though that whole may be compounded of many parts, the very essence of the term embodying the idea of a complete unity which runs throughout its whole physical structure.
Apart from some such hypothesis as will be suggested in this chapter, that ultimate unity is incapable of a physical or mechanical conception.
In Art. 29 we learned that the Universe was composed of two cla.s.ses of things, matter and motion, while in Art. 30 we learned that the sum total of matter according to the law of the conservation of matter ever remains the same; while further, in Art. 53, according to the law of the conservation of energy, the sum total of energy ever remains the same.
We have also learned that the two are indissolubly united, so that wherever we found matter, whether that matter was in its atomic, molecular, planetary or stellar form, there, as its necessary complement and counterpart, was the ever-present and unceasing motion, in one or other of its many forms. Thus, throughout the entire Universe, we find the same two essentials ever working in unison and harmony.