No. 12.

On the Origin of the Visible Universe, Available Energy, &c.

Were the galaxy formed in the manner suggested in my last letter, there would be five sources of available energy. (1) The bodies' independent motion before commencing effective attraction. (2) Their energy of rotation, and that of the bodies rotating around them, page 13 (3) The heat in the bodies themselves, (4) The potential energy, due to the volume of the bodies; in other words, due to the fact that, if they were to do more work, they would be smaller; and lastly, the molar kinetic energy developed by the mutual attraction of two bodies. This last source is of course generally much greater than any of the others. It is probable that the sum of these energies is generally less than would be sufficient to diffuse the whole materials equally throughout apace at absolute zero. It is only possible that it may be greater when the original proper motion forms a large part of the total energy. Except in this ease, the following reasoning seems satisfactory:—1st. Suppose the two large bodies to have been formed by the aggregation of particles, it is clear that the heat developed by the compression and impact must have been radiating all the time, and thus in all probability a considerable ratio of the heat has been thus disposed of. It is certainly so, if the masses have attained to any great density, and generally it does not appear reasonable, on several grounds, to suppose that the other causes can compensate for this loss.

The amount of potential energy lost by the impact of two spheres coalescing to a sphere of the volume of one, will be about equal to the potential energy lost by the formation of the two spheres themselves from diffused gas. Therefore, it is reasonable to suppose that this, with the other energies, will probably, on an average, be a large fraction, generally considerably over three-fourths of the total energy, sometimes a very large ratio. I have shewn that a case of partial impact tends to develop a lenticular mass. Although the outer parts may frequently have a position approximately at maximum potential, yet it must be remembered that considerable work must be done upon such a mass to render it spherical; in other words, there is more potential energy in a sphere of uniformly diffused matter than in a lenticular equal mass of the same diameter. Again, in the case of a mass consisting of distinct bodies, there is less potential energy than in a similar mass of diffused gas, namely, that due to the lessened potential energy of these bodies. On the other hand, if these bodies be heated, it is evident they contain more energy than if they were cool, but very exceptionally, as previously shewn, as much as diffused matter. Thus, without assuming a largo proper motion, it is evident that the impact of two large bodies in space could certainly, on the grounds of energy, develope a system such as our galaxy. It thus appears that, both kinematically and kinetically, it is possible that the milky way and the nebulous matter, at its poles, may have been formed by the impact of two bodies. It is not necessary to suppose the whole visible universe to have been formed at once in this manner; it is probable that some of the stars and systems may have been here before, and some like 1830 Groom bridge has visited since, and probably such masses as the nebuculæ may have been formed by subsequent impacts of the larger masses. I hope in future papers to discuss some considerations as to these masses and the larger nebulae, also to deal with the more systematic want of uniformity found in the milky way and in the stars of that zone; aleo the possibilities of nebular aggregation, and other matters connected with the visible universe. But I wish in this letter to point out one conclusion that forces itself upon the mind in considering this theory, namely, the relation it bears to the extent of the visible universe. If this speculation represents the truth, there must be an inconceivable number of small bodies which have been cooled by radiation, and which are travelling through space. These, in their journeys, must be constantly meeting others, and their gravitating energy being small compared to their kinetic energy, impacts would shatter them into dust. Thus the whole of space is possibly dusty from this cause, and as a sufficient thickness of the lightest fog becomes impenetrable to light, so would this dust. It is well known that Struvé never gave up the idea of extinction of light by distance, and this speculation was based on distinct numerical data in connection with the number of stars visible in the telescope. Struvé supposed the light to be extinguished by mere distance, but here is a "vera causa" which renders the conclusion probable. Thus, according to this idea, we see no distant universe.

This is also Proctor's opinion, based on what appears to be indisputable evidence; but although all distant space (all that probably more distant than a few hundred years of the motion of light; is utterly cut off from sight, it is not so from our imagination. If the galaxy proves itself, on final examination, to be undoubtedly the result of a single impact, then, on the evidence this fact supplies, our ideas of the extension of matter in space must be indefinitely increased. For what right have we to suppose our Gallactic system to be the largest in space, any more than our useful earth to be the largest of orbs. In short, in the face of these extensions of our ideas, nothing less than an infinity of space, with endless variety of systems and moving bodies, appears to satisfy the mind. I hope to shew in my next letter that all evidence seems also to point to a possible extension of the present order of things, both backwards and forwards, through an eternity of duration.