mum of some affection of the fluid in which they are immersed. Regard it as we please, there can be no doubt that the properties of the ether are of a much higher order in the arcana of nature than those of tangible matter. And as even the high-priests of science still find the latter far beyond their comprehension, except in numerous but minute and often isolated particulars, it would not become us to speculate further. It is sufficient for our purpose to know from what the ether certainly does that it is capable of vastly more than any one has yet ventured to guess.

149. If we review the attempts recorded in this chapter we see how the scientific mind is led from the visible and tangible to the invisible and intangible.

In the first place, we know that one body, such as the sun, can part with its radiant energy to another body, such as the earth, and observation and experiment alike lead us to acknowledge a stage in which the energy has left the one body and has not yet arrived at the other. But this means that there is something between these two bodies capable of moving and transmitting energy, and therefore, from the very conception of energy, possessing mass--this something we agree to call the ethereal medium.

Again, we know that different masses of visible matter attract one another apparently at a distance. Our first attempt is to analyse the nature of this force. Does it proceed from the surfaces of the attracting bodies, or does it penetrate their entire mass? This question was answered by Newton, who came to the conclusion that every particle of matter attracts every other particle with a force proportional to the product of their masses, and inversely proportional to the square of their distances.

But this only drives the mystery of gravitation from the

mass to the particle, and here the same set of questions again occur. A particle as truly as a mass occupies space, and we wish to know if the force proceeds from the surface of the particle or from its interior.

150. Then again we likewise wish to know how this force is communicated between one particle and another? Now before we can solve these questions we must have some definite conception of the nature of a particle and of the constitution of the surrounding medium. Sir W. Thomson, as we have seen, has attempted to advance towards the nature of an atom or particle in his supposition that atoms are vortex-rings generated out of a perfect fluid filling all space. While, however, this conception accounts for some of the properties of an atom it does not easily account for gravitation, and hence he adopts in addition the hypothesis of ultra-mundane corpuscles, which he supposes to be only a finer form of vortices.

151. There is, however, one objection to the precise form of vortex-ring hypothesis introduced by Thomson which from our point of view is very strong. The act by which the atom was produced must necessarily by this hypothesis have been an act of creation (Art. 133) in time, that is to say, an act impressed upon the universe from without, and it must therefore have denoted a breach of continuity (Art. 85); for if the invisible universe be nothing but a perfect fluid, can we imagine it capable of originating such a development in virtue of its own inherent properties, and without some external act implying a breach of continuity?—we think not. In the production of the atom from a perfect fluid we are driven at once to the uncondi tioned to the Great First Cause; it is, in fine, an act of creation and not of development. But from our point

of view (Art. 86) creation belongs to eternity and development to time, and we are therefore induced to modify the hypothesis so as to make it consistent with this view. We cannot, in fact, if we agree to hold at the same time the principle of unbroken continuity and the vortex-ring theory of formation of the visible universe, regard the invisible universe as an absolutely perfect fluid.

152. This way of regarding the invisible universe is strengthened by the fact that the hypothesis which seems most likely to account for gravitation presumes the existence of ultra-mundane corpuscles, and the observations of Struve upon the extinction of star-light tend (whatever they are worth) towards the same conclusion, since the absorption of light is more compatible with a corpuscular constitution than with that of a perfect fluid. But if the visible universe be developed from an invisible which is not a perfect fluid, then the argument deduced by Sir W. Thomson in favour of the eternity of ordinary matter disappears, since this eternity depends upon the perfect fluidity of the invisible. In fine, if we suppose the material universe to be composed of a series of vortex-rings developed from an invisible universe which is not a perfect fluid, it will be ephemeral, just as the smoke-ring which we develop from air, or that which we develop from water, is ephemeral, the only difference being in duration, these lasting only for a few seconds, and the others it may be for billions of years.

153. Thus, in our last chapter, we came to the conclusion that the available energy of the visible universe will ultimately be appropriated by the invisible, and we may now perhaps imagine, at least as a possibility, that the separate existence of the visible universe will share the same fate,

so that we shall have no huge useless inert mass existing in after ages to remind the passer-by of a form of energy and a species of matter that is long since out of date and functionally effete. Why should not the universe bury its dead out of sight?

of

"So careful of the type'? but no,

From scarped cliff and quarried stone
She cries, A thousand types are gone :
I care for nothing, all shall go.""-TENNYSON.

"All nature is but art, unknown to thee;

All chance, direction, which thou canst not see,

All discord, harmony not understood;

All partial evil, universal good;

And spite of pride, in erring reason's spite,

One truth is clear, whatever is, is right."-POPE.

154. IN Chapters III. and IV. we have dwelt upon the laws

energy and the ultimate constitution of matter; in other words, we have discussed those laws according to which the machine called the visible universe works, as well as the probable nature of that material of which it is composed. We have in this process (Arts. 86, 151) come to the conclusion that the visible universe has been developed out of the invisible. Once developed, it has its own laws of action which we may discover,-laws which at present appear to be invariably followed, as far at least as our strictly scientific experience can inform us.

In fine, the visible universe is that which we are in a