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 surely on this hypothesis have been an act of creation in time (Art. 133), 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 antecedent of the visible 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 most assuredly not. In the production of the vortex-atom from a perfect fluid we are driven at once to the unconditioned—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 at least 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 material whose rotating parts are ordinary matter as an absolutely perfect fluid. 152. This way of regarding this supposed material 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 starlight 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. Finally, the mere fact that the velocity of light is finite, tends also in the same direction. But if the visible universe be developed from a material 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 that out of which it was developed. In fine, if we suppose the material universe to be composed of a series of vortex-rings developed from something 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.