Comets appertain to, and travel with, the sun's cortège, and this is also inevitably true of comet-born meteors. But a multitude besides circulate independently of comets, and with much higher velocities. Their orbits are, then, hyperbolic; they belong to the category of 'irrevocable travellers,' and by their capture we are privileged to possess genuine shreds of sidereal matter. Universal space contains probably a vast stock of them, yet there is nothing to prove their collection into swarms. The spectroscope supplies no assurance to that effect; it has given its verdict against the meteoric constitution of nebulæ and temporary stars. And if we admit, through the persuasion of mineralogical testimony, that the aerolites so strangely landed on terrestrial soil are really the débris of ruined worlds, we can see for them no chance of restoration. Solitary they are, even if they occasionally pursue one another along an identical track, and solitary they must remain. Bodies do not of themselves initiate mutual circulation. Planetary or stellar outcasts cannot become re-associated into a gravitational system. Of a cosmic swarm, as of a poet, it may be said, _Nascitur, non fit_; and their birth-secret is undivulged. FOOTNOTES: [Footnote 45: _The New Astronomy_, p. 197.] [Footnote 46: _American Journal of Science_, vol. xi., p. 421, June, 1901.] [Footnote 47: Carbon does not liquefy under ordinary conditions. In the production of his artificial diamonds M. Moissan employed tremendous pressure and great heat; and, although the genuineness of his products has been denied (Combes, _Moniteur Scientifique_, November, 1903), his methods at least seem to have approximated to those by which Nature fabricates her most authentic crystals.] [Footnote 48: Sir R. Ball, _The Earth's Beginnings_, p. 243.] [Footnote 49: _Proceedings of the Royal Society_, vol. xlv., p. 4.] CHAPTER VIII COSMOGONY IN THE TWENTIETH CENTURY Prospective and retrospective inquiries into physical conditions stand very much on the same footing. The same degree of uncertainty attaches to results of both kinds; the same qualifications need to be applied to them; a similar reserve is understood to accompany our admission of them. The reserve grows more marked as science unfolds to our surprised apprehension the multiplex possibilities of Nature. The time has gone by when 'men of light and leading' could draw cheques for unlimited amounts on the bank of public credulity. Not that the balance has diminished, but that it is reserved for other uses. Most of us in these days, have learnt to 'look before and after' for ourselves, and we instinctively mix the proverbial grain of salt with what is told to us, even on the highest authority. Ideas are on the move; dim vistas are opening out; much that lies beyond the verge of actual experience is seen to be possible, and sedate reasoning may at any moment suffer outrage by fantastic discovery. Hence, finality of assertion is out of date.