One of the most important and secure additions to knowledge in the department of cosmogony made during the nineteenth century was the establishment of comets in a position of entire, perennial, and aboriginal dependence upon the sun. That is to say, a vast majority, if not the whole of them, attend him on his sidereal journey. They are, accordingly, and have immemorially been his clients, and they can lose that status only through the effects of violent disturbance compelling them to depart irrevocably from their closed orbits along hyperbolic tracks. A trifling leakage of comets from our system is thus possible, which may or may not be compensated by annexations of adventitious members of the class, similarly banished from the precincts of remote stars. But this is a secondary consideration; the essential point to be borne in mind is that comets are native-born subjects of the sun, that they make an integral part of his cortège, that they own the same substantial origin, are dominated by his power, and must share his fortunes. Their study should then prove strongly illuminative as to the pre-history of our system, and for this especial reason, that they seemingly belong by right to that vanished world which it is the chosen task of cosmogony to reconstruct. They are, we can infer, the genuine primitives of the solar company; they retain something of prairie wildness, not having been broken in by steadily enforced gravitational discipline. Each perihelion passage is an adventure; between it and the next, fateful incidents may occur. Forces negligible on dense planetary globes act sensibly on their tenuous materials; they in part strikingly illustrate, and in part fantastically invert, the common modes of natural procedure. But it is their antiquarian significance that mainly concerns us here. Admitting for the inchoate solar nebula such a constitution as that devised by Kant, and adopted with amendments by M. du Ligondès, we find ourselves confronted with the almost inevitable consequence of symptomatic survivals. Wisps of crude matter, in other words, which escaped being drawn into the vortices of embryo planets should continue to circulate, as they had from the first circulated, in all possible planes, and with no partiality for either a right-handed or a left-handed direction. These waifs and wastrels should, in fact, be indistinguishable from comets--'les seuls témoins,' according to the French cosmogonist, 'qui nous restent sur le mode de la circulation première.'[109] The identification is seductive to the imagination, and does not fall far short of convincing the reason.