Comets which have or seem, to have a common origin–Double comets–Systems of comets according to M. Hoek–Distribution of aphelia over the celestial vault; region of the heavens particularly rich in aphelia.

When, in accordance with the actual facts of science, we endeavour to form an idea of the constitution of the visible universe, we see that the celestial bodies which compose this whole are everywhere distributed into groups and associations united by the common bond of universal gravitation.

There are the planetary systems. In the centre of each group is a star or central sun, whose preponderating mass retains near him, circulating in regular orbits, other stars or planets, to which this central sun distributes heat and light. Our planetary system is the type of associations of this kind.

There are the stellar systems, groups of two, three, or more suns gravitating about one another, probably in accordance with the same laws. These systems are themselves the elements of greater associations, which, like the resolvable nebulas known under the name of stellar masses, are composed of myriads of suns. The Milky Way is one of the most splendid examples of these immense agglomerations.

In certain regions of the heavens the nebulae are themselves to all appearance grouped into systems, so that the general plan of the universe is one vast synthesis of associations of different orders encompassing each other without end.