If in the immense annular group of bodies two centers of aggregation formed the two incipient worlds, ever increasing, their attractive power would be likely to form a binary system, both moving around the common center of gravity between them. It is when their conjunction takes place near the point where their orbits come nearest together that such a change may be expected. The inner planet having, then, its minimum and the outer its maximum velocity, the movement in the new binary system would be in the same direction as the common orbital motion around the central suns. To such a course of events may be ascribed the origin of the earth and moon, as well as the connection which exists between them; for even tidal action would be sufficient to reduce the eccentricity of the lunar orbit to its present state. If at that early period meteoric and cometary matter were so abundant that both orbs could become twenty times as large and massive, their distance apart would be so much reduced that the moon would long since have incorporated with our globe by a series of paroxysms which would arouse electro-magnetic forces into action and give birth to a family of satellites.
When, however, two embryonic planets, in the contiguous zones of the great ring of meteors, formed a binary system long before attaining their full size, their union would take place like that of greater masses, and be attended with like consequences. It is reasonable to suppose that, in the early stage of its existence on the verge of the solar-system, Mars, like our earth, received a companion having about one or two per cent. of his mass, but confined to a small orbit. This primitive attendant, which was probably over one thousand miles in diameter, subsequently united with Mars by a series of convulsive stages; and, by awakening electric agencies, gave birth to a family of satellites of which Deimos and Phobos alone remain. The career of Jupiter and Saturn was characterized by the same train of changes and events. When they first sprang into existence, in the outer zone of our system, each of these great planets was attended with a large companion which subsequently incorporated with the superior orb by a series of paroxysms, and thus occasioned the birth of a family of minor worlds. Accordingly, in a system of classification based on their modes of origin, neither our moon nor perhaps that of Neptune could be assigned to the same class which includes the satellites of Mars, Jupiter, Saturn, and Uranus.
The very great disproportion between the world-forming power in great and in small binary systems, will appear in a clearer light by considering the violence in both cases attending precipitation from the less to the greater orb. Were our moon placed so near us that it must yield to the rupturing forces, each paroxysmal dismemberment would give to the earth a ring of lunar matter having a transverse section of 30,000 square miles, and forcing its way through the outer terrestrial structure with a velocity of five miles a second. But if the linear dimensions of
