8 THE POPULAR SCIENCE MONTHLY. 



If in the immense annular group of bodies two oenters of aggrega- 

 tion 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 maybe expected. The inner planet having, then, its min- 

 imum 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 dis- 

 tance apart would be so much reduced that the moon would long since 

 have incorporated with our globe by a series of paroxysms which w r ould 

 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 -sysr 

 tern, Mars, like our earth, received a companion having about one or 

 two percent, 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 par- 

 oxysms, and thus occasioned the birth of a family of minor worlds. Ac- 

 cordingly, in a system of classification baaed 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 con- 

 sidering 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 



