THE ORIGIN OF THE EARTH. 35 



If the orbit of the small body is such that it is caused to pass in front 

 of the large body, say the planet Jupiter, its course will be diverted 

 toward the sun, and its orbit shortened. If its course causes it to pass 

 close behind the large body, its path will be diverted into a larger orbit. 

 If a small body were to pass in this way sufficiently near to Jupiter, it 

 might be thrown entirely out of the solar system. 1 



In these two sets of principles, there is a combination peculiarly 

 fitted for the results required, for, by their joint action, a small body 

 passing near a large body is liable to be disrupted into fragments, 

 and, at the same time, to be thrown into an erratic course which may 

 carry it entirely outside the system to which it belonged, and may give 

 it a parabolic or hyperbolic course in stellar space. Fragmentation 

 and dispersal by the differential attraction of very close approach 

 escapes all of the adverse contingencies of liquefaction and pulveriza- 

 tion incident to explosion or collision. 



If the question be pushed a step farther to inquire how small bodies 

 like the asteroids may be rendered specially subject to the requisite 

 close approach, the answer may be found in the approach of suns, 

 attended by such secondaries, to one another. For example, if the 

 solar system were to pass even within five or six billion miles of a simi- 

 lar system, the orbits of the secondaries would be very greatly per- 

 turbed, and the balance between the centripetal and centrifugal ac- 

 celerations, which now preserves the harmony of the system, would 

 be so seriously disturbed that an intricate and prolonged series of 

 changes would ensue. These are too complicated to be followed com- 

 pletely, but it is reasonable to believe that they might involve, sooner 

 or later, the close approach of some of the smaller bodies to some of 

 the larger. These smaller bodies in the solar system are numbered 

 by hundreds, and the same may be suspected of other systems, and 

 this largeness of number adds to the probabilities of some close ap- 

 proaches during a condition of general disturbance. 



The solar system is probably not the most favorable selection for 

 illustrating the contingencies of such disturbance, for it is a simple 

 isolated system, with a single overpowering center that sways its 

 attendants by a scarcely disputed control. It has swept through 

 space undisturbed throughout the period of its present organization. 



1 These principles have been worked out elaborately by H. A. Newton, Am. Jour. 

 Sci. 16, 1878, pp. 165-179. 



