MECHANICAL PHILOSOPHY. 433 



It was soon after found that the eccentricities of the orbits of 

 the planets, and their inclinations to a fixed plane, in like manner 

 oscillated within certain small limits which they could never trans- 

 gress. Thus, though the inclination and eccentricity of the orbit 

 of each planet is continually changed by the action of the rest, yet, 

 after certain periods, the same forces which have deranged it from 

 its mean state, will bring it back to that state "again, and repair 

 their work of disturbance. To use the words of a distinguished 

 French writer of the present day " La stabilite du systeme solaire 

 est done a jamais assuree: les orbites des planetes dans les ages 

 futurs ne pourront que s'aplatir legerement en conservant les memes 

 grandes axes, et les plans de ces orbites ne feront que de petites 

 oscillations autour d'une position moyenne : immenses pendules 

 de I'eternite, qui battent les siecles, comme les notres battent les 

 secondes." 



Thus it appeared that the planetary system contained in itself 

 the principle of reparation and permanence. So far as depended 

 on the mutual action of the great bodies which compose it, the 

 system would endure for ever ; and would not (as Newton seems 

 to have supposed) ever require the repairing hand of its Divine 

 Author to check the progress of destruction. Late observations, 

 however, render it in the highest degree probable, that there exists 

 an external cause which, in the course of time, must bring all this 

 vast machinery to rest, and precipitate the gigantic masses which 

 compose it into the body of the sun. There are, in fact, strong 

 reasons for believing that a resisting medium is diffused throughout 

 the planetary spaces, the effect of which must be to diminish the 

 velocity and the distance of each revolving body from the sun, 

 until it at length reaches that centre. This medium is of such 

 tenuity, that it has, as yet, produced no perceptible effect upon 

 the motions of the denser bodies of the solar system. Our own 

 gross atmosphere, we know, offers a comparatively feeble resistance 

 to the bullet in its fall ; while the descent of the feather may be so 

 retarded, that it may seem almost suspended in the air. If then 

 the spaces which intervene between the great bodies of the solar 

 system be filled with a medium far rarer, as compared with the 

 lower regions of our atmosphere, than these are in relation to the 

 globe* they envelop, we are not to look for its effects upon the 

 motions of such bodies as the planets and their satellites. 



But there are other mysterious bodies connected with our 



2F 



