230 COSMOS. 



plan of creation, and the nature of the formation of the 

 planets, they have all a translatory and rotatory motion in 

 one direction ; that this motion takes place in orbits of slight 

 and but little varying ellipticity, in planes of moderate dif- 

 ferences of inclination ; and that the periods of the planeta- 

 ry revolutions have among each other no common .measure. 

 Such elements of stability, as it were the maintenance and 

 duration of the planets' existence, are dependent upon the 

 condition of mutual action with a separate circle. If, by the 

 entry of a cosmical body coming from without, and not pre- 

 viously belonging to the planetary system, that condition 

 was disturbed (Laplace, Expos, du Syst. du Monde, p. 309 

 and 391), then this disturbance, as the consequence of new 

 attractive forces, or of a collision, might certainly become 

 destructive to the existing system, until finally, after long con- 

 flict, a new equilibrium was produced* The arrival of a 

 comet upon an hyperbolic orbit from a great distance, even 

 when want of mass is made up for by immense velocity, can 

 excite apprehension only in an imagination which is not sus 

 ceptible of the earnest assurances of the calculation of proba- 

 bilities. The wandering clouds of the interior comets are 

 not more dangerous to our solar system than the great incli- 

 nation of the orbits of some of the small planets between 

 Mars and Jupiter. Whatever must be characterized as mere 

 probability, lies beyond the domain of a physical description 

 of the universe ; science must not wander into the cloud- 

 land of cosmological dreams. 



