AND THEORY OF THE HEAVENS. 67 



may be perhaps just as gradual as in the case of those within 

 its orbit ; and that the planets are brought into relation 

 with the race of comets by so much the less sudden 

 deviations? For it is certain that it is just this eccentricity 

 that makes the essential difference between the comets 

 and planets ; and the tails and vapour heads of the 

 comets are merely the effect of it. And in like manner 

 it is certain that the cause, whatever it may have been, 

 which has communicated their circular movements to the 

 heavenly bodies, has not only been too weak at these 

 greater distances to equalize the rotatory impulse with 

 the force of attraction, and has thereby made the move- 

 ments eccentric, but it has also on that account not 

 been powerful enough to bring the orbits of these bodies 

 into a common plane with that in which the inferior bodies 

 move, and this has given occasion to the comets diverging 

 in all directions. 



According to this conjecture we may cherish the hope 

 that new planets will perhaps yet be discovered beyond 

 Saturn, and that these will be found to be more eccentric 

 in their orbit than Saturn, and therefore nearer the 

 character of comets. But for the same reason they 

 would be perceptible only for a short time, namely, dur- 

 ing the period of their perihelion, which circumstance, 

 together with the slight degree of their approach to us 

 and the feebleness of their light, has hitherto prevented 

 the discovery of them, and will make their discovery 

 difficult even in the future. The last planet and first 

 comet might, if it so pleased, be styled the one whose 

 eccentricity would be so great that in its perihelion it 

 intersected the orbit of the planet nearest it perhaps that 

 of Saturn. 



