NOMOS. 105 



tive principle is the sole force which is concerned in 

 maintaining the movements of the heavenly bodies. 



Now there is no manner of doubt that the hea- 

 venly bodies will continue to describe their several 

 orbits if they were originally projected with a given 

 velocity in a tangent to their orbits, and then left to 

 the action of the force of gravity, if they encounter 

 no resistance in moving. But is it certain 

 that they do not encounter such resist- C uies 4hich 



ance? Now, that it is not certain, we 

 may perhaps argue, partly from the re- 

 tarded movements of Encke's comet, and 

 partly from the previous considerations 

 respecting law. It does not appear possible to 

 account for the retarded movements of 



-n , , .., jt Theprobabi- 



Jiincke s comet, without assuming the pre- uty that 



sence of some resisting medium in the theTncopo- 



track along which this body travels a "h? C h1 s d ne . 



medium of exceeding rarity, it is true, *saryto 



. , n allow the un- 



and one which might only tell in a short impeded con- 

 time upon bodies like comets, but which the motion 

 must tell somewhat upon the movements from^rfginai 

 of the densest bodies. We know so little P r J ection - 

 about comets, however, that any argument which is 

 derived from their movements alone can be of little 

 weight ; and, on the other hand, it may be said that 

 if space be sufficiently empty to allow a comet to 

 move along with comparative freedom, it is to all 

 intents and purposes a vacuum. The other objection, 

 which arises out of the views which have been ex- 

 plained in the foregoing pages views which discard 



