14 NATURAL THEOLOGY. 



degree, therefore, of complexity is necessary to 

 render a subject fit for this species of argument. 

 But the heavenly bodies do not, except perhaps 

 in tlie instance of Saturn's ring, present them- 

 selves to our observation as compounded of parts 

 at all. This, which may be a perfection in them, 

 is a disadvantage to us, as inquirers after their na- 

 ture. They do not come within our mechanics. 

 And what we say of their forms is true of their 

 inotions. Their motions are carried on without 

 any sensible intermediate apparatus ; whereby 

 we are cut off from one principal ground of argu- 

 mentation — analogy. We have nothing where- 

 with to compare them ; no invention, no discovery, 

 no operation or resource of art, which, in this re- 

 spect, resembles them. Even those things which 

 are made to imitate and represent them — such as 

 orreries, planetaria, celestial globes, &c., bear no 

 affinity to them, in the cause and principle by 

 which their motions are actuated. I can assign 

 for this difference a reason of utility — viz., area- 

 son why, though the action of terrestrial bodies 

 upon each other be, in almost all cases, through 

 the intervention of solid or fluid substances, yet 

 central attraction does not operate in this manner. 

 It was necessary that the intervals between the 

 planetary orbs should be devoid of any inert mat- 

 ter, either fluid or solid, because such an interve- 

 ning substance would, by its resistance, destroy 

 those very motions, w^hich attraction is employed 

 to preserve. This may be a final cause of the 



