AND THEORY OF THE HEAVENS. 85 



denser materials will generally be found more abundantly 

 at the centre than further from it ; and therefore, notwith- 

 standing that the planets will be mixtures of very diverse 

 materials, yet generally their masses must be denser in 

 the proportion in which they are nearer to the sun, and 

 they must be of less density according as their distance 

 from it is greater. 



As regards this law ruling the density of the planets, 

 our system shows a superiority over all other conceptions 

 which have been formed, or can be formed, regarding its 

 cause. Newton, who had determined the density of some 

 of the planets by calculation, believed that the cause of 

 its ratio being constituted according to their distance 

 was to be found in the fitness of the Divine choice and 

 in the motives of the Divine purpose. It was because 

 the planets which are nearer the sun must endure more of 

 its heat, while the more distant planets must do with less 

 degrees of warmth ; and this appears not to be possible 

 unless the planets near the sun were composed of a denser 

 matter, and the more distant ones of a lighter kind. But 

 it does not require much reflection to perceive the 

 inadequacy of such an explanation. A planet for example, 

 our earth is composed of kinds of matter very different 

 from each other. Of these it was necessary that the lighter 

 particles, which are more permeated and moved by the 

 same action of the sun, and whose composition has a ratio 

 to the heat with which its rays operate, must be distributed 

 on the surface. But it is not at all evident from this that 

 the mixture of the other materials in the whole of the mass 

 must have this relation ; because the sun has no effect at 

 all upon the interior of the planets. Newton was afraid 

 that if the earth were plunged in the rays of the sun, as 



