OF SOLAR LIGHT. 271 



The safest mode of investigating the cause of 

 planetary motion, is to follow the lights of ana- 

 logy. When it is found that the quantity and 

 force of light diminish inversely as the squares 

 of the distance, and that the sun operates upon 

 the planets by gravity in obedience to the same 

 law, it is difficult to avoid the conclusion that 

 they are connected together as cause and effect. 



When commenting on the Newtonian law of 

 gravity, by which every particle of matter in the 

 universe is supposed to attract every other par- 

 ticle inversely as the squares of the distance, 

 Mr. Whewell asks, " Why do the attractions of 

 masses, or those of their constituent particles, 

 follow this law of the inverse square of the dis- 

 tance?" (Bridgewater Treatise, Chapter X.) 



This question admits of a satisfactory answer, 

 in accordance with the hypothesis that solar 

 light is the cause of solar attraction, though we 

 may not fully comprehend the mode in which it 

 operates. The truth is, that the force of all 

 aethereal emanations is inversely as the squares 

 of the distance, for the obvious reason that they 

 are necessarily diffused in the same ratio. Other 

 things being equal, the repulsive force of caloric 

 in gases and vapours diminishes in the ratio of 

 the distance of their particles from each other. 

 Its heating power decreases in the same pro- 

 portion, while the attractive and repulsive forces 

 of electricity are known to follow the same law. 



