OF NATURAL PHILOSOPHY. 269 



portion, and presenting to the eye of sense, at a 

 single glance, that disposition of parts which in the 

 planetary system itself is discerned only by the eye of 

 reason and imagination (see 195.). Kepler had the 

 satisfaction of seeing it ascertained, that the law which 

 he had discovered to connect the times of revolution 

 of the planets with their distances from the sun, holds 

 good also when applied to the periods of circulation 

 of these little attendants round the centre of their 

 principal ; thus demonstrating it to be something 

 more than a mere empirical rule, and to depend on 

 the intimate nature of planetary motion itself. 



(299.) It had been objected to the doctrine of 

 Copernicus, that, were it true, Venus should appear 

 sometimes horned like the moon. To this he an- 

 swered by admitting the conclusion, and averring 

 that, should we ever be able to see its actual shape, 

 it would appear so. It is easy to imagine with what 

 force the application would strike every mind when 

 the telescope confirmed this prediction, and showed 

 the planet just as both the philosopher and his ob- 

 jectors had agreed it ought to appear. The history 

 of science affords perhaps only one instance analogous 

 to this. When Dr. Hutton expounded his theory of 

 the consolidation of rocks by the application of heat, 

 at a great depth below the bed of the ocean, and 

 especially of that of marble by actual fusion ; it was 

 objected that, whatever might be the case with 

 others, with calcareous or marble rocks, at least, it 

 was impossible to grant such a cause of consolid- 

 ation, since heat decomposes their substance and 

 converts it into quicklime, by driving off the car- 

 bonic acid, and leaving a substance perfectly in- 



