iect. iv.] DISSERTATION SECOND. 145 



It was not astronomy alone which was benefited by this 

 revolution, and the discussions to which it had given rise. 

 A new light, as already remarked, was thrown on the phy- 

 sical world, and the curtain was drawn aside which had so 

 long concealed the great experiment, by which nature her- 

 self manifests, at every instant, the inertia of body, and the 

 composition of forces. To reconcile the real moiion of (he 

 earth with its appearance of rest, and with our feeling of its 

 immobility, required such an examination of the nature of 

 motion, as discovered, if not its essence, at least its most 

 general and fundamental properties. The whole science of 

 rational mechanics profited, therefore, essentially by the 

 discovery of the earth's motion. 



A great barrier to philosophick improvement had arisen 

 from the separation so early made, and so strenuously sup- 

 ported in (he ancient systems, between terrestrial and celes- 

 tial substances, and between the laws which regulate motion 

 on the earth, and in the heavens. This barrier was now 

 entirely removed ; the earth was elevated to the rank of a 

 planet ; the planets were reduced to the condition of earths, 

 and by this mutual approach, the same rules of interpreta- 

 tion became applicable to the phenomena of both. Princi- 

 ples derived from experiments on the earth, became guides 

 for the analysis of the heavens, and men were now in a 

 situation to undertake investigations, which the m«sf hardy 

 adventurer in science could not before have dared to ima- 

 gine. Philosophers had ascended to the knowledge of the 

 affinities which pervade all nature, and which mark so 

 strongly both the wisdom and unity of its author. 



The light thus struck out darted its rays into regions the 

 most remote from physical inquiry. When men saw opi- 

 nions entirely disproved, which were sanctioned by all anti- 

 quity, and by the authority of the greatest names, they be- 

 gan to have different notions of the rules of evidence, of the 



