SEQUEL TO THE EPOCH OF COPERNICUS. 459 



inevitably, after some vagueness and perplexity, to 

 a sound science of mechanics ; and this science in 

 time gave a new face to astronomy. But in the 

 mean time, while mechanical mathematicians were 

 generalizing from the astronomy already establish- 

 ed, astronomers were accumulating new facts, which 

 pointed the way to new theories and new gene- 

 ralizations. Copernicus, while he had established 

 the permanent length of the year, had confirmed 

 the motion of the sun's apogee, and had shown that 

 the eccentricity of the earth's orbit, and the obli- 

 quity of the ecliptic, were gradually, though slowly, 

 diminishing. Tycho had accumulated a store of 

 excellent observations. These, as well as the laws 

 of the motions of the moon and planets already 

 explained, were materials on which the Mechanics 

 of the Universe was afterwards to employ its most 

 matured powers. In the mean time, the telescope 

 had opened other new subjects of notice and specu- 

 lation ; not only confirming the Copernican doctrine 

 by the phases of Venus, and the analogical examples 

 of Jupiter and Saturn, which with their satellites ap- 

 peared like models of the solar system; but disclosing 

 unexpected objects, as the ring of Saturn, and the 

 spots of the sun. The art of observing made rapid 

 advances, both by the use of the telescope, and by the 

 sounder notions of the construction of instruments 

 which Tycho introduced. Copernicus had laughed 

 at Rheticus, when he was disturbed about single 

 minutes ; and declared that if he could be sure to 



