256 INTRODUCTION. 



cover truths, they felt also a persuasion of a right and a growing will 

 so to do. 



Thus the revived clearness of ideas, which made its appearance at 

 the revival of letters, brought on a struggle with the authority, intel- 

 lectual and civil, of the established schools of philosophy. This clear- 

 ness of idea showed itself, in the first instance, in Astronomy, and was 

 embodied in the system of Copernicus ; but the contest did not come 

 to a crisis till a century later, in the time of Galileo and other disciples 

 of the new doctrine. It is our present business to trace the principles 

 of this series of events in the history of philosophy. 



I do not profess to write a history of Astronomy, any further than is 

 necessary in order to exhibit the principles on which the progression 

 of science proceeds ; and, therefore, I neglect subordinate persons and 

 occurrences, in order to bring into view the leading features of great 

 changes. Now in the introduction of the Copernican system into 

 general acceptation, two leading views operated upon men's minds ; 

 the consideration of the system as exhibiting the apparent motions of 

 the universe, and the consideration of this system with reference to its 

 causes ; — ike formal and the physical aspect of the Theory ; — the rela- 

 tions of Space and Time, and the relations of Force and Mattel - . These 

 two divisions of the subject were at first not clearly separated ; the 

 second was long mixed, in a manner very dim and obscure, with the 

 first, without appearing as a distinct subject of attention ; but at last it 

 was extricated and treated in a manner suitable to its nature. The 

 views of Copernicus rested mainly on the formal condition of the uni- 

 verse, the relations of space and time ; but Kepler, Galileo, and others, 

 were led, by controversies and other causes, to give a gradually in- 

 creasing attention to the physical relations of the heavenly bodies ; an 

 impulse was given to the study of Mechanics (the Doctrine of Motion), 

 which became very soon an important and extensive science ; and in 

 no long period, the discoveries of Kepler, suggested by a vague but in- 

 tense belief in the physical connection of the parts of the universe, led 

 to the decisive and sublime generalizations of Newton. 



The distinction of formal and •physical Astronomy thus becomes 

 necessary, in order to treat clearly of the discussions which the pro- 

 pounding of the Copernican theory occasioned. But it may be ob- 

 served that, besides this great change, Astronomy made very great 

 advances in the same path which we have already been tracing, 

 namely, the determination of the quantities and laws of the celestial 

 motions, in so far as they were exhibited by the ancient theories, or 



