eacT. n] DISSERTATION SECOND. 9<> 



the reveries of ingenious men who had no steady principle 

 deduced from experience and observation to direct their in- 

 quiries; and who, even when in their conjectures they hit on 

 the truth, could hardly distinguish it from error. 



Copernicus, as might be expected, is considerably more 

 precise. "I do not think," says he, "that gravity is any- 

 thing but a natural appetency of the parts (of the earth) given 

 by the providence of the Supreme Being, that, by uniting to- 

 gether, they may assume the form of a globe. It is proba- 

 ble, that this same affection belongs to the sun, the moon, 

 and the fixed stars, which all are of a round form." 1 



The power which Copernicus here speaks of, has nothing 

 to do, in his opinion, with the revolutions of the earth or the 

 planets in their different orbits. It is merely intended as an 

 explanation of their globular forms, and the consideration 

 that does the author most credit is, that of supposing the 

 force to belong, not to the centre, but to all the parts of the 

 earth. 



Kepler, in his immortal work on the Motions of Mars, 

 treats of gravity as a force acting naturally from planet to 

 planet, and particularly from the earth to the moon. " If 

 the moon and the earth were not retained by some animal or 

 other equivalent force each in its orbit, the earth would as- 

 cend to the moon by a 54th part of the interval between 

 them, while the moon moved over the remaining 53 parts, 

 that is, supposing them both of the same density." 2 This 

 passage is curious, as displaying a singular mixture of know- 

 ledge and error on the subject of the planetary motions. 

 The tendency of the earth and moon being mutual, and pro- 

 ducing equal quantities of motion in those bodies, bespeaks 



1 Revolulionum, Lib. I. cap. 9. p. t7. 



2 On that supposition their quantities of matter would be as 

 their bulks, or as 1 to 53. 



