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disorderly movement, but that God afterwards regu- 

 lated their course by laws natural and proportional. 



5. Anaxagoras, cited by Diogenes Laertius, being 

 asked what it was fhat retained the heavenly bodies 

 in their orbit, notwithstanding their gravity, an- 

 swered, that the rapidity of their course preserved 

 them in their stations, antl should the celerity of 

 their motions abate, the equilibrium of the world 

 being broke, the whole machine would fall to ruin. 



6. Plutarch, who knew almost all the shining truths 

 of astronomy, took notice also of the reciprocal ener- 

 gy which causes the planets to gravitate towards one 

 another, and in explaining what it was that made 

 bodies tend towards the earth, he attributes it to a 

 reciprocal attraction, whereby all terrestrial bodies 

 have this tendency, and which collects into one the 

 parts constituting the sun and moon, and retains them 

 in their spheres. He afterwards applies these parti- 

 cular phenomena to others more general, and from 

 iv hat happens in our globe, deduces according to the 

 same principle, whatever must thence happen re- 

 spectively in each celestial body ; and then considers 

 them in their relative connections one towards ano- 

 ther. He illustrates this general connection, by 

 instancing what happens to our moon in its revolu- 

 tion round the earth, comparing it to a stone in a 

 sling which is impressed by two powers at once, that 

 of projection which would carry it away, were it not 

 retained by the embrace of the sling: which like 

 the central force, keeps it from wandering, whilst the 

 combination of the two moves it in a circle. In 

 another place he speaks of an inherent power in bo- 

 dies ; that is, in the earth and other planets, of at- 

 tracting to themselves whatever is within their reach. 

 It is impossible, not to perceive in all these passages 

 a plain reference to the centripetal force, which binds 

 the planets to their proper or common centers, and 



