422 RISE AND PROGRESS OF 



with much clearness and simplicity. Thus was laid the foundation 

 of the doctrine of central forces a doctrine which, in the hands of 

 Newton, served as the basis of the theory of universal gravitation. 

 I must pass over the names of Leibnitz and Varignon, Wallis, 

 Wren, Hooke, and Halley, all of whom have made valuable 

 contributions to mechanical science. We have now reached a 

 period, in which the achievements of a single individual outweigh 

 the collected labours of all his predecessors in discovery; and 

 before the lustre of whose genius the lesser lights of science 

 " pale their ineffectual fires." The time had indeed arrived in 

 which one great mind was wanting, to concentrate the rays of 

 knowledge, which were now beginning to dawn in various quarters ; 

 and the state of physical science was prepared for a vast revolution. 

 The cumbrous apparatus of cycles and epicycles, with which 

 Ptolemy had deformed the heavens, had disappeared ; and the 

 true system of the universe was established by Copernicus. The 

 planetary motions were reduced by Kepler to three general laws ; 

 and one of these laws was found by Cassini to hold in the 

 miniature system of Jupiter and his satellites, showing thereby 

 that it was not the result of any accidental congruity, but had its 

 origin in the nature of things. Again, the barrier which the 

 ancient physics had raised between celestial and terrestrial motions 

 had crumbled away, and the dogmas of Aristotle were no longer 

 articles of belief. Lastly, the true road to philosophical discovery 

 was pointed out by Bacon: to precept, Gralileo added the more 

 powerful influence of example, and laid the foundations of 

 dynamical science in the laws which regulate the motions of 

 bodies at the surface of our globe. In such a time Newton 



There is not a single department of knowledge approached by 

 Newton, that did not receive the impress of his mighty genius. 

 Some branches of science were his exclusive creation ; and when 

 the difficulties of the investigations, into which his physical 

 speculations led him, surpassed the power of the geometry of his 

 day, he at once created an instrument which enabled him to 

 grapple with, and overcome them. But I must confine myself 

 here to those discoveries of Newton which are connected with 

 the subject of mechanical philosophy : to some of his other 

 discoveries I shall have occasion to draw your attention hereafter. 



The theory of equilibrium, in the different simple machines, 



