NOMOS. 95 



around the sun are proportional to the cubes of 

 the distance from the sun. 



These discoveries were the fruit of most laborious 

 enquiry. They were sifted out of myriads of other 

 facts by a man of extraordinary patience and pene- 

 tration. They are themselves facts of very high 

 practical value, for by them astronomical predictions 

 became possible ; but they were mere isolated and 

 empirical facts until Newton undertook to interpret 

 them. 



Interpreted by Newton, the true significance of 

 Kepler's discoveries became apparent. The equa- 

 ble description of areas in equal times became a 

 proof that the centre of these areas is the centre of 

 the force or forces acting upon the planet or planet- 

 oid body. The fact became significant 

 of law, but it did not declare the nature 



of the law. The elliptical form of the of the laws of 



. . -IP Kepler, and 



orbit with the sun or primary in the focus Newton's 



became a proof that the central force or the 

 forces acts or act with an energy which 

 is inversely proportional to the square of the dis- 

 tance, increasing as the distance diminishes, and 

 decreasing as the distance increases. And, lastly, 

 the fact that the squares of the periodic times are 

 inversely proportional to the cubes of the distance, 

 became the proof that all the planets and satellites 

 are retained in their orbits by the same force or 

 forces, modified only by distance. 



But Newton did not content himself with this 

 interpretation. On the contrary, he laid down three 

 laws or axioms, the three laws of motion, as they 



