LAW; ITS DEFINITIONS. 67 



facts, or rather three series of facts, which, 

 during many years * of intense application 

 to physical inquiry, remained the highest truths 

 known to Man on the phenomena of the Solar 

 System. They were known as the Three Laws 

 of Kepler. It is not necessary to describe in 

 detail here what these laws were. Suffice it to 

 say, that the most remarkable among them 

 were facts of constant numerical relation be- 

 tween the distances of the different Planets from 

 the Sun, and the length of their periodic times ; 

 and again, between the velocity of their motion 

 and the space enclosed within certain cor- 

 responding sections of their orbit. These Laws 

 were simply and purely an " Order of facts " 

 established by observation, and not connected 

 with any known cause. The Force of which that 

 Order is a necessary result had not then been 

 ascertained. A very large proportion of the 

 laws of every science are laws of this kind 

 and in this sense. For example, in Chemistry 

 the behaviour of different substances towards 



* The "Third Law" of Kepler was* made known to the world 

 in 1619. Newton's " Principia" appeared in 1687. 



