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CHAPTER XVI. 

 OF EMPIRICAL LAWS. 



1. EXPERIMENTAL philosophers usually give the 

 name of Empirical Laws to those uniformities which 

 observation or experiment has shown to exist, but 

 upon which they hesitate to rely in cases varying 

 much from those which have been actually observed, 

 for want of seeing any reason why such a law should 

 exist. It is implied, therefore, in the notion of an 

 empirical law, that it is not an ultimate law; that if 

 true at all, its truth is capable of being, and requires 

 to be, accounted for. It is a derivative law, the 

 derivation of which is not yet known. To state the 

 explanation, the why of the empirical law, would be to 

 state the laws from which it is derived ; the ultimate 

 causes upon which it is contingent. And if we knew 

 these, we should also know what are its limits ; under 

 what conditions it would cease to be fulfilled. 



The periodical return of eclipses, as originally 

 ascertained by the persevering observation of the 

 early eastern astronomers, was an empirical law, until 

 the general laws of the celestial motions had accounted 

 for it. The following are empirical laws still waiting 

 to be resolved into the simpler laws from which they 

 are derived. The local laws of the flux and reflux of 

 the tides in different places : the succession of certain 

 kinds of weather to certain appearances of sky : the 

 apparent exceptions to the almost universal truth that 

 bodies expand by increase of temperature : the law 

 that breeds, both animal and vegetable, are improved 

 by crossing : that gases have a strong tendency to 



