EXTENSION OF LAWS TO ADJACENT CASES. 93 



gives rise to the derivative uniformity, may be de- 

 stroyed or counteracted. With every prolongation 

 of time the chances multiply of such an event, that is 

 to say, its non-occurrence hitherto becomes a less 

 guarantee of its not occurring within the given time. 

 If, then, it is only to cases which in point of time 

 are adjacent (or nearly adjacent) to those which we 

 have actually observed, that any derivative law, not 

 of causation, can be extended with an assurance equi- 

 valent to certainty, much more is this true of a merely 

 empirical law. Happily, for the purposes of life it is 

 to such cases alone that we can almost ever have 

 occasion to extend them. 



In respect of place, it might seem that a merely 

 empirical law could not be extended even to adjacent 

 cases ; that we could have no assurance of its being true 

 in any place where it has not been specially observed. 

 The past duration of a cause is a guarantee for its 

 future existence, unless something occurs to destroy 

 it ; but the existence of a cause in one or any number 

 of places, is no guarantee for its existence in any other 

 place, since there is no uniformity in the collocations 

 of primeval causes. When, therefore, an empirical 

 law is extended beyond the local limits within which 

 it has been found true by observation, the cases to 

 which it is thus extended must be such as are pre- 

 sumably within the influence of the same individval 

 agents. If we discovered a new planet within the 

 known bounds of the solar system (or even beyond 

 those bounds, but indicating its connexion with the 

 system by revolving round the sun), we might conclude, 

 with great probability, that it revolves upon its axis. 

 For all the known planets do so ; and this uniformity 

 points to some common cause, antecedent to the first 

 records of astronomical observation: and although the 



