84 INDUCTION. 



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 heing 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 ex- 

 tended 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 presumably within the influence of the 

 same individual agents. If we discover a new planet within 

 the known bounds of the solar system (or even beyond those 

 bounds, but indicating its connexion with the system by re- 

 volving round the sun), we may conclude, with great proba- 

 bility, that it revolves on 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 though the nature of this cause can only be matter of 

 conjecture, yet if it be, as is not unlikely, and as Laplace's 

 theory supposes, not merely the same kind of cause, but the 

 same individual cause (such as an impulse given to all the 

 bodies at once), that cause, acting at the extreme points of 

 the space occupied by the sun and planets, is likely, unless 

 defeated by some counteracting cause, to have acted at every 

 intermediate point, and probably somewhat beyond; and 

 therefore acted, in all probability, upon the supposed newly- 

 discovered planet. 



When, therefore, effects which are always found conjoined, 

 can be traced with any probability to an identical (and not 

 merely a similar) origin, we may with the same probability 

 extend the empirical law of their conjunction to all places 

 within the extreme local boundaries within which the fact has 

 been observed; subject to the possibility of counteracting 

 causes in some portion of the field. Still more confidently 

 may we do so when the law is not merely empirical ; when 

 the phenomena which we find conjoined are effects of ascer- 



