92 INDUCTION. 



periodical occurrence of sunrise depends. We could 

 have extended this empirical law to cases adjacent in 

 time, though not to so great a distance of time as 

 we can now. Having evidence that the effects had 

 remained unaltered and been punctually conjoined 

 for five thousand years, we could infer that the 

 unknown causes on which the conjunction is de- 

 pendent had existed undiminished and uncounteracted 

 during the same period. The same conclusions, there- 

 fore, would follow as in the preceding case ; except 

 that we should only know that during five thousand 

 years nothing had occurred to defeat perceptibly this 

 particular effect ; while, when we know the causes, 

 we have the additional assurance, that during that 

 interval no such change has been noticeable in the 

 causes themselves, as by any degree of multiplication 

 or length of continuance could defeat the effect. 



To this must be added, that when we know the 

 causes, we may be able to judge whether there exists 

 any known cause capable of counteracting them : while 

 as long as they are unknown we cannot be sure but that 

 if we did know them, we could predict their destruc- 

 tion from causes actually in existence. A bedridden 

 savage, who had never seen the cataract of Niagara, 

 but who lived within hearing of it, might imagine 

 that the sound he heard would endure for ever ; but 

 if he knew it to be the effect of a rush of waters over 

 a barrier of rock which is progressively wearing 

 away, he would know that within a number of ages 

 which may be calculated, it will be heard no more. 

 In proportion, therefore, to our ignorance of the 

 causes on which the empirical law depends, we can 

 be less assured that it will continue to hold good ; and 

 the further we look into futurity, the less improbable 

 is it that some one of the causes, whose coexistence 



