466 INDUCTION. 



6. There remains a class of laws which it is 

 impracticable to ascertain by any of the three methods 

 which I have attempted to characterize ; namely, 

 the laws of those Permanent Causes, or indestructible 

 natural agents, which it is impossible either to exclude 

 or to isolate; which we can neither hinder from being 

 present, nor contrive that they shall be present alone. 

 It would appear at first sight that we could by no 

 means separate the effects of these agents from the 

 effects of those other phenomena with which they 

 cannot be prevented from co-existing. In respect, 

 indeed, to most of the permanent causes, no such 

 difficulty exists ; since, though we cannot eliminate 

 them as coexisting facts, we can eliminate them as 

 influencing agents, by simply trying our experiment 

 in a local situation beyond the limits of their influ- 

 ence. The pendulum, for example, has its oscillations 

 disturbed by the vicinity of a mountain : we remove 

 the pendulum to a sufficient distance from the moun- 

 tain, and the disturbance ceases : from these data we 

 can determine by the Method of Difference, the 

 amount of effect really due to the mountain; and 

 beyond a certain distance everything goes on precisely 

 as it would do if the mountain exercised no influence 

 whatever, which, accordingly, we, with sufficient 

 reason, conclude to be the fact. 



The difficulty, therefore, in applying the methods 

 already treated of to determine the effects of Per- 

 manent Causes, is confined to the cases in which it is 

 impossible for us to get out of the local limits of their 

 influence. The pendulum can be removed from the 

 influence of the mountain, but it cannot be removed 

 from the influence of the earth : we cannot take away 

 the earth from the pendulum, nor the pendulum from 

 the earth, to ascertain whether it would continue to 



