438 INDUCTION. 



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 influence. The pendulum, 

 for example, has its oscillations disturbed by the vicinity of a 

 mountain : we remove the pendulum to a sufficient distance 

 i'rom the mountain, and the disturbance ceases : from these 

 data we can determine by the Method of Difference, the amount 

 of effect 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 Permanent 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 vibrate 

 if the action which the earth exerts upon it were withdrawn. 

 On what evidence, then, do we ascribe its vibrations to the 

 earth's influence ? Not on any sanctioned by the Method of 

 Difference ; for one of the two instances, the negative in- 

 stance, is wanting. Nor by the Method of Agreement ; for 

 though all pendulums agree in this, that during their oscil- 

 lations the earth is always present, why may we not as well 

 ascribe the phenomenon to the sun, which is equally a co- 

 existent fact in all the experiments ? It is evident that to 

 establish even so simple a fact of causation as this, there was 

 required some method over and above those which we have 

 yet examined. 



As another example, let us take the phenomenon Heat. 

 Independently of all hypothesis as to the real nature of the 

 agency so called, this fact is certain, that we are unable to 

 exhaust any body of the whole of its heat. It is equally cer- 

 tain, that no one ever perceived heat not emanating from a 

 body. Being unable, then, to separate Body and Heat, we 

 cannot effect such a variation of circumstances as the fore- 



