428 INDUCTION. 



chemistry of digestion, but from no knowledge of the 

 properties of those substances could we ever predict 

 that it could taste, unless gelatine or fibrin could 

 themselves taste ; for no elementary fact can be 

 in the conclusion, which was not first in the pre- 

 misses. 



There are thus two different modes of the conjunct 

 action of causes ; from which arise two modes of con- 

 flict, or mutual interference, between laws of nature. 

 Suppose, at a given point of time and space, two or 

 more causes, which, if they acted separately, would 

 produce effects contrary, or at least conflicting with 

 each other ; one of them tending to undo, wholly or 

 partially, what the other tends to do. Thus, the expan- 

 sive force of the gases generated by the ignition of 

 gunpowder tends to project a bullet towards the sky, 

 while its gravity tends to make it fall to the ground. 

 A stream running into a reservoir at one end tends to 

 fill it higher and higher, while a drain at the other 

 extremity tends to empty it. Now, in such cases as 

 these, even if the two causes which are in joint action 

 exactly annul one another, still the laws of both are 

 fulfilled; the effect is the same as if the drain had 

 been open for half an hour first*, and the stream had 

 flowed in for as long afterwards. Each agent pro- 

 duced the same amount of effect as if it had acted 

 separately, though the contrary effect which was 

 taking place during the same time obliterated it as 

 fast as it was produced. Here, then, we have two 

 causes, producing by their joint operation an effect 



* I omit, for simplicity, to take into account the effect, in this 

 hitter case, of the diminution of pressure, in diminishing the flow of 

 the water through the drain; which evidently in no way affects the 

 truth or applicability of the principle. 



