372 INDUCTION. 



(as mathematicians know) the same quantity of effect, as it 

 does in its ordinary operation of causing the fall of bodies 

 when simply deprived of their support. If an alkaline solution 

 mixed with an acid destroys its sourness, and prevents it from 

 reddening vegetable blues, it is because the specific effect of 

 the alkali is to combine with the acid, and form a compound 

 with totally different qualities. This property, which causes of 

 all descriptions possess, of preventing the effects of other 

 causes by virtue (for the most part) of the same laws according 

 to which they produce their own,* enables us, by establishing 



but they happened to be the only ones which there could be any necessity to 

 state ; for he walked, most likely, in exactly his usual manner, and the negative 

 conditions made all the difference. Again, if a person were asked why the army 

 of Xerxes defeated that of Leonidas, he would probably say, because they were 

 a thousand times the number ; but I do not think he would say, it was because 

 they fought, though that was the element of active force. To borrow another 

 example, used by Mr. Grove and by Mr. Baden Powell, the opening of floodgates 

 is said to be the cause of the flow of water ; yet the active force is exerted 

 by the water itself, and opening the floodgates merely supplies a negative 

 condition. The reviewer adds, "there are some conditions absolutely passive, 

 and yet absolutely necessary to physical phenomena, viz, the relations of space 

 and time ; and to these no one ever applies the word cause without being 

 immediately arrested by those who hear him." Even from this statement I 

 am compelled to dissent. Few persons would feel it incongruous to say (for 

 example) that a secret became known because it was spoken of when A. B. was 

 within hearing ; which is a condition of space : or that the cause why one of 

 two particular trees is taller than the other, is that it has been longer planted ; 

 which is a condition of time. 



* There are a few exceptions ; for there are some properties of objects which 

 seem to be purely preventive ; as the property of opaque bodies, by which 

 they intercept the passage of light. This, as far as we are able to understand 

 it, appears an instance not of one cause counteracting another by the same law 

 whereby it produces its own effects, but of an agency which manifests itself in 

 no other way than in defeating the effects of another agency. If we knew on 

 what other relations to light, or on what peculiarities of structure, opacity de- 

 pends, we might find that this is only an apparent, not a real, exception to the 

 general proposition in the text. In any case it needs not affect the practical 

 application. The formula which includes all the negative conditions of an 

 effect in the single one of the absence of counteracting causes, is not violated 

 by such cases as this ; though, if all counteracting agencies were of this descrip- 

 tion, there would be no purpose served by employing the formula, since we 

 should still have to enumerate specially the negative conditions of each pheno- 

 menon, instead of regarding them as implicitly contained in the positive laws of 

 the various other agencies in nature. 



