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CHAPTER XV. 



OF PROGRESSIVE EFFECTS; AND OF THE 

 CONTINUED ACTION OF CAUSES. 



1 . IN the last four chapters, we have traced the 

 general outlines of the theory of the generation of 

 derivative laws from ultimate ones. In the present 

 chapter our attention will be directed to a particular 

 case of the derivation of laws from other laws, but a 

 case so general, and so important,, as not only to 

 repay but to require a separate examination. This is, 

 the case of a complex phenomenon resulting from one 

 simple law, by the continual addition of an effect to 

 itself. 



There are some phenomena, some bodily sensa- 

 tions for example, which are essentially instanta- 

 neous, and whose existence can only be prolonged 

 by the prolongation of the existence of the cause by, 

 which they are produced. But most phenomena are 

 in their own nature permanent; having begun to exist, 

 they would exist for ever unless some cause inter- 

 vened having a tendency to alter or destroy them. 

 Such, for example, are all the facts or phenomena 

 which we call bodies. Water once produced, will not 

 of itself relapse into the state of hydrogen and oxygen; 

 such a change requires some agent having the power 

 of decomposing the compound. Such, again, are the 

 positions in space, and the movements, of bodies. 

 No object at rest alters its position without the 

 intervention of some conditions extraneous to itself; 

 and when once in motion,, no object returns to a state 

 of rest, or alters either its direction or its velocity, 



