EXPLANATION OP LAWS. 271 



CHAPTER XII. 



OF THE EXPLANATION OF LAWS OF NATUR6. 



§ 1. The Jetluctive operation, by which we derive the law of an effect 

 from the laws of the causes of which the concurrence gives rise to it, 

 may he undertaken either for the purpose of discovering the law, or 

 of explaining a law already discovered. The word es-planat'ion occurs 

 so continually, and holds so important a place in philosophy, that a 

 little time spent in fixing the meaning of it will he profitably em- 

 ployed. 



An individual fact is said to be explained, by pointing out its cause, 

 that is, by stating the law or laws of causation, of which its production 

 is an instance. Thus, a conflagration is explained, -when it is proved 

 to have arisen from a spark falling into the midst of aheap of combus- 

 tibles. And in a similar manner, a law or uniforrnity in nature is said 

 to be explained, when another law or laws are pointed out, of which 

 that law itself is but a case, and from which it could be deduced. 



§ 2. There are three distinguishable sets of circumstances in which 

 a law of acusation may be explained from, or, as it also is often ex- 

 pressed, resolved into, other laws. 



The first is the case already so fully considered ; an intermixture of 

 laws, producing a joint effect equal to the sum of the effects of the 

 causes taken separately. The law of the complex effect is explained, 

 by being resolved into the separate laws of the causes which contribute 

 to it. Thus, the law of the motion of a planet is resolved into the law 

 of the tangential force, which tends to produce an miiform motion in 

 the tangent, and the law of the centripetal force, which tends to pro- 

 duce an accelerating motion towards the sun ; the real motion being a 

 compound of the tWo. 



It is necessary here to remark, that in this resolution of the law of a 

 complex effect, the laws of which it is compounded are not the only ele- 

 ments. It is resolved into the laws of the separate causes, together 

 with the fact of itheir coexistence. The one is as essential an ingredi- 

 ent as the other ; whether the object be to discover the law of the effect, 

 or only to explain it. To deduce tKe laws of the heavenly motions, 

 we require not only to know the law of a rectilineal and that of a grav- 

 itative force, but the existence of both these forces in the celestial 

 regions, and even their relative ajnoimt. The complex laws of causa- 

 tion are thus resolved into two distinct kinds of elements : the one, 

 simpler laws of causation, the other (in the aptly selected language of 

 Dr. Chalmers) collocations ; the collocations consisting in the existence 

 of certain agents or powers, in certain circumstances of place and time. 

 We shall hereafter have occasion to return to this distinction, and to 

 dwell upon it at such alenj^th as dispense^ with the necessity of further 

 insisting iipon it here. The first mode, then, of the explanation of 

 Laws of Causation, is when the law of an effect is resolved into the va- 

 rious tendencies of which it is the result, and into the laws of those 

 tendencies. 



