LAWS OF NATURE. 229 



CHAPTER IV. 



OP LAWS OF NATURE. 



§ 1. In the contemplation of that uniformity in the course of nature, 

 which is assumed in every inference from experience, one of the first ob- 

 servations that present themselves is, that the uniformity in question is not 

 properly uniformity, but uniformities. The general regularity results from 

 the co-existence of partial regularities. The course of nature in general is 

 constant, because the course of each of the various phenomena that com- 

 pose it is so. A certain fact invariably occurs whenever certain circum- 

 stances are present, and does not occur when they are absent; the like is 

 true of another fact; and so on. From these separate threads of connec- 

 tion between parts of the great whole which we term nature, a general tis- 

 sue of connection unavoidably weaves itself, by which the whole is held to- 

 gether. If A is always accompanied by D, B by E, and C by F, it follows 

 that A B is accompanied by D E, A C by D F, B C by E F, and finally A 

 B C by D E F ; and thus the general character of regularity is produced, 

 which, along with and in the midst of infinite diversity, pervades all nature. 



The first point, therefore, to be noted in regard to what is called the uni- 

 formity of the course of nature, is, that it is itself a complex fact, com- 

 pounded of all the separate uniformities which exist in respect to single 

 phenomena. These various uniformities, when ascertained by what is re- 

 garded as a sufficient induction, we call, in common parlance. Laws of Na- 

 ture. Scientifically speaking, that title is employed in a more restricted 

 sense, to designate the uniformities when reduced to their most simple ex--^ 

 pression. Thus in the illustration already employed, there were seven uni- 

 formities ; all of which, if considered sufliciently certain, would, in the more 

 lax application of the term, be called laws of nature. But of the seven, 

 three alone are properly distinct and indej)endent : these being presup- 

 posed, the others follow of course. The first three, therefore, according to 

 the stricter acceptation, are called laws of nature; the remainder not; be- 

 cause they are in truth mere cases of the first three ; virtually included in 

 them ; said, therefore, to result from them : whoever affirms those three has 

 already affirmed all the rest. 



To substitute real examples for symbolical ones, the following are three 

 uniformities, or call them laws of nature : the law that air has weight, the 

 law that pressure on a fluid is propagated equally in all directions, and the 

 law that pressure in one direction, not opposed by equal pressure in the 

 contrary direction, produces motion, which does not cease until equilibrium 

 is restored. From these three uniformities we should be able to predict 

 another uniformity, namely, the rise of the mercury in the Torricellian 

 tube. This, in the stricter use of the phrase, is not a law of natui*e. It is 

 the result of laws of nature. It is a case of each and eveiy one of the 

 three laws : and is the only occurrence by which they could all be fulfilled. 

 If the mercuiy were not sustained in the barometer, and sustained at such 

 a height that the column of mercury were equal in weight to a column of 

 the atmosphere of the same diameter ; here would be a case, either of the 



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