LAWS OF NATURK. 189 



CHAPTER IV. 



OF LAWS OF NATURE. 



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

 which is assumed in every inference from exjierience, one of the iirst 

 observations that present themselves is, that the uniformity in question 

 is not properly uniformity, but uniformities. The general regularity 

 results from the coexistence of partial regularities. The course of na- 

 ture in general is constant, because the course of each of the various 

 phenomena that compose it is so. A certain fact invariably occurs 

 whenever certain circumstances 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 connexion between parts of the great whole 

 which we term nature, a general tissue of connexion unavoidably 

 weaves itself, by which the whole is held together. If A is gilways 

 accompanied by D, B by E, and C by F, it follows that AB is accom- 

 panied by D E, A C by i) 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 

 uniformity of the course of nature, is, that it is itself a complex fact, 

 compounded of all the separate uniformities which exist in respect to 

 single phenomena. These various uniformities, when ascertained by 

 what is regai'ded as a sufficient induction, we call in common parlance, 

 Laws of Nature. Scientifically speaking, that title is employed in a 

 more restricted sense to designate the uniformities when reduced to 

 their most simple expression. Thus in the illustration already em- 

 ployed, there were seven uniformities ; all of which, if considered suf- 

 ficiently certain, would, in the more lax application of the term, be 

 called laws of nature. But of the seven, three alone are properly dis- 

 tinct and independent ; these being presupposed, the others follow of 

 course : the three first, therefore, accoi'ding to the stricter acceptation, 

 are called laws of nature, the remainder not ; because they are in truth 

 mere cases of the three first ; virtually included in them ; said, there- 

 fore, to result from them : whoever affirras those three has abeady 

 affiimed 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 

 an equal pressure in a contrary direction, produces motion, which does 

 not cease imtil equilibi'ium 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 

 phra-se', is not a law of nature. It is a result of laws of nature. It is 

 a case of each and every one of the three laws ; and is the only occur- 

 rence by which they could all be fulfilled. If the mercury were not 

 sustained in the barometer, and sustained at such a height that the col- 

 umn of mercury were equal in weight to a column of the atmosphere, 

 of the same diameter j here would be a case, either of the air not 



