(26.) The first thing impressed on us from our earliest infancy is, that events do not succeed one another at random, but with a certain degree of order, regularity, and connection;--some constantly, and, as we are apt to think, immutably,--as the alternation of day and night, summer and winter,--others contingently, as the motion of a body from its place, if pushed, or the burning of a stick if thrust into the fire. The knowledge that the former class of events _has_ gone on, uninterruptedly, for ages beyond all memory, impresses us with a strong expectation that it will continue to do so in the same manner; and thus our notion of an _order of nature_ is originated and confirmed. If every thing were equally regular and periodical, and the succession of events liable to no change depending on our own will, it may be doubted whether we should ever think of looking for causes. No one regards the night as the cause of the day, or the day of night. They are alternate effects of a common cause, which their regular succession alone gives us no sufficient clue for determining. It is chiefly, perhaps entirely, from the other or contingent class of events that we gain our notions of cause and effect. From them alone we gather that there are such things as laws of nature. The very idea of a law includes that of contingency. “_Si quis mala carmina condidisset, fuste ferito_;” if such a case arise, such a course shall be followed,--if the match be applied to the gunpowder, it will explode. Every law is a provision for cases which _may_ occur, and has relation to an infinite number of cases that never have occurred, and never will. Now, it is this provision, _à priori_, for contingencies, this contemplation of possible occurrences, and predisposal of what shall happen, that impresses us with the notion of a _law_ and a _cause_. Among all the possible combinations of the fifty or sixty elements which chemistry shows to exist on the earth, it is likely, nay almost certain, that _some_ have never been formed; that some elements, in some proportions, and under some circumstances, have never yet been placed in relation with one another. Yet no chemist can doubt that it is _already fixed_ what they will do when the case does occur. They will obey certain laws, of which we know nothing at present, but which must _be_ already fixed, or they could not be laws. It is not by habit, or by trial and failure, that they will learn what to do. When the contingency occurs, there will be no hesitation, no consultation;--their course will at once be decided, and will always be the same if it occur ever so often in succession, or in ever so many places at one and the same instant. This is the perfection of a law, that it includes all possible contingencies, and ensures implicit obedience,--and of this kind are the laws of nature.