CHAPTER II ASTRONOMY The object of astronomy is the discovery of the laws of the geometrical and mechanical phenomena presented by the celestial bodies; and, by the knowledge of these laws to obtain the precise and rational prevision of the state of our system at any given period whatever. It is in a word, “the application of mathematics to celestial phenomena.”[116] Mr. H. Spencer has taken occasion of this definition to criticise the place assigned by Comte to astronomy in his classification of the sciences. He makes him contradict himself. He says: you term fundamental sciences the abstract sciences which do not study beings in nature, but the laws which govern phenomena in those beings; by what right is astronomy placed among these sciences, between mathematics and physics? Is not the object of astronomy the study of certain beings in nature? In what does the application of mathematics to celestial phenomena differ from their application to other cases? It appears evident that here Comte introduces into the series of abstract sciences a science which is really concrete, or at least, according to Mr. Spencer’s expression, abstract-concrete. Comte had foreseen the objection. The answer which he makes throws a strong light upon the sense in which he understands the words “abstract” and “general” as applied to the sciences. He partly accepts the objection. The true astronomical notions, he says, only differ from purely mathematical notions by their special restriction to the celestial case; and this, at first sight, must appear contrary to the essentially abstract nature of the speculations which belong to the first philosophy. But on the other hand, these speculations bear upon the phenomena given in experience, and the order of the abstract sciences should reproduce the real order of dependence of the phenomena. Thus the first of these sciences, mathematics, determines the essential laws of the most general phenomena, which are common to all material beings (form, position, movement). Now, are not the most general phenomena after these, those “of which the the continuous ascendency inevitably dominates the course of all the other phenomena?”[117] In other words, before passing to the study of physical, chemical, biological phenomena, etc., it is indispensable to know the general laws of the _milieu_ in which these phenomena are manifested. Outside of this _milieu_, they would be impossible, or at any rate, it so conditions them that, were it otherwise, these phenomena would also be different from what they are.