Besides it is only thus, _i.e._, by creating a system, that the sciences, exact as well as moral, are made to progress. Chemistry was not, as some have pretended, created by Lavoisier; it was founded by Stahl, it was not the pneumatic theory of Lavoisier, but really the _system of phlogiston_ devised by Stahl, which instituted chemistry in the last century. Stahl, it is well known, had the immense merit of collecting all the facts known up to his time, into a general theoretical explanation of composing a summary of them, and of creating the _system of phlogiston_. This system was, undeniably, incorrect, but the facts which had been collected towards its construction had been perfectly well selected, and included every useful element of information or research. Thus, when ten years later than Stahl, came Lavoisier, he had only, so to speak, to turn the system of his predecessor inside out, as one turns a coat. For phlogiston Lavoisier substituted oxygen; he preserved all the facts, and changed only the explanation. Thus chemistry was founded.
A well constructed synthesis must necessarily precede every theory of nature. Descartes, when working out his system of whirlwinds, formulated a conception which was certainly very inexact; but the facts upon which this theory rested were so well selected, they responded so exactly to the requirements of science, that when Newton came, with his _system of attraction_, it only remained to apply the new hypothesis to the facts collected by Descartes for his _whirlwinds_, and there was real astronomy, the true physics. When Linnæus created his _system of botany_, he made an undeniably artificial distribution of the vegetables, and Linnæus himself perfectly understood the defects of his system. But, owing to this artificial method, he succeeded in grouping all the plants into a methodical catalogue. If the principle of classification was bad, the service rendered to botany by this catalogue was immense. It was not, in fact, until after Linnæus' time that the immense mass of facts which he collected could be put in order, and the study of the vegetable world made to progress from those data. Botany dates from the publication of the _systema naturæ_ of the immortal botanist of Upsal.