Before engaging in the study of practical zoology, Lamarck had rendered himself conspicuous by the boldness and originality of his speculations regarding a variety of physical phenomena. The general laws of chemistry, the origin of the globe and its inhabitants, the condition of the atmosphere and of living bodies, and most other great questions fitted to attract an active fancy, had by turns been the subjects of his contemplation; and on many of them he had elaborated a theory which he conceived calculated to elucidate the most abstruse phenomena they presented. To these views he attached the highest importance, considering them destined to place almost every branch of knowledge on a new and secure foundation. He therefore took advantage of every opportunity to enforce and illustrate them, and they will be found to pervade most of his published works, even such as afford no obvious plea for their introduction. Although most of them are exploded as fanciful and untenable, these theories display much ingenuity and extensive knowledge, and a pretty full account of them is necessary to show the character of Lamarck’s mind, and the wide range of his studies. As early as 1780, he had presented his Theory of Chemistry to the Academy of Sciences; but it was not published for several years afterwards, when it appeared under the title of “Researches on the Causes of the most important physical Facts, and particularly on those of Combustion; of the raising of Water in the State of Vapour; of the Heat produced by the Friction of solid Bodies against each other,” &c. &c. A condensed view of the opinions promulgated in that work, and some others on the same subject, is thus given by Cuvier. According to our author, “Matter is not homogeneous; it consists of simple principles, essentially different among themselves. The connexion of these principles in compounds varies in intensity; they mutually conceal each other, more or less, according as each of them is more or less predominant. The principle of no compound is ever in a natural state, but always more or less modified: as, however, it is not agreeable to reason that a substance should have a tendency to depart from its natural condition, it must be concluded, that combinations are not produced by Nature, but that, on the contrary, she tends unceasingly to destroy the combinations which exist, and each principle of a compound body tries to disengage itself according to the degree of its energy. From this tendency, favoured by the presence of water, dissolutions result: affinities have no influence; and all experiments by which it is attempted to be proved that water decomposes, and consists of many kinds of air, are mere illusions, and that it is fire which produces them. The element of fire[2] is subject, like the others, to modification when combined. In its natural state, everywhere diffused and penetrating every substance, it is absolutely imperceptible: only,