It is difficult for a sound and contemplative mind to form any conception of the character of a philosopher, according to the true meaning of the term, more especially of an astronomer, of a man observant of the works of nature and acquainted with her laws; and yet wanting in a due sense of religion. And hence Dr. Young has declared, that— “An undevout Philosopher is mad.” Instances, however, of this kind of mania, are known to have existed; produced by that presumptuous pride, which is too often engendered by a sophistication of true philosophy with the wild fantasies of some modern metaphysical sects, affecting extraordinary illumination. By thus engrafting a bad scion upon a good stock, pernicious fruit is propagated: or, to drop metaphorical allusions, by attempting to blend into one system, principles so discordant in their nature, as those of the experimental philosopher and the visionary theorist who deals in abstract speculations and reasonings _â priori_, the appropriate powers of the mind are weakened, while its moral faculty is at the same time, and by the same means, greatly deteriorated. An extraordinary but deplorable instance of this kind was exhibited to the world by the justly celebrated astronomer Lalande, in his own conduct and character, towards the concluding part of a long life. These are so well portrayed in the very interesting _Letters on France and England_, published in _The American Review of History and Politicks_, that the writer of the present memoirs cannot forbear presenting to his reader the following extract from Letter III. “Lalande, if not the most profound and original, was certainly the most learned astronomer of France, and the principal benefactor of the science to which he was so passionately devoted. He was remarkable for the most egregious vanity, and for the broadest eccentricities of character, and almost equally eminent for the most noble virtues of the heart. By a very singular perversion of intellect, he became a professed atheist, about the commencement of the revolution; pronounced, in the year 1793, in the Pantheon, a discourse against the existence of a God, with the red cap upon his head; and displayed, on this subject, the most absolute insanity, during the rest of his life. This monstrous infatuation betrayed him into the most whimsical acts of extravagance, and particularly into the publication of a Dictionary of Atheists, in which he enregistered not only many of “the illustrious dead,” but a great number of his cotemporaries, and among these, some of the principal dignitaries of the empire.