PREFACE.

errors and prejudices of previous and less enlightened ages; and even those philosophers who have devoted themselves to the cultivation of what have been called the exact sciences, are not always exempt, as is sometimes imagined, from the common weakness of being seduced by the common prejudices of less enlightened minds. Tycho Brahe, the modern restorer of astronomical science, that most tireless observer of the starry heavens, who made such a large number of valuable observations within the field of his favorite studies, and was so tireless in the investigation of facts;—even this great matter-of-fact philosopher divided his time between the study of astronomy and the research of alchemy. He also supported the doctrines of judicial astrology, and a large portion of his books was devoted to the defense and propagation of these empty daydreams. His successor, Kepler, the precursor to Newton, the most profound physical philosopher of his age, attributed the motions of the celestial bodies to certain animal forces, and wrote a treatise on the mysterious properties of numbers. Newton himself—the most illustrious physical philosopher of his own, or of any age—after explaining the laws of the material universe, wrote a commentary on the Apocalypse. Indeed, the influence of this mystical disposition, even among very practical men, appears to be