The present Lecture, embodying a variety of subjects, under the general title of CHIMERAS OF SCIENCE, not only reviews them in succession, but expresses sentiments with regard to each which result from a long acquaintance with ancient and modern scientific authors; supported by an experimental, and, not unfrequently, by a practical acquaintance with several branches of natural philosophy. The consequence of this intimacy with various scientific studies, has been a thorough conviction of the necessity of possessing a knowledge of elementary principles, before professing a belief in new doctrines, whose only recommendation is their novelty, extravagance, and inutility. Without absolutely pretending to any golden road, or short path to learning, superficial but ambitious scholars are the first to seize on first impressions, build up some grand theory, lay down certain postulates, seek proselytes, and display a wonderful amount of enthusiasm in creating systems which, however beautiful in appearance, can boast of no solid foundation. Imperfectly educated, and shallow, but not unfrequently highly imaginative, men, if not themselves absolute charlatans, are the easily led dupes, who become the admirers and abettors of every "new wind of doctrine." Every age has been sensational. Man delights in mystery, and mysticism is a certain sign of imperfect knowledge. A classic age was not proof against the tricks and deceitful practices of the oracles, soothsayers and jugglers. The dark ages only served to keep alive the human desire for sensation; and less than a century ago, poor, simple, half idiotic women, were burnt at the stake as witches. The Mahometans had their prophet, and so have the Mormons. Mesmer had his disciples, and so have many modern Spiritualists. The Astrologer of the 17th century, is presented to us in a modern dress by the seer Zadkiel. Jacob Behmen and Emanuel Swedenborg, but represent a class that is continually dying out, yet is as continually reproduced; the authors of pious romances, theological enigmas, scientific spiritualisms, and spiritualized transcendental philosophisms. Swedenborg introduces us to the inhabitants of the moon; they are short, the size of a youth of seven years of age; and they speak with a thunderous voice for want of an atmosphere, and not from the mouth, but from the abdomen! But many persons admire such wanderings of a pretended inward and prophetic light. There are still living a few faithful believers in _Alchemy_, who earnestly look forward to the coming of the day when the grand, the glorious secret, shall be fully revealed; not, however, to the vulgar crowd, but to the noble, true, and virtuous adept,--to him, and him only.