PREFACE.

more common than is generally suspected; and a notable instance of the occasional predominance of such hallucinations, even in men who have distinguished themselves in the department of material science, occurs in the well-known case of Emanuel Swedenborg.

But another, and to some degree opposite, aberration in the domain of scientific research deserves to be mentioned as even more relevant to the science we are about to present for our readers' consideration. For a considerable period, the efforts of philosophers have been mainly directed toward the discovery and understanding of those mechanical forces which appear to regulate the motions of the material universe, and which have been found to be capable of precise calculation. The labors of those eminent men who have worked in this field of investigation have given a decided bias toward the study of material nature and the action of those physical forces which are recognized as predominant in the external universe. We would be very unwilling to try to detract, in any way, from the legitimate fame of those enterprising and intelligent philosophers whose commendable efforts have led to the development of so many interesting and useful results. But we feel compelled to acknowledge that, in our humble opinion, they have