Page:Popular Science Monthly Volume 17.djvu/142



has been the object of Dr. Carter, in preparing this work, to furnish such information on the structure and function of the eye and to give such hints on the care of the eyesight as everybody should know and take heed of. Experience as an ophthalmologist has shown him the need of such a work, as a large portion of the time of such a practitioner is, he says, "occupied, day after day, in repeating to successive patients precepts and injunctions which ought to be universally known and understood." The work considers the structure of the eye, the action of lenses in forming images, the like action of the eye, and the various ways in which these images are distorted, imperfectly formed, etc., according as the eye is defective. The care of the eyes, the effect on them of natural and artificial illumination, and some practical hints on spectacles, are among the subjects treated. The volume will be found valuable in every household, both as a means of obtaining such knowledge in regard to the eyes as it is important to know and as a convenient reference-book.

this volume Mr. Walter has propounded a theory of perception differing widely from any of previous writers. He reviews and criticises the theories of Reid, Hamilton, Bain, and Spencer, none of which are to his mind satisfactory explanations of the mode in which we perceive the external world. He denies that the existence of such a world is immediately given in consciousness; or that from our experience of force an idea of an extended external cause can arise; or that the postulating of laws of thought, constraining us to invest the external world with space relations, offers a satisfactory solution of the problem of perception. That which the mind knows immediately is only the way in which it is affected and the relations between those various affections. These relations are, however, only relations of sequence, and there are no elements given in these time relations by which the mind can arrive at space-relations. In order, therefore, that the mind should be able to clothe external things with space-attributes, it must have immediate knowledge of spatial relations among its own sensations—that is, mind must be extended. "There must be," he says, "something really capable of prompting the mind to look outward. But this condition is not supplied in any mysterious innate laws of cause and effect or of association. It is supplied in the immediate perception of spatial exteriority within the sphere of the mind itself or of its phenomena. . . . We come to think of a cause, or causes, external to and independent of the mind, for the reason only that we previously have had the immediate experience of the mind acting as an external cause, so to speak, on mind." This doctrine of mind being an entity occupying space he regards as satisfactorily resolving the difficulties that have hitherto remained irresolvable. The work is original in its results, lucid in its exposition, and direct in its arguments, and will be found a valuable and interesting discussion of the subject.

the reaction of modern thought against the discussions and teachings of the schoolmen, Mr. Harper thinks there has been little or no discrimination between the good and the bad, and that with some that was frivolous there has been cast aside much that was of value. He avows himself a disciple of the scholastic doctors, and, in the preface to the present volume, undertakes to show that their metaphysics does not deserve the unstinted reproach cast upon it, either on account of its terminology, or of the subjects discussed, or of the manner in which the discussions were carried on. He has, therefore, undertaken to present the essential parts of the writings of the scholastics, especially those of St. Thomas and Saurez, in a form acceptable to modern readers. The exposition will run through four large volumes, of which this is the first.