Forty-nine volumes having been published, ending with Number 100, October, 1845, it was deemed expedient to close the series with a fiftieth volume, which should contain an ample and well digested INDEX of the whole. This great labor, vastly more arduous and protracted than had been anticipated, is at last accomplished. The strict verification of every reference in this Index, by actual comparison of the proof with the volume and page, has been a labor surpassed only by the toil of constructing the Index itself. The printing was commenced in October, 1846, and so toilsome and time-consuming has been the correction of the proofs, that although the work has gone steadily forward, without interruption, it is only at this late day completed. We may confidently believe that the volume will prove useful, not only to those who may possess the whole series, but to all who are connected in any way with the arts or sciences; for, whatever the department, the reader is directed by it to the various memoirs that have been published in the Journal on the subject that interests him, whether relating to the progress of science, to details of facts in the different departments of knowledge, or to the various resources of this and other countries: with such a guide, the entire copies of the work in public libraries or in those of individuals, become available. As this volume may be consulted by many who have never seen the plan and prospectus of the Journal with which the first volume began, we republish, on this occasion, both the "Plan of the Work," and also those parts of the "Introductory Remarks" in which our early views were explained. Our readers will thus be able to judge how far we have fulfilled our engagements, and also how far our prospective views have been realized in the course of our now long experience. They will have moreover before them in this Prospectus of 1817, the principles that are still to guide us in our continued editorial labors. "PLAN OF THE WORK.[B] "This Journal is intended to embrace the circle of the PHYSICAL SCIENCES, with their applications to the ARTS, and to every useful purpose. It is designed as a deposit for original American communications; but will contain also occasional selections from Foreign Journals, and notices of the progress of Science in other countries. Within its plan are embraced, NATURAL HISTORY, in its three great departments of MINERALOGY, BOTANY and ZOOLOGY:-- CHEMISTRY and NATURAL PHILOSOPHY, in their various branches; and MATHEMATICS, pure and mixed. It will be a leading object to illustrate AMERICAN NATURAL HISTORY, and especially our MINERALOGY and GEOLOGY. The APPLICATIONS of these sciences are obviously as numerous as physical arts and physical wants; for no one of these arts or wants can be named which is not connected with them.