The two volumes octavo now presented to the reader are a translation from the original Latin of the first of three volumes folio, published by Swedenborg at Dresden and Leipsic, in the year 1734, under the general title of Opera Philosophica. The first of the three is entitled specifically The Principia and is a treatise upon the First Principles of Natural Things: it forms in itself an independent work, being appropriated to certain philosophical and scientific subjects, while the two latter volumes are confined to such as are commonly called practical.