I must not, however, omit to mention that the doctrine of Kant referred to, which forms the fundamental thought of the second part of his “Metaphysical First Principles of Natural Science,” thus of the Dynamics, was distinctly and fully expounded before Kant by Priestley, in his excellent “Disquisitions on Matter and Spirit,” § 1 and 2, a book which appeared in 1777, and the second edition in 1782, while Kant’s work was published in 1786. Unconscious recollection may certainly be assumed in the case of subsidiary thoughts, flashes of wit, comparisons, &c., but not in the case of the principal and fundamental thought. Shall we then believe that Kant silently appropriated such important thoughts of another man? and this from a book which at that time was new? Or that this book was unknown to him, and that the same thoughts sprang up in two minds within a short time? The explanation, also, which Kant gives, in the “Metaphysical First Principles of Natural Science” (first edition, p. 88; Rosenkranz’s edition, p. 384), of the real difference between fluids and solids, is in substance already to be found in Kaspar Freidr. Wolff’s “Theory of Generation,” Berlin 1764, p. 132. But what are we to say if we find Kant’s most important and brilliant doctrine, that of the ideality of space and the merely phenomenal existence of the corporeal world, already expressed by Maupertuis thirty years earlier? This will be found more fully referred to in Frauenstädt’s letters on my philosophy, Letter 14. Maupertuis expresses this paradoxical doctrine so decidedly, and yet without adducing any proof of it, that one must suppose that he also took it from somewhere else. It is very desirable that the matter should be further investigated, and as this would demand tiresome and extensive researches, some German Academy might very well make the question the subject of a prize essay. Now in the same relation as that in which Kant here stands to Priestley, and perhaps also to Kaspar Wolff, and Maupertuis or his predecessor, Laplace stands to Kant. For the principal and fundamental thought of Laplace’s admirable and certainly correct theory of the origin of the planetary system, which is set forth in his “_Exposition du Système du Monde_,” liv. v. c. 2, was expressed by Kant nearly fifty years before, in 1755, in his “_Naturgeschichte und Theorie des Himmels_,” and more fully in 1763 in his “_Einzig möglichen Beweisgrund des Daseyns Gottes_,” ch. 7. Moreover, in the later work he gives us to understand that Lambert in his “_Kosmologischen Briefen_,” 1761, tacitly adopted that doctrine from him, and these letters at the same time also appeared in French (_Lettres Cosmologiques sur la Constitution de l’Univers_). We are therefore obliged to assume that Laplace knew that Kantian doctrine. Certainly he expounds the matter more thoroughly, strikingly, and fully, and at the same time more simply than Kant, as is natural from his more