Decidedly the most important of the pieces of which we have not yet spoken must be counted the _Thoughts on the Interpretation of Nature_ (1754). His study of Bacon and the composition of the introductory prospectus of the Encyclopaedia had naturally filled Diderot's mind with ideas about the universe as a whole. The great problem of man's knowledge of this universe,--the limits, the instruments, the meaning of such knowledge, came before him with a force that he could not evade. Maupertuis had in 1751, under the assumed name of Baumann, an imaginary doctor of Erlangen, published a dissertation on the _Universal System of Nature_, in which he seems to have maintained that the mechanism of the universe is one and the same throughout, modifying itself, or being modified by some vital element within, in an infinity of diverse ways.[207] Leibnitz's famous idea, of making nature invariably work with the minimum of action, was seized by Maupertuis, expressed as the Law of Thrift, and made the starting-point of speculations that led directly to Holbach and the _System of Nature_.[208] The _Loi d'Epargne_ evidently tended to make unity of all the forces of the universe the keynote or the goal of philosophical inquiry. At this time of his life, Diderot resisted Maupertuis's theory of the unity of vital force in the universe, or perhaps we should rather say that he saw how open it was to criticism. His resistance has none of his usual air of vehement conviction. However that may be, the theory excited his interest, and fitted in with the train of meditation which his thoughts about the Encyclopaedia had already set in motion, and of which the _Pensees Philosophiques_ of 1746 were the cruder prelude. [207] As to the precise drift of Maupertuis's theme, see Lange, _Gesch. d. Materialismus_, i. 413, _n._ 37. Also Rosenkranz, i. 134. [208] In 1765 Grimm describes the principle of Leibnitz and Maupertuis as "gaining on us on every side."--_Corr. Lit._, iv. 186. The _Thoughts on the Interpretation of Nature_ are, in form as in title, imitated from those famous _Aphorismi de Interpretatione Naturae et Regni Hominis_, which are more shortly known to all men as Bacon's _Novum Organum_.[209] The connection between the aphorisms is very loosely held. Diderot began by premising that he would let his thoughts follow one another under his pen, in the order in which the subjects came up in his mind; and he kept his word. Their general scope, so far as it is capable of condensed expression, may be described as a reconciliation between the two great classes into which Diderot found thinkers upon Nature to be divided; those who have many instruments and few ideas, and those who have few instruments and many ideas,--in other words, between men of science without philosophy, and philosophers without knowledge of experimental science.