The notion of freedom and of the spontaneity of the spirit became watchwords of the new spiritualist philosophers. Under the work and influence of Boutroux (1845-1921) these ideas were further emphasised and worked out more definitely to a position which assumes a critical attitude to the dogmatism of modern science and establishes a contingency in all things. Boutroux’s thesis _De la Contingence des Lois de la Nature_ appeared in 1874 and was dedicated to Ravaisson. His chief fame and his importance in the development of the spiritualist philosophy rest upon this book alone. In 1894 he published a course of lectures given at the Sorbonne in 1892-3, _Sur l’Idée de Loi naturelle_, which supplements the thesis. Outside his own country attention has been more readily bestowed upon his writings on the history of philosophy, of which subject he was Professor. In his own country, however, great interest and value are attached to his work on _The Contingency of the Laws of Nature_. In this Boutroux combines the attitude of Ravaisson with that of Lachelier. The totality of the laws of the universe manifests, according to him, a contingency. No explanation of these laws is possible apart from a free spiritual activity. The stress laid upon contingency in the laws of nature culminates in the belief in the freedom of man. The critique of science which marked Boutroux’s work has profoundly influenced thinkers like Hannequin, Payot and Milhaud,[40] and in the following century appears in the work of Duhem and of Henri Poincaré, the noted mathematician, whose books on _La Science et l’Hypothèse_ (1902), _La Valeur de la Science_ (1905), and _Science et Méthode_ (1909) have confirmed many of Boutroux’s conclusions.[41] [40] Hannequin’s notable work is the _Essai critique sur L’Hypothèse des Atomes_ (1896). Payot’s chief book is _La Croyance_ (1896). Milhaud’s critique of science is contained in his _Essai sur les Conditions et les Limites de la Certitude logique_ (1894), and in _Le Rationnel_ (1898). Duhem’s book is _La Théorie physique_ (1906). [41] It is interesting to note that Boutroux married Poincaré’s sister, and that his son, Pierre Boutroux, whose education was guided by both his uncle and his father, is now Professor at the Collège de France. Emile Boutroux was a pupil of Zeller, whose lectures on Greek philosophy he attended in Heidelberg, 1868. He expressed to the writer his grief at the later prostitution of German thought to nationalist and materialist aims. He was Professor of the History of Philosophy in Paris from 1888, then Honorary Professor of Modern Philosophy. In 1914 he gave the Hertz Lecture to the British Academy on _Certitude et Vérité_. He was until his death Directeur de la Fondation Thiers, a college for post-graduate study, literary, philosophical and scientific.