Grove's remarkable work on the unity of all physical forces, written in 1843—no attention was paid to it till 1856. One must read the history of science in the first half of the nineteenth century to realise how dense was the obscurity which enveloped Europe at that time.
The veil was suddenly rent when, towards the end of the "fifties," under the impulse of the revolutionary year of 1848, there began in Western Europe the movement which brought about Garibaldi's rising, the liberation of Italy, the abolition of slavery in America, liberal reforms in England, and a few years later the abolition of serfdom and the knout in Russia. The same movement overthrew in Europe the philosophical authority of Schelling and Hegel, and in Russia it gave vise to an open rebellion against intellectual serfdom and cringing to all sorts of authority, which rebellion was known by the name of Nihilism.
Now that we can look backwards upon the history of those times, it is evident for us that it was the propaganda of Republican and Socialist ideas in the "thirties" and "forties" of the nineteenth century, and the Revolution in 1848, which helped science to rend the bonds that had stifled it since the anti-revolution reaction had begun after the crushing, by the united Kings, of the revolutionary French Republic of 1789–1793.
Without entering into details, it will be sufficient to remember a few facts. Séguin, whose name has just been mentioned as the promoter of the mechanical theory of heat; Augustin Thierry, the historian who first laid the basis of the study of the rule of the people in the small Republics of the early Middle Ages, and of the Federalist ideas of those times; Sismondi, the historian of the free mediæval Republics in Italy, were followers of Saint-Simon—one of the three great founders of Socialism in the first half of the nineteenth century; and Alfred R. Wallace, who discovered at the same time as Darwin the theory of origin of species through natural selection, was in his youth a convinced partisan of Robert Owen; Auguste Comte was a follower of Saint-Simon; Ricardo, as well as Bentham, followed Owen; and the materialists Carl Vogt and George Lewes, as well as Grove, Mill, Herbert Spencer, and so many others, were under the influence of the Radical-Socialist movement in the "thirties" and "forties." From this movement they drew their scientific courage.
The appearance, in the short space of five or six years, 1856–1862, of the works of Grove, Joule, Berthelot, Helmholtz, Mendéléeff; of Darwin, Claude Bernard, Spencer, Moleschott,
