“Positive science,” he says, “seeks neither first causes nor the ultimate goal of things. In order to link together a multitude of phenomena by one single law, general in character and conformable to the nature of things, the human spirit has followed a simple and invariable method. It has stated the facts in accordance with observation and experience, compared them, extracted their relations, that is the general facts, which have in turn been verified by observation and experience, which verification constitutes their only guarantee of truth. A progressive generalisation, deduced from prior facts and verified unceasingly by new observations, thus brings our knowledge from the plane of particular and popular facts to general laws of an abstract and universal character. But, in the construction of this pyramid of science, everything from base to summit rests upon observation and experience. It is one of the principles of positive science that no reality can be established by a process of reasoning. The universe cannot be grasped by a _priori_ methods.” Like Comte, Berthelot believed in the progress of all knowledge through a theological and metaphysical stage to a definitely scientific or positive era. The sciences are as yet young, and we cannot imagine the development and improvement, social and moral, which will accrue from their triumph in the future. For Berthelot, as for Renan, the idea of progress was bound up essentially with the triumph of the scientific spirit. In a Discourse at the Sorbonne given in commemoration of the fiftieth anniversary of his being appointed Professor at the Collège de France, we find this faith in science reiterated. “To-day,” he remarks, “Science claims a triple direction of societies, materially, intellectually and morally. By this fact the role of the men of science, both as individuals and as a class, has unceasingly come to play a great part in modern states.”