"The turn of his mind always led him towards the positive; he disliked vague ideas, and hated equally the dreams of visionaries and the abstraction of idealists, and treated as mere nonsense everything that was not clearly and practically presented to him. He valued only those sciences which can be controlled and verified by the senses or which rest on observation and experience. He had the greatest contempt for the false philosophy and the false philanthropy of the eighteenth century. Among the chief teachers of these doctrines, Voltaire was the special object of his aversion, and he even went so far as to attack, whenever he had the opportunity, the general opinion as to his literary power."