We find it hard to picture to ourselves the state of mind of a man of older days who firmly believed that the Earth was the centre of the Universe, and that all the heavenly bodies revolved around it. He could feel beneath his feet the writhings of the damned amid the flames; very likely he had seen with his own eyes and smelt with his own nostrils the sulphurous fumes of Hell escaping from some fissure in the rocks. Looking upwards, he beheld ... the incorruptible firmament, wherein the stars hung like so many lamps.

Change is the essence of life.

One thing above all gives charm to men's thoughts, and this is unrest. A mind that is not uneasy irritates and bores me.

It is the certainty that they possess the truth that makes men cruel.

The faculty of doubting is rare among men. A few choice spirits carry the germs of it in them, but these do not develop without training.

When a history book contains no lies it is always tedious.

Never lend books, for no one ever returns them; the only books I have in my library are books that other folks have left me.