_Amnesia._--Forgetfulness is another of the characters of genius. It is said that Newton once rammed his niece’s finger into his pipe; when he left his room to seek for anything he usually returned without bringing it.[79] Rouelle generally explained his ideas at great length, and when he had finished, he added: “But this is one of my arcana which I tell to no one.” Sometimes one of his pupils rose and repeated in his ear what he had just said aloud; then Rouelle believed that the pupil had discovered the arcanum by his own sagacity, and begged him not to divulge what he had himself just told to two hundred persons. One day, when performing an experiment during a lecture, he said to his hearers: “You see, gentlemen, this cauldron over the flame? Well, if I were to leave off stirring it an explosion would at once occur which would make us all jump.” While saying these words, he did not fail to forget to stir, and the prediction was accomplished; the explosion took place with a fearful noise: the laboratory windows were all smashed, and the audience fled to the garden.[80] Sir Everard Home relates that he once suddenly lost his memory for half an hour, and was unable to recognise the house and the street in which he lived; he could not recall the name of the street, and seemed to hear it for the first time. It is told of Ampère that when travelling on horseback in the country he became absorbed in a problem; then, dismounting, began to lead his horse, and finally lost it; but he did not discover his misadventure until, on arrival, it attracted the attention of his friends. Babinet hired a country house, and after making the payments returned to town; then he found that he had entirely forgotten both the name of the place and from what station he had started.[81]