Page:The wonders of optics (1869).djvu/77

 leaping from his couch, mad with rage, he seized his sword and rushing at a swallow's nest that was near, beat it down, killing the poor birds inside it, crying out that these insolent birds dared to reproach him with the murder of his father. Surprised at such a sight, his courtiers gradually disappeared, and it became known some time afterwards that Bessus was really guilty, and that the senseless action he had performed simply resulted from the voice of conscience.

The illusions of sight and hearing are often found to take an epidemic form, and historians relate an immense number of anecdotes bearing on this particular phase of self-delusion. One of the commonest of them is that which transforms the clouds into armies and figures of all kinds. Religious prejudices, optical phenomena, physical laws that are still unknown, dangerous fevers, derangements of the brain, afford a natural explanation of these hallucinations.

We have borrowed most of these examples from Brière de Boismont's works, for the special purpose of showing how easy it is to deceive the imagination, and to demonstrate the facility with which the sense of sight is led astray without the intervention of complicated apparatus. In addition, we may quote instances from Brewster, showing the ease with which the imagination enables us to see distinct forms in a confused mass of flames, or in a number of shadows superposed upon each other. This great philosopher gives us an anecdote of Peter Heamann, a Swedish pirate and murderer. One day that his crew were repairing some unimportant portion of the ship, after having pitched the place well he took the brush in order to tar the other parts of the vessel, which were much in want of such treatment; but as soon as he spread the pitch over the timbers of the ship, he was thunderstruck at seeing apparently reflected in its shining surface the image of a gallows