Shelley lay on the hearthrug with his head close to the fire. All these are instinctive methods for augmenting momentarily the cerebral circulation at the expense of the general circulation. It is known that very often the great conceptions of thinkers have been organized, or at all events have taken their start, in the shock of a special sensation which produced on the intelligence the effect of a drop of salt water on a well-prepared voltaic pile. All great discoveries have been occasioned, according to Moleschott’s remark, by a simple sensation.[58] Some frogs which were to furnish a medicinal broth for Galvani’s wife were the origin of the discovery of galvanism; the movement of a hanging lamp, the fall of an apple, inspired the great systems of Galileo and Newton. Alfieri composed or conceived his tragedies while listening to music, or soon after. A celebrated cantata of Mozart’s _Don Giovanni_ came to him on seeing an orange, which recalled a popular Neapolitan air heard five years before. The sight of a porter suggested to Leonardo da Vinci his celebrated _Giuda_. The movements of his model suggested to Thorwaldsen the attitude of his Seated Angel. Salvator Rosa owed his first grandiose inspirations to the scenes of Posilipo. Hogarth conceived his grotesque scenes in a Highgate tavern, after his nose had been broken in a dispute with a drunkard. Milton, Bacon, Leonardo da Vinci, liked to hear music before beginning to work. Bourdaloue tried an air on the violin before writing one of his immortal sermons. Reading one of Spenser’s odes aroused the poetic vocation in Cowley. A boiling teakettle suggested to Watt the idea of the steam-engine. In the same way a sensation is the point of departure of the terrible deeds produced by impulsive mania. Humboldt’s nursemaid confessed that the sight of the fresh and delicate flesh of his child irresistibly impelled her to bite it. Many persons, at the sight of a hatchet, a flame, a corpse, have been drawn to murder, incendiarism, or the profanation of cemeteries. It must be added that inspiration is often transformed into a real hallucination; in fact, as Bettinelli well says, the man of genius sees the objects which his imagination presents to him. Dickens and Kleist grieved over the fates of their heroes. Kleist was found in tears just after finishing one of his tragedies: “She is dead,” he said. Schiller was as much moved by the adventures of his personages as by real events.[59] T. Grossi told Verga that in describing the apparition of Prina, he saw the figure come before him, and was obliged to relight his lamp to make it disappear.[60] Brierre de Boismont tells us that the painter Martina really saw the pictures he imagined. One day, some one having come between him and the hallucination, he asked this person to move so that he might go on with his picture.[61]