The most frequent method consists of artificially increasing the flow of blood to the brain. Rousseau would think bare-headed in full sunshine; Bossuet would work in a cold room with his head wrapped in furs; others would immerse their feet in ice-cold water (Grétry, Schiller). Very numerous are those who think "horizontally"--that is, lying stretched out and often flattened under their blankets (Milton, Descartes, Leibniz, Rossini, etc.)
Some require motor excitation; they work only when walking,[26] or else prepare for work by physical exercise (Mozart). For variety's sake, let us note those who must have the noise of the streets, crowds, talk, festivities, in order to invent. For others there must be external pomp and a personal part in the scene (Machiavelli, Buffon). Guido Reni would paint only when dressed in magnificent style, his pupils crowded about him and attending to his wants in respectful silence.
On the opposite side are those requiring retirement, silence, contemplation, even shadowy darkness, like Lamennais. In this class we find especially scientists and thinkers--Tycho-Brahé, who for twenty-one years scarcely left his observatory; Leibniz, who could remain for three days almost motionless in an armchair.
But most methods are too artificial or too strong not to become quickly noxious. Every one knows what they are--abuse of wine, alcoholic liquors, narcotics, tobacco, coffee, etc., prolonged periods of wakefulness, less for increasing the time for work than to cause a state of hyperesthesia and a morbid sensibility (Goncourt).
Summing up: The organic bases of the creative imagination, if there are any specially its own, remain to be determined. For in all that has been said we have been concerned only with some conditions of the general working of the mind--assimilation as well as invention. The eccentricities of inventors studied carefully and in a detailed manner would finally, perhaps, be most instructive material, because it would allow us to penetrate into their inmost individuality. Thus, the physiology of the imagination quickly becomes pathology. I shall not dwell on this, having purposely eliminated the morbid side of our subject. It will, however, be necessary to return thereto, touching upon it in another part of this essay.