Wiseacres were, of course, at once to the fore, and set up a quasi-scientific theory of ‘colour-hearing.’ Sounds are said to awaken sensations of colour in many persons. According to some, this was a gift of specially finely organized nervous natures; according to others, it was due to an accidental abnormal connection between the optic and acoustic brain-centres by means of nerve filaments. This anatomical explanation is entirely arbitrary, and has not been substantiated by any facts. But ‘colour-hearing’ itself is by no means confirmed. The most complete book hitherto published on this subject, the author of which is the French oculist, Suarez de Mendoza,[149] collects all the available observations on this alleged phenomenon, and deduces from them the following definition: ‘It is the faculty of associating tones and colours, by which every objective acoustic perception of sufficient intensity, nay, even the memory-image of such a perception, arouses in certain persons a luminous or non-luminous image, which is always the same for the same letters, the same tone of voice or instrument, and the same intensity or pitch of tone.’ Suarez well hits the truth when he says, ‘Colour-hearing’ (he calls it _pseudo-photesthésie_) ‘is often a consequence of an association of ideas established in youth ... and often of a special action of the brain, the particular nature of which is unknown to us, and may have a certain similarity to sense-illusion and hallucination.’ For my part, I have no doubt that colour-hearing is always the consequence of association of ideas, the origins of which must remain obscure, because the combination of certain presentations of colour with certain sensations of sound may possibly depend upon the very evanescent perceptions of early childhood, which were not powerful enough to arouse the attention, and have therefore remained undiscerned in consciousness. That it is a question of purely individual associations brought about by the accident of associated ideas, and not of organic co-ordinations depending upon definite abnormal nervous connections, is made very probable by the fact that every colour-hearer ascribes a different colour to the same vowel or instrument. We have seen that to Ghil the flute is yellow, to L. Hoffmann (whom Goethe cites in his _Farbenlehre_) this instrument is scarlet. Rimbaud calls the letter ‘a’ black. Persons whom Suarez mentions heard this vowel as blue, and so on.