If the dreams evoked by sounds within the ear are usually difficult to trace in normal persons under ordinary circumstances, this is not the case with dreams suggested by sounds which strike the ear from without. These constitute one of the most interesting groups of dreams as well as one of the easiest to explain, and they are very frequent.[60] Their mechanism may, indeed, be observed under some circumstances even in the waking state. In some persons, music, a voice, a bird's song, even a word, a comment, arouse phantoms of colour and form, light and shade, coloured clouds, streams, waves, etc. The phenomena are especially rich when produced by an orchestra. Such 'music-phantoms,' as they are termed, are a special and freer development of the narrow and rigid phenomena of 'colour-hearing.' They have been studied by Dr. Ruths.[61] We have to remember that music possesses a fundamental motor basis. As Dauriac remarks, music may be defined as 'movement clothed with sound.'[62] It tends to produce movement, or, failing movement, to produce motor imagery.[63] Dreams excited by definite external auditory stimuli may be of various character. A not uncommon source--especially for those who live on a wind-swept coast--is the occurrence of storms. A lady dreams, for instance, that her little dog has fallen off a high cliff and that she hears his shrieks; it was an extremely windy night, and her window was open. The dream has some resemblance to one which Burdach recorded that he shared with a companion in an hotel during a storm; they both dreamed they were wandering at night among high precipices. On one occasion I awoke in the middle of a windy night imagining I had been listening to an opera of Gluck's (which in reality I had never heard), and experiencing all the sense of delicious waves of melody which one actually experiences in listening to such operas as _Alceste_. A fragment of a melody I had heard in the dream still persisted in my memory on awaking, so that I could mentally repeat it, when it seemed as agreeable as in the dream, though unfamiliar. The following dream had also a similar origin. I imagined that I was assisting at a spectacle of somewhat dubious erotic character, in company with other persons who, out of modesty, covered their faces with their hands with the decorous gesture which recalled (as dream consciousness evidently realised) that of people during prayer in church. Thereupon a beautiful voice was heard in the background loudly chanting a versicle of the Te Deum. This awoke me, and I seemed to realise when half awake that the voice I had heard in the dream was a real voice. There had, however, been no real voice, only the loud howling of the wind and the beating of the rain on the window panes.