The association between high notes and physical ascent, between low notes and physical descent, is certainly in any case very fixed.[135] In Wagner's _Lohengrin_, the ascent and descent of the angelic chorus is thus indicated. Even if we go back to the early composers, the same correspondence is found. In Purcell it is very definite. In Bach--pure and abstract as his music is generally considered--not only this elementary association, but an immense amount of motor imagery is to be found; Bach shows, indeed, a curious pre-occupation in translating the definite sense of the words he is musically illustrating into corresponding musical terms; the skill and subtlety with which he accomplishes this, can often, as Pirro and Schweitzer have shown, be appreciated only by musicians.[136] It is sometimes said that this is 'realism' in music. That is a mistake. When the impressions derived from one sense are translated into those of another sense, there can be no question of realism. A composer may attempt a realistic representation of thunder, but his representation of lightning can only be symbolical; audible lightning can never be realistic. Not only is there an instinctive and direct association between sounds and motor imagery, but there is an indirect but equally instinctive association between sounds and visual imagery which, though not itself motor, has motor associations. Thus Bleuler considers it well established that among colour-hearers there is a tendency for photisms that are light in colour (and belonging, we may say, to the 'high' part of the spectrum) to be produced by sounds of high quality, and dark photisms by sounds of low quality; and, in the same way, sharply-defined pains or tactile sensations, as well as pointed forms, produce light photisms. Similarly, bright lights and pointed forms produce high photisms, whole low photisms are produced by opposite conditions. Urbantschitsch, again, by examining a large number of people who were not colour-hearers, found that a high note of a tuning-fork seems higher when looking at red, yellow, green, or blue, but lower if looking at violet. Thus two sensory qualities that are both symbolic of a third quality are symbolic to each other.