HELMHOLTZ IN BONN 



steady stream of air at low pressure, is analogous to 

 that of a pure colour, such as the red, green, or violet 

 of the spectrum. Such tones, however, are seldom 

 heard, the majority of tones being compound and 

 analogous to mixtures of simple colours, such as red 

 and violet producing purple, and so on. This fact 

 was long known to writers on acoustics, but it was 

 Helmholtz who first made an exhaustive examination 

 of such compound tones, and pointed out their im- 

 portance in connection with the question of quality, 

 timbre, or klangfarbe (clang tint), as he termed the 

 nature of the sensation by which we distinguish one 

 tone from another, although of the same pitch and 

 of the same intensity. 



If we help the mind by representing to ourselves 

 the varying forms of waves on the surface of water, 

 some with long smooth backs, others with narrow 

 crests and longer troughs, some with the slope in 

 the ascent sudden and with others more gradual, we 

 see that there may be an almost infinite variety of 

 wave-forms. ( By the term ' wave-forms ' we mean 

 only the manner in which the changes of pressure are 

 represented diagrammatically.) So it is with sound. 

 Instead of a simple pendular vibration we may have 

 vibrations or pressures of complicated form, which may 

 cause the drumhead to move outwards and inwards 

 through a complicated path of excursion. These 

 movements correspond to the action of a compound 

 wave. Thus pressures of a similar character pass into 

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