82 ON THE PHYSIOLOGICAL CAUSES OF 



see single are those at which they are looking, and that all other 

 objects behind or before these appear double ? I could adduce 

 a long list of similar examples, which have not been brought to 

 light till the actions of the senses were scientifically investigated, 

 and which remain obstinately concealed till attention has been 

 drawn to them by appropriate means often an extremely diffi- 

 cult task to accomplish. 



To this class of phenomena belong the upper partial tones. 

 It is not enough for the auditory nerve to have a sensation. The 

 intellect must reflect upon it. Hence my former distinction of 

 a material and a spiritual ear. 



"We always hear the tone of a string accompanied by a certain 

 combination of upper partial tones. A different combination of 

 such tones belongs to the tone of a flute, or of the human 

 voice, or of a dog's howl. Whether a violin or a flute, a man 

 or a dog, is close by us is a matter of interest for us to know, and 

 our ear takes care to distinguish the peculiarities of their tones 

 with accuracy. The means by which we can distinguish them, 

 however, is a matter of perfect indifference. 



"Whether the cry of the dog contains the higher octave or the 

 twelfth of the fundamental tone has no practical interest for us, 

 and never occupies our attention. The upper partials are con- 

 eque.ntly thrown into that unanalysed mass of peculiarities of a 

 tone which we call its quality. Now as the existence of upper 

 partial tones depends on the wave-form, we see, as I was able to 

 state previously (p. 65), that the quality of tone corresponds to 

 iheform of wave. 



Tha upper partial tones are most easily heard when they are 

 not in harmony with the fundamental tone, as in the case of 

 bells. The art of the bell-founder consists precisely in giving 

 bells such a form that the deeper and stronger partial tones shall 

 be in harmony with the fundamental tone, as otherwise the bell 

 would be unmusical, tinkling like a kettle. But the higher 

 partials are always out of harmony, and hence bells are unfitted 

 for artistic music. 



On the other hand, it follows, from what has been said, that 

 the upper partial tones are all the more difficult to hear, 



