92 ON THE PHYSIOLOGICAL CAUSES OF 



simple wave-forms. All other wave-forms, such as those 

 produced by the greater number of musical instruments, 

 excite sensations of a variety of simple tones. 



Consequently, all the tones of musical instruments 

 must in strict language, so far as the sensation of musical 

 tone is concerned, be regarded as chords with a pre- 

 dominant fundamental tone. 



The whole of this theory of upper partials or harmonic 

 overtones will perhaps seem new and singular. Probably 

 few or none of those present, however frequently they 

 may have heard or performed music, and however fine 

 may be their musical ear, have hitherto perceived the 

 existence of any such tones, although, according to my 

 representations, they must be always and continuously 

 present. In fact, a peculiar act of attention is requisite 

 in order to hear them, and unless we know how to perform 

 this act, the tones remain concealed. As you are aware, 

 no perceptions obtained by the senses are merely sensa- 

 tions impressed on our nervous systems. A peculiar 

 intellectual activity is required to pass from a nervous 

 sensation to the conception of an external object, which 

 the sensation has aroused. The sensations of our nerves 

 of sense are mere symbols indicating certain external 

 objects, and it is usually only after considerable practice 

 that we acquire the power of drawing correct conclusions 

 from our sensations respecting the corresponding objects. 

 Now it is a universal law of the perceptions obtained 

 through the senses, that we pay only so much attention to 

 the sensations actually experienced, as is sufficient for us 

 to recognise external objects. In this respect we are very 

 onesided and inconsiderate partisans of practical utility ; 

 far more so indeed than we suspect. All sensations which 

 have no direct reference to external objects, we are accus- 

 tomed, as a matter of course, entirely to ignore, and we 

 do not become aware of them till we make a scientific 



