HARMONY IN MUSIC. 81 



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 

 sensations 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 per- 

 ceptions 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 

 one-sided 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 accustomed, as a 

 matter of coiirse, entirely to ignore, and we do not become 

 aware of them till we make a scientific investigation of the 

 action of the senses, or have our attention directed by illness to 

 the phenomena of our own bodies. Thus we often find patients, 

 when suffering under a slight inflammation of the eyes, become 

 for the first time aware of those beads and fibres known as 

 inouches volantes swimming about within the vitreous humour 

 of the eye, and then they often hypochondriacally imagine all 

 sorts of coming evils, because they fancy that these appearances 

 are new, whereas they have generally existed all their lives. 



Who can easily discover that there is an absolutely blind 

 point, the so-called punctum caecum, within the retina of every 

 healthy eye ? How many people know that the only objects they 



