en. xv.] THE COMPOSITION OF MIND. 127 



they severally produce, that we obtain the so-called elemen 

 tary sensation of noise or rap. 



In every way, therefore, the conclusion is forced upon us 

 that every one of our apparently simple auditory sensations 

 is made up of a vast multitude of psychical affections, of 

 which the really simple ones would never rise into con 

 sciousness save by being joined with others. Our simplest 

 cognizable sensation of sound is in reality a compound of the 

 fourth or fifth, or even of some higher, order. 



In the case of visual sensations, the same conclusion is 

 reached by a precisely similar argument, sensations of colour 

 differing from those of sound only as answering to wave 

 lengths immeasurably shorter and more rapid in succession. 

 It is unnecessary to insist upon the manifold analogies be 

 tween sound and light, which are each day brought more 

 vividly before the attention of the physical inquirer, as, for 

 example, in the wonderful but plausible hypothesis lately pro 

 pounded, that all the lines in the spectrum are simply the 

 harmonic overtones of a fundamental colour, which, being a 

 couple of octaves below red, is itself invisible. Restricting 

 our statement to ascertained points of resemblance, it may be 

 said that the argument from the phenomena of musical pitch 

 applies step by step to the phenomena of colour as we rise in 

 the scale from red to violet ; the only difference being that, 

 as the slowest vibrations which the eye receives occur at the 

 rate of about 458,000,000,000,000 in a second, we cannot 

 experimentally distinguish, as in the case of the lowest 

 sounds, the seemingly elementary sensation which answers 

 to each couple of vibrations, Nevertheless, from experiments 

 with the electric spark it has been shown that a sensation of 

 light which endures for one second is composed of at least a 

 million successive sensations, each one of which, if sepa 

 rately excited, would rise into consciousness and be recog 

 nized as a flash of light. Now, as this flash of electric light 

 is cojsiiized as white, it follows that the cognizable sensation 



