CH. XV.] THE COMPOSITION OF MIND. 123 



Now, this conclusion, wliich admirably explains the begin- 

 nings of conscious intelligence in the young child, is com- 

 pletely confirmed by experiments lately made with reference 

 to the continuous genesis of sensations in the adult. Not 

 only does the infant frame its earliest conscious sensations 

 by the compounding of unconscious or sub conscious psy- 

 chical changes, but in every sensation of sound, colour, 

 odour, taste, or touch, which the adult receives, there is a 

 precisely similar formation of a conscious state by the com- 

 pounding of unconscious or sub-conscious psychical states. 

 In the case of sound, the evidence for this statement amounts 

 to complete demonstration; the evidence is hardly less 

 strong in the case of sight ; and, in the case of the other 

 senses, all the evidence thus far obtained points toward the 

 same conclusion. Let us first examine the composition of a 

 sensation of sound, as admirably elucidated by M. Taine in 

 his recent treatise on " Intelligence." 



In musical sounds three characteristics are to be distin- 

 guished — loudness, pitch, and quality or timhre. The first 

 of these, the loudness, depends upon the amplitude of the 

 atmospheric waves by which the sensation of sound is caused. 

 A series of sound-producing waves, like any other series of 

 waves, has its elevations and depressions, and the height of 

 the elevation above the depression is called the amplitude of 

 the wave. The loudness of the sound varies as the square 

 of the wave's amplitude. From this it follows that every 

 elementary sound has a period of minimum intensity, 

 answering to the wave's minimum amplitude when it is just 

 beginning to rise ; secondly, a period of maximum intensity 

 anwering to the wave's maximum amplitude when it has 

 risen to its greatest height ; and, thirdly, a period of mini- 

 mum intensity, answering to the wave's minimum amplitude 

 when it has sunk nearly to the level again ; while between 

 ahese minima and the maximum there are many varying 

 degrees of loudness. In other words, every elementaiy 



