168 SPECIAL SENSES. 



ments and different registers of the human voice, as in grand 

 choral and orchestral compositions, shades of effect, almost 

 innumerable, may be produced. The modification of tones 

 in this way constitutes harmony ; and an educated ear, not 

 only experiences pleasure from these musical combinations, 

 but can distinguish their different component parts. 



A chord may convey to the ear the sensation of complete- 

 ness in itself, or it may lead to a succession of tones before 

 this sense of completeness is attained. Different chords of 

 the same key may be made to follow each other, or we may, 

 by transition-tones, pass to the chords of other keys. Each 

 key has its fundamental note, and the transition from one 

 key to another, in order to be agreeable to the ear, must be 

 made in certain well-defined and invariable ways. These reg- 

 ular transitions constitute modulation. The ear becomes fa- 

 tigued by long successions of tones, always in one key, and 

 modulation is essential to the enjoyment of elaborate musical 

 compositions ; otherwise, the tones would not only become 

 monotonous, but their correct appreciation would be im- 

 paired, as the appreciation of colors becomes less distinct 

 after looking for a long time at an object presenting a single 

 vivid tint. 



The history of music dates far back into antiquity, first 

 consisting of the melodious succession of tones, and later, of 

 both melody and harmony. Until within a comparatively re- 

 cent period, the only analysis of tones was that of Pythago- 

 ras, who analyzed the sound produced by vibrating strings. 

 He divided a vibrating string into two unequal sections, one 

 twice the length of the other. Upon sounding these two di- 

 visions simultaneously, he found the note of the shorter di- 

 vision to be the octave of the longer. He then divided the 

 string, so that its parts had the relation of two to three, and 

 found the notes separated by an interval of a fifth. " Thus, 

 dividing his string at different points, Pythagoras found the 

 so-called consonant intervals in music to correspond with cer- 

 tain lengths of his string ; and he made the extremely im- 



