HARMONY IN MUSIC. 75 



a compressed fluid beneath the curve, which would expand 

 to the height of the curve in order to regain its natural 

 density. 



Unfortunately, the form of waves of sound, on which 

 depends the quality of the tones produced by various 

 sounding bodies, can at present be assigned in only a very 

 few cases. 



Amons: the forms of waves of sound which we are able 

 to determine with more exactness, is one of great im- 

 portance, here termed the simple or pure wave-form, and 

 represented in Fig. 3. 



Fig. 3. 



It can be seen in waves of water only when their height 

 is small in comparison with their length, and they run 

 over a smooth surface without external disturbance, or 

 without any action of wind. Eidge and hollow are gently 

 rounded off, equally broad and symmetrical, so that, if ^7e 

 inverted the curve, the ridges would exactly fit into the 

 hollows, and conversely. This form of wave would be 

 more precisely defined by saying that the particles of 

 water describe exactly circular orbits of small diameters, 

 with exactly uniform velocities. To this simple wave- 

 form corresponds a peculiar species of tone, which, from 

 reasons to be hereafter assigned, depending upon its rela- 

 tion to quality, we will term a simple tone. Such tones 

 are produced by striking a tuning-fork, and holding it 

 before the opening of a properly-tuned resonance tube. 

 The tone of tuneful human voices, singing the vowel oo 

 in too, in the middle positions of their register, appears 

 not to differ materially from this form of wave. 



We also know the laws of the motion of strings with 



