66 



ON THE PHYSIOLOGICAL CAUSES OF 



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

 small in comparison with their length, and they rim over a 

 smooth surface without external disturbance, or without any 

 action of wind. Ridge and hollow are gently rounded off, 

 equally broad and symmetrical, so that, if we inverted the curve, 

 the ridges would exactly fit into the hollows, and conversely. 

 This form of wave would be more precisely defined by saying 



FIG. 4 



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 relation 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 



