SENSOPJAL FUNCTIONS. 



surface of a calm lake is thrown into circular waves by 

 the force of a stone thrown into it 



564. The velocity of sound through the atmosphere is 

 about 1,100, or more nearly 1,142 feet in a second. 

 Hence we see the flash of a gun, and after an interval, 

 depending on the distance, hear the report. Thus in a 

 thunder-storm, if we allow 1,100 feet per second, between 

 the time when the flash of lightning is seen, and the thun- 

 der heard, we may ascertain very nearly the distance of 

 the cloud. 



565. Solids and liquids convey sounds much more per- 

 fectly and rapidly than air. Franklin found that a sound, 

 after travelling above a mile through water, lost little of 

 its intensity ; and Chladni states, that, according to his ex- 

 periments, the velocity of sound in water is at the rate of 

 about 4,900 feet in a second, being between four and five 

 times more rapid than it is through the air. 



. 566. In musical tones, if the intervals between the vi- 

 brations be short, the tone is acute, if long the tone is 

 grave. Hence in the violin, and other musical instruments, 

 the strings designed for h'gh or acute notes are small, that 

 their vibrations may be rapid ; while those which make 

 the low or grave tones are large, and sometimes wound 

 around with fine wire, in order to increase their weight, 

 and thus to make them vibrate slowly. 



567. In musical tones, it is the quality and variety of 

 the sounds which give the hearer so much pleasure. The 

 string of the harpsichord, when fastened to a piece of 

 board, or to the ground, may be made to give the same 

 pitch, or grade of tone with respect to gravity or acuteness, 

 as when on the instrument, but an instrument having such 

 a quality of tone would give no pleasure to the ear. 



568. The ear is susceptible of much cultivation with 

 respect to music, as is the eye with respect to painting. 

 The finest and -most complex strains of music are often 

 lost upon the uneducated ear, as the noblest works of 

 the painter are unappreciated by the uncultivated eye. 

 Hence tones, and pictures, which raise the most enthu- 



In what direction is sound propagated ? What is the velocity with 

 Vrhich sound passes through the air? How may we tell the distance of 

 a thunder-cloud ? What is said of the propagation ol sounds by solids 

 and fluids ? How are grave or acute musical tones formed ? 



