148 EXPERIMENTS OF M. SATART. [SECT. xvi. 



the current of air is momentarily interrupted at the instant 

 each arm of the bar passes before the card ; it is compressed 

 above the card and dilated below ; but the instant the spoke 

 has passed a rush of air to restore equilibrium makes a kind 

 of explosion, and, when these succeed each other rapidly, a 

 musical note is produced of a pitch proportional to the velocity 

 <)f the revolution. When M. Savart turned this bar slowly, 

 a succession of single beats was heard ; as the velocity became 

 greater, the sound was only a rattle ; but, as soon as it was 

 sufficient to give eight beats in a second, a very deep musical 

 "note was distinctly audible corresponding to sixteen single 

 vibrations in a second, which is the lowest that has hitherto 

 been produced. When the velocity of the bar was much 

 increased, the intensity of the sound was hardly bearable. 

 The spokes of a revolving wheel produce the sensation of 

 sound, on the very same principle that a burning stick whirled 

 round gives the impression of a luminous circle. The vibra- 

 tions excited in the organ of hearing by one beat have not 

 .ceased before another impulse is given. Indeed it is indis- 

 pensable that the impressions made upon the auditory nerves 

 should encroach upon each other in order to produce a full 

 and continued note. On the whole, M. Savart has come to 

 the conclusion, that the most acute sounds would be heard 

 with as much ease as those of a lower pitch, if the duration 

 of the sensation produced by each pulse could be diminished 

 proportionally to the augmentation of the number of pulses 

 in a given time : and on the contrary, if the duration of the 

 sensation produced by each pulse could be increased in 

 proportion to their number in a given time, that the deepest 

 tones would be as audible as any of the others. 



The velocity of sound is uniform and independent of the 

 nature, extent, and intensity of the primitive disturbance. 

 Consequently sounds of every quality and pitch travel with 

 equal speed. The smallest difference in their velocity is 

 incompatible either with harmony or melody, for notes of 

 different pitches and intensities, sounded together at a little 



