248 DISCOURSE ON THE STUDY 



of cases comparatively simple, by any direct reason- 

 ing from first principles. 



(271.) Whenever an impulse of any kind is con- 

 veyed by the air, to our ears, it produces the im- 

 pression of sound; but when such an impulse is 

 regularly and uniformly repeated in extremely rapid 

 succession, it gives us that of a musical note, the 

 pitch of the note depending on the rapidity of the 

 succession (see art. 153.). The sense of harmony, 

 too, depends on the periodical recurrence of coinci- 

 dent impulses on the ear, and affords, perhaps, the 

 only instance of a sensation for whose pleasing im- 

 pression a distinct and intelligible reason can be 

 assigned. 



(272.) Acoustics, then, or the science of sound, 

 is a very considerable branch of physics, and one 

 which has been cultivated from the earliest ages. 

 Even Pythagoras and Aristotle were not ignorant of 

 the general mode of its transmission through the 

 air, and of the nature of harmony ; but as a branch 

 of science, independent of its delightful application 

 in the art of music, it could be hardly said to exist, 

 till its nature and laws became a matter of experi- 

 mental enquiry to Bacon and Galileo, Mersenne and 

 Wallis ; and of mathematical investigation to Newton, 

 and his illustrious successors, Lagrange and Euler. 

 From that time its progress, as a branch both of 

 mathematical and experimental science, has been 

 constant and accelerated. A curious and beautiful 

 method of observation, due to Chladni, consists in 

 the happy device of strewing sand over the surfaces 

 of bodies in a state of sonorous vibration, and mark- 

 ing the figures it assumes. This has made their 



