328 HISTORY OF ACOUSTICS. 



says 4 , " An echo takes place, when the air, being as 

 one body in consequence of the vessel which bounds 

 it, and being prevented from being thrust forwards, 

 is reflected back like a ball." Nothing material was 

 added to such views till modern times. 



Thus the first conjectures of those who philoso- 

 phized concerning sound, led them to an opinion 

 concerning its causes and laws, which only required 

 to be distinctly understood, and traced to mecha- 

 nical principles, in order to form a genuine science 

 of Acoustics. It was, no doubt, a work which re- 

 quired a long time and sagacious reasoners, to 

 supply what was thus wanting ; but still, in conse- 

 quence of this peculiar circumstance in the early 

 condition of the prevalent doctrine concerning 

 sound, the history of Acoustics assumes a peculiar 

 form. Instead of containing, like the history of 

 Astronomy or of Optics, a series of generalizations, 

 each including and rising above preceding gene- 

 ralizations; in this case, the highest generalization 

 is in view from the first; and the object of the 

 philosopher is to determine its precise meaning and 

 circumstances in each example. Instead of having 

 a series of inductive Truths, successively dawning 

 on men's minds, we have a series of Explanations, 

 in which certain experimental facts and laws are re- 

 conciled, as to their mechanical principles and their 

 measures, with the general doctrine already in our 

 possession. Instead of having to travel gradually 



4 De Animd, ii. 8. 



