32 HISTORY OF ACOUSTICS. 



rian curve ; so that, for the ends of physical philosophy, the solutior 

 was not very incomplete. 



John Bernoulli, a few years afterwards, 7 solved the problem of 

 vibrating chords on nearly the same principles and suppositions as 

 Taylor ; but a little later (in 1747), the next generation of great ma- 

 thematicians, D'Alembert, Euler, and Daniel Bernoulli, applied the 

 increased powers of analysis to give generality to the mode of treating 

 this question ; and especially the calculus of partial differentials, in- 

 vented for this purpose. But at this epoch, the discussion, so far as it 

 bore on physics, belonged rather to the history of another problem, 

 which comes under our notice hereafter, that of the composition of 

 vibrations ; we shall, therefore, defer the further history of the pro- 

 blem of vibrating strings, till we have to consider it in connexion with 

 new experimental facts. 



CHAPTER III. 



PROBLEM OF THE PROPAGATION OF SOUND. 



E have seen that the ancient philosophers, for the most part, held 

 that sound was transmitted, as well as produced, by some 

 motion of the air, without defining what kind of motion this was ; 

 that some writers, however, applied to it a very happy similitude, the 

 expansive motion of the circular waves produced by throwing a stone 

 into still water ; but that notwithstanding, some rejected this mode 

 of conception, as, for instance, Bacon, who ascribed the transmission 

 of sound to certain " spiritual species." 



Though it was an obvious thought to ascribe the motion of sound 

 to some motion of air ; to conceive what kind of motion could and 

 did produce this effect, must have been a matter of grave perplexity 

 at the time of which we are speaking ; and is far from easy to most 

 persons even now. We may judge of the difficulty of forming this 

 conception, when we recollect that John Bernoulli the younger 1 

 declared, that he could not understand Newton's proposition on this 

 subject. The difficulty consists in this ; that the movement of the 

 parts of air, in which sound consists, travels along, but that the parts 



Op. iii. p. 207. * Prize Dis. on Light. 1736. 



