12 SCIENTIFIC THOUGHT. 



and of magnetism. On the other side there was the 

 highly developed theory of sound, which had succeeded 

 in explaining and analysing the properties of sound- 

 ing bodies by studying experimentally and mathe- 

 matically the vibrations of sounding strings, membranes 

 and plates, and also of the air in organ-pipes and other 

 _, 7. musical instruments. Acoustics, the branch of science 



Undulatory 



prepared by w hih treats of these phenomena, was, next to physical 

 ;1CS ' astronomy, the furthest developed and best founded of 

 the physical sciences. By following up the elemen- 

 tary and primitive experience, known already to the 

 ancients, that sound is everywhere to be traced to the 

 vibrations or the tremor of some body which has been 

 struck or otherwise excited, a very complete theory, 

 substantiated by many experiments, had been built up. 

 Common-sense and everyday experience had originally 

 suggested this line of inquiry and explanation. 1 No 

 other physical science was so early in possession of the 

 right road of inquiry. In astronomy and optics the 

 suggestion of common-sense, which regards the earth 

 as stationary and light as an emission travelling in 

 straight lines, had indeed allowed a certain amount of 

 definite knowledge, based upon measurement and cal- 



] Acoustics is probably the only 

 physical science where this has 

 been the case ; as is well re- 

 marked by Whewell in his ' History 

 of the Inductive Sciences.' He 

 there contrasts acoustics with as- 

 tronomy and optics. He might 

 have added dynamics, where Gal- 

 ileo's principle of inertia similarly 

 reversed the dicta of common -sense. 

 Whewell says (vol. ii. p. 237) of 

 acoustics : " Instead of having to 

 travel gradually towards a great dis- 



covery, like universal gravitation, or 

 luminiferous undulations, we take 

 our stand upon acknowledged truths, 

 the production and propagation of 

 sound by the motion of bodies 

 and of air ; and we connect these 

 with other truths, the laws of 

 motion, and the known properties 

 of bodies, as for instance their 

 elasticity. Instead of epochs of 

 discovery, we have solutions of 

 problems." 



