'!' 



KINETIC OR MECHANICAL VIEW OF NATURE. 31 



He must have fully realised the difticulty of imagining a 

 substance more subtle than air and yet endowed with the 

 property of rigidity, known to us only in solid Ixidies. 

 The elaboration of the theory of light pressed upon 

 physicists and mathematicians a more careful study of 

 the different states in which matter can exist. The 

 different properties which this hypothetical substance 21. 

 called ether must possess had to be mathematically de- 

 fined ; and, further, it had to be shown whether it 

 would be physically possible for a body, subject to the 

 empirical laws of motion, to possess certain of the pro- 

 perties of what we term solids, and yet to be in other 

 respects the very opposite of a solid. Tlie solution of the 

 first problem was a purely mathematical performance, in 

 which many eminent mathematicians, such as Cauchy, 

 Neumann, Green, M'Cullagh, and Stokes,^ have been 



complished abroad " (vol. i. p. 10.')). : brothers Weber, whose ' Wellenlehre 



"It is difficult to picture the re- auf Experimente gegriindet' ap- 



markable scientific ignorance of peared in 1825. In it wave-motion, 



practical men iu England in the ' such a,s the theories of sound and 



first quarter of the century. One light had made specially interesting 



can only trust that there may be a and important, was experimentally 



closer union of practice and theory examined and illustrated. The 



in our own day " (p. 106). This I theory of elasticity now received a 



passage was probably written iu the ' new ally, viz., tlie ela-stic theory 



'seventies. " of light or of the ether. Thougli 



According to Todhuntor, the true , suggested by Fresnel, its real 



theory of elasticity was founded founder was Cauchy. 



in France between the years 1820 j ^ The natural philosojiher to whiun 



and 1830, by Xavier, Poisson, and , we are most indebted for l>ringing 



Cauchy on the one side ; by the ex- clearness and definiteness into our 



perimeutal work of Savart on the | ideas and our language in these 



other. It had been allied with very intricate subjects is Sir Ceoi-ge 



theoretical acoustics since Euler's Stokes. In two ])apers, |)ublishcd 



time. Chladni in Germany fur- respectively in 184.') and 1849 (see 



thered that branch of the subject in ' Matliematical and Thysical I'ajwrs,' 



three celebrated works: ' Theorie vol. i. pp. In-l'ld, and vol. ii. pp. 



des Klanges' (1787), ' Akustik ' 8-13), he haa done more than any 



(1802), 'Beitriige zur Akustik' other writer to fix for nearly half 



(1817). Chladni infiuenced the a century the conceptionn and tlie 



