G 



successively to the velocity of (1) normal waves in the first medium, (2) transverse 

 waves in tiie (iist medinm, (3) normal waves in the second medium, (4) transverse 

 waves in the second me(linm. Tjct these arcs cnt the circle in Q, Q', Q,, and Q/ 

 resjjectively. Then PQ, PQ' , PQ„ and PQ/ represent in direction as well as in 

 velocity of transit the four waves whieh result from the incident wave OP. In 

 the littnre liie incident wave has hcen assumed to he of the normal type: the same 

 eonsti iiriiiiii with a different length of /'J,' will :ipplv to determine the distuth- 

 anees produced liy tln' incidence of a transverse wave. 



In special cases !he system <if waves which jiroceeds from the houndary 

 will 111' less complicated : ihus, in the case (f per]iendicular incidence, each incident 

 wave will i;-ive I'isc to onlv one rclVactcd and one rcllc<'tci| wavt', liofh of the same 

 type as the first. And, ^I'lierally, uny transverse wave in which the displace- 

 ments arc al iij;ht angles to the jilane ol' incidence will be i-efraeted and rcHected 

 as a transverse wüvo only. 



§ fi. ll'i/yvv' (irii/iiiallnij in or tiudiKinillril iiitii all a'ololropic goliiL 

 W'Ik II the niediimi in which the disturhance orit^inatcs is JBolotropic with 

 ros|)eef to its elasticity three dillirciit modes of vihralion will in ücneral he set up, 

 and propaijafed with ihree different velocities.* And consequently when waves, 

 of whatever typ<', impins^e on an jt'olotropic medium, each incident wave will in 

 tjeneral cause three i-cfracted waves to he transmitted in dili'erent directions and 

 with diirei'cut velocities. 



Ü 7. K[l'irl iif II strdliim ill >■< (iiiji/iciiliiif/ ii'ni'cs. 

 \a'\ AlU'l) \iv a stratum with plane |;arallcl sides lyiiii;' hctween two other 

 mediums, in one of which (that on the left of the Hi:;ure) a plane wave is advanc- 

 in«'- in the direction OP or (f'R. 



* Sir W. Tliomson, Enc. Brit. Nintti Edition, Art. "Elasticity", Chap. XVII. 



