Tiiu amplitiuli' oftlic wavo ti-ansmitffil into llio air is 



8.6 



0.0()13 + 4.3 1/ 1 + 0.947 tail- <? 

 wliicii is a maxiniiiiii (oinial to 2 very nearly) whvn tlio wave strikes tiie iHiimdary 

 iioimaliy, ami dimiiiislies to zero as II is iii.-nascd tu 'MY'. 



The example will serve to slmw Imw, dii acroiint nf the <4iv;it ililVricncr in 

 (Iciisitv ami elasticity of the two niediums, wliilr an cart li(|tiaki' is almusl pcr- 

 ftcilv reflfrt''il wlieii it )earlu's the atiiKisplicrf, it iievertlielcss may eaiise ai rial 

 vi!)i-ations oi" considfral-lc iiiaj,'iiitiide, wliieli, iC tlie waves follow each other willi 

 stinieioiit frc<[HOncy, will lie (icrceived as soiiiul. 



§ 5. Jicjlcdimi anil Jli-fnirlliiii at Ihr hiiiitiilunt <if lii'ii ^aliil iiieiliiini-'. 

 The ehaiK'es which elastic vii>iatiuiis iiiidci<;<) at the surface ol' sc|)aralioM pf 

 fWK solid substances arc of a more c(.iii|ili\ kind than tliu-c descrilicd aliovc. 

 The incident wave may lie of either the ni>rmal ur (he Iransverse type. In either 

 case there will, ^<'nerally, he two reHcclcd and two refracted waves, «me of eaeii 

 jrair lieinji normal and the other transvei-se. Tiie relation dl' velocity and dirceticm 

 is mo.-t simply expressed hv sayine- that the velucity uitli wiiieli (lie liace nf each 

 of the live waves (one incident, two reili'cted, and two refractedi moves over the 

 plane oi" separation of the mediums mu.^t he the same for all. The velocity of the 

 trace is the yeloeitv of th<' wave di\i(le<l liy (he slue of the aneje whieli tiie line of 



transit makes with the iieiiii'ndicular to the l)ouiidar\-, and hence ha- tiie 



' ' sin f^ 



.saint! value for eveiv of the li\-e wa\es coneeril'd. Ill the (iullie, let OJ'\\r 



as hefnre the direct ion of inciilenci', All the lioiindaiy and ;1/.\' pi'i |iendieular to il. 



From P set olf a distance I'/l eipial, on any e<Mi\enient scmIc. to the Ncloelly of 



tran-.il of the incident wave (livided hy the siiii' of the anele of iiiei<Iincc. ( >n 



I'Ji as diameter descrihe a cireli'. I'roni J' as ivntri' descrihe arcs w itii radii cijual 



K 



M 



