REFLEXION OF ELASTIC WAVES 135 
4% of the incident wave. This percentage rapidly decreases almost to 
zero until the critical angle is reached, and at greater angles of inci- 
dence 100% of the energy is reflected as a longitudinal wave. These 

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Fic. 1.—Time-distance graph of wave fronts resulting from two layers. 
figures do not seem to be borne out in practical cases, as for angles of 
incidence ranging from perpendicular to 30° I have not observed any 
substantial reduction in the amplitude of reflected impetii. Consider 
now a seismograph placed at a point C and again erect an ordinate to 
7195, 
