156 MAURICE EWING AND A. P. CRARY 
EMERGENCE ANGLE 
A new method was used to measure the emergence angle 4 of the 
waves. The seismograph was of the type technically known as a 
Depth (ft) 

2000 4000 
Velocity (ft./sec) 
Fic. 3.—Velocity-depth relation (Green Pond). 
geophone. It was originally designed to measure only vertical motions 
but after an alteration of the spring suspension was made it would 

4 oO 0.2 
Fic. 4.—Seismograms illustrating method used to determine emergence angle. 
Angles given represent tilt of seismograph from vertical position. A, low sensitivity; 
B, high sensitivity; C, timing line. 
816 
