Seismic Radiations. 
31 
1909-10.] 
In the case of earthquake waves, according to the views adopted in the 
former paper, the angles of incidence become less than 30° at a compara- 
tively short arcual distance from the source of the disturbance. The 
vertical displacement is therefore distinctly greater than the horizontal 
displacement, so that a horizontal pendulum, assumed to record only 
horizontal movement, will respond to a small fraction of the whole. 
2. Distortional Wave Incident in the Rock. 
I now pass to the case of the incident distortional wave. 
As in the previous case, the surface displacements are affected so slightly 
by the presence of air that we may treat the problem as practically equiva- 
lent to reflexion within the solid. Leaving out the condensational wave in 
air, we have the required solution in the form 
^ — Pgt&(cz+2/+wi) _j_ -g^ e ib(-cx+y+(tit) > 
</> = A 1 e <6( - J 7*+»+" < ) J ' ' ^ ) 
The equations of motion (I.) give 
n(c 2 + 1) = poo 2 = (m + n)(y 2 + 1) , 
or (m + n)y 2 = net — m , 
showing that when c 2 becomes less than m/w, y becomes imaginary — there is 
no reflected condensational wave. 
The surface conditions (2) and (3) hold as before, leading to the 
equations 
(e 2 - 1)A, + 2c(B - Bj) —0 ^ 
2yAj + (c 2 - 1)(B + Bj) = 0 ) ' ' K ' 
The component displacements at the surface x = 0 are 
+ a/, = B ) }« e < «»+»<> 
dxd y . (4-j 
B + Bj _ 4y c 
blw/”(^T7 2 
B + B 1 = 
^ B 
4yC + (c 2 - l) 2 
B-B 1 
_ 2(c 2 -l) 2 
4yc + (c 2 - l) 2 
k(c 2 -l) t) 
4yc+ (c 2 - l ) 2 
From (3') we find 
