SURFACE REFLEXION OF EARTHQUAKE WAVES. 
389 
9‘0 mm. along a and I'4 mm. at right angles to a and H/Y = 3, the same as in the 
first movement. The angle of impingence deduced is 57° or 73°, the ambiguity 
arising from the fact that in this region of reflexion H/V has the same value for two 
different angles. We cannot settle the ambiguity except by observations for different 
distances, and the fact that case (2) gives e close to 60 c (the minimum value of H/V 
being about 2 at this point), suggests that the larger angle 73° is probably the right 
one. The value from the time curve is 65°, and the discrepancy is of importance. 
I consider the test by direct observation of the angle a very searching one, and likely 
to throw considerable light on the question of the accuracy of the time curves. 
Passing to the reflexion of transversal waves SR„, we have to observe that when 
the vibration is perpendicular to the azimuth plane no change is introduced by 
reflexion, so that such waves proceed as before. The vibration in the azimuth plane 
undergoes change in type for A less than 4000 km., and at greater distances change 
of magnitude and change of sign. This introduces very profound changes in the 
character of the effects to be expected. 
In Table V. I have calculated the relative magnitudes of S and SE^ to be expected 
on account of reflexion alone and for the waves vibrating in the azimuth plane. 
Table V. 
A in kilometres. 
Vibration in 
azimuth plane. 
S. 
Time interval 
in seconds. 
SRl 
1,000 < 
r H 
W 
0-52 
1-0 
4 
0-46 
0-79 
2,000 < 
r h 
0-36 
28 
0-52 
[V 
1 • 22 
1-0 
3,000< 
fH 
IV 
0-50 
1-52 
71 
0-48 
1-1 
4,000 < 
r H 
V 
2-3 
0-82 
131 
0-36 
1 • 22 
5,000 < 
fH 
IV 
1-8 
0-92 
197 
0-16 
1-36 
6,000 < 
rH 
L v 
1-78 
0-90 
254 
0-50 
1-52 
7,000 < 
fH 
LV 
1-78 
0-88 
298 
1-62 
0-76 
8,000 < 
fH 
1-78 
329 
0-28 
IV 
0-86 
o-io 
9,000 < 
fH 
IV 
1-80 
0-84 
354 
0-13 
0-06 
10,000 < 
fH 
IV 
1-80 
0-82 
373 
0-25 
0-13 
11,000 
fH 
IV 
1-83 
0-76 
397 
0-32 
0-16 
12,000 
fH 
IV 
1-85 
0-72 
427 
0-32 
0-16 
3 F 
VOL. CCXVIII.—A. 
