182 Proceedings of the Royal Society of Edinburgh. [Sess. 
make the necessary comparisons and obtain direct evidence of this 
minimum in the outcropping seismic energy. But there is another 
difficulty. The seismograms indicate displacement and not energy, and 
Primary Wave. 
Epicentral 
Distance, 
2a. 
0- 
1 
5E/5A 
Energy per 
Unit Area. 
/5E 
\ 8A * 
sin 0. 
Horizontal 
Displacement 
in Plane 
of Ray. 
o 
9 
43 
69 
22 
15-25 
3*9 
•936 
3*65 
22 
57 
45 
38 
4-50 
2*03 
•715 
1-45 
33 
43 
36 
25 
2-88 
170 
•594 
1-01 
44 
23 
28 
6 
1-26 
1-12 
•471 
•528 
52 
48 
25 
30 
•431 
•66 
•431 
•284 
61 
36 
24 
28 
•064 
•25 
•414 
•104 
69 
42 
24 
15 
•044 
•21 
•411 
•096 
82 
43 
22 
21 
•255 
•505 
•380 
•192 
102 
1 
19 
28 
•175 
•43 
•333 
140 
116 
17 
16 
31 
•483 
•69 
•284 
197 
150 
4 
7 
30 
•269 
•52 
131 
068 
Secondary Wave. 
2a. 
0. 
5E/8A. 
VsE/SA. 
COS 0. 
Average 
Horizontal 
Displacement. 
O 
12 
49 
60 
7 
11-2 
335 
•405 
2*56 
33 
22 
35 
57 
278 
1-67 
•799 
1-51 
47 
37 
27 
21 
•571 
•756 
•888 
•715 
65 
18 
25 
51 
113 
•336 
•900 
•320 
84 
29 
23 
24 
*295 
•543 
•918 
•521 
101 
26 
19 
57 
•237 
•487 
•940 
•473 
118 
2 
18 
•246 
•496 
•951 
•484 
152 
52 
7 
44 
•241 
•491 
•991 
•489 
the records would be comparable with the y/S'K/SA and not with <5E/SA. 
When the square roots are calculated and tabulated as in column 4 of 
the table just given, we may assume these to be proportional to the 
amplitudes of the vibratory motion existing just within the surface of 
the earth. 
In the case of the Primary wave the to-and-fro motion in the 
direction of the ray is the most important feature of the vibration, and 
the component of this along the surface will be comparable with the 
record on the horizontal pendulum seismograph. This component is 
obtained by multiplying -\/$E/SA by the sine of <p ; and the last column 
in the table for the Primary wave contains these numbers, which may be 
