ON SEISMOLOGICAL INVESTIGATION. 195 
\Velocity in kms. per sec.| 
| 
Localiti | Distance ' te | 
ocalities : be = == S | apth | 
in degrees Are | Chord dv in kms. | 
22 Eee arsed we Ww 4 eee ot | 
S 
Nicolaiew . 2 e é 81° 9-9 8-1 | 8-0 | 
Potsdam’. : 3 ; 92° 93. | 8-4 91 
Catania, Ischia . rs | 45 ‘ | = | ze 
Rocea di Papa, Rome . J 96 104 | 20a be : 
Shide . : > 103° 11°2 | 9°8 10:2 
The slight discrepancy in the Potsdam record no doubt depends on the 
want of accuracy in the original observation as indicated in the first 
table. 
The figures in the fifth column express in kilometres one quarter of 
the square root of the average or mean depth of the chords connecting 
the origin and each of the observing stations. |The close correspondence 
between these figures and those in the third and fourth columns so long as 
the records refer to wave paths exceeding 2,000 kms. was pointed out in 
the Report for 1898, p. 22i. These two earthquakes have been discussed 
by Dr. G. Agamennone in the ‘ Atti della Reale Accademia dei Lincei,’ 
September 18, 1898, vol. vii. Fas. 6, p. 135. Inasmuch as he has calcu- 
lated velocities for the preliminary tremors, based on the supposition that 
the disturbance had only reached the Batavian isoseist when the magneto- 
meters at that station were disturbed, he arrives at velocities practically 
reaching 30 kms. per second, which are very much higher than those dis- 
cussed in the preceding tables. He also gives velocity tables for the 
large waves which are somewhat higher than those which are obtained 
when it is assumed that the disturbances originated at the times used in 
our calculations. For example, the shock of September 20, if it originated 
at 7h. 4m. 20s. apparently gives for the velocities of the large waves 
results like the following :— 
Velocity in kms. per sec. 
On Are On Chord 
2-7 
First large wave ° r one 
Largest wave Z : 7 Ben 2°3 
Last large wave 18 16 
In calculations of this description the assumption is that all the waves 
recorded at a distant station left their origin at practically the same time. 
If this were so, inasmuch as the last trace of movement at Shide took place 
three hours after the arrival of the preliminary tremors, then the last 
movement only travelled at a rate of 0:9 km. or 0:8 km. per second, a con- 
clusion that is very improbable. The inference to be derived from the 
sections in this report relating to Earthquake Echoes (p. 227) and 
Earthquake Precursors (p. 280) is that the only movements which started 
from an origin at approximately the same time, are those lying between 
the first preliminary tremor and the large slow waves representing the 
maximum motion. The limiting velocities for this earthquake, therefore, 
lie between 9°3 and about 2-7 kms. per second. 
No. 180, March 29, 1898. 
H M. S. H MM. S§S 
Shide . E ‘ 0 5 11t023 0 39 Series of disturbances. 
Bidston 5 F About these times. 
02 
