228 REPORT—1899. 
observing station, the seismogram shows a single set of preliminary tremors, 
of short duration, a single set of pronounced vibrations corresponding to 
irregularly delivered originating impulses, and finally a series of concluding 
vibrations which rise and fall in value every three or four minutes. That 
which appears on a seismogram as a two-blow earthquake terminates 
with dual reinforcements. As illustrative of this I may refer to the Isle 
of Wight seismogram of the South Indian Ocean earthquake of August 31, 
1898 (see Earthquake No. 230). We have apparently here two large dis- 
turbances—the first I regard as the shock, and the second as its echo. 
They are followed by pairs and groups of echoes, If we closely examine 
the group of movements which I call the shock, and compare the same 
with its echo (the second pair being too small to exhibit details), we find 
that the sub-divisions of each roughly agree in character ; each shows five 
phases (three of which are very distinct) of the same relative magnitudes. 
After this we get another five-phase group, followed by two groups each 
of four phases, beyond which point rhythmical recurrence is lost. 
Fig. 2—Shide, Isle of Wight, August 31, 1898. 
Duration, 2h. 18m. Os. Max. Amp.=9 mm.=5''-4. 
A very good illustration of what may be multiple echoes is found in the 
Isle of Wight seismogram for June 29, 1898 (see Earthquake No. 215). 
This is a very large earthquake which probably caused the whole of the 
earth to pulsate, and the duration of its preliminary tremors indicates that 
it originated at a very great distance. It had a duration exceeding three 
hours. The main disturbance shows more than fourteen maxima of motion 
which have a fairly symmetrical arrangement to the right and left of a 
central dividing line. In the accompanying figure (Fig. 3), which is an 
enlargement (1-7 times) of the central portion of the original seismogram, 
the line of symmetry is marked SS. To the left of this is the main shock 1, 
and on the right is its echo, 1’, a repetition common to many earthquakes. 
That violent shocks are, a few minutes later, sometimes followed by a 
second severe movement, is well recognised in certain earthquake coun- 
tries. In Japan they are called the Uri Kaishi, or return shaking, and 
conditions leading to their production are readily imagined. All that can 
be said about 2, 3, 4, and 5 is that they have approximately the same 
characters as 2’, 3’, 4’, and 5’, but inasmuch as the first series have 
