Oct. 1, 1885] 
oscillations inwards are described more rapidly than those out- 
wards. (7) As a disturbance radiates the period increases. 
Finally it becomes equal to the period of the transverse motion. 
From this it may be inferred that the greater the initial disturb- 
ance the greater the frequency of waves. (8) Certain of the 
inward motions of ‘‘shock” have the appearance of having 
been described in less than no time. (9) The first outwards 
motion, which on diagrams has the appearance of a quarter- 
waye, must be regarded as a semi-oscillation. (10) The waves 
on the diagrams taken at different stations do not correspond. 
(11) At a station near the origin, a notch in the crest of a wave 
of shock gradually increases as the disturbance spreads, so that 
at a second station the wave with a notch has split up into two 
waves. (12) Near the origin the normal motion has a definite 
commencement. At a distance the motion commences irregu- 
larly, the maximum motion being reachéd gradually. 
IV. Transverse Motion.—(1) Near to an origin the transverse 
motion commences definitely but irregularly. (2) Like the 
normal motion, the first two or three movements are decided, 
and their amplitude slightly exceeds that of those which follow. 
(3) The amplitude of transyerse motion as the disturbance 
radiates decreases at a slower rate than that of the normal 
motion. (4) Asa disturbance dies out at any particular station 
the period decreases. (5) As a disturbances radiates the period 
increases. This is equivalent to an increase in period as the 
intensity of the initial disturbance increases. (6) As we recede 
from an origin the commencement of the transverse motion 
becomes more indefinite. 
V. Relation of Normal to Transverse Motion.—(1) Near to an 
origin the amplitude of normal motion is much greater than that 
of the transverse motion. (2) As the disturbance radiates, the 
amplitude of the transverse motion decreases at a slower rate than 
that of the normal motion, so that at a certain distance they may 
be equal toeach other. (3) Near to an origin the period of the 
transverse motion may be double that of the normal motion ; 
but as the disturbance dies out at any given station, or as it 
radiates, the periods of these two sets of vibrations approach 
each other. 
VI. Maximum Velocity and Intensity of Movement.—(1) An 
earth particle usually reaches its maximum velocity during the 
first inward movement. A high velocity is, however, sometimes 
attained in the first outward semi-oscillation. (2) The intensity 
of an earthquake is best measured by its destructive power in 
overturning, shattering, or projecting various bodies. (3) The 
value 
$ =—— — (I — cos é 
v? = $¢,/a* + 6° X (— 
used by Mallet and other seismologists to express the velocity of 
shock as determined from the dimensions of a body which has 
been overturned, is a quantity not obtainable from an earthquake 
diagram. It represents the effect of a sudden impulse. (4) In 
an earthquake a body is overturned or shattered by an accelera- 
tion, f, which quantity is calculable for a body of definite 
dimensions. The quantity f as obtained from an earthquake 
: : v Vi : : 
diagram lies between — and —*, where v is the maximum velo- 
a@ 
city, is the quarter-period, and @ is the amplitude. (5) The 
initial velocity given in the formula v? = = 
(for horizontal pro- 
jection) used by Mallet as identical with v? in 3, are not identical 
quantities. (6) In discussing the intensity of movement I have 
used the values - - (7) The intensity of an earthquake at first 
decreases rapidly as the disturbance radiates ; subsequently it 
decreases more slowly. (8) A curve of intensities deduced from 
observations at a sufficient number of stations would furnish the 
means of approximately calculating an absolute value for the 
intensity of an earthquake. 
VII. Vertical Motion.—(1) In soft ground vertical motion 
appears to be a free surface-wave which outraces the horizontal 
component of motion. (2) Vertical motion commences with 
small rapid vibrations, and ends with vibrations which are long 
and slow. (3) High velocities of transit may be obtained by 
the observation of this component of motion. It is possibly an 
explanation of the preliminary tremors of an earthquake and the 
sound phenomenon, (4) The amplitude and period of vertical 
wayes as observed at the same or different stations have been 
measured. 
VIII. Velocity.—(1) The velocity of transit decreases as a 
NATURE 
527 
disturbance radiates. (2) Near to an origin the velocity of 
transit varies with the intensity of the initial disturbance. (3) 
The rate at which the normal motion outraces the transverse 
motion is not constant. (4) As the amplitude and period of the 
normal motion approach in value to those of the transverse 
motion, so do the velocities of transit of these motions approach 
each other. (5) That the ratio of the speed of normal and 
transverse motions is not constant is shown from a table of these 
velocities calculated for different rocks from their moduli of 
elasticity. 
IX. Miscellaneous.—(1) At the time of an earth-disturbance, 
currents are produced in telegraph lines. (2) The exceedingly 
rapid decrease in the intensity of a disturbance in the immediate 
neighbourhood of the epicentrum has been illustrated by a 
diagram. (3) For the duration of a disturbance due to a given 
impulse in different kinds of ground, reference must be made to 
the detailed descriptions of the first four sets of experiments. 
Experiments on a Building to resist Earthquake Motion.—In 
the Report of last year I described a house which rested at its 
foundations upon cast-iron balls. These balls were ro-inch 
shell. The records obtained from an instrument placed inside 
this house showed that, although it was subjected to consider- 
able movement at the time of an earthquake, all sawdden motion 
had been destroyed. Although the balls did very much to 
mitigate earthquake motion, wind and other causes produced 
movements of a far more serious nature than the earthquake. 
To give greater steadiness to the house, 8-inch balls were tried, 
and then I-inch balls. Finally the house was rested at each of 
its piers upon a handful of cast-iron shot, each 4-inch in 
diameter. By this means the building has been rendered 
astatic, and, in consequence of the great increase in rolling 
friction, sufficiently stable to resist all effects like those of wind. 
The shot rest between flat iron plates. That the house had 
peculiar foundations would not be noticed unless specially 
pointed out. From these experiments it seems evident that it 
is possible to build light one-storied structures of wood or iron 
in which, relatively to other houses, but little movement will be 
felt. 
Observations in a Pit 10 feet deef.—The instrument placed in 
this pit is similar to all the other instruments, and is installed in 
a similar position. Comparing the maximum amplitudes, maxi- 
mum velocities, and maximum accelerations obtained in the pit 
with those obtained at about thirty feet distance, they are for 
one particular earthquake respectively in the ratios of 1 : 43, 
{:52, and 1:82, In most earthquakes the extent of motion has. 
been too small to admit of measurement, and that there had 
been any movement could only be detected by holding the plate 
on which the record was written up to the light and glancing 
along it lengthways. This investigation tends to confirm the 
view which I have previously put forward, that an earthqual:e 
at a short distance from its epicentrum is practically a surface 
disturbance, principally consisting of horizontal movements. 
The vertical motion is small, and is best seen in the preliminary 
tremors either of an actual earthquake or of a dynamite ex- 
plosion. From a practical point of view these results must be of 
the greatest importance to those who have to erect heavy 
structures in earthquake districts. 
Buildings in Earthquake Countries.—As during the last few 
years so much destruction both to life and property has taken 
place in various parts of Europe, it seems that an epitome of the 
results of observations and experiments carried on in Japan 
relative to construction in seismic districts might not only be 
interesting, but possibly it might also be of practical value. 
When erecting a building it appears that we ought first to reduce 
as far as possible the quantity of motion which ordinary 
buildings receive ; and, second, to construct a building so that 
it will resist that portion of the momentum which we are unable 
to keep out. To reduce the momentum which usually reaches a 
building the following may be done :— 
(1) Institute a seismic survey of the district or area in which it 
is intended to build, and select a site where experiment shows 
that the motion is relatively small. (2) For heavy buildings 
adopt deep foundations (perhaps with lateral freedom), or at 
least let the building be founded on the hardest and most solid 
ground. It is perhaps because the tops of the hills in Fokio 
are harder than the plains that they have relatively the least 
motion. A building only fartially isolated may be exceedingly 
dangerous from the fact that motion entering in the unprotected 
| side will make the excavations (cuttings, valleys, &c.) upon the 
opposite side into free surfaces which will swing forward through 
a range greater than they would have swung had the excavations 
