ON THE EARTHQUAKE PHENOMENA OF JAPAN. 365 
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 transverse motion as the disturbance radiates 
decreases at a slower rate than that of the normal motion. 
4. As a disturbance dies out at any particular station the period 
decreases. 
5. As a disturbance 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. 
7. It will be observed that the laws governing the transverse motion 
are practically identical with those which govern the normal motion, the 
only difference being that in the case of normal motion they are more 
clearly pronounced. 
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 to each 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 
inthe 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 v?=$gV a?+b? x (=5- 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 diagram lies be- 
tween ; and, where vy is the maximum velocity, ¢ is the quarter- 
a 
period, and a is the amplitude. 
