364 REPORT—1885. 
2. A bracket seismograph indicating normal motion at a given station 
commences its indications before a similar seismograph arranged to write 
transverse motion. 
3. If the diagrams yielded by two such seismographs be compounded, 
they yield figures containing loops and other irregularities not unlike the 
figures yielded by the seismograph with the single index. 7 
4. Near to an origin, the first movement will be in a straight line 
outwards from the origin; subsequently the motion may be elliptical, 
like a figure 8, and irregular. The general direction of motion is, however, 
normal. 
5. Two points of ground only a few feet apart may not synchronise in 
their motions. 
6. Earthquake motion is probably not a simpJe harmonic motion. 
III. Normal Motion. 
1. Near to an origin the first motion is outwards. At a distance 
from an origin the first motion may be inwards. 
‘As to whether it will be inwards or outwards is probably partly de- 
pendent on the intensity of the initial disturbance, and on the distance of 
the observing station from the origin. 
2. At stations near the origin the motion inwards is greater than the 
motion outwards. At a distance the inwardsand outwards motion are 
practically equal. 
3. At a station near the origin, the second or third wave is usually 
the largest, after which the motion dies down very rapidly in its am- 
plitude, the motion inwards decreasing more rapidly than the motion 
outwards. 
4. Roughly speaking, the amplitude of normal motion is inversely as 
the distance from the origin. 
5. At a station near an origin the period of the waves is at first short. 
It becomes longer as the disturbance dies out. 
6. The semi-oscillations inwards are described more rapidly than those 
outwards. 
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 disturbance 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. Tables have been calculated to show the maximum velocity of 
normal motion. 
10. Diagrams have been drawn to show the intensity of normal 
motion. 
11. The first outwards motion, which on diagrams has the appearance 
of a quarter-wave, must be regarded as a semi- oscillation. 
12. The waves on the diagrams taken at different stations do not 
correspond. 
13. Ata 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. 
14. Near the origin the normal motion has a definite commencement. : 
At a distance the motion commences irregularly, the maximum motion 
being reached gradually. 
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