366 REPORT—1885. 
5. The initial velocity given in the formula v?= = (for horizontal 
projection), used by Mallet as identical with v? in 3, is not an identical 
‘quantity. ; 
The velocity calculated from the range af projection when projection 
occurs is identical with the maximum velocity as measured directly or 
calculated from a diagram. 
2 
6. In discussing the intensity of movement I have used the values Wet 
a 
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. 
VIL. 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 waves as observed at the 
same or different stations have been measured. 
VIII. Velocity. 
1. The velocity of transit decreases as a disturbance radiates. 
2. Near toan origin the velocity of transit varies with the intensity of 
the initial disturbance. 
3. In different kinds of ground, with different intensities of initial 
disturbance, and with different systems of observation, I determined 
velocities lying between 630 and about 200 feet per second. Mallet 
determined a velocity in sand of 824 feet, and in granite of 1,664 feet, per 
second. General Abbot has observed velocities of 8,800 feet per second. 
All of these determinations I regard as being practically correct, the 
great difference between them being due partly to the nature of the rock, 
the intensity of the initial disturbance, and the kind of wave which was 
observed. 
4. In my experiments the vertical free surface wave had the quickest 
rate of transit, the normal being next, and the transverse motion being 
the slowest. 
5. The rate at which the normal motion outraces the transverse 
motion is not constant. 
6. 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. : 
7. By cross-bending and torsion of cylinders of rocks the velocity — 
with which normal and transverse vibrations would be propagated in — 
such rocks has been determined. These determinations show that the 
