MESSRS. J. MILNE AND T. GRAY ON SEISMIC EXPERIMENTS. 
877 
synchronously palpitates. These palpitations are recorded by means of a pointer or 
lever axled in the centre of the flexible bottom and again to a point in contact with 
the framework of the can; with this contrivance the actual up and down motion of the 
bottom of the can is multiplied 21 times. 
Vertical motion on the line A D. 
Fall of 
ball. 
Station. 
Bise of 
ground. 
Fall of 
ground. 
Total 
motion. 
32 
50 
6 
3 
9 
33 
100 
2 - 5 
2 
4-5 
35 
150 
. , 
1 
34 
200 
0 
From this table it will be observed that the vertical motion, which may be a com¬ 
ponent of the transverse vibrations, dies out very rapidly. The rapid dying out of the 
vertical movement is possibly due to the free surface. It is remarkable that this wave 
of distortion should die out so much more quickly than that at right angles to it. 
Fall 36. 100 feet station. 
Here the vertical motion was registered on a moving glass plate attached at 
right angles to a plate on which normal vibrations were being written. The first 
distinct movement appears as if the earth had gone downwards. The double 
amplitude of the first large wave is 6 - 5 millims., the downward half of the 
movement being larger than the upward half. The largest motion to one side 
3 ‘5 millims. It diminishes very rapidly at first but afterwards more slowly. 
In the following four experiments also made on the fine A D, two similar and similarly 
placed horizontal lever seismographs were allowed to write the movements of the 
ground simultaneously at two stations. For the object of these experiments, see 
eighth set of experiments. 
Normal vibrations. 
Fall 37. 50 feet station. 
There were about 8 vibrations per second. The first movement appeared to 
be one of compression. The vibrations were sensible for 1*5 seconds. The first 
2 vibrations are very distinct. 
250 feet station. 
There were about 8 vibrations per second. The first movement is one of 
compression. The greatest double amplitude is 1*5 millims. The vibrations are 
more regular than they are at the 50 feet station. The first 4 vibrations can be 
easily compared with the first 4 at the 50 feet station. 
