MESSRS. J. MILNE AND T. GRAY ON SEISMIC EXPERIMENTS. 
865 
pared with the production of them by the ignition of some explosive material, is that 
we are able to make a more definite estimate of the force of the blow. 
In giving the following results, which have been classified, so far as it was convenient, 
according to their object, we call attention to the fact that the fall of the ball was, 
when we could obtain observers and instruments, used to determine several distinct 
results. 
Thus a blow which was used to measure the velocity along the line A B was used to 
determine the relative amount of vibration transmitted along various other lines. 
This remark explains why the same fall of the ball is referred to in different groups of 
experiments. These experiments were first projected in November, 1880. During 
the month of December instruments, &c., were being prepared and the necessary 
arrangements entered into for the carrying of them out. Of days actually spent in 
making experiments there were nine. As in some cases, after a set of experiments, 
new base lines had to be measured, old instruments altered, or new ones designed for 
the improvements of the work already done, or for the carrying out of new work, and 
as at the same time much college work, &c., had to be attended to, these nine days 
were not consecutive. 
In consequence of having on each day of experiment to relay our telegraph, reset 
the various instruments, obtain coolies to work at the windlass in winding up the ball, 
&c., it was but seldom that more than four or five falls could be obtained in one day. 
The following table shows the numbers of the falls which took place upon each of the 
days. 
Experiments at the Akabane Works, Tokio, January and February, 1881. 
Number of falls. 
First day.1, 2. 
. Second day.3, 4, 5, 6, 7, 8. 
Third day.9, 10, 11, 12. 
Fourth day.13, 14, 15, 16. 
Fifth day.17, 18, 19, 20. 
Sixth day. 21, 22, 23, 24. 
Seventh day. 25, 26, 27, 28, 29, 30. 
Eighth day. 31, 32, 33, 34, 35, 36. 
Ninth day. 37, 38, 39, 40. 
The object in giving the above table is that, having numbered our experiments 
according to the fall of the ball, it can be seen on which day the experiment took 
place. This is necessary, because after every fall on any particular day the ground on 
which the ball fell became harder, and this hardening has apparently had its effect in 
the nature of the records. Also on different days the ground generally varied slightly 
in its character, according as it had or had not been subjected to severe frost during 
the previous night. 
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