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XVIII. On Seismic Experiments. 
By J. Milne, F.G.S., and T. Gray, B.Sc., F.RS.E. 
Communicated by A. C. Ramsay, LL.D., Director-General of the Geological Survey, 
and of the Museum of Economic Geology. 
Received November 5,—Read December 8, 1881. 
[Plate 52.] 
The following paper is an account of a series of experiments made at the Akabane 
Engineering Works, Tokio, for the purpose of investigating a number of phenomena 
connected with earthquake motion. 
In 1851 Mr. Robert Mallet, by means of a number of carefully-performed experi¬ 
ments, determined the velocity with which vibrations were transmitted through various 
media. These vibrations were produced by exploding charges of gunpowder. (See 
Report of British Association, 1857, also Philosophical Transactions, 1861, 1862, 
Appendix). As maximum and minimum velocities obtained in feet per second, 
Mr. Mallet found 
Feet per second. 
In sand. 824'915 
In solid granite. . . . 166P576 
In 1876, at the time of the Hellgate explosions at the entrance to the New York 
Harbour, experiments were arranged by General Abbott for like determinations. 
These experiments gave velocities varying between 3,000 and 8,300 feet per second. 
By a different series of experiments on the “ compressibility of solid cubes ” of rock, 
Mr. Mallet determined “the mean modulus of elasticity of the material,” and inferred 
the fact that “ owing to discontinuity of rocky masses as found in nature, nearly -J of 
the full velocity is lost.” (See ‘The Eruption of Vesuvius in 1872,’ by Professor 
Luigi Palmieri, with notes by Robert Mallet, p. 18.) 
These determinations of velocity of wave transit are, so far as we are aware, all that 
has yet been done in the experimental investigation of phenomena connected with the 
transmission of vibratory motion through the earth’s crust. 
In the experiments described in this paper the disturbance was produced by allowing 
a heavy weight to fall from a height which could be varied from zero up to 35 feet. 
MDCCCLXXXII. 5 S 
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