EARLY HISTORY OF GEOPHYSICS 7 
method, remains to be noticed, for obtaining part of our data as to the 
specific period of wave transit, viz., by direct experiment, which in all 
matters of inductive science may be pronounced, whenever it is pos- 
sible, better than mere observation. 
I have already stated that it is quite immaterial to the truth of my 
theory of earthquake motion what view be adopted, or what mecha- 
nism be assigned to account for the original impulse; so, in the de- 
termination of the time of transit of the elastic wave through the 
earth’s crust, if we can only produce a wave, it is wholly immaterial 
in what way, or by what method, the original impulse be given. 
Now the recent improvements in the art of exploding, at a given 
instant, large masses of gunpowder, at great depths under water, give 
us the power of producing in fact, an artificial earthquake at pleasure; 
we can command with facility a sufficient impulse to set in motion an 
earth wave that shall be rendered evident by suitable instruments at 
the distance, probably, of many miles, and there is no difficulty in 
arranging such experiments, so that the explosion shall be produced 
by the observer of the time of transit himself, though at the distance 
of twenty or thirty miles, or that the moment of explosion shall be 
fixed, and the wave period registered by chronometers, at both ex- 
tremities of the line of transit. 
In presenting this paper, Mallet stressed the necessity for experi- 
ments to determine the time of wave transit through rocks of different 
type, and three years later we find him giving notice of experiments 
in progress for the direct measurement of the velocity of transit of 
earthquake waves. He describes experiments to be carried out over 
a measured mile with a charge of ‘‘a few pounds of gunpowder buried 
four or five feet in the ground” connected by a wire circuit with a 
battery so that it could be fired by the experimenter at the other end 
of the line with his crude seismometer for observing the arrival of 
the earth wave. A chronograph was to be attached to the battery 
for determining the time of transit of the wave. 
The author stated that if the elasticity of the earth’s crust were 
known, it would be possible to determine the point from which an 
earthquake shock originated, and also to form an estimate of the 
nature of the intervening formations— whether solid or plastic— 
through depths of perhaps hundreds of miles, and even under the 
ocean.” 
In 1849, Mallet actually carried out experiments in the field at 
Killiney Bay on the coast of County Dublin, Ireland, and at the 
nearby Dalkey Island. At Killiney Bay he had a widely extended 
2 The Athenium, Vol. 22, Num. 1144, p. 991, London, Sept. 29, 1849. 
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