Mr. Mattet on the Dynamics of Earthquakes. 97 
But another, and much more rapid, and perhaps even certain, method, re- 
mains 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 possible, 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 mechanism be assigned to 
account for the original impulse ; so, in the determination 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 extremities of the line of 
transit. 
For this alone very moderate charges of powder will answer, but if the explo- 
sion be made out at sea with sufficient energy, there will not only be produced 
the transit of the earth wave and the sound waves through the sea and air, but 
the accumulation and subsequent coming in of the great sea wave, so that all 
the phenomena of the natural earthquake are thus placed within our power of 
production, observation, and control. 
These are experiments, the value of which, to general physics as well as to 
geology, will be admitted ; but they cannot be made without the aid and appli- 
ances which our Government can afford, through the Admiralty and Royal 
Engineer departments. It cannot be doubted, but that application made for such 
assistance, through the Royal Irish Academy, or some other of our learned 
bodies, to the proper authorities, would meet with a favourable reception. 
It is to be remembered, however, that these direct experiments can only give 
the time of wave transit for the substances forming the very uppermost crust of 
VOL. XXI. ) 
