Mr. Matter on the Dynamics of Earthquakes. 59 
from a point where it has been produced by an original impulse. ‘This impulse 
he conceives to arise from the sudden production or condensation of aqueous 
vapour, under the bed of the ocean, by the agency of volcanic heat, the supposed 
mechanism of which he minutely describes. He supposes the crust of the earth 
either to float on liquid matter, so that undulations would be easily propagated 
through the former, or to float upon vast pent-up receptacles of aqueous vapour ; 
and he proceeds: *‘ As a small quantity of vapour, almost instantly generated at 
some considerable depth below the surface of the earth, will produce a vibratory 
motion, so a very large quantity (whether it be generated almost instantly or in 
any small portion of time) will produce a wave-like motion. The manner in 
which this wave-like motion will be propagated may, in some measure, be repre- 
sented by the following experiment. Suppose a large cloth or carpet (spread 
upon a floor) to be raised at one edge, and then suddenly brought down again 
to the floor, the air under it being, by this means, propelled, will pass along till it 
escapes at the opposite side, raising the cloth in a wave all the way as it goes. 
In like manner, a large quantity of vapour may be conceived to raise the earth 
in a wave, as it passes along between the strata, which it may easily separate in 
an horizontal direction, there being little or no cohesion between one stratum and 
another.” His views, at length, may be found in his paper in the Phil. Trans. 
vol. li. sec. 58, &c. &e. 
Michell wholly mistook the nature of the wave itself; and the existence of 
such a wave as he assumes is totally inconsistent with the phenomena of earthquake 
motion, as recorded by himself and others; and the mechanism which he imagines 
to account for the origin of his wave, and its propagation through the floating 
crust, is inconsistent with the conditions essential to that order of wave which 
the ascertained phenomena of earthquakes shew to be the true one. 
Michell also states, that the great waves of the sea, which frequently succeed 
the shock of earthquakes, and roll to shore at an enormous height and velocity, 
are due to the same cause, namely, an undulation given to the ocean water, at a 
point directly above that at which the primary terrestrial undulation takes place. 
He considers that the greater earthquakes have their centre of effort generally, 
if not always, under the ocean, and proposes to determine the position of this 
centre, in any case, by observation of the direction of these great waves, and the 
times at which they reach several distant shores, illustrating his view by such a 
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