Earthquakes through the Earth. 
235 
waves in the substance in front of it as it advanced. It would 
arrive at a station producing a large movement following the two 
preliminary phases, which would depend in magnitude and period 
upon the character of the original impulse. This solitary wave 
possibly causes the “ shock ” recorded in seismograms in the case of 
nearer earthquakes, and may perhaps have some connection with 
the one or two waves of slow period shown at cd in Prof. Omori’s 
diagram. 
Mr Oldham in his article in the Quarterly Journal of the 
Geological Society for August, 1906, though referring somewhat 
favourably to my theory, nevertheless says : “We know nothing of 
the behaviour of matter exposed to the pressures prevailing in the 
interior of the earth, and it is not wholly inconceivable that a fluid 
under pressure of millions of atmospheres might be enabled to 
transmit the distortional waves, which it is unable to transmit 
under pressures with which we are familiar.” It seems however 
to be a question also of temperature. As in the case of a liquid 
and its vapour there is a certain critical temperature at and above 
which no pressure however great will produce condensation*, so 
it seems probable that there may be a critical temperature for 
the fusion of a solid, above which no pressure would reconvert 
the liquid into a solid. This may possibly be the case within 
the earth ; and although pressure under such circumstances might 
so increase friction among the molecules as to oppose the deforma- 
tion of an element of it, yet, supposing that to occur, and that (say) 
a cube of it has been distorted into a rhombohedron, there seems 
no reason why pressure should impart that resiliency which would 
cause the volume in question to return to its original shape, and 
without this property it could not transmit a distortional wave. 
In fact resiliency after shear implies solidity. Consequently if 
there is a liquid layer, however thin, beneath the earth’s crust, 
distortional waves, if existing in the interior, could not be trans- 
mitted through it to the surface rocks ; and it must be remembered 
that, even if it could, it is the movements of the heterogeneous 
matter of these which are instrumentally recorded, and it is hardly 
to be expected that they should reproduce in kind the movements 
of the interior, even if responding in period and intensity. 
Maxwell’s Heat , 5th ed. p. 119. 
