[5] Gerlands, "Beitrage zur Geophysik," XI., Band, 1 Heft,
1911, p. 132. "Das kolumbianische Erdbeben am 31 January,
1906."



The second preliminary tremors arriving later are due to the
lateral disturbance. Their propagation is much less rapid when
the point of origin is nearly opposite the point of receival.
In other words there is a core within the earth about 0.4 of
the radius in radius, in which according to Oldham, these
lateral waves have much less velocity. Now in a gas there is
less resistance to lateral displacement than in a solid, and
the less the resistance the less the velocity, so that this
fact fits in with the idea of a gaseous core perfectly. If
there is such n core, moreover, of less rigidity it would have
less refraction. Consequently waves not striking the border
above the angle of total reflection would be totally reflected,
and just as around a bubble there is a dark border where the
light does not get through so at a certain distance from the
source of an earthquake there would be a circle (it is really
about 140 degrees of arc away), where no second tremors would
be felt. Here again, though seismograph stations are as yet
few, fact and theory are apparently going to correspond.

The last type of earthquake waves follow around the outer layer
of the crust.

There is one farther line of verification to which I had
addressed myself. Is it likely that the loss of heat and energy