2. The pressures in the Earth increase from zero at the surface
to the order of 3,000,000 atmospheric pressures at the center.
We know that rock structure, or iron or other metals, can be
slightly compressed by pressure, but the experiments at very
high pressures, notably those conducted by Bridgman, give no
indications that matter under such pressures breaks down and
obeys different or unknown laws. It should be said, however,
that laboratory pressure-effects alone are not a safe guide as
to conditions within the Earth, where high pressures are
accompanied by high temperature. Unfortunately it has not been
found possible to combine the high-temperature factor with the
high-pressure factor in the laboratory experiments. It is well
known that the melting points of metals, including rocks,
increase with increase of pressure; and although the
temperatures in the Earth"s interior are very high, it is easy
to conceive that the materials of the Earth"s interior are
nevertheless in the solid state, or that they act like solids,
because of the high pressures to which they are subjected.
