nequal, the heated matter or lava burst through the thinner
parts, and caused high-peaked mountains; the same cause also
producing all volcanic action." The arguments in favor of this
doctrine are almost innumerable; these are among the most
prominent:

_First._ The form of the earth is just that which an igneous
liquid mass would assume if thrown into an orbit with an axial
revolution similar to that of our earth. Not many years ago
Professor Faraday, assisted by Wheatstone, devised a most
ingenious apparatus by which, in the laboratory of the Royal
Society, he actually was enabled, by injecting a flame into a
vacuum, to exhibit visibly all the phenomena of the formation of
the solar universe, as contended for by La Place and by Humboldt
in his "Cosmos."

_Secondly._ It is perfectly well ascertained that heat increases
with depth, in all subterranean excavations. This is the
invariable rule in mining shafts, and preventive measures must
always be devised and used, by means generally of air apparatus,
to temper the heat as the depth is augmented, else deep mining
would have to be abandoned. The rate of increase has been
variously estimated by different scientists in widely distant
portions of the globe. A few of them may be mentioned at this
place, since it was upon a total miscalculation on this head that
led to the present most deplorable results.

The editor of the _Journal of Science_, in April, 1832,
calculated from results obtained in six of the deepest coal mines
in Durham and Northumberland, the mean rate of increase at one
degree of Fahrenheit for a descent of forty-four English feet.

In this instance it is noticeable that the bulb of the
thermometer was introduced into cavities purposely cut into the
solid rock, at depths varying from two hundred to nine hundred
feet. The Dolcoath mine in Cornwall, as examined by Mr. Fox, at
the depth of thirteen hundred and eighty feet, gave on average
result of four degrees for every seventy-five feet.

Kupffer compared results obtained from the silver mines in
Mexico, Peru and Freiburg, from the salt wells of Saxony, and
from the copper mines in the Caucasus, together with an
examination of the tin mines of Cornwall and the coal mines in
the north of England, and found the average to be at least one
degree of Fahrenheit for every thirty-seven English