I have
further assumed, that throughout the glacier the change of the snow and
porous ice into compact ice is the result of successive freezing,
alternating with melting, or at least with the resumption of a
temperature of 32 deg. Fahrenheit in consequence of the infiltration of
liquid water, to which the effects of pressure must be added, the
importance of which in this connection no one could have anticipated
prior to the experiments of Dr. Tyndall. Of course, if the interior
temperature of the glacier never falls below 32 deg., the changes here
alluded to could not take place. But if the _vacuous spaces_ observed by
Dr. Tyndall are really identical with the spaces I have described as
_extremely flattened air-bubbles_, I think the arrangement of these
spaces as above described proves that it freezes in the interior of the
glacier to the depth at which these crosswise fragments have been
observed: that is, at a depth of two hundred feet. For, since the
experiments of Dr. Tyndall show that the vacuous spaces are parallel to
the surface of crystallization, and as no crystallization of water can
take place unless the surrounding temperature fall below 32 deg.
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