The excerpt represents the core issue or deciding factor on which you must meditate, and is drawn from Off on a Comet by Jules Verne:|
a diminution that was far more rapid than that which is
experienced in making the descent of terrestrial mines.
In this case it was a volcano, not a colliery, that was
the object of exploration, and thankful enough they were
to find that it had not become extinct. Although the lava,
from some unknown cause, had ceased to rise in the crater,
yet plainly it existed somewhere in an incandescent state,
and was still transmitting considerable heat to inferior strata.
Lieutenant Procope had brought in his hand a mercurial thermometer,
and Servadac carried an aneroid barometer, by means of which he could estimate
the depth of their descent below the level of the Gallian Sea. When they