d; in general, the proximity of land is indicated by a number of
icebergs, and not one is to be seen near us."

"We can't see very far for the fog," said Johnson.

"Without doubt; but since we started we have crossed a smooth field of
which we cannot see the end."

"Do you know, Doctor, it's a dangerous walk we are taking! We get used
to it and don't think of it, but we are walking over fathomless
depths."

"You are right, my friend, but we need not fear being swallowed; with
such cold as this the ice is very strong. Besides, it has a constant
tendency to get thicker, for snow falls nine days out of ten, even in
April, May, and June, and I fancy it must be something like thirty or
forty feet thick."

"That is a comfort," said Johnson.

"In fact, we are very much better off than those who skate on the
Serpentine, and who are in constant dread of falling through; we have
no such fear."

"Has the resistance of ice been calculated?" asked the old sailor, who
was always seeking information from the doctor.

"Yes," the latter answered: "everything almost that can be measured is
now known, except human ambition! and is it not that which is carrying
us towards the North Pole? But to return to your question, my answer
is this. Ice two inches thick will bear a man; three and a half inches
thick, a horse and rider; five inches thick, an eight-pound cannon;
eight inches, a fully harnessed artillery-piece; and ten inches, an
army, any number of men! Where we are now, the Liverpool Custom House
or the Halls of Parliament in London could be built."

"One can hardly imagine such strength," said Johnson; "but just now,
Doctor, you spoke of snow falling nine days out of ten; that is true,
but where does all the snow come from? The sea is all frozen, and I
don't see how the vapor can rise to form the clouds."

"A very keen observation, Johnson; but, in my opinion, the greatest
part of the snow or rain which we receive in the polar regions is
formed from the water of the seas in the temperate zones. One flake
arose into the air under the form of vapor from some river in Europe,
it helped make a cloud, and finally came here to be condensed; it is
not impossible that we who drink it may be quenching our thirst at the
rivers of our own country."

"That is true," answered Johnson.

At that moment Hatteras's voice was heard directing their steps and
interrupting their conversation. The fog was growing thicker, and
making a strai