vative of heat is this arrangement that
every particle of caloric created in the living rooms, or cabin below,
helps by that much to float the great globe. All the warmth from cooking
and heating; the heat and smoke from our pipes and cigars; yea, even the
animal heat which radiates from our bodies, all subserve the one great
purpose and function--keeping up the temperature and buoyant effort of
the globe. Do you begin to catch on?" fairly shouted the enthusiastic
Doctor.

"Well, it looks very well so far," returned Denison slowly. "But, my
dear sir, I foresee one difficulty that in your enthusiasm you seem to
have overlooked. You can never guide or steer this immense ship. It must
go with the wind, and you are just as likely to go to the South Pole as
to the North, and very unlikely to go to either. You must excuse me,
but this last is certainly an insuperable obstacle to your making
anything practicable of your idea."

"I admit at once that this great body could not be steered, nor in any
degree guided by any apparatus that we could devise," assented the
Doctor. "But that we should be obliged to float aimlessly, hither and
thither, altogether the creatures of chance, I do not for a moment
admit. The equator, receiving as it does, the vertical rays of the sun,
is by far the hottest portion of the earth. The atmosphere at that
quarter, being constantly superheated and correspondingly rarified,
ascends into the vault above. This creates a semi-vacuum below, and the
cooler atmospheres north and south of the equator rush in and fill the
aforesaid vacuum. Pouring in from opposite directions with an impetus
that often amounts to hurricanes, they boil up as they meet, miles into
the firmament above. They then set off in two strong currents toward
either Pole. What is the natural inference? The navigators of our
air-ship have the power to raise and lower at pleasure. Obviously, there
is but one thing for sensible men to do: Let her rise until we strike a
northerly current, if necessary, and remain in it so long as it is
favorable; when it changes, rise or lower until another favorable
current is found, etc. Do you happen to think of any more 'insuperable'
obstacles, my dear sir?"

"Well, I must say that while I am not convinced of the practicability of
your scheme, still you meet my objections in a way that is quite
surprising, and which shows that you have given the matter much thought;
yet I am not sure that you will not