stream, then in that case, either by paddle or rudder, the log
could be guided, and the same might be said of Lana's air boat
if only he had thought of some adequate paddle, fan, or other
propeller. But he did not. One further explanatory sentence
may here be needed; for we hear of balloons which are capable
of being guided to a small extent by sail and rudder. In these
cases, however, the rudder is a guide rope trailing on earth or
sea, so introducing a fresh element and fresh conditions which
are easy to explain.

Suppose a free balloon drifting down the wind to have a sail
suddenly hoisted on one side, what happens? The balloon will
simply swing till this sail is in front, and thus continue its
straightforward course. Suppose, however, that as soon as the
side sail is hoisted a trail rope is also dropped aft from a
spar in the rigging. The tendency of the sail to fly round in
front is now checked by the dragging rope, and it is
constrained to remain slanting at an angle on one side; at the
same time the rate of the balloon is reduced by the dragging
rope, so that it travels slower than the wind, which, now
acting on its slant sail, imparts a certain sidelong motion
much as it does in the case of a sailing boat.

Lana having in imagination built his ship, proceeds to make it
float up into space, for which purpose he proposes four thin
copper globes exhausted of air. Had this last been his own
idea we might have pardoned him. We have, however, pointed out
that it was not, and we must further point out that in copying
his great predecessor he fails to see that he would lose
enormous advantage by using four globes instead of one. But,