borne along in a torrent; but to compare such a log
properly with the air ship we must conceive it WHOLLY submerged in the
water and having no sail or other appendage projecting into the air,
which would, of course, introduce other conditions. If, however, a man
were to sit astride of the log and begin to propel it so that it travels
either faster or slower than the 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, beyond all, he failed to see what the master genius of Bacon saw
clearly--that his thin globes when exhausted must infallibly collapse by
virtue of that very pressure of the air which he sought to make use of.

It cannot be too strongly insisted on that if the too much belauded
speculations of Lana have any value at all it is that they throw into
stronger contrast the wonderful insight of the philosopher who so long
preceded h