on the air.'

With four globes of these dimensions Lana proposed to make an
aerial ship of the fashion shown in his quaint illustration. He
is careful to point out a method by which the supporting globes
for the aerial ship may be entirely emptied of air; this is to
be done by connecting to each globe a tube of copper which is
'at least a length of 47 modern Roman palm).' A small tap is to
close this tube at the end nearest the globe, and then vessel
and tube are to be filled with water, after which the tube is to
be immersed in water and the tap opened, allowing the water to
run out of the vessel, while no air enters. The tap is then
closed before the lower end of the tube is removed from the
water, leaving no air at all in the globe or sphere. Propulsion
of this airship was to be accomplished by means of sails, and
also by oars.

Lana antedated the modern propeller, and realised that the air
would offer enough resistance to oars or paddle to impart motion
to any vessel floating in it and propelled by these means,
although he did not realise the amount of pressure on the air
which would be necessary to accomplish propulsion. As a matter
of fact, he foresaw and provided against practically all the
difficulties that would be encountered in the working, as well
as the making, of the aerial ship, finally coming up against
what his religious training made an insuperable objection.
This, again, is best told in his own words:--

'Other difficulties I do not foresee that could prevail against
this invention, save one only, which to me seems the greatest of