avier than air, of which two kinds the simplest types are the
soap-bubble and the arrow. These two kinds have often been in
competition with each other; and their rivalry, which has sometimes
delayed progress, still continues. The chief practical objection to
machines lighter than air is that they are buoyed up by vulnerable
receptacles containing hydrogen or some other highly inflammable gas. As
soon as helium, which is a light non-inflammable gas, shall be produced
in quantity at a reasonable expense, this objection will be lessened.
The advantage of the lighter-than-air, or floating, machine over the
heavier-than-air, or soaring, machine is that it can remain stationary
in the air without loss of height, and that its great size and lifting
power enable it to supply comfortable quarters for its staff, who not
only travel in it, but, if need be, can inhabit it for days. The airship
has a promising future, but it can never wholly supersede the soaring
machine, which is heavier than air, and flies as birds fly.

A fascinating story, part legend, part fiction, might be told of the
earliest reputed inventors. The fable of Daedalus perhaps grew up round
the memory of a man of mechanical genius, for Daedalus was the author of
many inventions before he flew from Crete to Italy. Aulus Gellius, in
his entertaining book of anecdotes called the _Attic Nights_, tells how
the philosopher Archytas of Tarentum invented a mechanical pigeon,
which was filled with some kind of light air, and flew. The two schools
of aeronautics were here reconciled. Other mechanists were Roger Bacon,
who is reported to have designed a flying chariot; and Regiomontanus,
astronomer and mathematician, who made a mechanical eagle which flew to
meet the Emperor Charles the Fifth, on his solemn entry into the city of
Nuremberg. It is not necessary to inquire whether these stories are true
or false; what is certain is that the inventors did not leave their
inventions as a legacy to their fellows. For a like reason Leonardo da
Vinci, who busied himself with a mechanism which should enable man to
operate wings with his legs, and who left a short treatise on the art of
flight, has no place in the history. His mechanism is merely a drawing;
his treatise remained in manuscript. The adventurers who risked their
lives on wings of their own making are truer ancestors of the flying
man. In 1507 John Damian, who was held in esteem as an alchemist and
physician at the cou