entire weight of a man. Wherefore either the strength of the
muscles ought to be increased or the weight of the human body
must be decreased, so that the same proportion obtains in it as
exists in birds. Hence it is deducted that the Icarian
invention is entirely mythical because impossible, for it is not
possible either to increase a man's pectoral muscles or to
diminish the weight of the human body; and whatever apparatus is
used, although it is possible to increase the momentum, the
velocity or the power employed can never equal the resistance;
and therefore wing flapping by the contraction of muscles cannot
give out enough power to carry up the heavy body of a man.'

It may be said that practically all the conclusions which
Borelli reached in his study were negative. Although
contemporary with Lana, he perceived the one factor which
rendered Lana's project for flight by means of vacuum globes an
impossibility--he saw that no globe could be constructed
sufficiently light for flight, and at the same time sufficiently
strong to withstand the pressure of the outside atmosphere. He
does not appear to have made any experiments in flying on his
own account, having, as he asserts most definitely, no faith in
any invention designed to lift man from the surface of the
earth. But his work, from which only the foregoing short
quotations can be given, is, nevertheless, of indisputable
value, for he settled the mechanics of bird flight, and paved
the way for those later investigators who had, first, the steam
engine, and later the internal combustion engine--two factors in
mechanical flight which would have seemed as impossible to
Borelli as would wireless telegraphy to a student of Napoleonic
times. On such foundations as his age afforded Borelli built