th the most difficult problem that confronts
the flying man of to-day, namely, landing effectively, and his remarks
on this subject would be instructive even to an air pilot of these days:
'Now the ways and means by which the speed is slackened at the end of
a flight are these. The bird spreads its wings and tail so that their
concave surfaces are perpendicular to the direction of motion; in this
way, the spreading feathers, like a ship's sail, strike against the
still air, check the speed, and so that most of the impetus may be
stopped, the wings are flapped quickly and strongly forward, inducing a
contrary motion, so that the bird absolutely or very nearly stops.'

At the end of his study Borelli came to a conclusion which militated
greatly against experiment with any heavier-than-air apparatus, until
well on into the nineteenth century, for having gone thoroughly into the
subject of bird flight he states distinctly in his last proposition
on the subject that 'It is impossible that men should be able to fly
craftily by their own strength.' This statement, of course, remains true
up to the present day for no man has yet devised the means by which he
can raise himself in the air and maintain himself there by mere muscular
effort.

From the time of Borelli up to the development of the steam engine it
may be said that flight by means of any heavier-than-air apparatus was
generally regarded as impossible, and apart from certain deductions
which a little experiment would have shown to be doomed to failure, this
method of flight was not followed up. It is not to be wondered at, when
Borelli's exaggerated estimate of the strength expended by birds in
proportion to their weight is borne in mind; he alleged that the motive
force in birds' wings is 10,000 times greater than the resistance of
their weight, and with regard to human flight he remarks:--

'When, therefore, it is asked whether men may be able to fly by their
own strength, it must be seen whether the motive power of the pectoral
muscles (the strength of which is indicated and measured by their size)
is proportionately great, as it is evident that it must exceed the
resistance of the weight of the whole human body 10,000 times, together
with the weight of enormous wings which should be attached to the arms.
And it is clear that the motive power of the pectoral muscles in men is
much less than is necessary for flight, for in birds the bulk and weight
of the muscles fo