square sail extended by four rods of equal size and having four
cords attached at the corners,' by means of which 'a man could without
danger throw himself from the top of a tower or any high place. For
though at the moment there may be no wind, yet the effort of his falling
will carry up the wind, which the sail will hold, by which means he does
not fall suddenly but descends little by little. The size of the sail
should be measured to the man.' By this last, evidently, Veranzio
intended to convey that the sheet must be of such content as would
enclose sufficient air to support the weight of the parachutist.

Veranzio made his experiments about 1617-1618, but, naturally, they
carried him no farther than the mere descent to earth, and since a
descent is merely a descent, it is to be conjectured that he soon got
tired of dropping from high roofs, and took to designing architecture
instead of putting it to such a use. With the end of his experiments the
work of da Vinci in relation to flying became neglected for nearly four
centuries.

Apart from these two experimenters, there is little to record in the
matter either of experiment or study until the seventeenth century.
Francis Bacon, it is true, wrote about flying in his Sylva Sylvarum, and
mentioned the subject in the New Atlantis, but, except for the insight
that he showed even in superficial mention of any specific subject,
he does not appear to have made attempt at serious investigation.
'Spreading of Feathers, thin and close and in great breadth will
likewise bear up a great Weight,' says Francis, 'being even laid without
Tilting upon the sides.' But a lesser genius could have told as much,
even in that age, and though the great Sir Francis is sometimes adduced
as one of the early students of the problems of flight, his writings
will not sustain the reputation.

The seventeenth century, however, gives us three names, those of
Borelli, Lana, and Robert Hooke, all of which take definite place in
the history of flight. Borelli ranks as one of the great figures in the
study of aeronautical problems, in spite of erroneous deductions through
which he arrived at a purely negative conclusion with regard to the
possibility of human flight.

Borelli was a versatile genius. Born in 1608, he was practically
contemporary with Francesco Lana, and there is evidence that he either
knew or was in correspondence with many prominent members of the Royal
Society of Great Britain, m