shape of birds' wings, or the sails of a windmill, or some such
shape, and should be tilted obliquely upwards, and made so as to
collapse on the upward stroke and expand on the downward.
Fourth, place a balance or beam below, hanging down
perpendicularly for some distance with a small weight attached
to its end, pendent exactly in line with the centre of gravity;
the longer this beam is, the lighter must it be, for it must
have the same proportion as the well-known vectis or steel-yard.
This would serve to restore the balance of the machine if it
should lean over to any of the four sides. Fifthly, the wings
would perhaps have greater force, so as to increase the
resistance and make the flight easier, if a hood or shield were
placed over them, as is the case with certain insects. Sixthly,
when the sails are expanded so as to occupy a great surface and
much air, with a balance keeping them horizontal, only a small
force would be needed to move the machine back and forth in a
circle, and up and down. And, after it has gained momentum to
move slowly upwards, a slight movement and an even bearing would
keep it balanced in the air and would determine its direction at
will.'

The only point in this worthy of any note is the first device
for maintaining stability automatically--Swedenborg certainly
scored a point there. For the rest. his theory was but theory,
incapable of being put to practice--he does not appear to have
made any attempt at advance beyond the mere suggestion.

Some ten years before his time the state of knowledge with
regard to flying in Europe was demonstrated by an order granted
by the King of Portugal to Friar Lourenzo de Guzman, who claimed