to circumnavigate the globe without alighting--need
to carry a weight of fuel which would enable it to perform this journey
under conditions analogous to those of a steamship, but that the fuel
and weight need only be such as to enable it to take care of itself in
exceptional moments of calm."

Now that dynamic flying machines have been evolved and are being brought
under control, it seems to be worth while to make these computations and
the succeeding explanations known, so that some bold man will attempt
the feat of soaring like a bird. The theory underlying the performance
in a rising wind is not new, it has been suggested by Penaud and others,
but it has attracted little attention because the exact data and
the maneuvers required were not known and the feat had not yet been
performed by a man. The puzzle has always been to account for the
observed act in very light winds, and it is hoped that by the present
selection of the most difficult case to explain--i. e., the soaring in a
dead horizontal calm--somebody will attempt the exploit.

Requisites for Soaring Flights.

The following are deemed to be the requisites and maneuvers to master
the secrets of soaring flight:

1st--Develop a dynamic flying machine weighing about one pound per
square foot of area, with stable equilibrium and under perfect control,
capable of gliding by gravity at angles of one in ten (5 3/4 degrees) in
still air.

2nd.--Select locations where soaring birds abound and occasions where
rising trends of gentle winds are frequent and to be relied on.

3rd.--Obtain an initial velocity of at least 25 feet per second before
attempting to soar.

4th.--So locate the center of gravity that the apparatus shall assume a
negative angle, fore and aft, of about 3 degrees.

Calculations show, however, that sufficient propelling force may still
exist at 0 degrees, but disappears entirely at +4 degrees.

5th.--Circle like the bird. Simultaneously with the steering, incline
the apparatus to the side toward which it is desired to turn, so that
the centrifugal force shall be balanced by the centripetal force. The
amount of the required inclination depends upon the speed and on the
radius of the circle swept over.

6th.--Rise spirally like the bird. Steer with the horizontal rudder, so
as to descend slightly when going with the wind and to ascend when going
against the wind. The bird circles over one spot because the rising
trends of wind are generally