herein before assumed, will move the lateral margins of the aeroplanes
in the manner already described, so that the margins ad and eh will be
inclined downward and rearward, and the lateral margins bc and fg will
be inclined upward and rearward with respect to the normal planes of the
bodies of the aeroplanes. With the parts of the machine in this position
it will be seen that the lateral margins ad and eh present a larger
angle of incidence to the resisting air, while the lateral margins on
the other side of the machine present a smaller angle of incidence.
Owing to this fact, the side of the machine presenting the larger angle
of incidence will tend to lift or move upward, and this upward movement
will restore the lateral balance of the machine. When the other side of
the machine tends to drop, a movement of the cradle 18 in the reverse
direction will restore the machine to its normal lateral equilibrium. Of
course, the same effect will be produced in the same way in the case of
a machine employing only a single aeroplane.

In connection with the body of the machine as thus operated we employ
a vertical rudder or tail 22, so supported as to turn around a vertical
axis. This rudder is supported at the rear ends on supports or arms 23,
pivoted at their forward ends to the rear margins of the upper and lower
aeroplanes, respectively. These supports are preferably V-shaped, as
shown, so that their forward ends are comparatively widely separated,
their pivots being indicated at 24. Said supports are free to swing
upward at their free rear ends, as indicated in dotted lines in Fig.
3, their downward movement being limited in any suitable manner. The
vertical pivots of the rudder 22 are indicated at 25, and one of these
pivots has mounted thereon a sheave or pulley 26, around which passes a
tiller-rope 27, the ends of which are extended out laterally and secured
to the rope 19 on opposite sides of the central point of said rope. By
reason of this construction the lateral shifting of the cradle 18 serves
to turn the rudder to one side or the other of the line of flight. It
will be observed in this connection that the construction is such that
the rudder will always be so turned as to present its resisting
surface on that side of the machine on which the lateral margins of the
aeroplanes present the least angle of resistance. The reason of this
construction is that when the lateral margins of the aeroplanes are
so turned in the