200 Natural and Artificial Flight. (April, 
have what is virtually a down stroke added to them. Under 
these circumstances they inevitably dart forward, a struggle 
ensuing between the cork tending to fall vertically and the 
feathers tending to travel in a horizontal direction. Asa 
consequence, the apparatus describes a curve before 
reaching the earth. ‘This is due to the action and reaction 
of the feathers and air upon each other, and to the influence 
which gravity exerts upon the cork. The forward travel of 
the cork and feathers, as compared with the space through 
which they fall, is very great. Thus, in some instances, 
they advanced as much as a yard and a half in a descent of 
three yards. If the body of the sea gull depicted in Fig. 14 
be taken to represent the cork, and the flexible mobile helices 
Sea Gull suspending its body from its wings as from a parachute, and 
converting (by the aid of its wings) the vertical fall of the body 
into horizontal travel. This figure shows the twisted con- 
figuration of the wing of the bird, and how the anterior (x st v w) 
and posterior (q p 0) margins are disposed in different planes and 
appear to cross each other. 
formed by the wings of the bird the primary or quill 
feathers, the conditions of the above experiment are repro- 
duced with the utmost exactitude. A bird cannot be said to 
be flying until the trunk is swinging forward in space and 
taking part in the movement. 
When the gannet throws itself from a cliff the inertia of 
the trunk at once comes into play, and relieves the bird 
from those herculean exertions required to raise it from the 
water when it is once fairly settled thereon. A swallow 
dropping from the eaves of a house, or a bat from a tower, 
afford illustrations of the same principle. However flying 
creatures acquire momentum, whether by throwing them- 
selves from elevations or by the vigorous flapping of their 
wings, there can be no doubt, that the weight of their 
bodies operating upon the inclined planes formed by the 
pinions, contribute largely to the production of flight. This 
circumstance alone can explain why the albatross is able to 
sail about for an hour or more at a time, without once 
