PART SECOND. 
EXPLANATION OF THE DIAGRAM. 
No. 1. — Represents the course of the bird in ascending from the 
earth preparatory to a long excursion, the serpentine line 
showing the path described by the tips of the wings in action 
at the rate of four strokes, per second of time ; but the 
angles of which, with reference to the line of ascent, are many 
times greater than what occurs in flight. 
No. 2. — The altitude and line of motion in flight proper ; the ser- 
pentine line here showing by its depressed angles a reduc- 
tion of the number of strokes of wing one fourth, per second 
of time, as compared with No 1. 
No. 3. — The descending course of the animal under a further re- 
duction of one stroke of wing less, per second of time, 
than the number required to sustain him on the line of 
motion. 
No. 4. — The course of the animal under an entire suspension of 
the action, but while sustained on expanded wings. 
No. 5. — The manner in which the body falls, after suddenly folding 
those organs while progressing on the line of motion, de- 
scribing the parbaola, like any other body in descending to 
the earth after having been thrown up in the air. 
No. 6. — The oblique direction in which the body constantly tends 
to rise above the line of motion, arising from the tendency 
to reaction of the straightened quills, and the muscular 
action of the animal whilst on the wing. 
No. 7. — The effect, on the other hand, of imparting an additional 
stroke of wing, per second of time, above what is required 
to sustain the animal on the line of motion, raising him 
from that line, and also showing a corresponding decrease 
in his velocity. ^* 
