22 Natural and Artificial Flight. (January, 
reach its cote, causes the traces on the blackened cylinder 
shown in Fig. 3. 
The tracings vary with the kind of bird placed in the 
corset; but in all may be seen the alternation of two mo- 
FIG. 3. 
Tracings of the Expansion of the Pectoral Muscle of Various Birds 
during Flight. 
I. Tracings of a Tuning-Fork making 200 vibrations a second. II. From the muscle of a 
Pigeon. III. From a Wild Duck. IV. From a Hen Hawk. V. From a Harrier. 
tions, a and b, produced during each vibration of the wing, 
that of a corresponding to the a¢tion of the muscle elevating 
the wing, and that of 6 to the muscle depressing the wing, 
Anatomically, a shows the swelling of the median pectoral, 
and b that of the great pectoral. Nothing more should be 
expected from these tracings than they naturally furnish, 
that is to say, the number of vibrations of the wing, the 
Fic. 4. 
greater or less regularity of its movements, the equality, 
inequality, and energy of each of them. Confining the in- 
vestigation to these limits, we obtain the following results :— 
Number of Wing Vibrations 
per Second. 
SPAELOW cs ots) ce Res eeoeees pe ec 3 (00) 
Waldduck=./.aeele: os 2 ) O00 
Pigeon Z's. ,.ad100 
Buzzard (Buteo vulgaris) . « 5°75 
SCrEech (OWL eae ho comers eu to GOO. 
Harrier(Civcus:vujus) =~ = “3 37°00 
