• PHENOMENA OF FLIGHT IN THE ANIMAL KINGDOM. 267 



Fie. IB.* Fiff. 19. 



Fig. 18. Myographic tracings of the pectorals, obtained from various kinds of birds 

 during tlight. I. Tracing of the tuning-fork to be used in measuring the absolute 

 duration of each muscular motion ; this tuning-fork vibrates 200 times a second. II. 

 Tracing of the muscles of a pigeon obtained, as in Fig. 16. III. Tracing of a wild 

 duck. IV. Tracing of a hen-hawk. V. Tracing of a harrier. 



Fig. 19. Line a represents the electric tracing of the ascent and descent of the wing 

 of a harrier, as furnislied by the apparatus. Line 6 is a tracing of a tuning-fork vibrat- 

 ing 200 times a second. Line c, correction of the electric tracing, which latter does not 

 represent the changes with sufficient abruptness in the figure {a) obtained directly from 

 the wing. Line d, tracing of the action of the pectoral muscles in the harrier by the air 

 apparatus ; a', period of elevation of the wing ; &', period of depression. Line e will 

 be hereafter referred to; it represents the vertical oscillations of the bird during flight. 



