178 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



through an angle of about 60 ; but when the arm was re- 

 volved, so that the bird was translated about ten meters per 

 second, he observed that the amplitude of the beats of the 

 wings was reduced to 30, and even to 20. This influence 

 of the horizontal motion of the bird on the resistance opposed 

 to the beats of its wings explains how the jwint (Pappui is 

 obtained during flight, and accounts for the following facts 

 of observation and experiment : 



1. When a bird rises, and begins its flight, the amplitude 

 of the motion of its wings is very extended; but this ampli- 

 tude is greatly reduced when the horizontal transport of the 

 bird has become rapid. 



2. When a flying bird is attached to a string, it falls, not- 

 withstanding the beating of its wino-s, when the tension of 

 the string stops the bird's horizontal motion. 



3. A bird when rising in flight always, as nearly as pos- 

 sible, faces the wind. This is because, in this circumstance, 

 the wind carries continually fresh layers of air under its wings, 

 and places the bird in the same conditions as exist during its 

 horizontal translation. 



4. When a living bird is suspended at the end of the hor- 

 izontal arm, so that he can freely use his wings and fly round 

 in a circumference, if we now give to the arm a rapid mo- 

 tion of rotation, the motion of the wings of the bird are re- 

 duced to extreme slowness. The flap of the wing of a pigeon 

 may thus be reduced to one second in duration, whereas the 

 bird in flying freely makes eight flaps per second. As all 

 motion is retarded by the resistances opposed to it, this exper- 

 iment is one of the best proofs that one can bring forward 

 of the increase of the resistance of the air from the velocity 

 of the bird's translation. 



This explanation of the increase of resistance caused by the 

 motion of the bird was original with Marey, but it appears 

 that M. M. Planavergne, of Marseilles, published in 1872 a 

 similar explanation ; but certainly to Marey belongs the cred- 

 it of showing experimentally that this is not only a true 

 cause, but a sufficient one. Comptes Rendus, January 12, 

 26, and February 16, 1874. 



