228 



ANIMAL MECHANISM. 



able to study is very small as yet ; the following are- the 

 results obtained : — 



Revolutions of wing 

 per second. 



Sparrow .13 



Wild duck 9 



Pigeon ....... 8 



Moor buzzard 5| 



Screech owl . . . , , .5 

 Buzzard 3 



The frequency of the strokes of the wing varies also, according 

 as the bird is first starting, in full flight, or at the end of its 

 flight. Some birds, as we know, keep their wings perfectly 

 still for a time ; they glide upon the air, making use of the 

 velocity already acquired. 



Relative duration of the depression and elevation of the wing. — 

 Contrary to the opinion entertained^ by some writers, the 

 duration of the depression of the wing is usually longer than 

 that of its rise. The inequality of these two periods is more 

 distinctly seen in birds whose wings have a large surface, and 

 which beat slowly. Thus, while the durations are almost 

 equal in the duck, whose wings are very narrow, they are 

 unequal in the pigeon, and still more so in the buzzard. 

 The following are the results of our experiments : — 





Total duration of a 

 revolution of the wing. 



Ascent. 



Descent. 



Duck 



11 1 hundreds of a second 



5 



6| 

 84 



Pigeon . . 



,, ,, 



4 



Buzzard . 



324 ,, ,, 



121 



20 



It is more difiicult than would have been expected, to determine 

 the precise instant when the direction of the line traced by the 

 telegraph changes. The periods during which the soft iron 

 is first attracted and then set free, have an appreciable duration 

 when the blackened cylinder turns with sufficient rapidity to 

 enable us to measure the rapid movements which are the 

 subjects of this inquiry. The inflections of the line traced by 

 the telegraph then become curves, the precise commencement 



