RE-ACTIONS DURING FLIGHT. 



267 



After having convinced ourselves that the apparatus trans- 

 mits faithfully the movements which are communicated to it, 

 we connect it with the registering instrument by means of a 

 long tube, and place it on the back of a bird, which is then 

 allowed to fly. Experiments made on many different species, 

 pigeons, wild ducks, buzzards, moor-buzzards, screech owls, 

 have shown that there are very varied types of flight with 

 respect to the intensity of the oscillations in the vertical 

 plane. 



Fig. 113 shows the tracings furnished by different species 

 of birds. All these tracings, collected on a cylinder revolving 

 with a constant rapidity, and referred to a chronographic 

 tuning-fork vibrating 60 times in a second, enable us to 

 ascertain the absolute and relative duration of the oscillations 

 during the flight of different species of birds. 



We find from this figure, that the frequency and amplitude 

 of the vertical oscillations vary much according to the species 

 of the bird. In order to ascertain the cause of each of these 

 movements with greater accuracy, let us register at the same 

 time the vertical oscillations of the bird, and the action of the 

 muscles of the wing. If we make this double experiment on 

 two birds which differ much in their manner of flight, such 

 as the wild duck and the buzzard, we obtain the tracings 

 represented in fig. 114. 



The duck (upper line) presents at each elevation of its 

 wing two energetic oscillations ; that at b, at the moment when 

 the wing is lowered, is easy to be understood, as well as that 

 at a, at the moment that the wing begins to rise again. To 

 explain the ascent of the bird during the time of the elevation 

 of the wing, it seems indispensable to refer to the effect of 

 the child's kite, to which we have before alluded. The bird 

 having acquired a certain velocity, presents its wings to the 

 ^ir as inclined planes; an effect is immediately produced, 

 similar to the ascent of the hovering apparatus which trans- 

 form their acquired velocity into ascensional force. The 

 flight of the buzzard shows also, but in a less degree, the 

 ascent which accompanies the upward movement of the 

 wing. 



Determination of variations in the rapidity of flight — The 



V 



