242 PHENOMENA OF FLIGHT IN THE ANIMAL KINGDOM. 



He estimates that this force is euormous ; that it is, in the case of the bird, 

 more than ten thonsand times greater than the weight of its body. We still 

 find this exaggeration in recent -svorks. The academician Navier, falls 

 into an analogous error, and after him M. Babiuet accords, in his turn, 

 a power to the inhabitants of the air far superior to that with which 

 they are gifted by nature. However, by the side of these errors we find 

 a great number of correct ideas, since confirmed by observation. Borelli 

 knew that the principal motion of the wings was an elevation and depres- 

 sion, executed in a vertical plane, and he asked himself how it was pos- 

 sible that this motion, which, it seemed to him, could only serve to ele- 

 vate the animal or to depress it, should nevertheless contribute to onward 

 motion. For this, it was necessary that the vertical force should be 

 changed into a horizontal force. Examples of this transformation are 

 frequent. If a wind blowing horizontally strikes against a flat board 

 inclined forward at an angle of, say, forty-five degrees with the horizon, 

 the action of the wind will tend to throw it backward and upward ; or, 

 if the board is moving forward with a momentnm, it will tend to elevate 

 it. We have here an illusLratiou of a well-known principle of mechanics 

 — the resolntion of a single force by an inclined plane into two forces — 

 which gives in part an explanation of the flight of insects and of water 

 birds. But insects have four wings instead of two. Is the olfice of these 

 four organs the same ; and if not, in what do theydifter? Borelli does 

 not treat of this question. It it discussed, however, in a particular 

 case, by an anonymous author, who has left us an interesting manu- 

 script on the habits of bees. This work, intended to complete and to 

 correct the work of Eeaumur, came from the Condaraine Library, and 

 belongs to M. Harnet. The author has observed bees at the moment 

 when they hum at the mouth of the hive, trying to enter it and deposit 

 their treasure. In examining the play of light on their trembling wings, 

 he thinks that he saw the upper pair alone alternately raised and 

 depressed, while the lower pair were animated only with a feeble hori- 

 zontal motion. Here the question seems to have been abandoned, 

 although the interest with which it is now regarded is far from iucon- 

 siderable. Beside the interest which it oflers from the purely scientific 

 point of view, in the mechanism of a function as widely employed as 

 aerial locomotion, still another interest is attached to this study. The 

 insect and the bird realize one of the oldest and most unsuccessful aspi- 

 rations of the ambition of man. All space belongs to them; they go and 

 come in the aerial ocean, while he is chained by his weight to the earth. 

 Man has sought by various methods to escape from this confinement. 

 The knowledge of the processes by which nature attains the end to 

 which he aspires, woidd perhaps have spared him many fruitless attempts 

 and loss of much time and great waste of invention. In 1823 a work 

 appeared in which this question of aerial locomotion is treated exprofesso, 

 and no longer in an incidental manner. The author, the Chevalier de 

 Chabrier, studied the conditions of mobility of the wing, and arrived at 

 the solution of an important question : how muscular action is trans- 

 mitted to this movable organ. Is it directly, or by some intervention? 

 The muscle, responds Chabrier, is not directly attached to the wing; it 

 acts upon the arch of the back. When it contracts, the curvature of this 

 arch is augmented; when it relaxes, the back returns to its original 

 curve, like an unbent bow. In the motion of the wing, therefore, there 

 is only one active period, the moment of depression; the period of ele- 

 vation is passive. Elasticity, therefore, plays an important part in this 

 function. Here, as in all mechanical organs, it absorbs and then gives 

 out power; it regulates speed and produces continuity of motion. 



