25 ^ 



PHENOMENA OF FLIGHT IN THE ANIMAL KINGDOM. 



All tliiu curved bodies tend to slide upon the air in tlie direction of 

 the radius of their special curve. If we bend the anterior or posterior 

 edg^e of our little apparatus at a certain point in its oblique course, we 

 shall see it rise, notwithstanding the force of gravity, though its motion 

 soon ceases. What has happened in this case? 



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Eepreseutiug to tlie left Pline's apparatus placed in equilibrium by means of two 

 equal balls at the extremities of the rgd which lies at the bottom of the anj^le of tlio 

 beut paper. This, as is iudicated by the lower representations of the rod, falls verti- 

 cally. To the right the same apparatus, with only a single ball, is represented. It 

 descends in a parabolic curve, represented by the dotted hue. 



When there has been but little raindity in the fall of the object, the 

 curve of its surface remains motionless, because the air offers resistance 

 only in proportion to the rapidity with which they move. Therefore, 

 when this rapidity has been sufficiently great a steering effect is pro- 

 duced, which elevates 

 the anterior extremity 



of the object and im- >r-7 



parts an ascending -oA_ 



motion to it. But very 

 soon the weight, which h 



was the motive power -<^— 



of the apparatus, be- 

 comes a retarding 

 force, and in propor- 

 tion as the object as- 

 cends its motion be- ^ 

 comes slower, and 

 finally ceases. After 

 this, retrogradation 

 begins, to be followed 

 by another rise, and 

 so on, until by suc- 

 cessive oscillations the 

 apparatus finally reaches the earth. I may add that if a slight con- 

 cavity is given to the object below, the reverse takes place, and we see 

 at a certain moment the trajectory sharply deflected downward, and 

 the object strikes the earth with great violence. In the second case, 

 at the moment when the steering effect is produced, the weight is in a 

 favorable position for a precipitate descent, and opposed to the ascend- 

 ing reaction. 



The posterior corners of the two planes of the apparatus 

 have been bent upward and inward, so that after a descend- 

 ing curve the apparatus rises, as the dotted line indicates. 



