MOVEMENTS OF THE WINGS OF BIRDS. 243 



D'Esterno had already determined by his experiments that 

 this trajectory existed ; and he has even figured, in his work, 

 the curve described ; but, in his opinion, the larger axis of , 

 the ellipse would be directed downwards and backwards, which 

 is entirely opposed to the result of our experiments. 



Fig. 101. — Ellipse formed by a Wheatstone's rod tuned in unison, and 

 tracing on a revolving cylinder. 



We remark also the unequal amplitude of the strokes of 

 the wing from the commencement to the end of fig. 100. 

 This variation in size agrees with what we have already 

 stated concerning fig. 96. This showed that at the com- 

 mencement of its flight, the bird gives stronger strokes with 

 its wing. It is at that moment, in fact, that it has to effect 

 the maximum of work, in order to rise from the ground. 

 After this, it will only need to remain at the height which it 

 has attained. 



