INTRODUCTORY. 



every body knows who has eaten a chicken, or attended the 

 dissection of a Thanksgiving turkey, the soft parts are external, 

 attached to the bony framework comprising the skeleton, the 

 wing bones being directly connected with the central back 

 bone ; so that while these two sorts of animated flying machines 

 are so different in structure, they yet act in much the same man- 

 ner when on the wing. The difference between them is clearly 

 stated by Marey, some of whose conclusions we now give almost 

 word for word. 



The flight of butterflies and moths differs from that of birds 

 in the almost vertical direction of the stroke of their wiugs, and 

 in their faculty of sailing in the air without making any move- 

 ments ; though sometimes in the course they pursue they seem 

 to resemble birds in their flight. 



The flight of insects and birds moreover differs in the form 



of the trajectory in space ; in the inclination of the plane in 



which the wings beat; in the role of each of 



the two alternating (and in an inverse sense) 



movements that the wiugs execute ; as also in 



the facility with which the air is decomposed 



during these different movements. As the 



wings of a fly are adorned with a brilliant 



array of colors, we can follow the trajectory 



or figure that each wing writes in the air. It 



is of the form of a figure of eight (Fig. 9), first 



9. Figrurecutbyau discovered by Professor J. Bell Pettigrew of ' 



insect's wing. Edinburgh. 



By an ingenious machine, specially devised for 

 the pui-pose, Professor Marey found that a bird's 

 wing moves in an ellipse, with a pointed summit 

 (Fig. 10). The insect beats the air in a distinctly 

 horizontal plane, but the bird in a vertical plane. 



10. Fij^uio cut 

 The wing of an insect is impervious to the air; by a bird's 



while the bird's wing resists the air only on its wing. 



