190 



ANIMAL MECHANISM. 



The upper zone of the revolution of the wing gives tracings 

 analogous with that of fig. 74, in which the upper loops of the 

 8 are plainly visible. The tracings of the zone which corre- 



Fio. 73. — Tracing of the middle zone in the course described by the wii g of 

 a humming-bird moth. The numerous strokes ot which this tracing is 

 formed, arise from the extremity of the wing being fringed and present- 

 ing a rough surface. 



sponds with the lower course of the wing give also loops like 

 those of the upper arch (fig. 75 shows a specimen of them) ; 

 so that the figure 8 of the tracing can be reproduced by 



Fig. 74, — This figure shows, in the tracing made by a wasp, the upper loop, 

 and all the extent of one branch ol the 8. The middle part of this 

 branch is merely dotted because of the feeble friction of the wing. 



bringing together the three fragments of its course successively 

 obtained. 



If we could only once procure the entire tracing formed by 

 the wing of an insect, we should then get a figure identical 

 with that which our learned writer on acoustics, Koenig, was 

 the first to obtain with a Wheatstone rod tuned to the octave, 

 that is to say, describing an 8 in space. This typical form is 

 represented in fig. 76. We shall see that the graphic method 



