190 



ANIMAL MKCIIAXISM. 



The upper zone of the revolution of the wing jjives tracings 

 analogous with that of fig. 74, in which t' e upper 'oops of I lie 

 8 are plainly visiUe. The tracings of the zone which c< rre- 



Fm. ".'!. Tracing of the ini<l<ll> > -/.in- in tliu c..ur-c rtescribi .1 l.y tin- wit g of 

 a humming-bird moth. Tlic numerous strokesot wl,k-h this tracing is 

 formed, .-iris" fmni tho extremity of tho wing bein;i f ringed and present- 

 ing a rough sti. face. 



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

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

 so thnt the figure 8 of the tracing can lie reproduced l>y 



FlO. 74. Tins figure shows, in the tracing ni.-icle bj- a \v;is]>. tin 1 ii]'i T oop, 

 aiicl all I he fxti lit oi' , in: 1 rani-h o the S. The niMillu part of tbis 

 brnnclj is merely dut:e I liucaune of the feeble friction of the wing. 



bringing together the three fragments of its course successively 

 obtained. 



If \vc could only once pi-mire the entire tracing formed by 

 the wing of an ins-ret, we i-hould then get a figure identical 

 with that which our learned writer on acoustics, Ko'iiig, was 

 the first to obtain \\itli a \Vheatstone rod tuned to the octave, 

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

 represented in tiir. 70. We ^liall see that the graphic niet.hod 



