PHENOMENA OF FLIGHT IN THE ANIMAL KINGDOM. 235 



longed contact is desired, it can only be by curving the wing and fold- 

 ing it npon itself, and consequently the natural curve which the or- 

 ganization of the insect obliges it to traverse will be falsified and 

 altered. In any case the friction against the blackened surface will re- 

 tard the motion, and although the retardation which it causes may be 

 neglected when it is opposed to bodies of large size, such as a tuning- 

 fork or a vibrating rod, it cannot be when the vibrating object is the 

 delicate membrane which constitutes the wing of an insect. Again, the 

 friction, although exceedingly small, is found fully comparable Avith the 

 forces which come in play in the motion of the wing, and its interven- 

 tion notably alters the action of the latter. Experiment has confirmed 

 these views. In one case an insect executing the motions of flight, and 

 rubbing its wings somewhat roughly against the paper, furnished 240 

 movements per second ; by diminishing more and more the contact of 

 the wing with the cylinder, there have been obtained 282, 305, and 321. 

 If, therefore, we would have a faithful representation, it is necessary to 

 renounce the idea of obtaining those beautiful, regular, and continuous 

 lines which are i)roduced by the tuning-fork or vibrating rod, and content 

 ourselves with interrupted lines, half-strokes represented by fragments, 

 or even only isolated dots, the periodical return in these incomi)lete 

 markings of definite forms permits us to infer the repetition of similar 

 oscillations, and hence to determine their frequency. The operation is as 

 follows : With a delicate jiair of forceps we hold the insect by the lower 

 portion of its abdomen, in such a position that one of its wings at each 

 movement shall lightly touch the blackened paper. Each of these touches 

 takes off a portion of the soot which covers the paper, and, as the cylin- 

 der turns, new points incessantly present themselves to the contact of 

 the wing. A figure is thus obtained, formed of a series of points or 

 short strokes of perfect regularity if the insect has been maintained in 

 a fixed position. 



Fiff. 1. 



: VylAAA^AA^AA/'AAAA^^AAAAy^A/iAAAAA^AA'^AAA;^,AAAA^^AA/J\AJ\AAAA;ly'A/V^^ ' f .\l\" S'J\N\I\AI\N\rJ\N\r^Ar^ 



Showing the frequency of the win<^-strokes of a drone, (the three upper lines,) and 

 of a bee, (the lower line.) The fourth line is produced by the vibration of a tuuiufj- 

 fork, furnished with a style, which executes 250 double vibrations per second. 



Tracing produced by the wing of a drone rubbing a little more strongly on the paper 

 than in the preceding figure. 



We have obtained a large number of these tracings in which the wing 

 has only touched the surface of the registering cylinder, and has left 



