192 ANTMAL MECHANISM. 



If the cylinder revolve, the figure will be spread out like 

 the oscillation of a tuning-fork registered under the same 

 conditions, and we shall obtain a tracing more or less ap- 

 proaching in form to that which is represented in fig. 77. 



Fig. 77.--Tracm8r obtained with the win^ of a bee, oscillating in a plane 

 which is sensibly tangential to the generatrix of the registering cylinders. 



This form, which theory enables us to predict, is always 

 produced when the plane in which the wing moves is tan- 

 gential to the generatrix of the cylinder. 



But in examining these tracings we easily recognise changes 

 in the thickness of the stroke — parts which appear to have been 

 made by a greater or less friction of the wing on the cylin- 

 der ; we here find a new and certain proof of the existence of 

 a movement in the form of an 8, as we now propose to show 

 by a synthetic method. 



Let us take a Wheatstone's rod tuned to the octave ; let us fix 

 on it the wing of an insect as a style, and let us trace the vibra- 

 tions which it executes. We shall obtain, if the cylinder be 

 motionless, figures of 8 when the wing touches the paper by 

 its point applied perpendicularly to its surface ; and if the 

 cylinder revolve, we shall have lengthened figures of 8. 



We may obtain, with a rod tuned to the octave, tracings 

 identical with those given by the insect ; of which a proof is 

 afforded by the comparison of the two following figures : — 



Fig. 78.— Tracings of a wasp ; the insect is held so that its wing touches 

 the cylinder by its point, and traces especially the upper loop of the 8. 



