192 



ANIMAL MECHANISM. 



If the cylinder revolve, the figure will be spread out liki- 

 the oscillation of a tuning-fork registered under the samo 

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

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



M 



x 



Miajty ji j 



Fio. 77.- -Tracing olrtained with the wine of a lice "spillatinp in a piano 

 which is sensibly tangential to the generatrix ol tueru^. storing cylinders. 



Tliis 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. 



Hut in examining these tracings we easily recognise chainjc* 

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

 made by a grr.-ner or less friction of the wing <>n the cylin- 

 der; we here find a ne\v 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 tone' cs 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: 



L'lu. 7- Tracings nf a wnp ; the Insesl i- l> H *" tint its win- t..u.'hiH 

 tlie cylinder b> it--> j'uiul, .mJ ti.icc^ i;oi.c;all,> Uje mver loi.ji ..f the a. 



