238 



ANIMAL MECHANISM. 



one of the levers and to the left of the others, a drum whose 

 membrane, situated in the vertical plane, acts in a lateral 

 direction; the transmission of these movements is made by a 

 special tube, as in the case of the vertical movements. 



The apparatus having been thus constructed, if we take in 

 our fingers the extremity of one of the levers, and give it any 

 motion whatever, we shall see the other lever repeat it with 

 perfect fidelity. 



All the difference consists in a slight diminution of the am- 

 plitude of the movements in the second lever. This is because 

 the air contained in each of the systems of tubes and drums 

 is slightly compressed, and consequently does not transmit 

 completely the movement which it receives. It would be easy 

 to remedy this inconvenience, if it were found to be one, by 

 giving to the receiving apparatus a greater sensibility, which 

 might be effected by placing the Cardan joint a little nearer 

 the point where the movement is transmitted to the lever of 

 the second instrument. But it is better not to seek to amplify 

 the movements too much when we wish to register them by 

 tracings, since we then augment the friction, and diminish the 

 force by which it must be overcome. 



After having ascertained that the transmission of any move- 

 ment whatever is effected in a satisfactory manner by this ap- 

 paratus, we sought for a means of tracing this movement on a 

 plane surface. The difiiculty which occurred in the application 

 of the graphic method to the study of the movement of the 

 insect's wing, again presents itself here ; but in this case there 

 are no means of avoiding it by taking only partial tracings. 



The point of the lever No. 2 describes in space a spherical 

 figure incapable of becoming tangential, except in a single 

 point, to the smoked surface which is to receive the tracing. 

 Consequently, it has been necessary to register the projection 

 of this figure on a plane surface, and to arrange the lever in 

 such a manner that it may lengthen or shorten itself as re- 

 quired, in order to keep always in contact with the smoked 

 glass. This result was obtained by means of a spring which 

 served as a writing point. 



Fig. 98 shows the spring in question, at the extremity of a 

 lever. It is wide at the base, in order to resist any tendency 



