MOVEMENTS OF THE WINGS OF BIRDS. 239 



to lateral deviations under the. influence of the friction ; this 

 base is fixed to a vertical piece of aluminium, which is 

 attached by its lower part to the extremity of the lever. In 

 this manner, the point of the spring which acts as a style is 

 considerably in front of the lever whose movements it is to 

 register. Let us suppose the levtr to rise, and take the 

 position indicated by the dotted line in figure 98 ; while 

 traversing this space, it will have described an arc of a circle, 

 and its extremity will no longer be in the same plane as before, 

 but the elasticity of the spring will have carried the writing 

 point more forward ; it will still continue, therefore, to be 





Fio. 98. Elastic point tracing on a smoked glass. 







in contact with the plane on which it is to trace. Thus the 

 lever lengthens or shortens, as required, and its point 

 always presses on the plane. The surface on which the tracing 

 is received is a well-polished glass, and the spring which 

 forms the style is so flexible, that the elastic pressure which it 

 exerts upon the glass rubs it but slightly. 



The apparatus being thus arranged, it must be submitted 

 to a verifying process, to ascertain if movements are faithfully 

 transmitted and registered. 



For this purpose, arming the two levers of fig. 97 with 

 similar styles, we placed their points against the same piece 

 of smoked glass; we directed with the hand one of the levers 

 so as to trace any figure, to sign one's name for instance ; the 

 other lever ought to trace the same figure, to reproduce the 

 same signature. 



