MOVEMENTS OF THE WINGS OF , BIRDS. 231 



which raises the membrane. Alternate outward and inward 

 currents of air are thus established in the tube, and this 

 movement transmits to the registering apparatus the signals 

 of the less or greater pressures exerted on the membrane of 

 the small pan. 



The registering instrument is the lever drum, with which 

 the reader is already acquainted. It gives an ascending curve 

 while the muscle contracts, and a descending one when it is 

 relaxed. « 



Fig. 94 represents the general arrangement of the experi- 

 ment, in which the electric telegraph and the trans mission of 

 air are used at the same time. 



It shows a pigeon fitted with a corset, under which is 

 slipped the instrument which is to show the action of the 

 pectoral muscles. The transmitting tube ends in a registering 

 apparatus, which writes on a revolving cylinder. 



At the extremity of the pigeon's wing is the instrument 

 which opens or closes an electric current, as the wing rises 

 or sinks. The two wires of the circuit are represented as 

 separated from one another ; within the circuit are seen two 

 elements of Bunsen's pile, and the electro-magnet which, 

 being furnished with a lever, registers the telegraphic signals 

 of the movements of the wing. 



Experiment, — ^The bird is set free at one extremity of the 

 room, the dove-cot in which it is usually kept being placed 

 at the opposite end. The bird as it flies naturally seeks its 

 nest in which to rest. During its flight we obtain the tracings 

 represented by fig. 95. 



It is seen that the tracings differ according to the kind of 

 bird on which the experiment is made. However, we ob- 

 serve in each of the tracings the periodical return of the two 

 movements a and 6, which are produced at each revolution of 

 the wing. 



On what do these two muscular acts depend ? It is easy 

 to discover that the undulation a corresponds with the muscle 

 that elevates the wing, and b with that which depresses it. 

 This can be proved : first, by collecting, at the same time as 

 the muscular tracing, those of the ascending and descending 

 movements of the wing transmitted by electricity. When 



