216 THE STRUCTURE AND LIFE OF BIRDS chap. 



is often quite inaudible. Even when we can hear the 

 note it does not tell us much. It depends on the 

 rapidity with which the extremity of the wing moves, 

 not on the number of wing-beats in a second, and so 

 cannot tell us what we want. 



(3) We now come to the graphic method, in apply- 

 ing which Professor Marey has shown wonderful skill. 

 A sheet of paper blackened by the smoke of a candle 

 was stretched upon a cylinder, which was made to 

 revolve at a uniform rate. An insect, the frequency 

 of whose wing movements was to be studied, was held 

 by the abdomen in a delicate pair of forceps, and was 

 placed so that one of its wings, at every up or down 

 stroke, brushed against the blackened paper. With 

 birds the method was, necessarily, far more elaborate. 

 On the extremity of the wing an apparatus was placed 

 which at each alternate movement broke or closed an 

 electric circuit. In Professor Marey's book {Animal 

 Mechanism, p. 230) the bird may be seen carrying his 

 burden of electric wires and other machinery. As in 

 the case of the insect, a tracing was made on a 

 revolving cylinder. 



The results were : 



These results seem quite dependable, and it is much 

 to be regretted that we cannot arrive at conclusions 



