SPACE 2 I 



occupied by a particular part of a bird's wing during 

 the act of flight, and that this particular part is the 

 tip of one of the quills, called "remiges." Now, such 

 a quill, by reason of its flexibility, would be incapable 

 of giving the necessary motive power to an apparatus 

 for recording the trajectory of flight ; and, further, this 

 point is inaccessible because birds only fly freely at 

 a certain distance from the observer. A black crow 

 may be used in the experiment, and a small piece of 

 white paper may be fixed to the extremity of one of its 



Fig. 13. — Trajectory of the tip of a crow's wins. A brilliant spangle attached to the 

 second of the remiges follows the path indicated by tie small arrows. In the lower 

 part of the figure a straight and horizontal arrow sho»\s the direction of flight. 



longest "remiges." The bird is then allowed to fly 

 in front of a dark background, towards which a photo- 

 graphic camera is directed. Since the entire field of 

 the object-glass is dark, that is to say, the bird and its 

 background, the sensitized plate can receive no light 

 except that which is reflected by the small piece of 

 white, paper, which is illuminated by the sun. The 

 image of this white spot will leave a record of its 

 track on the sensitized plate. In this way Fig. 13 was 

 obtained, the arrows indicating the direction of flight. 

 Stereoscopic Trajectories. — The trajectory of the 



