G. GENERAL NATURAL HISTORY AND ZOOLOGY. 195 



watching the movement of gulls following a vessel at sea, 

 and regulating their motion by the speed of the vessel. It is 

 very difficult, however, according to Mr. Marey, to ascertain 

 to what movement of the wing these displacements of the 

 body of the bird correspond; and the determination of the 

 periodical variation of the quickness in the movement for- 

 ward of the bird is impossible by means of our senses. To 

 accomplish this object, the author has added to his previous 

 apparatus an arrangement for noting and recording these 

 movements with absolute precision; and from a critical study 

 of the indications, he conies to the conclusion that, on regis- 

 tering simultaneously both the vertical oscillations of the 

 bird and the movements of the wing, it will be found that 

 each revolution of the wing is accompanied by two complete 

 oscillations of the bird one of these coinciding with the de- 

 pression of the wing, and the other with its elevation. He 

 also finds, from the investigation bestowed upon the indica- 

 tions of the instrument, that in depressing its wings the bird 

 is raised, to fall again at the end of this period of depression, 

 while at the same time the bird accelerates its horizontal ve- 

 locity. In raising the wing the bird rises anew, again to fall 

 back, and in the second period it loses much of its horizontal 

 velocity ; and this latter fact gives the clew to the mechan- 

 ism of the second ascension, showing that this ascent is made 

 at the expense of the velocity acquired by a mechanism anal- 

 ogous to that of the boy's kite, which, moving against the air, 

 and presenting against it an inclined plane, is elevated at the 

 expense of the horizontal force applied to it. The experi- 

 ments of the author have satisfied him that this second as- 

 cent is wanting when the bird at the end of its flight has 

 not acquired a velocity at the expense of which it can be 

 produced. 



In a subsequent notice Mr. Marey promises to exhibit the 

 result of attempts made by him to reproduce synthetically 

 the mechanism of flight ; that is to say, for the purpose of 

 realizing by means of a weighty apparatus the effect # of sus- 

 tainment in the air, and of the horizontal forward motion 

 which the bird obtains by the action of its wings. 6 -Z?, xiv., 

 661. 



