263 



FLIGHT 



remiges, shewn by the short lines in the figure, taken in a line 

 parallel to the trajectory of the bird, is inclined at an angle with 



Fio. 6. (From Marey.) 



the line of flight, so that their under surface looks downwards 

 and backwards. The exact angle is not known, but it is certainly a 



small one, and probably 

 varies with the velocity of 

 the bird's motion. Having 

 made the down and forward 

 stroke, the wing moves 

 backward, being still ex- 

 tended, and still inclined 

 slightly backwards. The 

 diagram indicating a bird 

 flying from left to right, 

 though not to be taken as 

 more than approximately 

 exact, gives an idea of what 

 is knoAvn regarding the tra- 

 jectory of the wing and the inclinations of its plane Avith the axis 

 of flight. The down stroke, it should be added, takes a longer time 

 than the up stroke. In making the latter, as can be seen from the 

 figure (Fig. 8), the wing passes at first backwai'ds, and then, becom- 

 ing partially flexed Avith a whiplike action, it rises upwards, the plane 

 of the wing being altered during the up stroke, so that it looks 

 down and forward. If the bird be flying fairly rapidly through the 

 air, the up stroke is mainly a passive movement, the bird continuing 

 to rest on the wings, and the velocity of the forward motion of its 

 body diminishing, to be increased again with the next down stroke. 

 At starting, and before the bird has acquired velocity, the up 

 stroke is an active one, and the primary feathers can be proved 

 to separate from one another, facilitating thereby the movement 

 by reducing the resistance offered by the air to the back of the 

 wing. The above description applies mainly to the Pigeon and 



Fio. ". (From Marey.) 



