62 love's meinie. 



first meets the adverse force. It is the one to be sup- 

 ported. 



Kow for the manner of the support. You must all 

 know well the look of the machicolated parapets in medi- 

 geval castles. You know they are carried on rows of small 

 projecting buttresses constructed so that, though the up- 

 permost stone, far-2:)rojecting, would break easily under 

 any shock, it is supported by the next below, and so on, 

 dow^n to the wall. Now in this figure I am obliged to 

 separate the feathers by white spaces, to show you them 

 distinctly. In reality they are set as close to each other 

 as can be, but putting them as close as I can, you get a or 

 Z>, Fig. 5, for the rough section of the wing, thick towards 

 the bird's head, and curved like a sickle, so that in strik- 

 ing down it catches the air, like a reaping-hook, and in 

 rising up, it throws off tlie air like a pent-house. 



70. The stroke would therefore be vigorous, and the 

 recovery almost effortless, were even the direction of both 

 actually vertical. But they are vertical only with rela- 

 tion to the bird's body. In space they follow the forward 

 flight, in a softly curved line ; the downward stroke being 

 as effective as the bird chooses, the recovery scarcely en- 

 (jounters resistance in the softly gliding ascent. Thus, in 

 Fig. 5, (I can only explain this to readers a little versed 

 in the elements of mechanics,) if b is the locus of the 

 centre of gravity of the bird, moving in slow flight in the 

 direction of the arrow, w is the locus of the leading 

 feather of its wing, and a and J, roughly, the succes- 



