PllOGRESSION IN OR THROUGH THE AIR. 



145 



travelling at a high speed (as, e.g. the artificial currents pro- 

 duced by the rapidly reciprocating action of the wing). The 

 result is the same in both cases, inasmuch as a certain quan- 

 tity of air is worked up under the wing, and the necessary 

 degree .of support and progression extracted from it. It is, 

 therefore, quite correct to state, that as the horizontal speed 

 of the body increases, the reciprocating action of the wing de- 

 creases ; and vice versa. Tn fact the reciprocating and non- 

 reciprocating action of the wing in such cases is purely a 

 matter of speed. If the travel of the wing is greater than the 

 horizontal travel of the body, then the figure-of-8 and the 

 reciprocating power of the wing will be more or less perfectly 

 developed, according to circumstances. If, however, the 

 horizontal travel of the body is greater than that of the 

 wing, then it folio w^s that no figure of- 8 will be described by 

 the wing; that the wing will not reciprocate to any marked 



Fig. 74. Fig. 75. 



Figs. 74 and 75 show the more or less perpendicular direction of the stroke of the 

 wing in the flight of the bird (gull) — how the wing is gradually extended as it 

 is elevated {e f g of fig. 74)— how it descends as a long lever until it assumes 

 the position indicated by h of fig. 75— how it is flexed towards the termination 

 of the down stroke, as shown aXhij of fig. 75, to convert it into a short lever 

 {a b) and prepare it for making the up stroke. The diff'erence in the length 

 of the wing during flexion and extension is indicated by the short and long 

 levers a b and c d of fig. 75. The sudden conversion of the wing from a long 

 into a short lever at the end of the down stroke is of great importance, as it 

 robs the wing of its momentum, and prepares it for reversing its movements. 

 Compare with figs. 82 and 83, p. 158. — Original. 



extent ; and that the organ will describe a waved track, the 

 curves of which will become less and less abrupt, i.e. longer 

 and longer in proportion to the speed attained. The more 



