DR PETTIGREW ON THE PHYSIOLOGY OF WINGS. 



341 



the wing is successively and rapidly brought into contact with innumerable 

 columns of undisturbed air. It consequently is a matter of indifference whether 

 the wing is carried at a high speed against undisturbed air, or whether it operates 

 upon air 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 quantity 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 decreases, and vice versa. In 

 fact, the reciprocating and non-reciprocating function of the wing in such cases 

 is purely a matter of speed. If the travel of the wing is greater than the hori- 

 zontal 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 follows that no figure of 8 will be described by the wing, that the 

 wing will not reciprocate to any marked extent, and that the organ will describe 



Fi«. 10. 



Fig. 11. 



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 downward looped track 

 represented at fig. 10, is at once converted into an upward looped track, as shown 

 at figure 11, in virtue of the action and reaction of the wing and air upon each 



