322 DR PETTIGREW ON THE PHYSIOLOGY OF WINGS. 



great pectoral fins or pseudo-wings of the flying fish, I felt persuaded that a 

 close analogy existed between the flippers, fins, and tails of sea mammals and 

 fishes on the one hand, and the wings of insects, bats, and birds on the other ; 

 in fact, that theoretically and practically these organs one and all formed 

 flexible helices or screws, which, in virtue of their rapid reciprocating action, 

 operated upon the water and air after the manner of double inclined planes. 



Guided by these indications, I especially directed my attention to the 

 twisting flail-like movements of the wings of insects ; of the flippers and tails 

 of sea mammals, and of the fins and tails of fishes. These I found all acted 

 upon the air and water by curved surfaces, the curved surfaces reversing, 

 reciprocating, and engendering a wave pressure, which could be continued 

 indefinitely at the will of the animal. 



In order to prove that sea-mammals and fishes swim, and insects, bats, and 

 birds fly, by the aid of curved figure of 8 surfaces, which exert an intermittent 

 wave pressure, I constructed artificial fins, flippers, and wings, which curved 

 and tapered in every direction, and which were flexible and elastic, particularly 

 towards the tips and posterior margins. These fins, flippers, and wings were 

 slightly twisted upon themselves, and when applied to the water and air by 

 a sculling or figure of 8 motion, curiously enough not only reproduced the 

 curved surfaces referred to, but all the other movements peculiar to the fins 

 and tail of the fish when swimming, and to the wings of the insect, bat, and 

 bird when flying. 



History of the Figure of 8 or Wave Theory of Flying. 



The Wing a Tivisted Lever or Helix. — I announced this view in a lecture 

 delivered at the Royal Institution of Great Britain in the early part of 1867. 

 An abstract of the lecture appeared in the Proceedings of the Institution under 

 date the 22d of March 1867.* At pages 99, 100, and 101 of the abstract in 

 question, the spiral conformation of the wing in the insect and bird is adverted 

 to at length, and there described as a twisted lever or helix, which owes its 

 peculiar elevating and propelling power in a great measure to its shape. Par- 

 ticular emphasis is also placed upon the partial rotation of the wing on its long 

 axis during extension and flexion, and to its screwing and unscrewing action 

 during the down and up strokes, this being a " sine qua non " in flight. In the 

 pages alluded to, the subjoined passages occur : — " The wings of insects and 

 birds are, as a rule, more or less triangular in shape, the base of the triangle 

 being directed towards the body, the sides anteriorly and posteriorly. They are 

 also conical on section from within outwards and from before backwards ; this 

 shape converting the pinion into a delicately graduated instrument, balanced 

 with the utmost nicety to satisfy the requirements of the muscular system on 



* On the Various Modes of Flight in relation to Aeronautics. 



