DR PETTIGREW ON THE PHYSIOLOGY OF WINGS. 439 



speed quicker. When the speed, attained is high, the angles made by the 

 under surface of the wing with the horizon are diminished ; when it is low, 

 the angles are increased. From these remarks it will be evident that the 

 artificial wave wing reciprocates in the same way that the natural wing recipro- 

 cates, the reciprocation being most perfect when the wing is vibrating in a 

 given spot, and least perfect when it is travelling at a high horizontal speed. 



The Artificial Wing propelled at various degrees of speed during the down 

 and up strokes. — The tendency which the artificial wave wing has to rise again 

 when suddenly and vigorously dej)ressed, explains why the elevator muscles of the 

 wing should be so small when compared with the depressor muscles — the latter 

 being something like seven times larger than the former. That the contraction 

 of the elevator muscles is necessary to the elevation of the wing, is abundantly 

 proved by their presence, and that there should be so great a difference between 

 the volume of the elevator and depressor muscles is not to be wondered at, when 

 we remember that the whole weight of the body is to be elevated by the rapid 

 descent of the wings — the descent in question being entirely due to the vigorous 

 contraction of the pectoralis major. If, however, the wing was elevated with 

 as great a force as it is depressed, it is plain that the good effected during the 

 descent would be utterly undone, as the wing, during its ascent, would experience 

 a much greater resistance from the air than it did during its descent. The 

 wing is consequently elevated more slowly than it is depressed, the elevator 

 muscles exercising a controlling and restraining influence. By slowing the 

 wing during the up stroke, the air has an opportunity of reacting on its under 

 surface, as explained at page 351. 



The Artificial Wave Wing as a Propeller. — The wave wing makes an 

 admirable propeller if its tip be directed vertically downwards, and the wing 

 lashed from side to side with a sculling figure of 8 motion, similar to that executed 

 by the tail of the fish. Three wave wings may be made to act in concert and 

 with a very good result ; two of them being made to vibrate figure of 8 fashion 

 in a more or less horizontal direction with a view to elevating, the third being 

 turned in a downward direction, and made to act vertically for the purpose of 

 propelling. 



A New Form of Aerial Screiv. — If two of the wave wings represented at 

 fig. 62, page 423, be placed end to end, and united to a vertical portion of tube 

 to form a two-bladed screw, similar to that employed in navigation, a most 

 powerful elastic aerial screw is at once produced, as seen at fig. 73, page 440. 



This screw, which for the sake of uniformity I denominate the aerial wave 

 screw, possesses advantages for aerial purposes to which no form of rigid screw 

 yet devised can lay claim. The way in which it clings to the air during its 

 revolution, and the degree of buoying power it possesses are quite astonishing. 

 It is a self-adjusting, self-regulating screw, and as its component parts are 



VOL. XXVI. PART II. 5 X 



