DR. PETTIGREW ON THE MECHANISM OF FLIGHT. 21M 



The rudimentary wings or paddles of the Penguin (the movement! of which I had an 

 opportunity of studying in a tame specimen) are principally employed in swimming and 

 diving. The feet, which are of moderate size and strongly webbed, are occasionally 

 used as auxiliaries. There is this difference between the movements of the wings and 

 feet of this most curious bird, and it is worthy of attention. The wings are advanced 

 together, or synchronously, as in flying birds; the feet, on the other hand, are moved 

 alternately. The wings are wielded with great energy, and, because of their semirigid 

 condition, are incapable of expansion. They therefore present their maximum and 

 minimum of surface by a partial rotation or tilting of the pinion, as in the Walrus, Sea- 

 Bear, and Turtle. The feet, which are moved with less rigour, are, on the contrary, 



- 



rotated or tilted to a very slight extent, the increase and diminution of surface beii 

 secured by the opening and closing of the membranous expansion or web between the 

 toes. In this latter respect they bear a certain analogy to the feet of the Seal, the toes 

 of which, as has been explained, spread out or divaricate during extension, and the 

 reverse. The feet of the Penguin entirely differ from those of the Seal in being worked 

 separately, the foot of one side being flexed or drawn towards the body, while its 

 fellow is being extended or pushed away from it. The feet, moreover, describe defi- 

 nite curves in opposite directions, the right foot proceeding from within outwards and 

 from above downwards during extension, or when it is fully expanded and giving the 

 effective stroke (Plate XV. fig. 57a?), the left one, which is moving at the same time, 

 proceeding from without inwards and from below upwards during flexion, or when it is 

 folded up, as happens during the back stroke. In the acts of extension and flexion. 

 the legs are slightly rotated and the feet more or less tilted. The same movements are 

 seen in the feet of the Swan (Plate XV. fig. 64) and in those of swimming birds gene- 

 rally. Each foot consequently describes an ellipse; and these being joined, as they 



ly must be, in motion, give separate spirals (Plate XV. fig 



There 



sequently an obvious analogy between the movements of the fish (Plate XV. fig. 7G), 

 biped (Plate XV. fig. 78), quadruped, and bird (Diag. infra) ; and similar remarks might 

 be made with equal propriety regarding those of the reptile and insect. 



Mr. Macgillivray thus describes a flock of Red Mergansers which he observed pursuin 

 Sand-Eels in one of the shallow sandy bays of the Outer Hebrides :-" The birds seemed 

 to move under the water with almost as much velocity as in the air, and often rose to 

 breathe at a distance of 200 yards from the spot at which they had dived"*. 



Cayley's idea has been taken up with great warmth of late years by Mon, *adir, of Pans ; and ML Pon m d Arnc- 

 conrt and De la Landelle have constructed, quite recently, helicopteric models dnven by clockwork, which not only 

 rise into the air of themselves, but carry a very considerable amount of cargo in the shape of graduated weights. The 

 screws emploved in the French models are remarkable for the great length and narrowness of thc.r blades, it bang 

 found ceteris paribus that a greater degree of elevating-power is obtained from a long narrow blade, acting at a 

 small angle with the horizon, than from a shorter and broader blade acting at a greater angle. This principle is fully 

 explained in an ingenious paper read by Mr. Wenham before the Royal Aeronautical Society of Great BnUun « On 



1 ...,,• i i v~,i:,«, ;,v,,>ollo,l tlirniifrli the air are sustained. Vide Annua 



Aerial Locomotion and the laws by which heavy 

 Report of the Society for 1 86 7. 



* 



History of British Birds, vol. i. p. 48 



VOL. XXVI. 



2G 



