WALKING, SWIMMING, AND FLYING. 537 



fishes are astonishingly great. A blow from the head of a sperm-whale 

 may endanger a strong ship, and the sword of a sword-fish has been 

 driven through the oak-planks of a vessel more than twelve inches in 

 thickness. 



Fig. 10. 



^^S^^^ 35 ^^- ^^A*M^ 



The Porpoise. — Here the tail is principally engaged in swimming, the anterior extremities being 

 rudimentary, and resembling the pectoral fins of fishes. 



When the flying-fish rises in the air, it is by the momentum it at- 

 tains in the water by the lashing of its fins and tail. Fairly in the 

 air, its wings give it support, and, in the opinion of Dr. Pettigrew, 

 act as true pinions within certain limits, but are too small to sustain 

 the creature indefinitely. 



The transition from swimming to progression m the air is natural 

 and easy. The method by which the flying-fish rises from the water 

 is similar to that of the albatross, that prince of flying-birds, and, in- 

 deed, to perhaps all other birds, when in the act of taking flight upon 

 the water. Momentum is obtained by rushing forward with both feet 

 and wings. The albatross frequently goes in this way many rods be- 

 fore it is fairly launched upon the air. Then, with powerful strokes, 

 it rises above the waves. Its expenditure of force is chiefly in rising, 

 when, without further effort, except to screw and unscrew its pinions 

 upon the wind, it floats facing the gale. For more than an hour it 

 will sail with wings apparently motionless, and it seems most at rest 

 when the winds are highest. In this case it is sustained by the mo- 

 mentum it attained, and the wonderful kite-like position and adjust- 

 ment of its wings. But, it manifestly could not maintain its position 

 in this way, if moving before the wind, or in a perfectly calm atmos- 

 phere. The wings must then be called into play to afford lifting as 

 well as propelling power. The momentum must be supplied. 



Birds rise from the ground most readily facing the wind, but usually 

 run or leap, and the wings, by vigorous strokes, continue the impulse 

 secured. With the first down-stroke of the wings the body is lifted, 

 and some velocity attained ; when the wings rise, the body falls some- 

 what, but is at the same time advancing. This rise and fall of the 

 body in flying continue, and the body, in progressing, undulates 

 above and below a given line. In the flight of birds with large wings 

 and slow stroke, it is easily observed. The illustration, Fig. 11, shows 



