100 



ANIMAL LOCOMOTION. 



is necessary. Either the under surface of the wings must 

 be carried rapidly against still air, or the air must rush 

 violently against the under surface of the expanded but 

 motionless wings. Either the wings, the body bearing them, 

 or the air, must be in rapid motion ; one or other must be 

 active. To this there is no exception. To fly a kite in still 

 air the operator must run. If a breeze is blowing the operator 

 does not require to alter his position, the breeze doing the 

 entire work. It is the same with wings. In still air a bird, 

 or whatever attempts to fly, must flap its wings energetically 

 until it acquires initial velocity, when the flapping may be 

 discontinued ; or it must throw itself from a height, in which 

 case the initial velocity is acquired by the weight of the body 

 acting upon the inclined planes formed by the motionless 

 wings. The flapping and gliding action of the wings consti- 

 tute the diflerence between ordinary flight and that known 

 as skimming or sailing flight. The flight of the flying-fish is 

 to be regarded rather as an example of the latter than the 

 former, the fish transferring the velocity acquired by the 

 vigorous lashing of its tail in the water to the air, — an 

 arrangement which enables it to dispense in a great measure 

 with the flapping of the wings, w^hich act by a combined 

 parachute and wedge action. In the flying-fish the flying-fin 

 or wing attacks the air from beneath, whilst it is being raised 

 above the body. It has no downward stroke, the position 

 and attachments of the fin preventing it from descending 

 beneath the level of the body of the fish. In this respect the 

 flying-fin of the fish diff*ers slightly from the wing of the 

 insect, bat, and bird. The gradual expansion and raising of 

 the fins of the fish, coupled with the fact that the fins never 

 descend below the body, account for the admitted absence of 

 beating, and have no doubt originated the belief that the 

 pectoral fins are merely passive organs. If, however, they do 

 not act as true pinions within the limits prescribed, it is difli- 

 cult, and indeed impossible, to understand how such small 

 creatures can obtain the momentum necessary to project them 

 a distance of 200 or more yards, and to attain, as they some- 

 times do, an elevation of twenty or more feet above the water. 

 Mr. Swainson, in crossing the line in 1816, zealously attempted 



