PROGRESSION ON AND IN THE WATER. 



99 



certain limits, their inadequate dimensions and limited range 

 alone preventing them from sustaining the fish in the air for 

 indefinite periods. When the fins are fully flexed, as happens 

 when the fish is swimming, they are arranged along the sides 

 of the body ; but when it takes to the air, they are raised 

 above the body and make a certain angle with it. In being 

 raised they are likewise inclined forwards and outwards, the 

 fins rotating on their long axes until they make an angle of 

 something like 30'' with the horizon — this being, as nearly as 

 I can determine, the greatest angle made by the wings during 

 the down stroke in the flight of insects and birds. 



The pectoral fins, or pseudo-wings of the flying- fish, like 

 all other wings, act after the manner of kites — the angles of 

 inclination which their under surfaces make with the horizon 

 varying according to the degree of extension, the speed ac- 

 quired, and the pressure to which they are subjected by being 

 carried against the air. When the flying-fish, after a pre- 

 liminary rush through the water (in which it acquires initial 

 velocity), throws itself into the air, it is supported and carried 

 forwards by the kite-like action of its pinions ; — this action 

 being identical with that of the boy's kite when the boy runs, 

 and by pulling upon the string causes the kite to glide up- 

 wards and forwards. In the case of the boy's kite a pulling 

 force is applied to the kite in front. In the case of the flying- 

 fish (and everything which flies) a similar force is applied to 

 the kites formed by the wings by the weight of the flying 

 mass, which always tends to fall vertically downwards. 

 Weight supplies a motor power in flight similar to that 

 supplied by the leads in a clock. In the case of the boy's 

 kite, the hand of the operator furnishes the power; in 

 flight, a large proportion of the power is furnished by 

 the weight of the body of the flying creature. It is a 

 matter of indiff'erence how a kite is flown, so long as its 

 under surface is made to impinge upon the air over which 

 it passes.^ A kite will fly efl'ectually when it is neither 

 acted upon by the hand nor a weight, provided always 

 there is a stiff breeze blowing. In flight one of two things 



^ " On the Various Modes of Flight in relation to Aeronautics." By the 

 Authc^r.— Proceedings of the Royal Institution of Groat Britain, March 1867. 



