288 ANNUAL REPORT SMITHSONIAN INSTITUTION, 195 4 



its tail against the water, although the rest of its body remains in the 

 air. There is, however, some evidence to suggest that much longer 

 flights may occur, lasting for 10-12 seconds and covering perhaps 400 

 meters without touching the water. All observers agree that the fish 

 does not move its pectoral fins in flight, though they may vibrate pas- 

 sively as it speeds through the air. About these flights we have much 

 to learn, and exact observation is difficult, but there seems little doubt 

 that ordinary flights of 1 or 2 seconds and of 50 meters or less are 

 maintained by the kinetic energy (the energy of speed) given to the 

 body in swimming by the tail striking against the water before the 

 fish is airborne. 



The combined lift and drag of the body at various speeds of air- 

 flow has been measured in a wind tunnel, and although such observa- 

 tions are not yet altogether satisfactory, they suggest that flight could 

 be sustained for about 6 seconds and over a distance of 200 feet, if 

 the takeoff speed were something like 30-35 miles per hour. This 

 speed seems very high compared with that of other fishes, but it may 

 be that when the body of the fish is in air and only the tail is in water 

 these higher takeoff speeds could be reached. Still, it is difficult to 

 believe that the takeoff speed could ever be great enough for the fish 

 to fly for 10 or 12 seconds and for distances of 400 meters. If such 

 flights really occur, as they are said to do, we can only assume that 

 the fish is able to draw on some source of energy other than that given 

 to it (when it is in the water) by its tail. It may be that unusual air 

 conditions near the surface of the waves make longer flights possible ; 

 but all we can say at present is that long-sustained flights offer an 

 interesting and difficult problem. 



For the time being, however, we can look upon the normal short 

 flight of the flying fish as a typical example of velocity gliding : the 

 fish stores kinetic energy in its body by swimming — by moving its tail 

 in water — and expends this energy when it is airborne in overcoming 

 the drag effect of the air, gaining thereby lift enough to overcome 

 gravity. And after all, this is not so very different from the flight 

 of a small bird, where periods of passive glide occur between periods 

 of active wing beats. 



One member of the frog family is a glider — the only one, so far as is 

 known. This frog {Rhacophorus) was discovered in Borneo about 

 a hundred years ago, by a Chinese workman employed by the nat- 

 uralist Alfred Russel Wallace. The Chinese assured Wallace that "it 

 came down, in a slanting direction, from a high tree." Wallace noted 

 that the surface of the very large webbed feet was considerably larger 

 than that of the body, and there can be little doubt that these frogs 

 do launch themselves from trees to glide down to a point 30 or 40 

 yards from where they started. The webbed feet and the under sur- 

 face of the body act together as a wing, and the energy required to 



