INSECT OR REACTIVE-PASSIVE LOCOMOTION. 69 
with his wings ffretched forwards and upwards and flap¬ 
ping them vigoroufly, produces a powerful down-blaft of 
air, with the effed: of creating a fort of air-cufhion to 
alight on. Anyone who will take the trouble to look at a 
pigeon may fee this; the out-flying in all directions of the 
debris and duft upon the face of the ground bearing ample 
teftimony to the character of the wind-blaft. 
But the dragon-fly and all other infeCts of its clafs are 
organized with fpecial reference to the fort of locomotion 
I have defcribed as belonging peculiarly to them, viz. :— 
pafftve locomotion. To this end, they muft be able to not 
only fan the air in any and all direElions , but praCtically, at 
the fame infant of time. Upon no other theory can I 
account for the flanding-flill-in-the-air performance of the 
fly in an atmofphere unruffled by the flighted: breeze— 
for the floating movements of the bee, or the backward 
and forward floating of the dragon-fly. 
If then we affume for thefe infeCts the poffeflion of 
fuch a power, our reafoning in attempting to explain the 
mode by which the fly Hands flill in the' air will be this: 
When, for example, the dragon-fly fans the air only 
backward, it moves forward; when it fans the air only 
forward, it moves backward; let both operations be per¬ 
formed fimultaneoufly (and it has two pairs of wings), 
and it will Hand perfectly ftill, providing it fo manages the 
preffures as to produce forces that at the fame time anta¬ 
gonize all tendency to upward and downward movement. 
