70 
INSECT OR REACTIVE-PASSIVE LOCOMOTION. 
Now, whether the fly in queftion is fortunate, like the 
dragon-fly, in the poffeflion of two pairs of wings, I can’t 
fay. If it performs the feat with only one pair, it is fo 
much the fmarter, and we mu ft affume for it the wonderful 
power of being able, with its one pair of wings, turning 
in every direction (like the flaming fword of the Cherubim 
in Eden), to produce practically a hollow fphere or vacuum 
centre in the air, the fpherical wall of which is compofed 
of the wind-prefliires produced by the fanning aCtion of 
the wings in their univerfal play, this vacuum centre 
having practically the effeCt of the eleElric aura fome have 
imagined, and floating the creature as effectually as though 
enclofed within a fphere of hydrogen or other gas capable 
of creating a fpecific gravity of like denflty with the fur¬ 
rounding atmofphere. 
Upon this view of the cafe, it is eafy to fee that the 
dart-like locomotion of the barn-yard fly, like that of the 
dragon-fly, refults from an unbalancing of forces; the forces 
weakened at any point in the fpherical wall producing a 
preffure at the oppoflte point of correfponding force. 
If it be objeded to this theory of aerial locomotion 
for man on the ground that it is contrary to Nature—- 
feeing that bird-flying is the method of Nature for all 
creatures having fubftantial weight, and that the paflive 
locomotion I have defcribed has been confined by Nature 
to creatures poffeffed of praCtically no weight—I would 
call the attention of the objeCtor to the faCt that Nature, 
