* 116 NATURAL HISTORY OF WASPS. 
act on the passive insect body, or as the insect itself 
acts on the surrounding medium. And I have ar- 
ranged, as far as practicable, the successive steps of 
this inquiry according to this view. 
As to the PASSIVE element: Mr. Wenham calcu- 
lates that the area of the supporting surface bears 
the proportion of about one square foot to each 
pound weight to be supported. This would secure a 
descent of no more than twenty-two feet ina second 
of time at an uniform velocity: being the speed at 
which one meets the ground at the end of a drop of 
eight feet. This proportion is pretty generally ob- 
served in different kinds of birds, “ hornets, bees, and 
other insects.” But there are some striking excep- 
tions, “some of the duck-tribe, classed among the 
strongest and swiftest of flyers” having little more 
than half that area of wing. 
Having thus ascertained the extent of the surface 
which should be opposed to the air, we have next to 
consider the influence which the form and direction 
of this surface exercise. A round body heavier than 
the air, such as a bullet, falls straight to the ground 
through still air; or in a wind it falls diagonally. If 
this same body is flattened out to an area duly pro- 
portioned to its weight, it falls straight through still 
air, only more slowly. Butin a wind it will fall more 
or less obliquely, or it may even rise, like a kite, 
according’ to the force of the wind, and the direction 
in whien the wind meets its surface. So it is with 
insects or birds. A dead beetle or rook falls like a 
plummet: a live sea-gull, as motionless all the while 
as a dead rook, soars with her wings extended, 
driven upwards by the air through which she is 
