Nov., 1889. 
THE FLIGHT OF BIRDS AND INSECTS. 
261 
THE FLIGHT OF BIRDS AND INSECTS. 
BY EDMUND CATCHPOOL, B.SC. 
(Concluded from page 225.) 
If, as I have tried to make clear, an insect when moving 
forwards is partly supported by that motion, as well as by the 
vibration of its wings, it follows that it is easier for it to fly 
forwards than to remain in one place in the air, and it is 
easily shown by experiment that this is the case. If we catch 
a bluebottle fly, and cut away the hinder two-thirds of each 
wing (so as to leave the front rib with about one-third of the 
original surface attached), we shall find that it can no longer 
balance itself in the air, nor, if placed on the ground or on a 
table, can it rise ; yet, if dropped from a height of a few feet, 
though it cannot at first support itself, yet the active vibra¬ 
tion of the remaining portions of its wings soon gives it a 
forward motion, and as this becomes more rapid the fly falls 
less and less rapidly, then moves forward horizontally, with¬ 
out falling, and, finally, takes an upward slope, reaching the 
window, perhaps, at a higher point than it started from. 
Here we see not only that the forward motion helps to 
support the insect, but that this support is obtained with less 
expenditure of strength than the same amount obtained by 
the vibration of the wing alone, since the fly is not strong 
enough to support itself, with its diminished wing-surface, by 
the latter method. It is easy to see why; for the upward 
pressure resulting from the continuous forward motion is a 
continuous pressure acting always on the same side of the 
wing, and is, therefore, subject to none of the losses from 
want of rigidity and change of direction, which, as I have 
pointed out, waste much of the energy expended in the 
vibratory motion of the wings. We see, then, that a fly, 
when its wings are partly cut away, is forced to economise its 
strength under this disadvantage by using the vibration of its 
wings to propel it, instead of only to support it, and taking 
advantage of the support which its forward motion gives it. 
Now, the fly’s wings, so reduced, are still more than eight 
times as large in proportion to its weight as those of a pigeon, 
and nearly twenty times as large in proportion to its weight 
as those of an albatross. The wings of a pigeon, to be as 
- large in proportion to its weight as those of a gnat, must be 
nearly 6ft. each in length, and wide in proportion. And the 
bird, though rather stronger in proportion to its weight than 
the insect, is not much stronger; probably not half as strong 
