424 
winged insects, so as to lie above the centre of 
gravity. According to Dr. Derham, if either 
a poiser or winglet be cut off, the insect flies as 
if one side overbalanced the other, till it falls 
to the ground ; and if both be removed, it flies 
unsteadily. Shelver states that the removal of 
either winglets or poisers deprived the insect of 
the power of flight altogether. The pneumatic 
pressure which retains them inverted to the 
ceilings of rooms, gives them a position favour 
able for flying off instantaneously, the centre of 
gravity being below the articulation of the 
wings, enabling them to regain the pendant 
position of the trunk in flight. 
In the crane fly the centre of gravity is ad- 
justed, and the direction of flight directed by 
MOTION. 
. a 
4 
its long legs ; the two fore legs being extended 
forwards, and the four hind legs backwards. — 
According to Kirby, the one nts the “*” 
prow, the other the stern of a ship. The velo- 
city of the house, and large flesh flies (Musca 
domestica et vomitoria) appears to be from 
five to six feet in a second, or about four miles 
in an hour ; but if favoured by the wind, they 
are seen flying round the ears of horses when tra- 
velling at the rate of from ten to twelvemilesin — 
an hour.* Lg 
The following table presents at one view the — 
proportions of the areas of the wings in square — 
inches to their weight in grains of various spe= — 
—<— ¢ 
cies of insects which have been alread 
scribed in the text. 
Order. ies, Area of Wings in Weight 
eas poh A iaake pay tA 
CoLeorrera .......| LucanuS cervuS....eo...+| 1.2527126...sccce] 40% ’ 
Hymenoprera .....| Bombus...... eeadiccecce| O:966)eFcb cutesy eee r 
Ophion luteus .......+++-| 0.2644......... ee] 0.5. " 
DiprTera ........++| Musca vomitoria .........| 0.083333 or 7,.....] 0.8025. i* 
LEPIDOPTERA ...... Pontia brassiee ...6.56060)] 2:50 2s cediic cc vet teen i 
Triphena pronuba........| 2.6026 ..+seesse..| 8.545. 
NevuropTera ......} A’shna maculatissima..... 3.26408 |... «eso oes) oaes 
By the help of this table we are enabled to 
compare the proportions of the area of the wing 
to the weight of the insect in d.fferent orders, 
and to estimate the relation between these pro- 
portions and the absolute powers of flight, 
when the latter have been ascertained by expe- 
riment. 
Ifthe velocity and power of suspension varied 
in insects precisely in the same ratio as the 
areas of the wings to the weight of their bodies, 
we should be enabled to compare with tolerable 
accuracy the relative powers of the flight of in- 
sects from data similar to the preceding, but 
there are several other mechanical and physio- 
logical conditions involved; such as the ratio 
of the force of the muscles to the areas of the 
wings, and the figure and structure of the latter. 
The Lepidoptera which have the greatest 
surface of wing in proportion to their weight, 
should surpass all other insects in power of 
flight, yet the diurnal section at least yield to 
the Libellule in velocity, if not in the duration 
of their suspension in the air. From the pre- 
ceding data we conclude, that to render a man, 
whose weight is 150 pounds, capable of sus- 
pending himself in the air by the assistance of 
artificial wings, with the same facility as in- 
sects, would require an extent of surface be- 
yond the control of his muscular force, and 
consequently that the act is impossible. 
Flight of Birds.—In the organization of 
birds, we observe that many parts common to 
other animals are modified, the power of the 
muscular system is increased, and new forms 
of matter are introduced to confer on them 
the power of flight. The bulk of birds is 
less than that of quadrupeds of equal strength, 
and owing to many of their bones being per- 
meated with air, and their skin clothed with 
feathers, their specific gravity, and conse- 
quently the demand on their muscular power 
are diminished.t Instead of the cylindrical — 
form observed in animals which move ex- — 
clusively on solids, the anterior extremity of — 
birds is expanded into a triangular surface, of 
which the apex is the distal, and the base is the 
proximal section of the wing in reference tothe 
axis of rotation. The arm is articulated to the — 
trunk by a ball and socket joint, permitting all the - 
freedom of motion necessary for flight, whilstin 
consequence of the axes of motion oe 
moid joints of the fore-arm being di ei 1 
perpendicularly or obliquely to the ascent and 
descent of the wing, it is prevented from yield- 
ing to the resistance of the air during elevation 
and depression, and is more conveniently folded — 
on itself during repose. The surface of the 
wings may be increased or diminished by — 
abduction and adduction, in consequence of — 
which the resistance of the air to their motion — 
may be proportionally varied in the up and 
down strokes. The amount of this resistance is 
also varied by the surface of the wing being © 
convex above, and concave below. The feathers — 
are moreover provided with a curious me- 
chanism by which the barbules lock into each 
other, so as to unite all the parts of the vane, 
and present a continuous surface to the air 
The ten primary and the secondary feathers, 
which have the greatest leverage, are inserted 
into the arm and fore-arm, and directed so 
as to produce the greatest surface of wing 
-- 
* See Kirby and Spence, vol. ii. p. 357. 
+ 1. The Pelicanus onocrotalus is five feet 
length, but its skeleton weighs only twenty-th 
ounces, whilst the whole animal weighs twenty- 
pounds. See Roget’s Bridg. Treat. vol. i. p. 4 
2. The skeleton of the Carrion Crow whi 
weighs only twenty-three grains, Jaquamin, 
Sci. Nat. series 2, 11, p, 2718. 
3. Many entire Humming Birds weigh only 
eighth of an ounce, or one drachm. 
