328 ON THE VARIOUS MODES OF FLIGHT 



than that of aii}' other class of animals, their weight being proportionably less. 

 It ought, however, never to be forgotten that even the lightest insect or bird is 

 immeasurably heavier than the air, and that there is no fixed relation between 

 the weight of body and the expanse of wing in either class. We have thus 

 light-bodied and large-winged insects and birds, as the butterfly, heron, and 

 albatross ; and others, whose bodies are comparatively heav}^, while their wings 

 are insignificantly small, as in the sphinx-moth and stag-beetle among insects, 

 and the grebe, quail, and partridge among birds. Those apparent inconsisten- 

 cies are readily explained by the greater muscular development of the heav}^- 

 bodied, short- winged insects and l»irds, and the increased power and rapidity 

 with which the wing is made to oscillate. This is of the utmost importance in 

 tlie science of aerostation, as showing that flight may be attained by a heavy, 

 powerful animal with comparatively small wings, as well as by a lighter one 

 with enormously enlarged wings. While, therefore, there is apparently no cor- 

 respondence between the area of the wing and the animal to be raised, there is 

 an unvarying relation as to the weight and number of oscillations, so that the prob- 

 lem of flight seems to resolve itself into one of weight, power, velocity, and 

 small surfaces; versus buoyancy, debilit}', diminished speed, and extensive sur- 

 faces ; weight in either case being a sine qua non. 



In order to utilize the air as a means of transit, the body in motion, whether 

 it moves in virtue of the life it i)ossesses, or because of a force superadded, must 

 be heavier than it. If it were otherwise, if it were rescued from the operation 

 of gravity on the one hand, and l)ereft of independent movement on the other, 

 it must float about uncontrolled and uncontrollable, as happens in the ordinary 

 gas balloon. The ditference between an insect or bird and a balloon here 

 insisted upon was, I have learned since writing the above, likewise pointed out 

 by his grace the Duke of Argyll, in his very able and eloquent article in Good 

 Words, entitled " The lleign of Law"* — an article whose merits cannot be too 

 widely acknowledged or too universally known. The wings of insects and 

 birds are, as a rule, more or less triangular in shape, the base of the triangle 

 being directed towards the body, the sides anteriorly and posteriorly. They are 

 also conical on sections from within outwards and from before backwards, this 

 shape converting the pinion into a delicately-graduated instnnnent, balanced 

 Avith the utmost nicetv to satisfy the requirements of the muscular system on the 

 one hand, and the resistance and resiliency of the air on the other. While all 

 wings are graduated as explained, innumerable varieties occur as to their general 

 contour, some being falcated or scythe-like, others oblong, others rounded or 

 circular, some lanceolate, and some linear. 



Winf) of insect. — The wings of insects mny consist either of one or two pairs; 

 the anterior or upper pair, when two are present, being in some instances greatly 

 modified and presenting a corneous condition. When so modified they cover 

 the under wings when the insect is reposing, and have from this circumstance 

 been named elytra from the Greek ikurpov, a sheath. The elytra or wing-cases, 

 as they are sometimes called, are dense, rigid, and opaque in the beetles ; solid 

 in one part and membranous in another in the cockroaches ; more or less mera- 

 bi-anous throughout in the grasshoppers ; and completely membranous in the 

 dragon-flies. The superior or upper wings are indirectly connected with flight 

 in the beetles, cockroaches, and grasshoppers, and activel}' engaged in this func- 

 tion in the dragon-flies and butterflies. The true wings, and by this I mean the 

 membranous ones, present ditierent degrees of opacity ; those of the moths and 

 butterflies being non-transparent ; those of the dragon-flies, bees, and common 

 flies presenting a delicate, filmy, gossamer-like appearance. They have, how- 

 ever, this feature in common, and it is fundamental : both pairs are composed of 



* Good Words for February, 18G5. This article I am glad to tiud lias been reprinted in a 

 separate form with numerous illustrations, and should be read by all interested in the subject 

 ot ierouautics. (J. B. P.) 



