IN RELATION TO AERONAUTICS. 331 



ation, 1)V dhniuisliing the amount of air displaced. This sLating or overlapping 

 and nnslating- action of the feathers during extension and flexion is, however, one 

 of the peculiarities or refinements, and not necessarily an essential in flight, as 

 this function can he efficiently performed by the insect and bat where no feathers 

 are present, and where consequently no opening or closing of them can possibly 

 occur. The wing of the bird may be said to act in three different ways: ls;t, 

 during- extension, when it gradually makes an angle of 45° with the horizon ; 

 2d, during the dowu\vard stroke, when it maintains the angle of 45° with the 

 horizon, and makes a variable angle with the body; and 3d, during flexion, 

 when it acts at a gradually decreasing angle in virtue of its being* carried ag'ainst 

 the wind by the body of the bird which is in motion ; it being a matter of indiffer- 

 ence whether the wing acts on the air or the air on the wing, so long as the body 

 bearing the latter is irnder way ; and this is perhaps the chief reason why the 

 albatross, which is a very heavy bird,* can sail about for such incredible periods 

 without apparently moving the wings at all. Captain Hutton thus grapliically 

 describes the sailing of this magnificent bird : "■ The flight of the albatross is 

 truly majestic, as with outstretched motionless wings he sails over the surface of 

 the sea, now rising high in air; now, with a bold sweep and wings inclined at an 

 angle with the horizon, descending until the tip of the lower one all but touches 

 the crest of the waves as he skims over them." t 



"Tranquil its spirit seemed, aud floated slow, 

 Eveu ia its very motiou there was rest." 



As an antithesis to the apparently lifeless wings of the albatross, the ceaseless 

 activity of those of the humming bird might be adduced. " In those delicate 

 and exquisitely beautiful birds, the wings, according to Mr. Gould, move so 

 rapidly when the ])ird is poised before an object that it is impossible for the eye 

 to follow each stroke, and a hazy circle of indistinctness on each side of the bird 

 is all that is perceptible." 



The various movements involved in ascending, descending, wheeling, gliding, 

 and progressing horizontally are all the result of muscular power, properly 

 directed and acting upon appropriate surfaces — that apparent buoyancy in birds, 

 which we so highly esteem, arising not from superior liglitness l)ut from their 

 possessing that degree of weight which enables them to sul)j agate the air; weight 

 and independent motion being the two things indispensable in successful aerial 

 progression. The Aveight in insects and birds is in great measure owing to their 

 greatlj'-developed muscular system — this being in that delicate state of tonacity 

 Avhich enables them to act through its instrumentality with marvellous dexterity 

 and power, and to expend or reserve their energies, which they can do with the 

 utmost exactitude in their lengthened and laborious flights. The elastic struc- 

 tures Avhich receive or draw back the wing in the insect and bird during flexion 

 are of the utmost consequence in the movements of the wings ; these, by their 

 mere contraction, enabling the muscles of the wing to rest nearly half the time 

 they are in action. In this we have a probable explanation of the extraordinary 

 power of endurance displayed by insects and l)irds on the wing. 



The foregoing remarks on the wings of insects and birds lead me to speak of 

 the inclined plane as applied to the air, but before doing so it will be advisable 

 to allude briefiy to the balloon. 



Balloon. — This, as my audience is aware, is constructed on the obvious prin- 

 ciple that a machine ligliter than the air must necessarily rise through it. The 

 Montgolfier brothers invented sucli a machine in 1782. Their balloon consist<'d 

 of a paper globe or cylinder, the motor power being superheated air supplied by 



* The average weight of the albatross, as given by Gould, is 17 pounds. 'Ibis," 2d series, 

 vol. 1, 18d5, p. 2'Xi. 



The Pelicanus ouocrotalius weighs 25 pounds. Roget's Bird's .Tonrnal, vol. i, p. 490. 



t On some of the birds inhabiting the Southern ocean, by Captain \V. F. Hutton. "Ibis," 

 2d series, vol. i, 1865, p. 282. 



