IN RELATION TO AERONAUTICS. 331 



ation, l\v diminisliing tlic amount of air displaced. This slating or overlapping 

 and unslating action of the feathers during extension and flexii.in is, however, one 

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

 this function can be 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 ditterent ways : 1st, 

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

 2d, during the downward stroke, when it maintains the angle of 45° with the 

 horizon, and makes a variable angle Avith the bod^'; and 3d, during flexion, 

 Avhen it acts at a gradually decreasing angle in virtue of its being carried against 

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

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

 bearing the latter is under wa}-; and this is perhaps the chief reason why the 

 albatross, which is a very heavy l)ird,* can sail about for such incredible periods 

 without apparently moving the wings at all. Captain Ilutton thus graphically 

 describes the sailing of tliis magnificent bird: ''The flight of the albatross is 

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

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

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

 the crest of the Avaves as ho skims over them." t 



"Tranquil its spirit seemed, aud floated sIoav, 

 . Even in its very motion there was rest." 



As an antithesis to the apparently lifeless Avings of the albatross, the ceaselesg 

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

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

 rapidly Avhen the bird is poised before an object that it is impossible for the eye 

 to folloAv each stroke, and a hazy circle of indistinctness on each side of the biro 

 is all that is perceptible." 



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

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

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

 Avhich Ave so highly esteem, arising not from superior lightness but from their 

 possessing that degree of Aveight Avhich enables them to subjugate the air; Aveight 

 and independent motion being the tAvo things indispensable in successful aerial 

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

 greatl3^-developed muscular system — this being in that delicate state of tonacity 

 Avhicli enables them to act through its instrumentality Avith marvellous dexterity 

 and power, and to expend or reserA^e their energies, which they can do Avith the 

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

 tures AA'hich receive or draw back the Aving 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 Aving to rest nearly half the time 

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

 power of endurance displayed by insects and birds on the Aving. 



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

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

 to allude briefly to the balloon. 



Balloon. — This, as my audience is aAvare, is constructed on the obvioiis prin- 

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

 Montgolfier brothers invented such a machine in 1782. Their balloon consistftd 

 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. i, 1865, p. 29.0. 



Tlie Pelicanus ouocrotalius weighs 25 pounds. Roget's Bird's Journal, vol. i, p. 490. 



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

 8d series, vol. i, 1865, p. 28:i. 



