. The structure and life of birds . ows the limits of the rise and fall of theeye. The cross shows the position, according to calculation, of the centre of gravityat the moments when the wing is highest or lowest. centre of gravity ; it is at a higher point in the birdwhen he sinks, for at this moment his wings are raisedaloft. Thus the centre of gravity moves along in anundulating line, but its oscillations are not so great asthose of the eye, since every rise and fall of the birdis accompanied by a fall and rise of the centre ofgravity. Long Distance Flight. Long wings are best suited for lo
. The structure and life of birds . ows the limits of the rise and fall of theeye. The cross shows the position, according to calculation, of the centre of gravityat the moments when the wing is highest or lowest. centre of gravity ; it is at a higher point in the birdwhen he sinks, for at this moment his wings are raisedaloft. Thus the centre of gravity moves along in anundulating line, but its oscillations are not so great asthose of the eye, since every rise and fall of the birdis accompanied by a fall and rise of the centre ofgravity. Long Distance Flight. Long wings are best suited for long a single short stroke they send the bird far on VII FLKiHT 22 ^ his way, the further end of the lever moving withgreat velocity and force. The short wing must beatfrequently and with a longer swing. Put the wing ofa Swift beside that of a Duck, and compare the cut of them at once shows the flight of Swifts is long and very narrow towards the end,the ducks short for its size, and rounded. The Swift. Fig. 62 Breast-bone of (a) Frigate Bird, (/>) of Duck, ^rds natural size. cl, clavicle; co, coracoid ; k, keel ; st, sternum proper. covers, probably, 60 miles in the hour without greateffort and without a very rapid stroke : the duck keepsup a good pace, but only by means of strokesthat are at once very rapid and very long. If aGannet be watched as he goes leisurely onwards itwill be seen that his wings do not rise much aboveor descend much below a horizontal line from the Q 226 THE STRUCTURE AND LIFE OF BIRDS CHAP. shoulder. A gull as he travels keeps his wing slightlybent at the wrist, as photographs show, and probablyalso at the elbow, and does not flex them any morethan this for the upstroke : they are merely rotated{ a turn at the shoulder raises the front margin),and then lifted for the downstroke again (frontispiece). The birds which take long strokes have longpectoral muscles arising from long breastbones : thosewhich take short stro
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Keywords: ., bookcentury1800, bookdecade1890, bookidstructurelif, bookyear1895
