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Show 72 . ORIGIN OF SOCIETY. CANTO II. Shakes o'er the obedient pairs his silken thong, And goads the humble, or restrains the strong.Slow roll the silver wheels,-in beauty's pride Celestial PsYCHE blushing by his side.- The lordly Bull behind and warrior Horse With voice of thunder shake the echoing course, Chain' d to the car with herds domestic move, And swell the triumph of despotic LovE. 370 " Pleased as they pass along the breezy shore In twinkling shoals the scaly realms adore, Move on quick fin with undulating train, Or lift their slimy foreheads from the main. J¥ith undulating t1·ain. 1. 373. The side fins. of fish .seem ~o be chiefly used to poise them; as they turn upon theu bac~s Immediately when killed, the air-bladder assists them perhaps to nse or descend by its possessing the power to condense the air in. it by muscular co~traction; and it is possible, that at great depths 111 the ocean .the air in this receptacle may by the great pressure of the incumbent water ·become condensed into so small a space, as to cease to be useful to the animal, which was possibly the cause of the death of Mr. Day in his diving ship. See note on Ulva, Botan. Garcl. V. II.. The progressive motion of fish beneath the water IS pro.duced ,principally by the undulation of their tails. One oblique plam of a ' . CANTO II. REPRODUCTION OF LIFE. High o'er their heads on pinions broad clisplay'd !he feather'd nations shed a floating shade; part of the tail on the right side of the fish strikes the water at the same time that another oblique plain strikes it on the left side hence in respect to moving to the ri_ght or left these percussions of th~ water c.ounteract each o~her, but they coincide in respect to the progres~ wn of ~he fish; this power seems to be better applied to push forwards a body m water, than the oars of boats, as the particles of water recede ~rom the strok.e of the oar, whence the comparative power acquired 1s but. as the difference of velocity between the striking oar and the r~cedmg: water. So a ship moves swifter with an oblique wind, than With a wmd of the same velocity exactly behind it; and the common windmill sail placed obliquely to the \Vinci is more powerful than one w.hich dire~tly recedes from it. 1\!Iight not some machinery resemblmg the tatls of fish be placed behind a boat, so as to be moved with greater effect than common oars, by the force of wind or steam, or perhaps by hand? On pinions broad display;'d. I. 375. The progressive motion of birds in the air is principally-performed by the movement of their wino·s and not by that of their tails as in fish. The bird is supported in 0a n' element so much lighter than itself by the resistance of the air as it moves horizontally against the oblique plain made by its breast, expanded tail and wings, when they are at rest; the change of this obliquity also assists it to rise, and even directs its descent, though this is owing principally to its specific gravity, but it is in all situations kept upright or balanced by its wings. As the support of the bird in the air, as well as its progression, is performed by the motion of the wings; these require strong muscles as are seen on the breasts of partridges. Whence all attempts of men to fly by wings applied to the weak muscles of their arms have been ineffectual; but it is not certain whether light-macninery so contrived as to be moved by their feet, might not enable them to fly a little way, though not so as to answer any useful purpose. L |