Scientific amusements . centre of gravity. With a little skill,any one may construct it for himself. It consists of twolittle puppets, which turn round axles adapted to twoparallel tubes containing mercury. When we place thelittle toy in the position as above, the mercury being at a, thetwo dolls remain motionless, but if we lower the doll s, sothat it stands on the second step (No. 2) of the flight, asindicated in the second cut, the mercury descends to b at the THE PUPPETS. 45 Other end of the tube ; the centre of gravity is suddenlydisplaced ; the doll R then accomplishes a rotatory move-me
Scientific amusements . centre of gravity. With a little skill,any one may construct it for himself. It consists of twolittle puppets, which turn round axles adapted to twoparallel tubes containing mercury. When we place thelittle toy in the position as above, the mercury being at a, thetwo dolls remain motionless, but if we lower the doll s, sothat it stands on the second step (No. 2) of the flight, asindicated in the second cut, the mercury descends to b at the THE PUPPETS. 45 Other end of the tube ; the centre of gravity is suddenlydisplaced ; the doll R then accomplishes a rotatory move-ment, as shown by the arrow in the third cut, and finallyahghts on step No. 3. The same movement is alsoeffected by the doll S, and so on, as many times as thereare steps. The dolls may be replaced by a hollowcylinder of cartridge paper closed at both ends, and con-taming a marble ; the cylinder, when placed vertically onan mclined plane, descends in the same way as thepuppets. The laws of equilibrium and displacement of. Second positiun of the puppets. the centre of gravity, are rigorously observed by jugglers,who achieve many wonderful feats, generally facilitatedby the rotatory motion given to the bodies on which theyoperate, which brings into play the centrifugal force. Thejuggler who balances on his forehead a slender rod, onthe end of which a plate turns round, would never succeedin the experiment if the plate did not turn on its axiswith great rapidity. But by quick rotation the centre ofgravity is kept near the point of support. We needhardly remark, too, that it is the motion of a top thattends to keep it in a vertical position. Many experiments in mechanical physics may occur 46 SIMPLE PHYSICS. to ones mind. To conclude the enumeration of thosewe have collected on the subject, I will describe themethod of lifting a glass bottle full of water by means ofa simple wisp of straw. The straw is bent before beingpassed into the bottle of water, so that, when it is lifted, the
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Keywords: ., bookcentury1800, bookdecade189, booksubjectscientificrecreations
