. Practical physics. -ricelli argued that if water wouldrise 32 feet, then mercury, whichis about 13 times as heavy as water,ought to rise but ^g as high. Totest this inference he performed,in 1643, the followmg famousexperiment: Let a tube about 4 ft. long, which issealed at one end, be completely filledwith mercury, as in Fig. 25, (i), thenclosed with the thumb and inverted, andthe bottom immersed in a dish of mer-cury, as in Fig. 25, (2). When the thumbis removed from the bottom of the tube,the mercury will fall away from theupper end of the tube, in spite of the fact that in so doing it wi
. Practical physics. -ricelli argued that if water wouldrise 32 feet, then mercury, whichis about 13 times as heavy as water,ought to rise but ^g as high. Totest this inference he performed,in 1643, the followmg famousexperiment: Let a tube about 4 ft. long, which issealed at one end, be completely filledwith mercury, as in Fig. 25, (i), thenclosed with the thumb and inverted, andthe bottom immersed in a dish of mer-cury, as in Fig. 25, (2). When the thumbis removed from the bottom of the tube,the mercury will fall away from theupper end of the tube, in spite of the fact that in so doing it will leave a vacuum above it; and its uppersurface will, in fact, stand about Jg of 32 ft., tliat is, betweeu 29 and30 in., above the mercury in the dish. Torricelli concluded from this experiment that the riseof liquids in exhausted tubes is due to an outside pressureexerted by the atmosphere on the surface of the liquid,and not to any mysterious sucking p^wer created by thevacuum as is popularly believed even Fig. 25. Torricellisexperiment BAEOMETEIC PHENOMENA 29 38. Further decisive tests. xVn unanswerable argument infavor of this conclusion will be furnished if the mercury inthe tube falls as soon as the air is removed from above thesurface of the mercury in the dish. To test this point, let tlie dish and tube be placed on the table of an air piinip, as in Fig. 26, the tube passing through a tightly fitting rubber stop-per A in the bell jar. As soon as the pump is started the mercury in the tube will, in fact, be seen to fall. As the pumping is continued it will fall nearer and nearer to the level in the dish, although it will not usually reach it, for the reason that an ordinary Aacuum pump is not capable of prodiicingas good a vacuum as that which exists in thetop of the tube. As the air is allowed to returnto the bell jar the mercury will rise in the tubeto its former level.
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Keywords: ., bookcentury1900, bookdecade1920, booksubjectphysics, bookyear1922
