. The principles of physics. s. As thepiston s is raised and depressed, water is pumped up fromthe cistern A, is forced into the cylinder as, and exerts an upward pressure against thepiston t one hundred timesgreater than the downwardpressure exerted upon , if a pressure of onehundred pounds is appliedat s, the cotton bales will besubjected to a pressure offive tons. The pressure that may beexerted by these presses isenormous. The hand of achild can break a strong ironbar. But observe that, al-though the pressure exertedis very great, the upward movement of the piston t is veryslow. In o
. The principles of physics. s. As thepiston s is raised and depressed, water is pumped up fromthe cistern A, is forced into the cylinder as, and exerts an upward pressure against thepiston t one hundred timesgreater than the downwardpressure exerted upon , if a pressure of onehundred pounds is appliedat s, the cotton bales will besubjected to a pressure offive tons. The pressure that may beexerted by these presses isenormous. The hand of achild can break a strong ironbar. But observe that, al-though the pressure exertedis very great, the upward movement of the piston t is veryslow. In order that the piston t may rise 1 cm, the piston smust descend 100 cm. The disadvantage arising from slownessof operation is insignificant, however, when we consider thegreat advantage accruing from the fact that one man canproduce as great a pressure with the press as a hundred mencan exert without it. The press is used for compressing cotton, hay, etc., intobales, and for extracting oil from seeds. The modern engineer r r. Fig. 108. PEBSSUEB OF FLUID DUE TO ITS WEIGHT. 147 finds it a most efficient machine whenever great resistancesare to be moved through short distances. 124. Pressure of fluid due to its weight. — Fluids exertpressure due to their weight. Imagine a vessel filled withshot; you will understand that the upper layer of shot willpress upon the layer next beneath with a force equal to itsweight, the second upon the third with a force equal to thesum of the weights of the first two, and so on. You will alsoreadily conclude that the pressure exerted upon the successivelayers will be exactly proportional to their depths, unless inconsequence of the great pressure to which the lowest layersare subjected there should be a crowding together of the shotso as to make them more compact. In this case there wouldbe a slight variation from the rule as stated. For a like reasonthe downward pressure in a body of liquid increases as itsdepth except in so far as the pressure is
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectphysics, bookyear1895
