Fifth book of lessons for the use of schools . not the case with this pair of scales, for when we holdthem inclined, they instantly regain their reason of this is, that the centre of suspension,instead of exactly coinciding with that of gravity, is alittle above it. If, therefore, the equilibrium of thebe disturbed, the centre of gravity moves in asmall circle round the point of suspension, and is there-fore forced to rise; and the instant it is restored toliberty, it descends and resumes its situation im-mediately below the point of suspension, when theequilibrium is restored.
Fifth book of lessons for the use of schools . not the case with this pair of scales, for when we holdthem inclined, they instantly regain their reason of this is, that the centre of suspension,instead of exactly coinciding with that of gravity, is alittle above it. If, therefore, the equilibrium of thebe disturbed, the centre of gravity moves in asmall circle round the point of suspension, and is there-fore forced to rise; and the instant it is restored toliberty, it descends and resumes its situation im-mediately below the point of suspension, when theequilibrium is restored. It is this property whichrenders the balance so accurate an instrument forweighing goods. If the scales contain differentweights, the centre of gra;ity will be removed towardsthe scale which is heavier, and being no longer sup-ported, the heavier scale will descend. If the leverbe taken off the prop, and fastened on in another point,that other point then becomes the fulcrum. Inthis case the equilibrium is destroyed; the longer 276 Finn arm of the lever isheaviest, and centre of gravity isnot supported, because itis no longer immediatelybelow the point of sus-pension. But if we canbring the centre of gra-vity immediately belowthat point, as it is nowsituated, the scales willagain balance each if a heavy weightbe placed in the scale suspended to the shorter armof the lever, and a lighter one into that suspended to the longer arm, theequilibrium will be re-stored. It is not, there-fore, impracticable tomake a heavy body ba-lance a light one; andby this means an im-position in the weight ofgoods is sometimes ef-fected. An ingeniousbalance, called a steel-yard, has been invented, on the principle that aweight increases in effect in proportion to its distancefrom the fulcrum. When a lever is put in motion, the longer arm, oracting part of the lever, must move with greatervelocity than the shorter arm, or resisting part of thelever, because it is furthe
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