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THE NEW YORK PUBLIC LIBRARY

ASTOR, LENOX AND
TILDEN FOUNDATIONA

this is, that the centre of suspension, instead of exactly coinciding with that of gravity, is a little above it; if, therefore, the equilibrium of the scales be disturbed, the centre of gravity is forced to rise, and the instant it is restored to liberty, it descends and resumes its situation immediately below the point of suspension, when the equilibrium is restored. It is this property which renders the balance so accurate an instrument for weighing goods.

CAROLINE.

But if the scales contained different weights, the centre of gravity would be removed towards that scale which contained the heaviest weight; and since that point could no longer be supported, the heavy scale would descend.

MRS. B.

True; but tell me, can you imagine any mode by which bodies of different weights can be made to balance each other, either in a pair of scales, or simply suspended to the extremities of the lever? for the scales or basins are not an essential part of the machine, they have no mechanical power, and are used merely for the convenience of containing the substance to be weighed.

CAROLINE.

What! make a light body balance a heavy one? I cannot conceive that possible.

MRS. B.

The fulcrum of this pair of scales (fig. 2.) is movable, you see; I can take it off the prop, and fasten it on again in another part; this point is now become the fulcrum, but it is no longer in the centre of the lever.

CAROLINE.

And the balance is no longer true; for that which hangs on the longest side of the lever descends.

MRS. B.

The two parts of the lever divided by the fulcrum are called its arms: you should therefore say the longest arm, not the longest side of the lever. These arms are likewise frequently distinguished by the appellations of the acting and the resisting part of the lever.

Your observation is true, that the balance is now destroyed; but it will answer the purpose of enabling you to comprehend the power of a lever, the fulcrum of which is not in the centre.

EMILY.

This would be an excellent contrivance for those who cheat in the weight of their goods. By making the fulcrum a little on one side, and placing the goods in the scale which is suspended to the longest arm of the lever, they would appear to weigh more than than they do in reality.

MRS. B.

You do not consider how easily the fraud would be detected; for, on the scales being emptied, they would not hang in equilibrium.

EMILY.

True; I did not think of that circumstance. But I do not understand why the longest arm of the lever should not be in equilibrium with the other?

CAROLINE.

It is because it is heavier than the shortest arm; the centre of gravity, therefore, is no longer supported.

MRS. B.

You are right; it is no longer directly below the point of suspension: but if we can contrive to bring the centre of gravity directly below that point as it is now situated, the scales must again balance each other; for you recollect that the centre of gravity is that point about which every part of the body is in equilibrium.

EMILY.

It has just occurred to me how this may be accomplished: let us place a great weight into the scale suspended to the shortest arm of the lever, a smaller one into that suspended to the longest arm. Yes, I have discovered it — look, Mrs. B.,

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