Why an Equal-Armed Balance Rests at Equality
The swaying of the balance and the right-angled junction of arm and suspension
An unillustrated page of statics explaining why a balance of equal arms and weights settles in the position of equality. Leonardo argues by analogy with a heavy liquid of uniform weight, which rests with its opposite extremes level and, when disturbed, sinks on one side as much as it rises on the other, swaying up and down about its centre until its impetus is spent. He then asserts that the junction between the central line of the balance-arm and its suspension link is never a right angle, whereas the lines of the ponderous powers are always joined at right angles.
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The balance sways about its pole until its impetus is spent
The balance sinks on one side as much as it rises on the other, swaying now up, now down about its pole until its impetus is consumed. This is caused solely by the inequality of the opposite parts about the centre.
Junction of arm and suspension is never a right angle
The angle formed where the central line of the balance-arm meets the central line of its appendicle (suspension link) is never a right angle. Yet the lines of the ponderous powers are always in right-angled conjunction.
A heavy liquid rests at the level of equality
Every heavy liquid of uniform natural weight rests with its opposite extremes in the position of equality. Leonardo uses this leveling behaviour of water as the model for the equilibrium of the balance about its centre.