Real and Potential Arms of the Balance; a Graduated Wheel
Definition of real versus potential arms, with an experiment on subduple angles
Leonardo defines the two kinds of balance arm: real arms made of some material such as wood or iron, and potential arms that operate where matter is lacking, nearer the center of the balance. An experiment sets two cords equally loaded but meeting at angles in subduple proportion, and asks which arm will sink; because the arms are in subduple proportion with equal weights, the arm f descends until it rests. A large wheel divided by spokes and numbered marks accompanies the beam diagrams. Short figure labels attend each construction.
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Real arms and potential arms defined
Balances have real arms and potential arms. Real arms are those of some material, such as wood or iron; potential arms are those that operate where the material is lacking, that is, where the line of the potentia of the weight comes nearest to the center of the balance.
Equal weights on subduple angles
Two cords m a and m n are equally loaded with the weight they sustain, but the angles s f are subduple, one to the other. Because the arms are in subduple proportion and the weights are equal, the arm f will come down until it rests upon d.a.
A graduated wheel of numbered divisions
A large circle is divided by radiating spokes into numbered sectors, labelled with paired letters and figures such as a a, b b, c c and d d. The divisions set out the angular positions used to compare the weights and their arms.