The first, slowest wheel of a clock
A large circular diagram for the wheel of the 'first motion' in clockwork
A large circular diagram, drawn with concentric circles studded with small nodes and radiating connections, lays out the first wheel of clocks. Leonardo labels it the wheel of the first motion and notes that it is the very slowest of the movement. Numbers 8, 50 and 12 accompany the letter-labels a and b. A circular loss cuts into the sheet at the upper right.
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The wheel of the first motion in a clock
The large circular figure is described as being for the first wheel of clocks, that is, the wheel of the first motion, which Leonardo says is very slow. It is marked 8, 50-a and 12-b, keying counts to the lettered parts a and b of the mechanism.
The slowness of the first motion
By naming this the wheel of the first motion and noting that it is the slowest, the diagram addresses the ratio of motion through the geared train, where the driving wheel turns most slowly.