Jointed semicircles and a circle inscribed in a square
A note that the centre is an indivisible point, best imagined round
The upper sketch shows part of a mechanism made of jointed semicircular arms, while at lower right a circle is inscribed in a square and divided by radiating lines. The accompanying note treats the geometry of the centre: it is an indivisible point, better imagined as round than any other shape, so the round part first surrounding it is divisible; set in a square and beaten into a circle, it widens.
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The centre as an indivisible point
The note argues that what is called the centre is an indivisible part, sooner imagined round than of any other shape. Therefore the round part immediately surrounding it is divisible, however small. Placed within a square and beaten into a circle, it spreads out.
Part of a jointed-semicircle mechanism
The upper drawing shows a curved component built from nested semicircular arms meeting at a small jointed block. It appears to be a movable or articulated part of a larger device. It is drawn loosely in red chalk.
Circle inscribed in a square
At lower right a circle is drawn inside a square and divided by lines radiating from its centre, together with the square's diagonals. The figure illustrates the relation of a circle to its enclosing square discussed in the note.