Constructing a nonagon; a cross-lap timber joint and river-bank roads
A compass construction of the nine-sided figure, a halved cross joint of two beams, and roads across a river embankment.
The top of the sheet gives a compass construction for a nonagon by building, on a given line a b, a circle that contains exactly nine such lines. A cross-lap timber joint is drawn at the centre, where two beams are notched to fit into one another crosswise. A faint drawing at the foot shows roads carried across the embankment of a river.
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Constructing a nonagon (ennagono)
Upon a given line a b a circle is built that contains nine of these lines within itself; setting h b in the place g n makes g the centre of that circle, which then holds exactly nine of the given lines.
Cross-lap joint of two timbers
By sawing a timber down the middle, one piece can be set into the other crosswise, as shown in the drawing of two beams halved and interlocked.
Roads crossing a river embankment
A faint sketch at the foot of the sheet shows roads that run across the embankment of a river.