On Soldering: Copper Sheets and the Cathedral Ball
Joining drawn copper sheets over an earthen bed, recalling the ball of Santa Maria del Fiore
Under the heading 'On soldering', Leonardo describes joining drawn copper sheets edge to edge on a bed of annealed shearing-earth, laying a copper wire melted over each seam, then drawing the whole assembly through the same die so it becomes of uniform thickness. A marginal note tells him to remember the solderings used for the copper ball of Santa Maria del Fiore, worked from copper stamped in stone like the triangles of that ball, with wooden hammers. Lower on the sheet he turns to the 'percussion of the fire', calculating how a small unit enters an area 36,864 times in a square 4 braccia to a side, calling this an immense power. The right margin carries sketches of an apparatus, a holed beam, and curved and domed blocks.
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Soldering drawn copper sheets on an earthen bed
Drawn sheets of copper are joined by their touching edges on a flat bed of annealed shearing-earth, their straight edges meeting in uniform contact. A copper wire is laid melted over each joint; once the seams have gained thickness the whole is drawn through the same die used for the sheets, making the assembly of uniform thickness.
Recalling the soldered ball of Florence Cathedral
A margin note urges him to remember the solderings by which the ball of Santa Maria del Fiore was joined. The copper was stamped in stone like the triangular sections of that ball, and the figure beside it shows the impressions of those triangles.
Wire-drawing die and wooden hammers for finishing
The finished seams are pulled through the same drawing die as the original sheets so the joined work comes out even. Wooden hammers are noted for working the metal, and a mechanical apparatus is sketched at the top of the sheet.
The immense power of percussion in a square
For a square 2 braccia to a side the 'percussion of the fire' a b enters 36,864 times, because its diameter a c goes eight times into an oncia. Multiplying 96 by 96 gives 9216 per square braccio, and for a square 4 braccia to a side it enters 36,864 times, which he calls an immense power.