A sealed brazier, notes toward fusion, and a right angle in a circle
Two furnace cross-sections and an ornamental vessel on 145v; a circle with an inscribed triangle on 142r.
On 145v Leonardo draws two cross-sections of a domed furnace or brazier and, beneath them, an ornamental footed vessel with scrolling handles. The note explains that if the draught's inlet and the smoke's outlet are kept narrow the coals will burn a long time, and specifies a copper lid one braccio across and half a braccio high over a body of fire-proof clay. A second note sketches a program of study - from the motions of heavy solids to those of liquids, air and fire - proposing to compare fire's whirling with the vortices of air and water and to harness its 'boring' motion for fusions, using dampers and boiling water. On the facing leaf 142r a large circle with an inscribed triangle carries a geometry note that the curve n o b meets the semidiameter e b at a right angle.
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A sealed brazier to keep its coals alight
Leonardo advises that if the air's exit above and the draught's entry are both made very narrow, the coals will stay burning a good while. He specifies a lid of copper, one braccio in diameter and half a braccio high, with the rest of the body made of fired clay durable in the fire.
From the motion of solids to the whirling of fire, for fusion
A memorandum orders a course of study: having treated the motions of heavy solids, treat next of heavy liquids, air and fire, then compare fire's motion with the whirlings (vortices) of air and water. He expects to find the 'boring' revolutions of fire that make it powerful for fusions, to be managed with dampers and boiling water.
A curve meeting the semidiameter at a right angle
Beside the large circle, Leonardo notes that the curve n o b joins the semidiameter e b at a right angle. When that curve is straightened and laid flat upon the line n f, it too will make a right angle.