12. a 3 b 4 d. Here the adversary says that he will make the counterweight d equal to the friction b, and that these two powers will be made equal. To which one replies, by the fifth [proposition], that every counterweight of the friction sends to that friction a resisting power equal to a quarter of its weight. The adversary says that the 3 of the friction b is equal to the 3 he wants to put at d, and that if this 3 of b makes a quarter of its weight at e, which would be 3/4 — that is, the quarter of 3 — he would then multiply that 3/4 by 4, which would be 12/4, that is three whole [units], and would make good the counterweight of that 3/4. Here one replies that if 3 is the counterweight of the 3/4 of friction, then, the arms of the balance being equal, the 3 of the counterweight is too much for the friction of 3/4 and too little for the counterweight of the 3 and 3/4 of b c.

Invisible before restoration; 293 x 198 mm; ruled columns spaced 21 mm; a watermark at the centre (a 'wheel', 28 mm). After the note by C. Pedretti (An 'Arcus Quadrifrons' for Leo X, in 'Raccolta Vinciana' XX, 1964, p. 2⁴⁸, the restorers of the Codex Atlanticus reassembled this sheet, which in the old codex was divided into four fragments. Probably, when Leonardo wrote on it, it was already divided, perhaps into three parts, one of which was folded to form four little pages within whose exact measures he placed drawings and notes. The present recto, which in the old codex was visible or discernible only through the transparency of the paper, has now come back to light and been recomposed. The drawing, not by Leonardo, represents a hermaphrodite with wings in place of arms: the right side male and diabolical, with a bird's foot instead of a foot and hairy skin; the female side with pale skin, an eye in the knee and a large V on the chest. The head ends in a long, straight horn.