How a moving body loses its power; Salai's account of 1504
A law of moving bodies spending their power against the air, beside a dated expense account in another hand
The left leaf (f. 147v) sets out a law of motion: a moving body follows the line of its mover only while it keeps the whole power imparted at separation, and that power is consumed by the air it opens, so a starting power of 10 against a medium resisting by 1 is exhausted in nine degrees of motion. It opens with a barbed remark that men are chosen as physicians of maladies they do not understand, and carries small figures and further calculations in the margins. The right leaf (f. 148r) is a dated household account in another hand, probably Salai's, recording 15 gold ducats received from Leonardo on 25 May 1504 and the outlays that followed.
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A moving body spends its power against the air
Every moving body travels along the line of its mover's motion only while it retains the whole power given to it at separation, and that straight, transverse motion decays as the power is consumed by the air opened before it. From an initial power of 10 against a medium resisting uniformly by 1, the motion is exhausted after nine degrees, while the transverse percussion grows through the impetus gained in motion.
Account begun on San Zanobi, 25 May 1504
In another hand, an account records 15 gold ducats received from Leonardo on the morning of San Zanobi, 25 May 1504, after which the writer 'began to spend.' Daily outlays follow for Saturday through Monday, including cloth, resetting a ring, barber, wine, bread and food, with running totals.
A jibe at physicians
The passage opens with a barbed aside: get the definition and remedy of the case from 'the Saint and the other,' and you will see that men are chosen as physicians of maladies they themselves do not understand.