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Library/Paris Manuscript I/251

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Paris Manuscript I — 251

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Bibliothèque de l'Institut de France, Paris

I2 72 r. Balestra, con:

a b c - a b

Domanda i balestrieri che differenzia è da tenere la mano in a o in b o in c, che la freccia trae più alto o più basso, e donde viene.

De moto.

Dice Alberto di Sassonia1 nel suo Di proporzione che se una potenzia move un mobile in certa velocità, che moverà la metà d'esso mobile in duplo veloce. La qual cosa a me non pare, imperò che costui non mette che questa tale potenzia adoperi l'ultima sua valitudine; imperò che se essa così facessi, quella cosa che pesassi meno, non sarebbe alla proporzione della forza del motore, ovvero del mezzo donde passò; onde sarebbe cosa ventilante2 e non di retto moto e andrebbe meno.

I2 72 r. — Crossbow, with:

a b c — a b

Ask the crossbowmen what difference there is in holding the hand at a or at b or at c, so that the arrow shoots higher or lower, and whence it comes.

On motion.

Albert of Saxony says in his On Proportion that if a power moves a body at a certain velocity, it will move half that body at double the speed. This does not seem so to me, because he does not posit that this power employs its utmost capacity; for if it did so, the thing that weighed less would not be in proportion to the force of the mover, or of the medium through which it passed; whence it would be a fluttering, wavering thing and not of straight motion, and would go less far.

Crossbow Aim by Hand Position; Albert of Saxony on Motion

Where to hold the hand — a, b or c — and a critique of doubling speed by halving the load

Weapons & Fortification Physics & Mechanics

A crossbow is drawn across the top of the sheet with points labelled a, b and c along its stock. Leonardo notes to ask the crossbowmen what difference it makes to hold the hand at a, at b or at c, since the arrow flies higher or lower, and whence this comes. The lower text, headed 'On motion', reports Albert of Saxony's claim in his On Proportion that a power moving a body at a certain velocity will move half that body at double the speed — a claim Leonardo disputes, arguing that Albert does not assume the power exerts its utmost capacity.

On this page

Hand position on the crossbow: a, b, c

The crossbow is marked a, b, c along its stock. Leonardo means to ask the crossbowmen what difference it makes to hold the hand at a, at b or at c, since the arrow shoots higher or lower, and where that difference comes from.

Dispute with Albert of Saxony on doubling speed

Under 'On motion', Leonardo cites Albert of Saxony's On Proportion that a power moving a body at a given speed will move half the body at double speed. He objects that this holds only if the power does not already exert its utmost, otherwise the lighter body would fall out of proportion with the force and travel erratically rather than in a straight course.

Reader's Edition — described with AI from the e-Leo transcription.