The double crossbow, and force proportioned to its projectile
Why a bow outshoots a crossbow, with a warning against viewing the sun through glasses
A drawing dominates the folio: a crossbow reinforced by a second, smaller bow tied to its string, so a single arrow flies with the thrust of both drawn strings, with a catch marked n to release the smaller bow. Leonardo asks why a hand-bow shoots much farther than a crossbow and answers with a principle of proportion — a force can only carry a weight properly matched to it, an object too light or too heavy for the force travels little. A worked comparison contrasts a fifty-pound bow throwing 300 braccia against a three-hundred-pound crossbow reaching only 250, concluding that the bow wins because its longer arms let the motor accompany the arrow longer. A separate note at the top warns that looking at the sun through eyeglasses held from the eyes could destroy the sight forever.
On this page
A warning against viewing the sun through eyeglasses
You could hold your eyeglasses at a certain distance from your eyes and look through them at the sun, which would take away your eyesight forever.
A crossbow doubled with a second bow
A crossbow is reinforced by a smaller bow tied to its string, so one arrow is driven by both drawn strings; a catch at n releases the smaller bow, and two nuts release together so that the arrow never touches the crossbow's cord.
Force must be proportioned to the weight thrown
Whenever a force moves a weight, if the object thrust is not proportional to the force it will not make its proper voyage. A thing too light for a rapid arm moves little; a thing too heavy has a brief course.
Why a bow outshoots a crossbow
A fifty-pound bow throws a projectile 300 braccia, while a three-hundred-pound crossbow throws the same weight no more than 250, because of the disproportionate force. The bow wins because its longer arms let the motor accompany the arrow farther.