On the power of the crossbow
Loading weight, arrow and cord in proportion, minus three air resistances
The folio is headed 'On the power of the crossbow' and carries two crossed diagonal lines, one labelled a–c crossing the other at b. Leonardo states that the weight loading the crossbow stands to the weight of the arrow as the motion of the arrow stands to the motion of the cord. He then names three air resistances to be subtracted — the arc striking the air, the cord, and the cord acting against the arrow — and concludes that the thicker the cord, the less strongly it drives the arrow.
On this page
Heading: on the power of the crossbow
The folio opens with a heading announcing its subject, the power of the crossbow. It introduces the analysis of the weapon's loading weight, arrow and cord that follows.
Loading weight to arrow as arrow-motion to cord-motion
The proportion the weight loading the crossbow has to the weight of the arrow will be the same as that which the motion of the arrow has to the motion of its cord. The two ratios are set equal, tying the pull that spans the bow to the speed it imparts.
Three air resistances and the effect of a thicker cord
Three resistances produced by the air must be subtracted: the percussion of the arc of the crossbow into the air, that of the cord, and that made against the arrow. And the thicker the cord is, the less it will drive its arrow.