On the Blow: united and disunited percussion
A struck nail passes to meet the hammer; the pop-gun of compressed air; weights falling into water
This page of Leonardo's treatise on percussion (colpo) compares the 'united' blow of a nail fixed to its hammer with the 'disunited' blow, and describes how a nail set slightly into a board can pass through it to meet a hammer struck from the far side. He observes that compressed air released from a child's elder-wood pop-gun is of great power, and that a weight falling into water, unable to drive the water aside quickly enough, springs back up into the air, which resists it less. Small pen sketches at upper right show a nail with hammer and anvil, labelled 'disunito' and 'unito'. The sheet is numbered 58.
On this page
United versus disunited blow
The united blow — a nail fixed to the hammer — is of greater power than the disunited blow, exemplified by someone springing on tiptoe on a yielding board. The slowness of force adds to the powerful quickness of the blow in the act of pressing.
A nail driven through a board to meet the hammer
If a nail is set a little into a board and the board is struck from the opposite side with a hammer, the nail passes through the board and travels to meet the hammer.
Compressed air in the elder-wood pop-gun
Air that has been compressed and then returns to freedom is of great power, as shown in the pop-guns children make from elder-wood. A cherry-stone squeezed in the hand likewise illustrates the blow produced by vigorous motion.
A weight falling into water leaps back into the air
A weight falling into water cannot be obeyed quickly enough by the resisting water, so on account of the opposing water it leaps back up into the air, which resists it less.