Fortress plans, counter-mines, and a great bombard
Mine chambers and embrasures; a huge bombard; why distant towers seem pyramidal through hazy air.
The sheet is filled with military architecture: wall plans, one showing a chamber packed with round shot, another with four round bastions, and a large circular fort whose openings a and b are labelled as 'mouths' (embrasures). A note on counter-mining advises placing the last angle of the counter-mine, the first elbow of the mine (angle a), at the point of greatest resistance, and a massive bombard is specified as forty braccia long and three wide. A separate observation on profiles of towers and bell-towers explains why, seen from far off, they seem to taper to a point: the denser, mistier air low down obscures an object's edges so that perception falls back toward its central line.
On this page
Wall plan with a charged mine chamber
A long fortification wall is drawn in plan with a chamber packed with round shot, lettered f e b a and d c g f. It reads as the powder or projectile chamber of a mine or gun emplacement set within the rampart.
Round fort with two embrasures a and b
A circular fortification is drawn with radiating lines and lettered b and a. The note states that a is one mouth and b another, that is, two gun-embrasures piercing the round wall.
Counter-mine set at greatest resistance
The last angle of the counter-mine, the first elbow of the mine, is the point marked a, and it should always lie where resistance is greatest. A small fortification plan lettered a accompanies the rule.
A bombard forty braccia long
A very large piece of ordnance is specified as a bombard forty braccia long and three wide, drawn as a heavy fortification-scale gun. The scale marks it as a siege bombard rather than a field piece.
Why distant towers look pyramidal
Towers and bell-towers of parallel thickness appear pyramidal, like upside-down pyramids, when seen from a great distance. This happens because the air, denser and mistier the lower it lies, occupies and hides more of the object's edges, so that perception of the object collapses toward its central line. It is an argument from aerial perspective and the obscuring of extremities by atmosphere.