Perspective, the Visual Pyramid, and the Praise of Archimedes
A general rule for the pyramid's narrowing, with notes on Archimedes and observing the planets
The facing leaves continue the 'Prospettiva' investigation, giving a general rule for how a visual pyramid on a base of 4 braccia (48 inches) narrows over 200-braccia steps from a length of 1 mile up to 100 miles, worked out by dividing base and axis into fifteen equal parts. Amid the calculations Leonardo inserts a celebrated prose digression on Archimedes: he imagines the man who could perfect the bombard offering that secret to the Romans, then recalls how the Roman senate and people mourned and honoured Archimedes after the fall of Syracuse, and how Cato later restored his tomb. Another note proposes admitting a single planet's light through an opened roof so that its 'reflected motion' reveals the planet's nature. Diagrams labelled with letters (i e, h d, x c, g f, a b, m, f e) show the pyramid divided into quarters; a British Museum stamp is at lower left.
On this page
General rule for the narrowing of the one-mile pyramid
With a base of 4 braccia = 48 inches and a mile of 3000 braccia, the length is divided into 15 parts of 200 braccia each. To find how much the pyramid narrows at 200 braccia, divide 48 inches by 15, giving 3 inches and 1/5; for a 2-mile pyramid (30 pairs of hundreds) divide 48 by 30, giving 1 inch and 3/5, and so on to 100 miles.
Proportion of 'pairs of hundreds' of braccia
If 1 mile gives 15 pairs of hundreds, 2 miles give 30 pairs, i.e. hundreds of braccia. In the second method, if every 15 pairs of hundreds gives 1/15 of the base of 48 inches, then 30 pairs give the next proportional part, and so the calculation runs.
The praise and mourning of Archimedes
Whoever could perfect the bombard and give that secret to the Romans would have won every land; what reward could match such a benefit? Though Archimedes had harmed the Romans at the storming of Syracuse, they sought him out, mourned him more than a lost army when found dead, honoured him with burial and a statue under Marcus Marcellus, and Cato later rebuilt his tomb, glorying in nothing so much as that.
Reading a planet's nature by its reflected light
To see the nature of the planets, open the roof and show the base a single planet; the reflected motion from that base will tell the complexion of that planet — provided the base does not see more than one planet at a time.
Base and axis divided into equal quarters
The base i e is 4 braccia long and its divisions are made equal in number to the divisions of the pyramid's length. The part h d in the fourth quarter is narrowed 1/4 of the base f e, x c narrows another quarter (g f), a b another, and at m the last quarter i h is narrowed; hence base and axis are divided equally.
