h f – c a o – S – t – m – p b – m – a

The main mast, from the ground to the boom a c, will be 8 braccia, the depth of the ditch being 4 braccia; the boom a e will be 12 braccia, the width of the ditch being 28 braccia at the bottom and 32 braccia at the mouth. The reason will tell me exactly this: 4 braccia from the middle of the heap of earth dug from the ditch to its foot, which borders the road at the top of the embankment; 2 braccia for the said road; 2 braccia for the narrowing of the ditch from top to bottom by the slope; 2 braccia from the foot of that slope to the place where the post b is planted, which in all makes 10 braccia. The height of the embankment should not exceed 4 braccia; the height of the ox's place will be 3 braccia and 2 wide, so that it may shelter between the foot of the mast and the embankment; the rope c m will be 7 braccia, because 7 braccia is the straight line from the top of the heap, where the earth is unloaded, down to the level of the bottom of the ditch; m p will be one braccio and no more, otherwise one could not unload onto the top of the heap; and the rope S o is not joined to the rope f h, because the double wheels are arranged in the way one often sees at the friars' wells, and they are made so that when the smaller wheel unwinds 4 braccia, the larger gathers 7 braccia, so that the counterweight S t descends 4 braccia when the weight m p rises 7. The counterweight will be a man and an ox, and since that counterweight descends 4/7 of the rise of the opposed weight, so the weight lifted will be 4/7 of the amount of the counterweight that pulls it.

And this arrangement works well, because the beam comes to be more balanced at its opposite ends; for if you wanted the descending weight to equal the one being lifted, and the arms of the beam not being equal, it would last little and the hypotenuse would twist. The stair for climbing to the counterweight will be 4 braccia high and the length of its base 8 braccia, that is 2 squares. The men are these: 2 with the ox, 4 to fill the box, which is 6 in all per machine. Of those 4 who fill it, 2 will stand on the embankment and 2 at the foot. Those two above will then empty the box and send it down, and the 2 who stand with the ox will together with them serve as counterweight to the box, and then bring it up again anew.

This stair is far better than the straight stair a m, because, if a m is 4 braccia high, it must be 10 long and 14 for the climb back, making 24, whereas the spiral stair will be only 14. So if the ox climbs this stair a thousand times a day, it saves 4,000 braccia, which is a mile and a third.