d – f e – c – b a o. To make a mast of pieces, fixed in the ground, of very great height: first plant the two poles a b and bind them together at c. Then fasten the pulley-block at d and the other pulley-block at the foot of the pole at a, and put the head of the rope to the windlass o, and haul the beam e f up to the top of the pole a d; then turn it upright, setting f above the head of the beam c, and make it fast well at d. Then move the pulley-block from d and set it at e; and haul up another similar beam and plant it above d, doing with it as you did with the beam e f. And by this rule you may proceed up to a very great height. And it will be stronger if you set the beams in 3 thicknesses than in 2; and as you rise, always take care to taper the mast.

c a b d – e f. This screw is made as a means of descending quickly from a height without danger of impact. It is the rope c d, which is wound around the screw a b with three turns. This screw will be 1/2 braccio in length and 1/12 of a braccio thick. And then the screw must be sheathed with the reed e f, and thus the secret of the screw will be concealed and the rope strengthened. The friction of dense bodies of polished surface, made in the site of equality, resists its mover with a power equal to a quarter of its weight. That thing is higher which is more distant from the centre of the world, and the lowest is nearer to that centre. The site of equality is that of which all its parts are equally distant from the centre of the world. Here the adversary says that the said site would be spherical, that is curved and not flat, and that the definition of the flat is that from which, a straight line being drawn from either extremity, it touches the whole of that line. To him one answers: this is rather to be called a concavity than a flat site, because if water be poured from each extremity, that water will move with swift motion toward the middle of the flat and there come to rest, with great depth in the middle and not at the sides. Therefore bodies dragged over this mathematical plane from the middle toward the extremities would have their friction become the more difficult the more they approached those extremities. And this is against our proposition, which requires that the site where friction is generated be of such a quality that such friction does not come to be altered in any part of its power in any part of the motion.

n c b a h g – o – e – f. 8753 miles is more remote from the centre of the world c than a is. And this variation is over 875 miles of plane. a is lower than c by all the space o c, which is like the sixth of the diameter of the earth, which is seven thousand miles; a sixth of seven thousand is 1166; so that in the half of the earth's diameter a c, which is 3500 miles, there is a fall of 1166 2/3 miles. Now you can see what a site of equality or of level ground we may call that which, over 3500 miles of space, varies by 1166 2/3 miles of rise; for to the water given to canals one grants one braccio per mile, and here it comes, mile for mile, to 3 braccia 2/1166. Now you can see what a 'flat' this is.

Water. Earth – Earth. If the earth were cut through the middle, what would the water and the remainder of the half-earth do?