a - n

Why does the drop of water not fall perpendicularly beneath the angle a as it does beneath n? And why, the larger the body of water, the further it moves away from its angle?

t a S — o n m

If you wish to make a demonstration of the true measure of the world, you will proceed in this way. First place yourself upon a shore of the sea beach and choose a time when the sea is without any movement. Then take a stick, and set upon it a thin whitened board — or you may paste a paper upon it — and in the middle make a black line in this form (a figure follows); and fix it under the water so far that the line in the middle of that white field remains a palm or so above the water. But it will be better if you fix a stick down so far that its end remains a palm out of the water, and set your eye upon it, and have the aforesaid white board placed a mile away from you, and let it be lowered so far that the mark in its middle is almost hidden from you by the bulge of the water that lies between the eye and the board. Yet I say again and confirm that the first method is the better, for the mark S m must be as far out of the water as t o, and you may judge that the line a n is of the same length when the bulge of the water at a hides from the eye S the height t. And even if the space between S and t were not a mile, still note the number of braccia and multiply, reckoning every 3,000 braccia as one mile. But know that these lines S m and likewise t o must not be out of the water more than 1/4 of a braccio or so.