Established.

Force and weight — their many offices are so alike that they almost seem one and the same thing to name. And I see no other difference between them except that the one, that is the weight, is elemental, while force is contained in no element. The one is finite in its nature, and force may be called infinite. The one power and the other always contend with their begetter and maintainer, so that in the end the one and the other together consume themselves. Moreover this force, together with the weight, are generated by violent motion and then undone by natural motion.

[Editorial note: the manuscript has 'chonsumma' instead of 'consuma'.]

n m o, a b c d, a b c d

If the bridge set upon ships or barrels is fixed at a pole with one of its ends at the river's bank, and its opposite end given to the current of the water so that it may rest against the opposite bank, I say that one must first know the power of the various lines of the water, and beyond this the resistance of the bridge in the different places of its length. Since it is first in the power of the river's current, and then, fixing itself athwart the waters, it has various strengths and weaknesses against the river, and likewise the water's current against the bridge, we shall say, by the 9th of the second, that the bridge is weaker at its middle than in any other part, and likewise the part nearer to that middle. Again we shall say, by the 3rd of the 4th, that the river is more powerful in those parts nearer the middle than elsewhere, it being of straight course. Whence the bridge will be hard to govern, its weaker part set against the more powerful part of the waters. Again, of its motion it is shown that those parts of the circles which the parts of the bridge make in moving about their pole do not agree, when the water pushes it, inasmuch as all these circles wish to be begun at one time and finished at another. And because these circles are — 4

[continues on fol. 143 verso]