The effect of my rules. If you were to say to me: "What do these rules of yours bring forth, what are they good for?", I answer you that they hold the bridle on engineers and investigators, so that they do not let themselves promise, to themselves or to others, impossible things, and get themselves taken for madmen or cheats.

b — a — n

Again you will make a rule of the different courses the ball a makes, driven by the blow of the weight b, falling onto the head of the axle n from different heights. And note whether, if the weight b falls 4 braccia, the ball a flees 10 braccia; whether, b falling 8 braccia, a will flee 20 braccia, that is, whether the blow falls just as much more the one time as the other; and again whether the weight that flees before that blow doubles its flight.
Again note whether, if the weight b is 4 pounds and, falling 4 braccia, the ball a flees 10 braccia; whether, this weight b weighing half as much and falling as much higher, that flight of the ball a would be like the first flight, for if I diminish the weight b by half, I double its fall by half, so that it seems the blow of b ought to be the very same. Or else we shall hold to the verdict that experience will give. And note whether the rule of three serves you at all here.
Again note to set the little board n now flat and now sloping with different obliquities, the weight always falling perpendicular, and note the difference of the flight a.
Again note to let b fall along different obliquities.
Again the axle n of different weights. Again of different lengths. Again of different projections beyond the table. Again b of different weights, and the axle of different widths.