Apparent motion by distance; a load on an inclined plane
Why two unequal motions can look identical, and when nothing rests on a steep hypotenuse
Leonardo states that if the ratio of two bodies' motions equals the ratio of their distances from the eye, the two will always appear to move at the same speed, however different their true velocities. A second note treats a load on a slope: when the semi-diameter of the base reaches three-quarters of the hypotenuse nothing stays on it, whereas a longer, gentler hypotenuse will support any weight. A right-triangle diagram accompanies the reasoning, and lettered points d, c, e, f, g relate the space d g to the space d c through nearness to the eye.
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Equal-looking motions from matched distances
If the proportion between two bodies' motions is the same as the proportion of their distances from the eye, both will always appear to move at the same speed. This holds even when their real velocities differ almost infinitely.
When a slope sheds or holds a weight
When the semi-diameter of the base equals three-quarters of the hypotenuse, nothing will rest upon that hypotenuse. If the hypotenuse is longer (the slope gentler), it will instead support any load.
Space d g and nearness to the eye
The motion e e f seems very swift because it fills the whole space d g. That space d g stands to the space d c in the same proportion as the greater nearness of e to the eye stands to that of d.