On the Improvement of the Understanding
At this point, I cannot resist calling the reader's attention to the circles formed by expanding waves, whether of radio, or air, or even of water, as when a pebble is dropped into a still pond;
by the projection of light through a circular aperture onto a surface; by the section of spheres, cylinders, and the like; by bodies subject to a force perpendicular to their momentum; and ask whether these examples, which could be multiplied indefinitely, are formed by lines ``whereof one end is fixed and the other free.'' --- Even if it is objected that by ``proximate causes'' Spinoza did not, in fact, mean proximate causes, what of the circle formed by adding sides to regular polygons without limit? [CRS]