Definition of "radii"

Now the centrifugal forces of bodies revolving in the ſame time in different circles being to one another as the radii of the circles (as ſhall be ſhewn when I come to treat of thoſe forces) it follows that the centrifugal force muſt be greateſt at the æquator, and thence be continually diminished towards the poles.

1767, Richard Helsham, Bryan Robinson, A Course of Lectures in Natural Philosophy, page 31