Note 305 — BOOK II. AN ACCOUNT OF THE WORLD AND THE ELEMENTS.
John Bostock translation
The term here employed is “arcus,” which is a portion only of a circle or “orbis.” But if we suppose that the sun was near the horizon, a portion only of the halo would be visible, or the condition of the atmosphere adapted for forming the halo might exist in one part only, so that a portion of the halo only would be obscured.