If you want to prove why the moon appears larger than it is, when it
reaches the horizon; take a lens which is highly convex on one
surface and concave on the opposite, and place the concave side next
the eye, and look at the object beyond the convex surface; by this
means you will have produced an exact imitation of the atmosphere
included beneath the sphere of fire and outside that of water; for
this atmosphere is concave on the side next the earth, and convex
towards the fire.