splits the thing it strikes but does not scorch it at all.
We have now explained thunder and lightning and hurricane, and
further firewinds, whirlwinds, and thunderbolts, and shown that they
are all of them forms of the same thing and wherein they all differ.
Let us now explain the nature and cause of halo, rainbow, mock suns,
and rods, since the same account applies to them all.
We must first describe the phenomena and the circumstances in
which each of them occurs. The halo often appears as a complete
circle: it is seen round the sun and the moon and bright stars, by
night as well as by day, and at midday or in the afternoon, more
rarely about sunrise or sunset.
The rainbow never forms a full circle, nor any segment greater
than a semicircle. At sunset and sunrise the circle is smallest and
the segment largest: as the sun rises higher the circle is larger
and the segment smaller. After the autumn equinox in the shorter
days it is seen at every hour of the day, in the summer not about
midday. There are never more than two rainbows at one time. Each of
them is three-coloured; the colours are the same in both and their
number is the same, but in the outer rainbow they are fainter and
their position is reversed. In the inner rainbow the first and largest
band is red; in the outer rainbow the band that is nearest to this one
and smallest is of the same colour: the other bands correspond on
the same principle. These are almost the only colours which painters
cannot manufacture: for there are colours which they create by mixing,
but no mixing will give red, green, or purple. These are the colours
of the rainbow, though between the red and the green an orange
colour is often seen.
Mock suns and rods are always seen by the side of the sun, not above
or below it nor in the opposite quarter of the sky. They are not