; and
presently the ground got so wet from continual rain, that the whole
country was changed into an adhesive mud (for the soil is naturally
rich), and every plan was thrown into confusion; meantime, thunder with
incessant crashes and ceaseless lightning filled men's minds with fear.

26. To these portents were added continual rainbows. A short explanation
will serve to show how these appearances are formed. The vapours of the
earth becoming warmer, and the watery particles gathering in clouds, and
thence being dispersed in spray, and made brilliant by the fusion of
rays, turn upwards towards the fiery orb of the sun and form a rainbow,
which sweeps round with a large curve because it is spread over our
world, which physical investigations place on the moiety of a sphere.

27. Its appearance, as far as mortal sight can discern, is, in the first
line yellow, in the second tawny, in the third scarlet, in the fourth
purple, and in the last a mixture of blue and green.

28. And it is so tempered with this mixed beauty, as mankind believe,
because its first portion is discerned in a thin diluted state, of the
same colour as the air which surrounds it; the next line is tawny, that
is a somewhat richer colour than yellow; the third is scarlet, because
it is opposite to the bright rays of the sun, and so pumps up and
appropriates, if one may so say, the most subtle portion of its beams;
the fourth is purple, because the density of the spray by which the
splendour of the sun's rays is quenched shines between, and so it
assumes a colour near that of flame; and as that colour is the more
diffused, it shades off into blue and green.

29. Others think that the rainbow is caused by the rays of the sun
becoming infused into some dense cloud, and pouring into it a liquid
light, which, as it can find no exit, falls back upon itself, and shines
the more brilliantly because of a kind of attrition; and receives those
hues which are most akin to white from the sun above; its green hues
from the cloud under which it lies, as often happens in the sea, where
the waters which beat upon the shore are white, and those farther from
the land, which, as being so, are more free from any admixture, are
blue.

30. And since it is an indication of a change in the atmosphere (as we
have already said), when in a clear sky sudden masses of clouds appear,
or on the other hand, when the sky changed from a gloomy look to a
joyful serenity, therefore we