Page:Roman History of Ammianus Marcellinus.djvu/253

A.D. 360.] 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 often read in the poets that Iris is sent from heaven when a change is required in the condition of any present affairs. There are various other opinions which it would be superfluous now to enumerate, since my narration must hasten back to the point from which it digressed.