Page:The Natural History of Pliny.djvu/124

 ^0 Pliny's nattjeal histoet. [Book II. £racted and that the variety of colours is produced by a mixture of clouds, air, and fire^. The rainbow is certainly never produced except in the part oppositeto the sun, nor even in any other form except that of a semicircle. Nor are they ever formed at night, although Aristotle asserts that they are semetimes seen at that time ; he acknowledges, however, that it can only be on the 14th day of the moon^. They are seen in the winter the most frequently, when the days are short- ening, after the autumnal equinox^. They are not seen when the days increase again, after the vernal equinox, nor on the longest days, about the summer solstice, but frequently at the winter solstice, when the days are the shortest. "When the sun is low they are high, and when the sun is high they are low ; they are smaller when in the east or west, but are spread out wider ; in the south they are small, but of a greater span. In the summer they are not seen at noon, but after the autumnal equinox at any hour : there are never more than two seen at once. CHAP. 61. THE KATUEE OE HAIL, SNOW, HOAE, MIST, DEW ; THE EOEMS OE CLOUDS. 1 do not find that there is any doubt entertained respect- ing the following j)oints. (60.) Hail is produced by frozen rain, and snow by the same fluid less firmly concreted, and hoar ^ " Manifestum est, radium Solis irmnissum cavse nubi, repulsa acie in Solem, refringi." 2 Aiistotle treats of the Raiabow much in detail, principally in hia Meteor, iii. 2, 3, 4, and 5, where he gives an account of the pha?nomena, which is, for the most part, correct, and attempts to form a theory for them ; see especially cap. 4. p. 577 et seq. In the treatise De Mundo he also refers to the same subject, and briefly sums up his doctrine with the foUowing remark : " arcus est species segmenti Solaris vel lunaris, edita in nube humida, et cava, et perpetua ; quam velut in speculo intuemur, ima- gine relata in speciem circularis ambitus." cap. 4. p. 607. Seneca also treats very fidly on the phsenomena and theory of the Rainbow, in his Nat. Qusest. i. 3-8. ^ Vide supra, also Meteor, iii. 2, and Seneca, Nat. Qusest. i. 3. ^ Aristotle, Meteor, ui. 5. p. 581, observes, that the rainbow is less frequently seen in the summer, because the sun is more elevated, and that, consequently, a less portion of the arch is visible. See also Seneca, Nat. Qua'st. i. 8. p. 692.