90 
PLIKX'S I^ATUEAL HISTOET. 
[Book 11. 
fracted^, and tliat tlie variety of colours is produced by a 
mixture of clouds, air, and fire^. The rainbow is certaiioly 
never produced except in tlie part opposite to 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 
sometimes seen at that time ; h^ 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 IS^ATUBE OE HAIL, SKOW, HOAR, MIST, 
DEW ; THE rOEMS OE CLOUDS. 
1 do not jBnd that there is any doubt entertained respect- 
ing the following points. (60.) Hail is produced by frozen rain, 
and snow by the same fluid less firmly concreted, and hoar 
^ " Manifestmn est, radium Solis immissum cavse nnbi, repulsa acie in 
Solem, refringi." 
2 Aristotle treats of the Rainbow much in detail, principally in his 
Meteor, iii. 2, 3, 4, and 5, where he gives an account of the phsenomena, 
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 
following 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 fully on the phaenomena and theory of the Eainbow, in his 
3S[at. Qusest. i. 3-8. 
2 Vide supra, also Meteor, iii. 2, and Seneca, Nat. Qusest. i. 3. 
^ Aristotle, Meteor, hi. 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. 
Qusest. i. 8. p. 692. 
