Physical Science in the Time of Nero: Naturales Quaestiones (1910) - Page 14

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	apparently without intervals, fall, human vision fails to distinguish individually the reflections of the sun, which thus become blended and confused. Vision is similarly deceived in the case of an oar in water, apples in a glass globe, etc., even in the size and movements of the sun himself. At any rate, the rainbow requires both sun and cloud, and these opposite to each other. These two in operation produce the varieties of color. . . . . .	16
IV.	That the rainbow is an image is shown by the relation of sun to cloud in position, by the rapidity of formation and dispersion. Artemidorus' explanation of the shape of the cloud (concave), and the consequent position of the red in the rainbow. . . . . .	22
V.	Arguments to show that the cloud is colored by the sun, like a dove's neck or a peacock's tail, and that the rainbow is not a reflection of the sun. The position (opposite) would be equally necessary in this case. Answer to this contention by Posidonius. The color effects. Author agrees with Posidonius' position but not his arguments. The only proof is the geometrical one. . . . . .	23
VI.	Arguments from the size—never more than a semicircle—and shape of the bow. As the color, whether real or reflected, is derived from the sun, so must also the shape be. The size is accounted for by the magnifying power of water, glass, etc. The sun as he appears in the rainbow is seen through moisture.	28
VII.	The arguments from the dispersion of the sun's rays through glass (prism). Contention that they confirm author's view. . . . . .	30
VIII.	The form once more; why it is never larger than a semicircle. A wrong explanation refuted. Explanation of Aristotle's remark as to the seasons of rainbows: in summer only in the morning or evening, in autumn at any time. . . . . . . . . . . .	31
IX.	Streaks or weather-galls (parhelia). Merely abortive or imperfect rainbows.	33
X.	Relations and differences of halos, bows, and weather-galls. . .	34
XI.	Mock suns (parhelia). Their appearance and position in relation to the sun. They are a reflection of the sun in a suitable medium. . . . . .	34
XII.	The formation of a mock sun may be compared to the image of the sun in eclipse as seen reflected in a dish of oil or pitch: the medium must be adapted to give the impression. The mock sun requires a certain consistency of cloud, failing which, a different effect is produced—obscuration, dissipation, etc. . . . . .	35
XIII.	There may be two mock suns simultaneously. Some think the one is a reflection of the other, the clouds acting as mirrors set opposite to one another. Mock suns, especially in the South, are a sign of rain. . . . . . . . . . . . . . .	36
XIV.	Other celestial fires. “Cave meteors,” “Barrel meteors,” “Chasms,” with a brief description of each. The rapidity of their flight, just as of lightning, deceives the sight. Their origin and cause. They indicate wind. . . . . . . . . . .	37
XV.	Gleams (flashes, original: σέλα). Their production and motions, varieties of them. Some do damage. Some are analogous to comets. “Bearded,” “torches,” “cypress” are different kinds. “Beams” and “barrels” may be of the same class. A curious case where such an appearance raised an alarm of fire. They are real fires. On the contrary, rainbows and halos are mere reflections. Mirrors have this wonderful power of false presentation. . . . . .	39