PHYSICAL SCIENCE 



CHAP. PAGE 



apparently without intervals, fall, human vision fails to dis- 

 tinguish severally 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 colour . . . 1 6 



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 coloured 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 colour 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 colour, 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. Merely abortive or imperfect rainbows . 33 



X. Relations and differences of halos, bows, and weather-galls . . 34 



XI. Mock suns. 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, <rt\a). 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 



