The Reason Why / A Careful Collection of Many Hundreds of Reasons for Things Which, Though Generally Believed, Are Imperfectly Understood

by Robert Kemp Philp

482. Why do we see the sun before sunrise, and after sunset?

Because of the refractive effects of the atmosphere. Rays of light, passing obliquely from the sun through the air to the earth, are refracted three or four times by the varying density of the medium. Each refraction bends the rays towards the perpendicular; and hence we see the sun before it rises and after it sets.

Fig. 13.—DIAGRAM EXHIBITING THE REFRACTION OF THE SUN'S RAYS IN PASSING THROUGH THE ATMOSPHERE.

483. Why do figures, viewed through the hot air proceeding from furnaces, and from lime-kilns, appear distorted and tremulous?

Because the ever varying density of the air which is flying away in hot currents, and succeeded by cold, constantly changes the refractive power of the medium through which the figures are viewed.

484. Why do the stars twinkle?

Because their light reaches us through variously heated and moving currents of air. In this case the earth is the kiln, and the stars the object that is viewed through the refractive medium.

485. Why does much twinkling of the stars foretell bad weather?