If the sun is near the horizon, and the shadow of the observer falls upon the grass, upon a field of corn, or other surface covered with dew, there is visible an aureola, the light of which is especially bright about the head, but which diminishes from below the middle of the body. This light is due to the reflection of light by the moist stubble and the drops of dew. It is brighter about the head, because the blades that are near where the shadow of the head falls expose to it all that part of them which is lighted up, whereas those farther off expose not only the part which is lighted up, but other parts which are not, and this diminishes the brightness in proportion as their distance from the head increases. The phenomenon is seen whenever there is simultaneously mist and sun. This fact is easily verified upon a mountain. As soon as the shadow of a mountaineer is projected upon a mist, his head gives rise to a shadow surrounded by a luminous aureola.
[Illustration: FOG-BOW SEEN FROM THE MATTERHORN.]
The Illustrated London News of July 8, 1871, illustrates one of these apparitions, “The Fog-Bow, seen from the Matterhorn,” observed by E. Whymper in this celebrated region of the Alps. The observation was taken just after the catastrophe of July 14, 1865; and by a curious coincidence, two immense white aerial crosses projected into the interior of the external arc. These two crosses were no doubt formed by the intersection of circles, the remaining parts of which were invisible. The apparition was of a grand and solemn character, further increased by the silence of the fathomless abyss into which the four ill-fated tourists had just been precipitated.
Other optical appearances of an analogous kind are manifested under different conditions. Thus, for instance, if any one, turning his back to the sun, looks into water, he will perceive the shadow of his head, but always very much deformed. At the same time he will see starting from this very shadow what seem to be luminous bodies, which dart their rays in all directions with inconceivable rapidity, and to a great distance. These luminous appearances—these aureola rays—have, in addition to the darting movement, a rapid rotary movement around the head.
BY AGNES M. CLERKE.
HESPERUS AND PHOSPHOR.
The radiant planet that hangs on the skirts of dusk and dawn
“like a jewel in an Ethiop’s ear,”