. Elementary physical geography;. In the corona,which is not very common, there is usually a series of con-centric, colored rings. These, it is thought, result from ascattering of the light by the moisture of the halo of the moon appears when the air is very this reason it is apt to portend rain or snow. The halos of the sun are associated usually with coldweather. They are thought to result from the refractionof the light as the latter passes through the ice crystals ofcirrus clouds. Frequently there are several circles. Someof them are concentric; some are tangent on
. Elementary physical geography;. In the corona,which is not very common, there is usually a series of con-centric, colored rings. These, it is thought, result from ascattering of the light by the moisture of the halo of the moon appears when the air is very this reason it is apt to portend rain or snow. The halos of the sun are associated usually with coldweather. They are thought to result from the refractionof the light as the latter passes through the ice crystals ofcirrus clouds. Frequently there are several circles. Someof them are concentric; some are tangent one to another; 284 PHYSICAL GEOGRAPHY and others intersect one another. At the places of inter-section and of tangency more light is radiated, andthese spots, which are very bright, form sun dogs, or mocksuns. Rainbows.—During a summer shower, when the sunbreaks through a rift in the clouds, the light passes throughthe falling drops of water in such a way that it is not onlyrefracted but decomposed. The resulting decomposition. HALOS OBSERVED BY GENERAL is the arch of colored light that constitutes the bow is blue and violet on the inner, and red on the outerside. Sometimes there is a larger secondary bow in whichthe order of colors is reversed. The rainbow is best observed when the sun is near thehorizon. The observer sees the bow when his back isturned toward the sun. The rainbow is observable in thespray of waves, and also in the spray of cascades. ELECTRICAL AND LUMINOUS PHENOMENA 285 QUESTIONS AND EXERCISES.—Verify the statements concern-ing the mutual attraction and repulsion of electrified bodies, observingthe directions on p. 268. Verify the statements noted on p. 275, using one or more stout knit-ting-needles and strands of untwisted silk. For observing inclinationthe strand of silk may be fastened by a slip knot to the needle; for theother experiments the needle may be thrust through a bit of paperheld by the silk. In magnetizing the needles, ru
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