“Artificial” Vertical Beam

Abstract

THE vertical beam through a low sun is generally referred to the reflection of sunlight from the basal surfaces of thin plates of ice which are falling through the atmosphere with their crystal axes vertical and horizontal. It has been the writer's good fortune to examine such reflections from individual “plates” that were slowly falling within a metre or so of the observer. Most of the plates were asymmetric portions of flat crystal growths, and they, spun rapidly as they fell, with a motion resembling that of a falling maple-key. In this case, the vertical beam was observed to spread out slightly as it receded from the sun, and the angle subtended by the edges of the beam was obviously the complement of the vertical angle of the “cone” swept out by the rapidly rotating, but slowly falling flake.