The Halo in the Ricefield and the Spectre of the Brocken

Abstract

IN connection with the curious Japanese phenomenon of the halo seen around the head of the shadow of a person standing in a ricefield in early morning (NATURE, p. 419, December 12, 1912), it may be of interest to recall that some recent balloon voyagers have reported observations of a bright halo surrounding the shadow of the car thrown upon a horizontal cloudfield by oblique solar rays. Coloured diffraction rings are sometimes seen surrounding the head of the “spectre of the Brocken,” but for these to be visible theory requires that the drops constituting the mist should be of uniform size. In an article in the Meteorologische Zeitschrift (p. 282, June, 1912; see also Science Abstracts, p. 574, December, 1912), by Prof. F. Richarz, discussing the theory of the subject, reference is made to an observation by Dr. Bieber from the balloon Marburg of a halo around the shadow, and also to other verbal communications of a similar character. Prof. Richarz's article is followed by another describing a photograph taken by Dr. Wegener of a series of three diffraction rings seen around the shadow of the same balloon, the Marburg, on another voyage. The centre of the rings was the point corresponding to the shadow of the eye, or of the camera objective. On calculating the radius r of the cloud drops from the angular radius of a ring, a divergence from theory was found on this, and other, occasions. Theoretically all the rings should give the same value for r, but the calculated value of r was found to diminish with the order of the ring outwards.