THE HEART OF THE ANTARCTIC 



It began instantly when the sun set and got higher 

 as the sun sank further below the horizon, at least it 

 appeared so, perhaps through the arch becoming more 

 distinct as the darkness deepened. Some low arches which 

 were measured were 25° and 30° above the horizon, and it 

 was estimated that at its highest the arch reached to 45°. 

 Round the horizon it extended for about 90° or more. 



The accompanying figure gives an idea of its size and 

 of the breadth of the bands of colour. 



Though the rainbow colours are unmistakable, the 

 bands are very delicate, and their limits, as well as the 

 boundary of the whole arch, are very obscure, though the 

 latter is clearly a circular arc. The number of colours 

 which can be distinguished by the eye varies with the 

 distinctness of the display, and with the height of the arch. 

 In a low arch usually only two bands were visible, a lower 

 one of slaty blue (greenish quite close to the horizon), 

 and a higher one of purple. When the arch was high, 

 other colours could be distinguished. The order of their 

 arrangement is here given as they appeared, without bias 

 as to the correct order in a solar spectrum. On March 13, 

 1908, the colours noted were (reckoning from the horizon 

 upwards) pale blue, violet, orange, yellow, fading at the 

 outer edge with pale greenish blue. On April 7, at 7 a.m., 

 the colours distinguished were slaty blue, purple, pink, red, 

 orange, yellow, greenish-blue. No doubt these colours 

 were affected by atmospheric conditions, and by the colour 

 of clouds in the background, for the arch could often be 

 seen against clouds. 



Apparently the colours were not concentric bands, but 

 those near the horizon formed arcs of larger circles than 

 the upper ones. If not so the blue and purple bands 

 would be very small, but they have really the greatest 

 horizontal extension. Sometimes the reds and yellows did 



3T2 



