Page:Polar Exploration - Bruce - 1911.djvu/225

Rh as regards geographical distribution, auroræ and thunderstorms are complementary, auroræ being not more characteristically of polar than thunderstorms are of tropical origin; whereas thunderstorms may be regarded as completely dissociated from magnetic associations, and their periodicities are restricted to diurnal and annual variations" ("Aurora Borealis or Northern Lights," Chambers' Encyclopedia, 1901).

At Ben Nevis Observatory auroras have been frequently recorded, and indeed on many occasions there are very remarkable displays to be seen from the summit of that mountain. The most frequent form is a low arch of more or less elliptical form, rising not many degrees above the horizon to the north-west. On more than one occasion I have seen perfect coronas with their waving bands of streamers darting out from the zenith at times almost to the horizon. All the displays that I have seen on Ben Nevis had the streamers lighted with that lurid pale yellowish-green colour that every Arctic explorer is familiar with, but on one occasion at least there were mingled with it flashes of rosy red, which passed along the living bands. In Franz Josef Land during the winter of 1896–97 there were specially fine displays of auroras, and frequent observations were made upon them, by various members of the expedition. Armitage, who conducted