Photographs of Aurora

Abstract

ATTEMPTS to measure the height of aurora were made prior to the end of the eighteenth century, and have been repeated at intervals since that date. The most direct method is obviously to determine the parallax as given by synchronous observations at two stations a sufficient distance apart. In the case of the earlier attempts to apply this method, it was Only by the merest accident that observations would have been taken simultaneously, and even in that event it was improbable that the same point would have been selected for observation. Thus it was impossible to feel any great confidence in the older results, though, as a matter of fact, some of them were probably not far wrong. After the invention of the telephone, it became possible for two observers a sufficient distance apart to make simultaneous observations with theodolites, hut some uncertainty necessarily prevailed as to the identity of the points selected for observation. Observations made in this way at Godthaab, in Greenland, with a 5.8-kilometre base, discussed by Prof. Paulsen thirty years ago, gave for the lower edge of aurora heights varying from 0.6 to 67.8 km., the average being only some 20 km. At Godthaab, however, the parallax was too small to measure in some 20 per cent. of the cases.