Aurora Display and Magnetic Disturbance

Abstract

ON Saturday evening, Dec. 20, at about 18 h. 35 m., I noticed that the sky was strongly illuminated along the northern horizon, the light extending about 40° in azimuth, with its centre, as near as could be estimated from the position of the pole star, true north, and a maximum altitude of about 15°. It was at once suspected as an auroral arch, but as the magnetic curves which had come off that morning showed the magnetic conditions to be exceptionally quiet, some doubt was felt as to the auroral character of the light. A suspicion was entertained that it might be due to the illumination of a sheet of very high cloud, though the sun was far below the horizon. This, however, appeared unlikely, both from the length of time after sunset and from the fact that there was no illumination over the western or north-western horizon.