THE AURORA BOREALIS OF AUGUST 21.
To the Editor: I have been much interested in the account given by Dr. A. F. A. King of the unusual aurora observed by him on the twenty-first of August at York Harbor, Maine (Popular Science Monthly, Vol. LXIII., pp. 563-4), because I also observed it the same evening from a point near Baddeck, Cape Breton Island, Nova Scotia.
My attention was called to the display about 8:45 p. m., Halifax time (this would be about 7:45 p. m. by eastern standard time, which I presume is the time used by Dr. King). There was then nothing unusual about the aurora.
I went out of doors especially for the purpose of ascertaining whether any auroral arch was visible extending from east to west across the zenith; for I observed such a phenomenon here two or three years ago (but without the comet-like appendages described by Dr. King) and have been on the lookout since for its reappearance. Certainly no such arch was visible here at 8:45 p. m. on August 21, and the whole display seemed then to be on the wane. Shortly after 9:00 p. m. only a diffused glow remained in the northern sky above a bank of auroral cloud.
During the course of the night I observed the aurora occasionally to see if there was any change, but noticed nothing unusual until 12:45. The arch might have appeared between 9:00 p. m. and 12:45 without my noticing it, as intervals of at least an hour separated my observations. I can say positively that it did not appear between 12:45 and 2:30 a. m., as I was out of doors continuously watching the sky during that time. From 9:00 p. m. till after midnight I noticed nothing more than the usual faint glow in the north; but happening to glance out of the window at 12:45 I was startled by the tremendous activity then displayed. The maximum was reached about 1:00 a. m., and by 2:00 a. m. the display was practically over. At 2:30 a. m., I returned indoors and made a record of my observations, from which I quote the following extract:
. . . Looking out about 12:45 (a quarter to one a. m., Saturday) great activity was manifest. The whole northern sky was ablaze, pulsations of light streamed upwards from the horizon as though light phosphorescent clouds were being blown along by a hurricane. Upon going out I found that faint auroral clouds covered the whole sky even to the south. Faint pulsations of light in the south appeared to be streaming north while the northern streamers streamed south.
Observing attentively, there seemed to be a luminous streaming upwards from the horizon all around, converging—not at the zenith—but at a point of the sky which I should think would be opposite the sun. I was powerfully impressed by the idea that these were parallel rays directed away from the sun, rendered convergent by perspective.
At the point opposite the sun a considerable space—roughly circular in outline—seemed to be generally free from luminous cloud effects, except when a suffused glow would come and cover the space—a momentary glow without stream effect. Towards the circular space the stream effects were centrally directed all round, being most marked in the northern and northwestern sky, where the stream effects were vivid—luminous pulsations like light smoke driven by a hurricane. The stream effects were much less marked in the western, southern and eastern sky. Light glows would appear, but only by at-