March : 



1918] 



SCIENCE 



291 



versity since 1911 (of zoology and animal 

 biology at the College since 1905) ; Mr. 

 Francis Lydall, 13th Wrangler; special lec- 

 turer on Advanced Electrical Engineering 

 at the College, 1910-14. 



DISCUSSION AND CORRESPONDENCE 



THE AURORA BOREALIS 



The most extensive and brilliant aurora 

 witnessed in central Illinois within the mem- 

 ory of living men attracted unusual attention 

 on the evening of March 7, 1918, at Urbana, 

 Illinois, in lat. 40° 6' N., long. 88° 13' W. 

 Although the aurora is only rarely visible here 

 at all, this one reached beyond the zenith. 



The aurora first attracted my attention at 

 9 :25 P.M., central time, in the form of a band 

 of white light about 2° wide, extending in an 

 arc from a point on the horizon at about 

 N. 45° W. across the north sky, reaching a 

 maximurai altitude of about 20°, approximately 

 due north, and descending at about N. 45° E. 

 Through and beyond this, radiating white 

 bands extending upward, and two rosy areas 

 of about the color of the strontium flame ap- 

 peared, one about N. 45° E. and 20° above the 

 horizon, the other about N. 10° W. and 25° or 

 30° above the horizon. 



The illuminated area extended rapidly, 

 reaching a maximum at about 9 :45 p.m., 

 when it included the entire north half of the 

 sky and overlapped into the south half from 

 horizon to zenith. The main framework con- 

 sisted of streamers of white light converging 

 toward a point 30° or more south of and below 

 the zenith. These streamers rose vertically 

 from the north point of the horizon and its 

 vicinity, but those rising from the east and 

 west points of the horizon were inclined about 

 20° from the vertical (toward the south). 



The streamers were fairly steady, in large 

 part, extending, multiplying, and fading grad- 

 ually; but in many parts of the sky there was 

 a nearly continual play of light, in pulsations 

 proceeding swiftly upward along the rays. 

 Occasionally a streamer or a group of stream- 

 ers brightened suddenly, giving an effect like 

 that of the throwing on of a great searchlight. 



Against the background of white streamers 



the red color expanded in glowing patches, in- 

 creasing in brilliance as in area. During the 

 maximum brilliance and extent of the aurora, 

 the red was bright from the due east to the 

 due west vertical circles and beyond them, 

 and especially nfear the zenith (just below it 

 to the north). It was never a continuous 

 sheet of uniform brightness, but appeared 

 brightest in roundish patches, locally streak- 

 ing out parallel to the white streamers. The 

 red lights pulsated and played up and down 

 over the skj' like the white. 



About 9 :50 p.m., after the aurora had faded 

 slowly for a few minutes, the white streamers 

 shortening to an altitude of 45° or less, the 

 red light concentrated again in two patches, 

 one about N. 45° E. and 20° above the horizon, 

 the other N. 5°-10° W. and 25°-30° high. 

 They varied from 3 to 10 degrees or more in 

 diameter. About 9 :55 a third bright red area 

 appeared, about N. 40° W. and 20°-25° above 

 the horizon. It was less perfectly circular than 

 the other two, having a tendency to show 

 brightest and to expand along lines parallel 

 to the white streamers. 



About 10:05 p.m. the N. 40° W. and N. 

 45° E. red areas faded out, leaving a single 

 glowing patch N.-IST. 10° "W. and 20°-25° 

 above the horizon, which continued to pulsate 

 faintly and grow weaker. The white light 

 had now subsided to a rather uniform sector 

 of the north sky reaching from about N. 50° 

 W. to about N. 50° E. and from the horizon 

 to an arc whose maximum altitude lay in the 

 site of the red patch in the north. At 10:45 

 P.M. there was still a glow in the north sky, 

 apparent to an altitude of over 5°. 



The angles here given were estimated, as I 

 imfortunately had no instruments available at 

 the time. C. W. Tomlinson 



University of Illinois 



On the evening of Thursday, March 7, a re- 

 markable auroral display was visible here. 

 Some observers report a faint red glow in the 

 eastern sky as early as seven o'clock, and it 

 would appear from the testimony of several 

 observers that the phenomena increased in 

 brilliancy until about 9:45, at which time it 



