A. MATHEMATICS AND ASTKONOMY. 15 



Angstrom, made several years since, he being the pioneer in 

 this field. He announced that the light of the aurora was 

 almost monochromatic, showing in the spectroscope only a 

 single bright line in the yellow-green. This conclusion was, 

 however, contradicted by Professor Winlock, who found a 

 number of other lines, especially when the aurora was bright. 

 We have lately received a very fine list of spectroscopic 

 observations made by Dr. Vogel at the observatory of Both- 

 kamp. He finds that the fainter auroras show only Ang- 

 strom's line, of which the wave length is 557, the measures 

 being very exact. On the other hand, when the auroras be- 

 came brighter, a number of other lines showed themselves. 

 At one time, in the brightest part of the aurora, he succeeded 

 in measuring five different lines in the green of the spectrum, 

 as well as a somewhat diffuse line or band in the blue. In 

 the red part the spectrum showed seven or eight bright lines. 

 The following lines are well determined, four measures being 

 made on each : 



Wave length. 

 463-469. A bright band ; brighter in the centre. 

 500.3. Tolerably bright line. 

 518.9. Sometimes quite bright. 

 513.3. A quite bright line. 

 538.2. An extremely faint line. 



556.9. The brightest line in the spectrum (Angstrom's). 

 629.7. Bright streaks. 



From researches on the spectra of the gases forming the 

 atmosphere, and their comparison with the spectrum of the 

 aurora, Dr. Vogel considers it very probable that the spec- 

 trum of the aurora is only that of atmospheric air, modified 

 by temperature and pressure. 



The auroral lines have also been observed by Professor 

 Barker, of Yale College. Directing his spectroscope toward 

 a brilliant streamer, he saw five bright lines, of which the 

 wave lengths were about 623, 562, 517, 502, and 482. All 

 except the first and last are probably coincident with the 

 corresponding ones in the preceding list of Dr. Vogel. 



The brilliant aurora of February 4 last afforded a fine op- 

 portunity for spectroscopic observation, of which a large 

 number of amateur observers in Great Britain took advan- 

 tage. The only satisfactory measurements seem to have been 

 made by Professor C. Piazzi Smyth, Astronomer Royal for 



