728 THE AUROEA BOEEALIS. 



patches or coronce of TV'liite light with streamers stretching 

 upwards from them. 



The spectra were observed by Mr. Alvan Clark in America, 

 and in England by Mr. H. E. Procter, who observed a red line 

 in the spectrum. These displays were accompanied by great 

 magnetic disturbances, and by remarkable Earth-currents both in 

 England and also on the Madras-Bombay lines in India. 



Another brilliant display was seen at 6.30 p.m. and again at 

 7 p.m. on Dec. 19, 1870, in the Mediterranean, on the east coast 

 of Sicily. Towards the north, north-east, and east brilliant pink 

 streamers shot up out of a bank of faint hazy light on the horizon. 

 The planet Jupiter was clearly seen through some of the most 

 brilliant streamers. The sky became covered with a pinkish- 

 mauve colour. Toward the west a pale, steady white light, the 

 zodiacal light, was clearly seen during the evening. This dis- 

 play was followed in Sicily by a falling barometer and very stormy 

 winds, with thunder and lightning, and by very destructive storms 

 in Italy, causing the overflow of the Tiber and the flooding of 

 the city of Rome to a depth which had been scarcely ever known.] 



16. The Spectrum of the Aurora Borealis. 



The following account of Professor Angstrom's paper on this 

 subject is taken from " Nature," Vol. 10, No. 246 (for July 16, 

 1874) :— 



*' It may be assumed that the spectrum of the aurora is composed 

 of two different spectra, which, even although appearing some- 

 times simultaneously, have in all probability different origins. 



" The one spectrum consists of the homogeneous yellow light 

 which is so characteristic of the aurora, and which is found even 

 in its weakest manifestations. The other spectrum consists of 

 extremely feeble bands of light, which only in the stronger auroras 

 attain such an intensity as enables one to fix their position, though 

 only approximatively. 



" As to the yellow lines in the aurora, or the one-coloured spec- 

 trum, we are as little able now as when it was first observed to 

 point out a corresponding line in any known spectrum. True 

 Piazzi Smyth {Cowptes Rendus, Ixxiv., 597) bas asserted that it 

 corresponds to one of the bands in the spectrum of hydrocarbons ; 

 but a more exact observation shows that the line falls into a group 

 of shaded bands which belong to the spectrum, but almost midway 

 between the second and third Herr Vogel has observed that this 

 line corresponds to a band in the spectrun^i of rarefied air (Pogg. 

 Ann.,cxlvi., 582). This is quite right, but, in Angstrom's opinion, 

 is founded on a pure misconception. The spectrum of rarefied 

 air has in the green-yellow part seven bands of nearly equal 

 strength ; and that the auroral line corresponds with the margin 

 of one of these bands, which is not even the strongest, cannot be 

 anything else than merely accidental. 



" Observations on the spectrum have not hitherto agreed with 

 each other ; partly, perhaps, because of the weak light of the 



