THE AURORA AND THE SPECrROSCOPE. 321 



always had strange chai'ms for men of thoughtful mind. And gradually a. 

 series of laborious researches had revealed the laws which associate this 

 beautiful apparition with disturbances affecting the economy of our who^e 

 earth, and not indistinctly connected with the habitudes of the solar system 

 itself. But recently a discovery has been made which is even more remark- 

 able than any which had before rewarded the labours of physicists — a dis- 

 covery at once instructive and perplexing, revealing a bond of union between 

 the aurora and a phenomenon hitherto thought to be quite different in 

 character, but leaving us still to learn what the exact nature of that bond 

 of union may be. We had occasion recently to point out that a sudden 

 disturbance in the sun in 1859 had been presently followed by intense 

 magnetic action, the whole electric system of the earth quivering, so to speak» 

 under the influence of the solar forces educed by the disturbance. And 

 we mentioned that amongst the signs of this magnetic action brilliant dis- 

 plays of the auroral streamers had been witnessed in both hemispheres on 

 the night following the solar disturbance. This circumstance teaches us 

 the true character of the aurora as strikingly as any which astronomers 

 and physicists had patiently been gathering together during the past half 

 century. We learn at once that a relation subsists between the aurora, 

 terrestrial magnetism and the central luminary of our scheme. When our 

 skies are illuminated by the magic streamers, we may be sure that those 

 of Venus and of Mars, of Jupiter and of Saturn, nay, even the skies of those 

 unseen orbs which travel far out in space beyond the paths of Uranus and 

 Neptune, are lit up with auroral displays. When once it has been shown 

 that we owe our auroras to solar action, we recognise the cosmical character 

 of the display, and that, in a sense, the terrestrial magnetism on which it 

 depends is a bond of affinity between our earth and its sister orbs. The 

 auroral lights are undoubtedly to be ascribed to electric action taking place 

 at a very considerable height, where the air is very rare indeed. It became, 

 therefore, a question whether anything could be learned by analysing the 

 auroral light, as the condition of that particular part of our atmosphere in 

 which the electric action takes place. Spectroscopic analysis, that strange 

 and powerful mode of research which has revealed so many unlooked-for 

 facts, was accordingly applied to the light of a brilliant aurora. The result 

 was rather surprising. Instead of a rainbow-coloured streak of light, such 

 as would have appeared if the aurora were due to the existence of particles 

 excited to luminosity by electric action, a single line of coloured light 

 appeared. This indicated that the light is due to the incandescence of some 

 gas through which the electric discharges in upper air take place. But 

 this was not the circumstance which attracted surprise. Rather, this was 

 to have been looked for. It was the ])osition of the line which astonished 

 our physicists. If the gas had been one which chemists are acquainted 

 with, the bright line would have occupied the position proper to that gas, 

 and would at once have indicated its nature. But there is no known ele- 



