122 LIGHT SCIENCE FOR LEISURE HOURS. 



truth, appertains to the iron spectrum, implies the 

 existence of the glowing vapour of iron ; and heat of 

 great intensity is required to vaporise iron. It is, 

 however, possible that electrical discharges may be in 

 question. We know, indeed, that the aurora is an 

 electrical phenomenon, although we do not as yet know 

 exactly how the electrical action is caused, or what its 

 nature may be. We should certainly find many diffi- 

 culties obviated if we extended the same explanation 

 to the solar corona, since many of the phenomena 

 which it presents are strikingly suggestive of electrical 

 action. Viewing the green light in this way, and not 

 venturing at present to determine the precise manner 

 in which electrical action is excited, we should be led 

 to recognise the presence of iron in the corona, the iron 

 not being in the state of vapour, but giving the vapour 

 spectrum of iron on account of the electrical discharges 

 continually taking place between the particles of solid 

 or liquid iron. It might even be that the hydrogen 

 lines from the corona may be referred to electrical 

 action, and not to the actual heat of the hydrogen 

 present throughout the inner corona. In this way we 

 may obviate a difficulty referred to above when the 

 sierra was described. We may regard the sierra as the 

 region where the sun's hydrogen atmosphere actually 

 glows with the intensity of its own heat ; and the inner 

 corona as the region where the same atmosphere is 

 traversed by continual electrical discharges, which 

 cause the bright lines of the hydrogen to be recognised 

 by our spectroscopists, though not with the same 



