228 The Eclipse of Last December. [April, 



moon has concealed the whole of the sun's disc. The 

 views of astronomers and physicists respecting this striking 

 appearance had been growing gradually clearer, one theory 

 after another being disposed of until certain very definite 

 issues alone remained to be considered. The theory that 

 the glory is a lunar phenomenon had been rejected because 

 modern observations prove so conclusively that the moon 

 has not an atmosphere of appreciable extent. So, also, the 

 theory that the corona is due to the diffraction of the solar 

 rays as they pass by the moon, had been shown to be erro- 

 neous. But another theory which seemed much more 

 worthy of support had also been successfully oppugned : 

 the fact that all round the sun a glory of bright light 

 appears when the sun's disc is concealed, suggests, on the 

 face of it, that the sun has an atmosphere of great extent, 

 either self-luminous or brilliantly illuminated by the sun 

 himself. This view had been supported by astronomers of 

 eminence, despite certain difficulties which it undoubtedly 

 presents ; but recent researches had caused grave doubts 

 to be cast upon this imagined solar atmosphere. Let us 

 briefly consider the nature of these researches. 



The coloured prominences which are seen around the sun 

 during total eclipse had been shown to be gaseous, a chief 

 element in their constitution being the gas hydrogen. The 

 coloured sierra, too, which appears at a lower level — that is, 

 closer to the sun — had been found to be as its appearance 

 implied, almost identical in structure. During the spectro- 

 scopical examination of these objects, peculiarities of 

 appearance had been noted in their characteristic bright 

 lines which seemed to throw important light upon their 

 nature, and, indeed, on the general habitudes of the solar 

 atmosphere. The peculiarity which now specially concerns 

 us is this, that the spectrum, though undoubtedly indicating 

 an increase of pressure with approach to the sun's surface, 

 yet by no means indicated such an increase as was to have 

 been expected if the sun has an atmosphere of considerable 

 extent. The researches of Plucker, Hittorf, Frankland, and 

 Huggins had shown that the spectrum of hydrogen varies 

 according to the circumstances of pressure and temperature 

 under which the gas subsists ; and the widening of the 

 hydrogen lines had come to be regarded as in a special 

 manner indicative of increase of pressure. Mr. Lockyer to 

 whom Frankland exhibited the spectrum of hydrogen under 

 varying conditions, found thus a new significance in the 

 observations made at the telescope. He found that, so far 

 as the evidence of the laboratory experiments could be 



