30 LIGHT SCIENCE FOR LEISURE HOURS. 



Lieutenant-Colonel Tennant at one Indian station, 

 and from Lieutenant Herschel at another, from Kayet 

 and Janssen, and from the Prussian astronomers who 

 observed the eclipse at Aden, came the same answer 

 the prominences are masses of glowing vapour. A few 

 bright-coloured lines had in an instant taught the 

 great lesson astronomers had been so long waiting for. 

 Had the coloured prominences been mountains, as some 

 had supposed, the spectroscope would have shown the 

 rainbow-tinted streak which speaks of the solid nature 

 of a source of light. Had they been clouds suspended 

 in the solar atmosphere, there would have been seen 

 the rainbow streak crossed by dark lines, corresponding 

 to that structure. But, because they consist of glowing 

 gas, the rainbow-tinted background was wanting ; and 

 only a few bright-coloured lines, corresponding to the 

 particular gases present in these mighty flames, were 

 seen along the spectral range. 



Then followed one of those strange coincidences 

 which the history of science has so often presented. 

 Janssen, one of the observers of the eclipse, was struck 

 by the thought that since the light from the promi- 

 nences is thus gathered up concentrated, so to speak 

 into a few bright lines, it might be possible to see 

 those lines even when the sun is not eclipsed. It is 

 easy to see why this might k be possible. The promi- 

 nences shine faintly when compared with the solar 

 disc ; and so, if we use darkening glasses in observing 

 the latter, we obliterate their light altogether. Nay, 

 even if we absolutely get rid of the direct sunlight, 



