THE ECLIPSE OF 1871. 113 



to the spectrum of the gaseous solar surroundings. 

 How is the observer to tell, when he obtains these 

 bright lines from any given part of the corona, that 

 they actually belong to that part of the corona and 

 not to the light of the sky ? 



Now Professor Young, in December 1870, dealt 

 with this difficulty in a very subtle and masterly 

 manner. I have already mentioned two different 

 ways in which spectroscopic analysis can be applied. 

 In one we are analyzing the light from a considerable 

 range of space, in the other we study only that light 

 which comes from a certain definite direction. Pro- 

 fessor Young, who had applied both methods to the 

 shallow complex atmosphere, applied both, with similar 

 success, to the inner corona. Let us suppose that by 

 the former method the whole of the region of sky 

 occupied by the inner corona was supplying light for 

 the spectroscope to analyze ; and that by the latter 

 only a fine linear strip from the brighter part of the 

 inner corona was being analyzed. Then clearly and 

 without entering into niceties of detail, if the bright 

 line spectrum we are considering belongs in reality to 

 the inner corona, we should find the true coronal lines 

 relatively much brighter by the former method than 

 by the latter. For in the former there is the great 

 extent of the inner corona to compensate the feebleness 

 of its inherent luminosity, in the latter there is no 

 such compensation. 



Carefully studying the relative brightness of the 

 suspected coronal lines, when the two methods of 

 HI. I 



