CHAPTEK IX. 



MOKE RESULTS OF THE NEW METHOD. 



1. Artificial Eclipses. 



ALTHOUGH in 1866 much knowledge had been gathered con- 

 cerning the strange red prominences seen round the edge of the 

 moon in a total eclipse of the sun, they were still a mystery and 

 a source of wonder. After the spectroscope had been used to 

 help us in the study of the spots, it seemed worth while to inquire 

 whether it could also help us in other directions, for if it could 

 it was perfectly clear that we should not be contented with 

 merely observing the chemical nature of the photosphere alone. 



It did not take long to convince my friend Dr. Balfour Stewart 

 and myself, that by means of the spectroscope, the things which 

 up to that time had only been observed during eclipses, would 

 be more or less felt, if they were not absolutely rendered visible, 

 by this new instrument, if their real nature was anything like 

 what we were justified by our then knowledge in attributing to 

 them ; and for this reason : the things seen round the sun during 

 an eclipse are not there for the instant of the eclipse only : they 

 are always there : why then do we not see them ? The illumi- 

 nation of our own air prevents this. What is our own air 

 illuminated by ? By the sunlight. Now whereas increasing 

 dispersion does considerably dim a continuous spectrum for the 

 reason that it makes it extend over a much larger area, it 

 does not dim to any great extent the brightness of a line ; so 



