Oil the Spectrum of the Corona. 169 



In the course of my early observations of the spectrum of the 

 chromosphere, I discovered on June 6, 1869, a bright line at 1474 on 

 Kirchhoff's scale, which I stated to be coincident with a line of iron.* 



During the total eclipse of the sun on August 7, 1869, a green line 

 was recognised by Professor Young as belonging to the spectrum of 

 the corona, and the position of this line was also stated to be 1474K. 



Although other determinations of the position of the green line of 

 the corona during eclipses have not all agreed absolutely with Young's 

 observations, the differences have been attributed to errors of observa- 

 tion, so that Young's statement of the coincidence of the coronal and 

 chromospheric lines, and their correspondence with the solar dark line 

 at 1474K has been generally accepted. No special attention appears 

 to have been directed of late years to the measurement of the corona 

 line itself. 



This and other coronal radiations were photographed as rings by 

 the use of prismatic cameras in 1893, 1896, and 1898, but a full list of 

 them has only so far been published for the photographs taken by 

 Mr. Fowler during the eclipse of 1893.1 Among the brightest of 

 these rings, which is common to all three sets of photographs, is one 

 about wave-length 4231, which probably is identical with the corona 

 line photographed by Schuster in 1886, and stated to have a wave- 

 length of 4232-8 on Angstrom's scale (4233*4 Rowland). Schuster 

 stated that this line was "probably the same line as 4233'0 often 

 observed by Young in the chromosphere."^: The chromospheric line 

 at this wave-length has since been identified as an enhanced line of 

 iron, of which the precise wave-length is 4233*3. Captain Hills 

 photographed this corona line with a slit spectroscope in the last 

 eclipse, and he gives its wave-length as 4233'5, which within the 

 limits of error might be considered coincident with the enhanced line 

 of iron. 



The later researches on the spectrum of iron have shown that the 

 iron line which I observed in 1869 to be coincident with the bright 

 chromospheric line at 1474K (5316*79 Rowland) is also an enhanced 

 line, agreeing absolutely with Young's latest determination of the 

 wave-length of the 1474 chromospheric line,!| with which, according to 

 his eclipse observations, the green line of the corona is coincident. 



According to these results then, two of the chief lines in the 

 spectrum of the corona would be coincident with enhanced lines of 

 iron."" The remaining corona lines, which have so far been measured, 

 are not, however, coincident with enhanced lines. It did not seem 



* ' Roy. Soc. Proc.,' vol. 18, p. 76. 



f ' Phil. Trans.,' A, vol. 187, p. 593. 



J 'Phil. Trans.,' A, vol. 180, p. 341. 



' Roy. Soc. Proc.,' vol. 64, p. 54. 



|| Schemer's 'Astronomical Spectroscopy ' (Frost's translation), p. 425. 



