170 On the Spectrum of the Corona. 



possible, therefore, that two of the enhanced lines of iron should be 

 present without the others, even if it be admitted that the corona may 

 have a temperature high enough to produce any enhanced lines. 



It appeared then, either that the coincidences of the chromospheric 

 and coronal lines about 423 and 531 were accidental, or that they 

 were not real coincidences at all. A careful examination of the eclipse 

 photographs of 1896, taken by Mr. Shackleton, and those of 1898, 

 taken by Mr. Fowler, has therefore been undertaken, with special 

 reference to this point. 



The wave-length of the coronal ring at 4231, already published in 

 the case of the 1893 photographs, has been confirmed. 



The 1896 and 1898 photographs further indicate that the corona 

 line near 4231 is not coincident with the chromospheric line to which 

 reference has been made, and show that while the chromospheric line 

 is coincident with the enhanced line of iron at X 4233-3, the corona line 

 has a wave-length of 4231-3. 



With regard to the ring in the green, the lack of sufficient photo- 

 graphs on isochromatic plates in 1893 does not permit of a final 

 determination of wave-length. Important data, however, were 

 obtained, both in 1896 and 1898. A measurement of the position of 

 the chief ring in the green, as shown in these photographs, comparing 

 the ring with the spectrum of the chromosphere and a solar and iron 

 spectrum taken by the same prisms, shows beyond all question that the 

 wave-length is very different from that generally accepted. The mean 

 result of measurements of different parts of the ring made by Messrs. 

 Fowler and Shackleton and Dr. Lockyer is 5303*7, or about 13 tenth- 

 metres more refrangible than 1474K (5316-79). 



Although the new wave-length is not to be regarded as final, for the 

 reason that the conditions under which the photographs were taken 

 necessitate certain small corrections which have not yet been fully 

 worked out, it is not likely that it can be in error by so much as 

 1 tenth-metre. 



The examination of the photographs, which has been undertaken in 

 the first instance by Mr. Fowler, indicates that other important con- 

 clusions are to be drawn from the admirable series obtained by him, 

 among them the possible existence of one or more new gases, some of 

 the lines of which, as gathered from the dispersions as yet available, 

 appear also in the spectra of some stars and planetary nebulae. 



The photograph which accompanies this paper has been prepared by 

 Mr. Fowler. 



DESCRIPTION OF PLATE 4. 



1. Spectrum of Corona and upper Chromosphere. 



2. Spectrum of lower Chromosphere, showing that the chromospheric line at 



1474K is not coincident with the corona line. 



3. Solar Spectrum. 



