CHAP. IV.] THE SUN'S CHROMOSPHERE. 39 



researches I traced it to iron. From that day to this we have observed 

 a large number of lines. 



But useful as the method of observing the chromosphere without 

 an eclipse, which enables us 



" . . . to feel from world to world," 



as Tennyson has put it, has proved, we want an eclipse to see it face to 

 face. 



During the eclipses of 1893, 1896, and 1898, a tremendous flood of 

 light has been thrown upon it by the use of large instruments con- 

 structed on a plan devised by Kespighi and myself in 1871. These 

 give us images of the chromosphere painted by each one of its radia- 

 tions, so that the exact locus of each chemical layer is revealed. One 

 of the instruments employed during the Indian eclipse lias also been used 

 in photographing metallic spectra and the spectra of stars, so that it is 

 now easy to place photographs of the spectra of the chromosphere ob- 

 tained during a total eclipse, and of the various metals and stars side 

 by side. 



As in the case of the photographs taken with the prismatic cameras 

 in 1893 and 1896, the spectrum of the chromosphere in 1898 is very 

 different from the Fraunhofer spectrum, so that we have not to deal 

 with a mere reversal of the dark lines of ordinary sunlight into bright 

 ones. 



Many very strong chromospheric lines, the helium lines for example, 

 are not represented among the Fraunhofer lines, while many Fraunhofer 

 lines are absent from the chromospheric spectrum (Fig. 23). 



But the most remarkable result is that in the eclipse photograph of 

 the chromosphere spectrum, the most important of the metallic lines 

 are precisely those included in the " test-spectrum " (Fig. 22). This 

 photograph in fact deals chiefly with the enhanced metallic lines. 



I recognise in this result a veritable Rosetta stone, which will 

 enable us to read the terrestrial and celestial hieroglyphics presented 

 to us in spectra, and help us to study them and get at results much 

 more distinctly and certainly than ever before. The result proves 

 conclusively that the absorption in the sun's atmosphere which pro- 

 duces the Fraunhofer lines is not produced by the hottest lowest 

 stratum, the chromosphere. 



It is imperative in order to clear the ground for the future study 

 of stellar spectra, to inquire fully into the true locus of absorption. 

 One of the most important conclusions we draw from the Indian 

 eclipse is that, for some reason or other, the lowest hottest part of the 

 sun's atmosphere does not write its record among the lines which build 

 up the general spectrum so effectively as does another. 



