April 6, 1899] 



NA TURE 



537 



Wonderful anomalies were at once detected, lines 

 known to belong to the same chemical element behaved 

 differently in several ways. Some were limited to spots, 

 others to prominences, and in solar storms different iron 

 lines indicated different velocities. In the spectrum of 

 the hottest part of the sun open to our inquiries, the 

 region namely immediately overlying the photosphere 

 which I named the chromosphere the anomalies became 

 legion ; suffice to say that in the hottest part of the sun 

 we could get at, the spectrum of iron then represented in 

 Kirchhoff's map by 460 lines in the ordinary solar 

 spectrum was reduced to three lines. 



temperatures than those previously employed were doing 

 for chemistry what previous similar inquiries had done ; 

 namely, indicating the existence of finer constituents in 

 matter supposed at each point of time to be elementary. 



This was the first glimpse of dissociation in relatiort 

 to the production of changes in the line spectrum. 



15y the year 1S72 the work of Rutherfurd and Seccht 

 on stellar spectra enabled the base of the inquiry to- 

 include the stars as well as the sun. In some of the stars 

 the existence of hydrogen, magnesium and carbon were 

 beyond question. The point that first struck me was that 

 in white stars like a. Lyra' and .Sirius, with continuous 



Fig. 4.— The long and short hi 



Copy of a photograph taken with .t vertical slit when ( 

 volatilised between horizontal carbon poles. 



It was no longer a question merely of settling the 

 difficulties raised by the observations of Pliicker and 

 Hittorf. 



Many observations and cross references of this kind 

 during the next few years convinced me that the view 

 that each chemical element had only one line spectrum 



Fic. 5.— The longs and shorts of sodium taken under the same 

 conditions, showing that the orange line extends furthest from 

 the poles. 



was erroneous, and that the results obtained suggested 

 that the various terrestrial and solar phenomena were 

 produced by a series of simplifications brought about 

 by each higher temperature employed. That is, that 

 the new instrument, the spectroscope, showed that higher 



NO. 1536, VOL. 59] 



spectra extending far into the violet — stars therefore 

 hotter than their fellows of a yellow or red colour — we 

 had to do with hydrogen almost alone. 



It was in 1873 that I first called the attention of the 

 Royal Society to the very remarkable facts which had even 

 then been brought together regarding the possible action 

 of heat in the sun and stars. Referring more especially 

 to the classification of stars by Rutherfurd, I wrote as 

 follows : 1 



" I have asked myself whether all the above facts can- 

 not be grouped together in a working hypothesis which 



Fig. 6. — Spectrum of a sun-spot as compared with the' general 

 spectrum, showing that certain metallic lines (sodium and 

 calcium in this instance) are widened. The darker portion 

 represents the spectrum of the spot. 



assumes that in the reversing layers of the sun and stars 

 various degrees of ' celestial dissociation ' are at work, 

 which dissociation prevents the coming together of the 

 atoms which, at the temperature of the earth and at all 

 artificial temperatures yet attained here, compose the 

 metals, the metalloids, and compounds." 



Subsequently in a private letter to M. Dumas, who took 

 the keenest interest in my solar work, I wrote," II semble 

 que plus une dtoile est chaude plus son spectre est 

 simple." 



1 Phil. Trans. ^ vol. clxiv. part 2, p. 49J. 



