July 2 1, 1881] 



NATURE 



267 



SOLAR PHYSICS— THE CHEMISTRY OF THE 



SUN"- 

 I. 

 THEN we have familiarised ourselves with the general pheno- 

 mena presented to our notice by the analysis of the light 

 proceedmg from different sources, and wish to apply this know- 



W^ 



I 



Fig 1. — Steinheil's form of four-pn: 



employed to suggest the extreme probability of the existence of 

 sodium in the atmosphere of tlie sua, and the probability, 

 therefore, that the dark line D, which we see in the spectrum, was 

 caused by the absorption, by the cooler sodium vapour, of light 

 proceeding from the solar nucleus which was hotter than the 

 vapour; might be applied to other substances, such as iron, 

 cobalt, nickel, and s ) on ; and that if these were 

 experimented ou in the same manner, other of the 

 dark lines in the solar spectrum might be ex- 

 plained. 



Now I propose, in the first instance, to show 

 what Kirchhoff saw, and what he did— his manner 

 of work. Kirchhoff, and after him Angstrom and 

 Thalen, to whom further reference will be made 

 presently, used spectroscopes placed close or nearly 

 close to the source of light. Kirchhoff's work was 

 done by a spectroscope of this model. We have 

 a slit and collimating lens, a train of prisms, which, 

 of course, during the observations are carefully 

 covered up, and the observing telescope. This in- 

 strument may be turned to the sun, or to a cloud 

 illuminated by the sun in case the quantity of light 

 which enters the instrument when turned directly 

 towards the sun is too great to allow of easy ob- 

 servation ; or light from the sun or a cloud may be 

 reflected into the instrument by a mirror. Kirchhoff 

 was enabled by means of properly contrived measur- 

 ing apparatus to map down the positions of the 

 lines observed. 



Let us see, first of all, what kind of thing 



Kirchhoff saw. To give an idea of this I propose 



ing telescope, to throw on the screen photographs of that portion 



of the spectrum which is not so readily observable 



ledge to the study of the sun, the first work to which attention | as that upon which Kirchhoff began his work. Here then is an 

 must be given is a very admirable memoir of Kirclihoff (1861).' | absolutely untouched photogi'aph of a part of the solar spectrum 



in the blue and violet (Fig. 2). We get in great pro- 

 minence in the spectrum two very thick lines, which 

 are called II and K, the precise poiition of which 

 in the solar spectrum are shown by means of the 

 diagram of the spectrum (Fig. 3). By moving his 

 observing telescope along the spectrum, as it were, 

 the telescope being furnished with a delicate micro- 

 meter, or some projierly-contrived means for defin- 

 ing the exact position of each line, Kirchhoff was 

 in that way able to prepare a map of the whole 

 spectrum. Indeed he did prepare this map with 

 , the object of providing himself with a scale of ex- 

 treme value f jr the future work which he then laid 

 out for hiaiself. The future work being this : — he 

 In this, after referring to the prior work of Fraunhofer. and other-, I wished to determine the positions of the bright lines given by 

 lie goes on to show that the same principles w hich had then been the different chemical elements ; having got this information, he 



:. — C'lpy of a [holograph of the solar spCi 



f the lliick calc 



R QPO N ML m\ 7i G 



6 E 



ai^ 



X,X, IT p 



I I I I I I I T— 1 



:xi= 



^^ 



Fi(j. 3. — Wa\e-Iength map of the solar spectrum, including the infra-red. 



wished to put the same question to the solar spectrum with 



' Lectures in the Course on Solar Physics at South Kensington (see p. 150). 

 Revised from shorthand notes. The first lecture is omitted, as it dealt with 

 the general principles of spectrum analysis. 



~ " Researches on the Solar Spectrum and the Spectra of the Chemical 

 Elements." Transactions of the Berlin Academy for i86r. Translation by 



Prof. Roscoe (Ma 



1862). 



regard to each of those elements as already had been done in 

 the case of sodium. How then d.d he propose to do this? He 

 made an addition to the slit of the spectroscope, such as was then 

 employed. He put a prism in front of it, by means of which he 

 illuminated one half of the slit with the direct light of the sun, 

 and the [other half with the light from the vapour employed 



