316 HISTORY OF CHEMISTRY. [LECTURE xv. 



Other important investigations are those of Horstmann 98 on 

 the incomplete combustion of carbonic oxide and of hydrogen ; 

 that on the partial decomposition of ferrous salts by water, 

 which G. Wiedemann " carried out by the aid of a magnetic 

 method ; and that on the ratio of the distribution of acids 

 between two alkaloids, which Jelett 100 ascertained by deter- 

 mining the optical rotatory power. But it is not possible 

 to enter more particularly here into these and many similar 

 researches. 101 



To a certain extent in contrast with these investigations, 

 which are chiefly theoretical, there is the discovery of a method 

 of investigation which may certainly be regarded as one of the 

 most brilliant that has been brought forward in recent times as 

 the result of experimental research. I refer to the method of 

 spectrum analysis, which has enabled us to draw conclusions 

 regarding the chemical composition of distant heavenly bodies 

 whose material constitution was previously altogether unknown, 

 and by the aid of which the number of the known elements 

 has been very considerably increased. 



It would take too much space to deal with the early re- 

 searches prior to the classical investigations of Kirchhoff and 

 Bunsen ; 102 and therefore. I refer, with respect to these, to the 

 historical treatment of the subject by Mousson, 103 to some 

 notices by Tyndall, 104 and especially to a paper by Kirchhoff, 105 

 which deals with them. I must content myself by simply 

 making a few remarks on the matter here. 



Wollaston, in 1802, first observed the dark lines in the 

 spectrum of the sun. 10ti These were more fully examined and 

 determined in 1814 by Fraunhofer, 107 to whom Wollaston's 



98 Annalen. 190, 228. " Wiedem. Ann. 5, 45. 10 Trans. Roy. 



Irish Acad. 25, 371. 101 Compare the article " Affinitat " by E. Wiede- 

 mann, in Ladenburg's Handworterbuch der Chemie. I, 114. 10 ' 2 Pogg. 

 Ann. HO, 161 ; 113, 337 ; compare also Kirchhoff, Berlin Akad. Abhandl. 

 1861, 63 ; Untersuchungen liber das Sonnenspectrum und die Spectren 

 der chemischen Elemente. loa Connaissances sur le spectre ; Bibl. 

 Univers. de Geneve [2] 10, 221. 104 Phil. Mag. [4] 22, 155. 105 Pogg. 

 Ann. 118, 94. 10(i Phil. Trans., 1802, 378. 107 Gilb. Ann. 56, 278. 



