GRADUAL DISCOVERT OF SPECTRUM ANALYSIS. 179 



Fox Talbot, W. H. Miller, W. A. Miller, Draper, Stokes, 

 Swan, Wheatstone, Van der Willigen, Masson, Crookes, 

 and others. In 1822, the prism was first employed by 

 Brewster to examine coloured flames. In 1826, Fox 

 Talbot examined by means of the prism the spectra of 

 burning salts, and proposed the prism in place of ordinary 

 chemical analysis as a means of detecting substances. In 

 1832 Brewster discovered the dark absorption-bands pro- 

 duced by coloured gases. In 1835 Wheatstone examined 

 the spectra of various highly heated metals, and says he 

 ' found the appearances so different, that by this mode of 

 examination the metals may be readily distinguished from 

 each other.' Angstrom, in 1855, comparing the solar 

 spectrum with that of the electric arc, said : ' Regarded as 

 a whole, they produce the impression that one is a rever- 

 sion of the other. I am therefore convinced that the 

 explanation of the dark lines in the. solar spectrum em- 

 braces that of the luminous lines in the electric spectrum.' 

 The great discovery was now near, and this remarkable 

 prediction was in a few years afterwards completely veri- 

 fied. In 1857 Swan detected as small a quantity as 

 of a grain of sodium by means of spectrum 



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analysis. And finally in 1859 and 1860 KirchofF and 

 Bunsen showed how by means of the prism the compe 

 sition of the Sun and other distant luminous bodies might 

 be determined. Since then, by the labours of Huggins, 

 Lockyer, W. H. Miller, Jannsen, Thalen, Roscoe, Secchi, 

 and others, the discovery has been extended so as to 

 determine the composition of some of the fixed stars, 

 comets, and distant nebulae ; and five new elementary 

 bodies, viz., thallium (by Crookes), rubidium and caesium 

 (by Bunsen), indium (by Reich and Richter), and gallium 

 (by Boisbaudran), have been discovered by the same 

 method. 



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