Analysis' by Spectrum-observations, 107 



chemical properties as unalterable as the combining weights 

 themselves,, and which can therefore be estimated with an almost 

 astronomical precision. The fact, however, which gives to this 

 method of spectrum- analysis an extraordinary importance is, that 

 the chemical reactions of matter thus reach a degree of delicacy 

 which is almost inconceivable. By an application of this method 

 to geological inquiries concerning the distribution and arrange- 

 ment of the components of the various formations, the most 

 valuable results may be expected ; even the few random experi- 

 ments already mentioned have led to the unexpected conclusion, 

 that not only potassium and sodium, but also lithium and stron- 

 tium must be added to the list of bodies occurring, only indeed 

 in small quantities, but most widely spread, throughout the 

 matter composing the solid body of our planet. 



The method of spectrum-analysis may also play a no less im- 

 portant part as a means of detecting new elementary substances ; 

 for if bodies should exist in nature so sparingly diffused that the 

 analytical methods hitherto applicable have not succeeded in 

 detecting, or separating them, it is very possible that their 

 presence may be revealed by a simple examination of the spectra 

 produced by their flames. We have had opportunity of satis- 

 fying ourselves that in reality such unknown elements exist. We 

 believe that, relying upon unmistakeable results of the spectrum- 

 analysis, we are already justified in positively stating that, besides 

 potassium, sodium, and lithium, the group of the alkaline metals 

 contains a fourth member, which gives a spectrum as simple 

 and characteristic as that of lithium — a metal which in our ap- 

 paratus gives only two lines, namely a faint blue one, almost 

 coincident with the strontium line Sr S, and a second blue one 

 lying a little further towards the violet end of the spectrum, and 

 rivalling the lithium line in brightness and distinctness of out- 

 line. 



The method of spectrum-analysis not only offers, as we flatter 

 ourselves we have shown, a mode of detecting with the greatest 

 simplicity the presence of the smallest traces of certain elements 

 in terrestrial matter, but it also opens out the investigation of 

 an entirely untrodden field, stretching far beyond the limits of 

 the earth, or even of our solar system. For, in order to examine 

 the composition of luminous gas, we require, according to this 

 method, only to see it ; and it is evident that the same mode of 

 analysis must be applicable to the atmospheres of the sun and 

 of the brighter fixed stars. A modification must, however, be 

 introduced in respect to the light which these heavenly bodies 

 themselves emit. In a memoir published by one of us*, "On 



* Kirchhoff, Poggendorff's Annalen, vol. cix. p. 275 ; and Phil. Mag. 

 S.4, vol. xx. p. 1. 



1% 



