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Observations on the Lines of the Solar Spectrum, and on those pro- 

 duced by the Earth's Atmosphere, and by the action of Nitrous 

 Acid Gas. By Sir DAVID BREWSTER, K. H. LL.D. F.R.S. 

 LOND. V. P. R. S. EDIN. 



(Read \5th April 1833> 



AN a paper on the Monochromatic Lamp, &c., read before this 

 Society on the 15th April 1822, and published in their Transac- 

 tions, I recorded some of my earliest experiments on the action 

 of coloured media on the Solar Spectrum. These experiments 

 were continued at irregular intervals, with the view of obtaining 

 distinguishing characters of coloured media, of investigating the 

 cause of the colours of natural bodies, and of examining more 

 correctly the phenomena of the overlapping colours of equal re- 

 frangibili ty, the discovery of which I had announced in the pa- 

 per already referred to. The results to which I was conducted 

 on the two last of these subjects, have been already communica- 

 ted to the Society in two papers, one on the Analysis of Solar light, 

 and the other on the Colours of Natural Bodies. 



The first and the principal object of my inquiries, namely, 

 the discovery of a general principle of chemical analysis, in which 

 simple and compound bodies might be characterised by their ac- 

 tion on definite parts of the spectrum, still remained to be inves- 

 tigated. The coloured juices of plants artificial salts and their 

 solutions, and various glasses and minerals had afforded me 

 many beautiful examples of this species of action, and after deter- 

 mining the locality of these actions in reference to FRAUNHOFER'S 



