328 NINETEENTH CENTURY. pt. in. 



gases do which we bum here on earth. If you compare the 

 spectrum of sodium (No. 3), or of hydrogen (No. 4), with the 

 nebula spectrum (N0.6), you will see at once that the nebula 

 spectrum is made by a gas, and so the truth of Sir W. 

 Herschel's idea was proved, and there can be now no doubt 

 that some of the nebulae are composed of gaseous matter ; 

 chiefly, so far as we can learn, of nitrogen and hydrogen. 



Mr. Alexander Herschel examines the Spectrum of 

 Fallingc Stars. — I have said that it was difficult to examine 

 the spectrum of the stars and nebulae, but something which 

 to an ordinary observer seems still more wonderful has been 

 lately done. Mr. Alexander Herschel has actually caught the 

 light oi falling stars in the spectroscope, and in this way has 

 discovered that some of them give a continuous spectrum, 

 showing that they are solid bodies, while others give a gas 

 spectrum, on which are the bright lines of potassium, sulphur, 

 and phosphorus, but chiefly of sodium. 



Such wonderful facts as these about far-distant suns and 

 sun-matter, we have learnt, and are still learning by means 

 of spectrum analysis. The whole study was only begim 

 fifty years ago, and it is in the works of living men that 

 you must look for the details of its history. But though 

 many eminent names are connected with it, those of Fraun- 

 hofer and Kirchhoff should always be remembered as the 

 chief founders of the science. 



Chief Works consulted. — Roscoe's * Spectrum Analysis ; ' * Edin- 

 burgh Review,* vol. cxvi, ; * Philosophical Magazine,' i860; Proctor, 

 * The Sun ;' Tyndall's * Lectures on Light ; ' * Half-hours with Modern 

 Scientists;* Kirchhoff 's 'Researches on the Solar Spectrum,* 1862; 

 'Encyclopaedia Britannica,' art. 'Optics;* Ganot's 'Physics;* Wol- 

 laston, ' On Dispersion ' — 'Phil. Trans.' 1802; Lockyer, * The Spec- 

 troscope.* 



I 



