ADVANCE OF ASTRONOMY. 217 



disguise or modify their spectrum, or they may per- 

 haps be " dissociated " into more elementary forms 

 of matter. 



In short, the date 1859 or 1860 marks the widen- 

 ing of astronomy from being a science descriptive 

 of movements to be also a science descriptive of the 

 chemical constitution and changes of the heavenly 

 bodies. 



Extension to the Stars. There is no greater 

 triumph of scientific analysis than that by which a 

 minute beam of sunlight has been made to disclose 

 the chemical constitution of the sun's atmosphere, 

 and this, as we have seen, was the first general result 

 of the application of the spectroscope to astronomy. 

 But what can be done with sunlight can also be done 

 in some measure with starlight, and the application 

 of the spectroscope to the stars has been one of the 

 characteristic features of the astronomical work of 

 the second half of the nineteenth century. 



As early as 1814, Fraunhofer observed that the 

 dark lines of stellar spectra, though sometimes agree- 

 ing with those in the sun's spectrum, were oftener 

 different, both in arrangement and intensity; but 

 it was with Kirchhoff s researches that the spectro- 

 scopic study of the stars began in earnest. About 

 1863 Sir William Huggins and Dr. Miller began 

 the systematic study of stellar spectra, and the former 

 extended his observations to nebulae, showing that 

 some of these (with a spectrum of bright lines) are 

 not star-clusters but areas of incandescent gas. As 

 early as 1864, Huggins was able to identify some of 

 the dark lines in the spectra of stars with those of 

 known elements, such as hydrogen, iron, sodium, 

 and calcium, a kind of work which has since been 

 vigorously prosecuted. 



