186 THE CHEMISTKY OF THE SUN. [CHAP. 



constituent atoms, sufficient to establish between them an important 

 physical (and probably chemical) relationship." 



If I understand Professor Young aright, his last words refer 

 to what have been generally termed physical coincidences, that 

 is, cases in which the common lines, being proved not to be due 

 to impurity, are ascribed to common vibrations of dissimilar 

 molecules. 



It will thus be seen that the further the work was pushed 

 the greater became the difficulty, and it will, I think, be 

 gathered that in these observations of the lines visible in the 

 sun's chromosphere, by the new method, the idea that we 

 witnessed in solar storms the ejection from the photosphere 

 of vapours of metallic elements with which we are familiar on 

 the earth became more and more improbable. 



The work, in short, of which I have given only the germs, re- 

 vealed the most striking anomalies ; nevertheless, loyal to the old 

 views, we have all of us continued to talk of " injections of iron 

 into the chromosphere," " magnesium prominences," and the like. 



2. Phenomena presented by the Stars. 



Since the sun is after all but a star the nearest star to us, 

 it is of primary importance for our purpose that the spectra of 

 the more distant ones should be compared with it. This is now, 

 in part, possible, for although it was Fraunhofer who at the 

 beginning of the century laid the foundations of a science 

 which we may christen Comparative Stellar Chemistry, it is 

 only in our own day that the work has been begun in earnest 

 by Eutherfurd, Miller, Huggins, Secchi, Vogel, and others. 



Dealing with the knowledge already acquired, in 1873, along 

 this line, we may say roughly that there were four genera of 

 stars recognisable by their spectra. 



We have first the brightest and presumably hottest stars, and 

 of these the spectrum is marvellously simple so simple, in fact, 

 that we say their atmospheres consist in the main of only a very 



