PREFACE. ix 



papers was read at the Royal Society, many were not dis- 

 appointed that I did not incontinently then and there 

 " transmute " a ton of lead into a ton of .gold. 



Hence there have been misapprehensions of the nature of 

 my work, to say nothing of some denunciations of it on 

 the part of those who have not taken the trouble to inform 

 themselves concerning it; and in this I have a reason for 

 bringing together in the present volume the points touching 

 both the origin of the views I have advanced and the work 

 which has led up to them. 



It is now upwards of seventeen years since I began a series of 

 observations having for their object the determination of the 

 chemical constitution of the atmosphere of the sun. The work 

 which had this object merely, in the first instance, has opened up 

 a great number of problems above and beyond the initial ques- 

 tion, because we were dealing, with elements under conditions 

 which it is impossible to represent and experiment on here. 



In the first place, the temperature of the sun is beyond 

 all definition ; secondly, the vapours are not confined ; and 

 thirdly, there is an enormous number of them all mixed 

 together, and free, as it were, to find their own level. Nor is 

 this all. Astronomers have not only determined that the sun is 

 a star, and have approximately fixed his place in nature as 

 regards size and brilliancy, but they have compared its spectrum 

 with those of the other stars which people space. 



This, then, is one branch of the inquiry, which has con- 

 sisted in a careful chronicling of the spectrosqc/pic phenomena 

 presented to our study by the various stars. 



Experimentalists have observed the spectrum of hydrogen, 



