LSI 



PREFACE. 



THIS present volume contains an account of my most recent 

 inquiries into the chemistry of the stars, and of some questions 

 which have grown out of these inquiries. It has taken its 

 present form because several friends, upon whose judgment I 

 can rely, suggested that I should preface the account of the 

 work, and the conclusions I have derived from it, by a statement, 

 as clear and simple as I could make it, of the principles of 

 Spectrum Analysis and of the earlier steps in the various investi- 

 gations the convergence of which has led to the present stand- 

 point. 



In my " Chemistry of the Sun," published in 1887, I dealt 

 chiefly with the then state of the problem, so far as the Sun was 

 concerned. In two later volumes, " The Meteoritic Hypothesis " 

 and the "Sun's Place in Nature," I included the stars in the 

 survey. The short story which I give in the earlier portion of 

 the present book consists of a resume of the three volumes, so 

 far as the question of dissociation is concerned ; this is followed 

 by evidence recently accumulated by other inquirers, all of which 

 tends to strengthen my original thesis. In the latter part of the 

 volume I endeavour to show how, in the studies concerning dis- 

 sociation, we have really been collecting facts concerning the 

 evolution of the chemical elements ; and I point out especially that 

 the first steps in this evolution may possibly be best studied by, 

 and most clearly represented in, the long chain of facts now at our 

 disposal touching the spectral changes observed in the hottest 

 stars. 



My thanks are due (1) to Messrs. Lockyer, Fowler and Baxan- 



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