. 



PREFACE. vii 



it result of this work, then, we shall have a complete cataloguing 

 of everything on the sun, and a complete comparison of every- 

 thing which changes on the sun with every meteorological 

 phenomenon which is changeable in our planet. 



We next come to the third branch of the work, the newest 

 parallel in the quiet sap now going on; this has to do with 

 solar chemistry. 



The attempt to investigate the chemistry of the sun, in- 

 dependently even of the physical problems which are, and 

 indeed must be, connected with such an inquiry; is an attempt 

 aJmost to do the impossible, unless a very considerable amount 

 of time and a very considerable number of men be engaged 

 upon the work. If we can get as many investigators to take 

 up questions dealing with this subject as we find already 

 in other branches of knowledge more closely connected with 

 the old curriculum of studies, we may be certain that the 

 future advance of our knowledge of the sun will be associated 

 with a future advance of very many of those very problems 

 which at the present moment seem absolutely disconnected 

 and indeed distract attention, from it. 



I have, in the present volume, to limit myself to this 

 chemical branch of the inquiry. Here, as in other regions of 

 physical and chemical research, advance depends largely upon 

 the improved methods which all divisions of science are now 

 placing at the disposal of all others. Our knowledge of the 

 chemical nature of the sun is now being as much advanced by 

 photography, for instance, as that descriptive work to which I 

 have already referred, which deals with the chronicling and 

 location of the various phenomena. 



