INORGANIC EVOLUTION AS STUDIED BY 

 SPECTRUM ANALYSIS. 



BOOK L THE BASIS OF THE INQUIRY. 



CHAP. I. PRINCIPLES AND METHODS. 



THE thirty years' work to which I have to refer in this book has had 

 to do with various points raised by the investigation of the radiation 

 and absorption of light ; the science of spectrum analysis is involved. 



Spectrum analysis, indeed, is now becoming so far-reaching, espe- 

 cially in inquiries having to do with the conditions of the various 

 celestial bodies, that there are many who are anxious to know some- 

 thing of its teachings. To some of these, however, the terms used by 

 men of science, a very necessary shorthand, are unfamiliar, and appear 

 hard to understand, because the opportunity of seeing the things they 

 are intended to define, and which they generally do define in most 

 admirable fashion, has never presented itself. I propose, therefore, to 

 attempt to show that there is nothing recondite about these terms ; that 

 it is possible without any expensive apparatus for every one who will 

 take a little trouble, to observe the phenomena for himself, after which 

 the meanings of the terms employed will present no difficulty whatever. 



One key to the hieroglyphics, the light story, which is hidden in 

 every ray of light, is supplied to us by the rainbow. It teaches us that 

 the white light with which nature bountifully supplies us in the sun's 

 rays is composed of rays of different kinds or of different colours ; and 

 it is common knowledge that there is an almost perfect analogy 

 between these coloured lights and sounds of different pitches. 



The blue of the rainbow may be likened to the higher notes of the 

 key-board of a piano, and the red of the rainbow, on the. other hand, 

 may be likened to the longer sound waves which produce the lower 

 notes ; and as we are able in the language of music to define each 

 particular note, such as B flat and G sharp, and so on, so light- waves 

 are defined by their colours or wave-lengths. 



