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CHAPTER X. THE "SERIES" EVIDENCE. 

 Introduction. 



I DEFINED the meaning of the term "Series" on p. 10, and pointed 

 out how one of the important discoveries in recent years enables us 

 to study spectra from a new point of view. I propose in the present 

 chapter to deal with this subject in its most general aspect, and to 

 inquire whether this new method of inquiry helps us with any sug- 

 gestions or facts which may be utilized in the discussion of the disso- 

 ciation hypothesis : in other words, whether the new evidence afforded by 

 series, like the new evidence accumulated by the study of stellar spectra, 

 strengthens the view that the line spectra of the so-called chemical 

 elements are produced not by one but by more than one vibrating 

 particle. 



To explain what is meant by "series," it is well to begin by 

 studying what are termed fluted spectra. I have already referred to 

 these and given photographs on p. 10 ; these flutings are perfectly 

 rhythmic from end to end. The whole of a fluting may be regarded 

 as a unit ; it is generally strongest towards the right or the red end of 

 the spectrum, its elements gradually becoming dimmer as we approach 

 the violet end. It is well seen in the accompanying untouched photo 

 graph of some of the flutings in the spectrum of nitrogen (Fig. 30). 



But a fluting is generally more than this ; it is built up of sub- 

 sidiary flutings. Each of the subdivisions of it is in itself an almost 

 exact representatation in the small of what the whole thing is in the 

 great; so that we have the conceptions of a simple fluting and a 

 compound fluting. The compound flutings are well represented in 

 the flutings of carbon and magnesium (see Figs. 9 and 10). In all 

 cases we get exquisite rhythm, though in some cases it is apparently 

 overlaid by other lines, and generally the system is intensified towards 

 the red end of the spectrum. 



Now when we leave these flutings and study an ordinary line 

 spectrum, in a great many cases all rhythm seems to have disappeared. 

 There is apparently no law and no order. I have already in Fig. 1 1 

 given the series observed in the spectra of the cleveite gases. Let 

 us go into this a little closer and compare these " series " with the 

 spectrum as ordinarily observed. Let us take the lines seen when we 

 expose the gas obtained from the mineral cleveite to the act/ion of a 



G 2 



