CHAPTER XIX. 



DISCUSSION OF THE DISSOCIATION HYPOTHESIS. continued. 



IT will, I think, be generally conceded that the results referred 

 to in the preceding chapter, " gave us prima facie ground for 

 thinking that it was quite worth while to go on with the 

 consideration of the hypothesis which had been advanced. 



We saw that dissociation did seem to explain the changes in 

 the intensity of lines of spectra on the analogy of the dissocia- 

 tion of known compounds. 



I was careful at the very outset to point out that the view 

 advanced is based upon the analogies furnished by those bodies 

 which by common consent, and beyond cavil and discussion, are 

 compound bodies. Indeed, had I not been careful to urge this 

 point, the remark might have been made that the various 

 changes in the spectra to which I have drawn attention are not 

 the results of successive dissociations, but are effects due to 

 putting the same mass into different kinds of vibration or of 

 producing the vibration in different ways. Thus the many high 

 notes, both true and false, which can be produced out of a bell, 

 with or without its fundamental one, might have been put 

 forward as analogous with those spectral lines which are pro- 

 duced at different degrees of temperature with or without the 

 line due to each substance when vibrating visibly with the 

 lowest temperature. To this argument, however, if it were 

 brought forward, the reply would be that it proves too much. 

 If it demonstrates that the li hydrogen line in the sun is produced 

 by the same molecular grouping of hydrogen as that which 



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