CHAPTER XXVI. 



THE BASIC LINES. 



IT was pointed out in chapter xviii. that the arguments 

 which I have advanced in favour of the dissociation of the 

 chemical elements were based upon strict analogies. At the 

 time my early papers were presented to the Royal Society 

 we knew that in the case of mixed vapours the intensity of 

 the lines of each constituent of the mixture changes as the 

 relative proportions of the constituents change. We also knew 

 that in compounds having a common constituent, such for 

 instance as the salts of calcium, which have calcium common 

 to them all, the lines of the metal are common to all the 

 spectra when sufficient temperature is employed to decompose 

 the salt. 



Hence, arguing by analogy, short lines seen coincident in the 

 spectra of two or more elementary bodies with the disper- 

 sion employed a qualification which was never lost sight of 

 were easily explained on the hypothesis which suggested that 

 the action which produced them was the same as that which 

 had already been at work in the salts. 



Had my paper been presented to the Royal Society some 

 years later another series of facts would have had to be dealt 

 with, for during those years facts have been rapidly accumu- 

 lating which must have been taken into consideration in any 

 general view. 



Many observers have shown that in the case of various sub- 



