1881.] on the Origin and LJcntity of Spectra. . 703 



tlicrc wcro no two which could take up vibrations of the same period. 

 We certainly sliould liavc supposed tliat substances like iron and 

 titanium, with such a large number of lines, must each consist of 

 more than one kind of molecule, and that not single lines, but 

 several lines of each, would be found repeated in the spectra of some 

 other chemical elements. The fact that hardly single coincidences 

 can be established is a strong argument tliat the materials (-f iron 

 and titanium, even if they be not homogeneous, are still different 

 from those of other chemical elements. The supposition that the 

 ditferent elements may be resolved into simple constituents, or into a 

 single one, has long been a favourite speculation with chemists ; but 

 however probable this hypothesis may appear a ^priori, it must bo 

 acknowledged that the facts derived from the most powerful method 

 of analytical investigation yet devised give it scant support. 



[J. D] 



