XIII.] " FRACTION ATIOX EVIDENCE." 119 



elements differentiated by the lines of the wave-lengths to which he 

 refers ; but more recently, still ^dealing with yttria, he has made 

 another research, having for its objective the separation of the element 

 characterised by a group of lines in the neighbourhood of A 3110. 

 The discovery of victorium with an atomic weight near 117 ha 

 rewarded his efforts. 



By following up the spectroscopic evidence, then, Sir William 

 Crookes has already "split up" one "element" into five; another 

 argument, if one were needed, that the spectrum of an element is pro- 

 duced not by similar but by dissimilar molecules. 



