1881.] Identity of the Spectral Lines of Different Elements. 225 



as when rotation has been incomplete a mere mechanical vibration has 

 at once restored the maximum effect. 



10. That heat, magnetism, constant electric cnrrents, mechanical 

 strains and vibrations, have all some effect on the result. 



III. " On the Identity of Spectral Lines of Different Elements." 

 By G. D. LlVElNG, M.A., F.R.S., Professor of Chemistry, 

 and J. Dewae, M.A., F.R.S., Jacksonian Professor, University 

 of Cambridge. Received May 12, 1881. 



The question of the identity of spectral lines exhibited by different 

 elements is one of great interest, because it is very improbable that 

 any single molecule should be capable of taking up all the immense 

 variety of vibrations indicated by the complex spectrum of iron or that 

 of titanium, and it might therefore be expected that such substances 

 consist of heterogeneous molecules, and that some molecules of the 

 same kind as occur in these metals should occur in more than one of 

 the supposed elements. Further, the supposed identity of certain 

 lines in the spectra of more than one element has been made by Mr. 

 Lockyer the ground of an argument in support of a theory as to the 

 dissociation of chemical elements into still simpler constituents, and 

 in reference to this he wrote (" Proc. Roy. Soc." vol. 30, p. 31), " the 

 ' basic ' lines recorded by Thalen will require special study with a 

 view to determine whether their existence in different spectra can be 

 explained or not on the supposition that they represent the vibrations 

 of forms, which, at an early stage of the planet's history, entered into 

 combination with other forms, differing in proximate origin, to produce 

 different 1 elements.' " 



Young, on examining with a spectroscope of high dispersion the 



n 



70 lines given in Angstrom's map as common to two or more sub- 

 stances, has found that 56 are double or treble, 7 more doubtful, and 

 only 7 appear definitely single (" American Journal of Science," vol. xx, 

 119, p. 353), and he remarks, " The complete investigation of the 

 matter requires that the bright line spectra of the metals in question 

 should be confronted with each other and with the solar spectrum 

 under enormous dispersive power, in order that we may determine 

 which of the components of each double line belongs to one and which 

 to the other element." It is this confronting of the bright line spectra 

 of some of the terrestrial elements which we have attempted, and of 

 which we now give an account. For the dispersion we have used a 

 reflecting grating similar to that used by Young, with 17,296 lines to 

 the inch, and a ruled surface of about 3-J square inches ; telescope and 



