402 



Profs. Liveing and Dewar. 



[Nov. 27 r 



Between the first and second group Lecoq de Boisbaudran gives a 

 line which was not noticed by us in the arc. 



In the second group the two middle lines are very close, and Lecoq 

 de Boisbaudran gives only their mean wave-length. Measuring the 

 distances of the middle from the extreme lines of the group, the wave- 

 lengths of this quartet are 5355, 5338, 5334-5, 5319. These are all 

 about of equal brightness, but we have not seen the third (5334" 5) 

 reversed. 



The third group consists of the lines 5112, 5098, 5095, 5081. Of 

 these the second is not given by Lecoq de Boisbaudran, and only the 

 first has been seen by us reversed. 



Three lines given by Lecoq de Boisbaudran between the third and 

 fourth groups are not seen in the arc, or at least are not nearly so 

 conspicuous as the groups here described. 



The fourth group consists of lines for which we find the wave- 

 lengths about 4964, 4956, 4950, 4942. Of these the first and last only 

 are given by Lecoq de Boisbaudran as 4963 and 4936. 



The fifth group has lines of which we find the wave-lengths about 

 4870, 4863, 4856, 4850. 



The sixth group has lines of about the wave-lengths 4808, 4803 r 

 4796, 4788. 



The seventh group is too faint and diffuse to be distinctly resolved. 

 The wave-length of the least refrangible edge is about 4759. 



None of these last three groups are seen by Lecoq de Boisbaudran^ 

 and they are too diffuse for exact measurement ; on the other hand, he 

 gives several other lines which are not noticed by us in the arc. 



As in the case of sodium the repetition of these quartets of lines at 

 decreasing intervals with decreasing brightness and sharpness as they 

 proceed from the less to the more refrangible, gives the impression of 

 a series of harmonics ; bat the wave-lengths do not seem to be in a 

 simple harmonic progression, though simple harmonic relations may 

 be found between some of the groups. 



VI. <k On the Reversal of the Lines of Metallic Vapours." 

 No. VII. By G. D. Liveing, M.A., F.R.iS., Professor of 

 Chemistry, and J. Dewar, M.A., F.R.S., Jacksonian Pro- 

 fessor, University of Cambridge. Received November 18, 

 1879. 



The experiments of which the results are here giveu were all made 

 in the Chemical Laboratory of the Royal Institution, with the powerful 

 electric current from the Siemens dynamo- electric machine. Limestone 

 crucibles similar to those before employed were in all cases used, but 

 the opening through which the arc was observed was in general placed 



