122 On the Ultra-violet Spectra of the Elements. [June 15 y 



known that ammonia, reacts on carbon at a white heat, producing 

 cyanide of ammonium and hydrogen, so that the genesis of the 

 cyanogen spectrum under the present conditions is a crucial test of the 

 validity of our former observations on this subject, which are, however y 

 in marked disagreement with the results obtained by Mr. Lockyer, in 

 his review of the same field of investigation. 



Both the indium lines 4101 and 4509 are persistently reversed, 

 together with several lead lines, Tin gives flutings in highly refran- 

 gible portions of the spectrum, and silver gives a fine fluted-looking 

 spectrum in the blue. Chloride of calcium gives a striking set of 

 six or seven bands between L and M, which may be seen both bright 

 and reversed. 



When the small rod c is removed, it is easy at any moment to sweep 

 out the vapours in the tube by blowing through it ; it is equally easy 

 to pass in reducing or other gases. Ammonia introduced seems to 

 facilitate the appearance of reversed lines. On passing this gas- 

 through a tube containing magnesia, the set of lines jusfc below 5, 

 which we have always found to be associated with the presence of 

 magnesium and hydrogen, and is most probably due to some com- 

 pound, instantly appear. 



The above is a brief abstract of the few observations we have 

 been able to make as a preliminary to a more thorough research, and 

 we feel warranted in thinking that the method promises to solve some 

 intricate spectroscopic problems. When we can command several 

 electric arcs to heat a considerable length of carbon tube, and are 

 enabled to examine the radiation of a powerful arc passing through 

 vapours in the tube, valuable results may be anticipated. 



XI. " On the Ultra-violet Spectra of the Elements. Part I. 

 Iron." By G. D. Liyeixg, M.A., F.R.S., Professor of 

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

 fessor, University of Cambridge. Received June 8, 1882. 



(Abstract.) 



By means of photographs taken with a Rutherford grating of 

 17,296 lines to the inch, the authors have determined the wave-lengths 

 of ninety-one of the most prominent lines in the spark spectrum of 

 iron between wave-lengths 2948, the termination of Cornu's map of 

 the solar spectrum, and 2327, and also of fourteen of the strongest 

 lines in the spark spectrum of copper beyond that up to the wave- 

 length 2135. Using these lines as lines of reference they have, from 

 photographs taken with calcite prisms, deduced the wave-lengths of 

 584 more lines in the arc and spark spectra of iron within those 



