1879.] On the Reversal of the Lines of Metallic Vapours. 367 



The authors are now engaged in pursuing this inquiry into the con- 

 sonantal sounds. 



II. " On the Reversal of the Lines of Metallic Vapours." No. V. 

 By Gr. D. Liveing, M.A., Professor of Chemistry, and J. 

 Dewar, M.A., F.R.S., Jacksonian Professor, University of 

 Cambridge. Received February 20, 1879. 



Since our last communication we have continued our experiments, 

 using the electric arc as a source of heat, in lime and in carbon cru- 

 cibles as described before. Success depends on the getting a good 

 stream of vapour in the tubular part of the crucible. This is easily 

 attained in the lime crucibles, which quickly reach a very high tem- 

 perature, but are very soon destroyed ; not so certainly in the carbon 

 crucibles, which are good conductors of heat. The latter, however, 

 last for a very long time. 



In our experiments with tubes heated in a furnace we used a small 

 spectroscope with a single prism, which gave a good definition and 

 plenty of light ; but in the experiments here described we have used a 

 larger spectroscope by Browning, with two prisms of 60° and one of 

 45°, taking readings on a graduated circle instead of on a reflected 

 scale. 



Both in the lime and in the carbon crucibles we have found that the 

 finely channelled spectrum, extending with great uniformity from end 

 to end, always made its appearance so long as the poles were close 

 together. A few groups of bright lines appear on it. We have not 

 at present investigated this remarkable spectrum further. In several 

 cases we have observed the absorption lines of the metals put into the 

 crucibles on this channelled spectrum as a background, but generally 

 when the vapours in the crucibles become considerable, the channel- 

 lings give place to a spectrum of bright lines on a much less bright 

 continuous background ; we have used generally thirty cells in the 

 galvanic battery, sometimes only twenty-five, once forty. 



The calcium line with wave-length 4,226 almost always appears 

 more or less expanded with a dark line in the middle, both in the lime 

 crucibles and in carbon crucibles into which some lime has been in- 

 troduced; the remaining bright lines of calcium are also frequently 

 seen in the like condition, but sometimes the dark line appears in 

 the middle of K (the more refrangible of Fraunhofer's lines H), 

 when there is none in the middle of H. On throwing some alumi- 

 nium filings into the crucible, the line 4,226 appears as a broad 

 dark band, and both H and K as well as the two aluminium lines 

 between them appear for a second as dark bands on a continuous 

 background. Soon they appear as bright bands with dark middles ; 

 gradually the dark line disappears from H, and afterwards from K, 



vol. xxvin. • 2 D 



