(574 Professor Den-ar [June 10, 



WEEKLY EVENING MEETING, 



Friday, June 10, 1881. 



William Bowman, Esq. LL.D. F.E.S. Vice-President, in the Chair. 



James Dewar, Esq. M.A. F.E.S. 



FULLERIAX PROFESSOR OF CHEMISTRY AT THE ROTAL rN'STITCTIOK, AND JACK-'OXIAX IX THE 

 CXIVERSITX OF CAMBRIDGE. 



Origin and Identify of Sjpedra. 



On a former occasion I detailed the results of a joint research made 

 in concert with my esteemed colleague Professor Liveing, on the 

 "Reversibility of the Pays of Metallic Vapours."* The present 

 lecture will be devoted to a record of the results of our work in rela- 

 tion to three disputed questions in spectroscopic investigation, viz. 

 (1) the Carbon Spectrum, (2) the Magnesium Spectrum, and (3) the 

 Identity of the Spectral Lines of different Elements. 



S'pectrinn of Carbon Compounds, 



The spectrum of the flame of hydrocarbons burning in air has been 

 repeatedly described, first by Swan in 1856, and afterwards by Attfield, 

 Watts, Morren, Pliicker, Huggins, Boisbaudran, Piazzi Smyth, and 

 others. The characteristic part of this spectrum consists of four 

 groups of bands of fine lines in the orange, yellow, green, and blue 

 respectively, which are hereafter referred to as the hydrocarbon bands. 

 These four groups, according to Pliicker and Hittorf, also constitute 

 the spectrum of the discharge of an induction coil in an atmosphere of 

 hydrogen between carbon electrodes. They are also conspicuous in 

 the electric discharge in olefiant gas at the atmospheric and at reduced 

 pressures. 



Pliicker and Hittorf notice the entire absence in the flame of 

 olefiant gas of the two bright groups of lines (blue and violet as 

 described below) characteristic of the flame of cyanogen. 



Several observers have described the spectrum of the flame of 

 burning cyanogen. Faraday, as long ago as 1829, called the atten- 

 tion of Herschel and Fox Talbot to it, and the latter, writing of his 

 observations,"!" points out as a peculiarity that the violet end of the 

 spectrum is divided into three portions with broad dark intervals, and 

 that one of the bright portions is ultra-violet. More recently Dibbits, 

 Morren, Pliicker, and Hittorf have particularly described this spectrum. 

 Dibbits t mentions in the cyanogen flame fed with oxygen a series of 



♦ ' Proceedings of the Royal Institution,' vol. ix. p. 204. 

 t ' Phil. Mag.' .sor. iii. vol. iv. p. 114. 



