310 Royal Society : — 



appeared, and these new lines were referable to the carbon con- 

 tained in each of these gases. Each gas exhibits special lines which 

 are continued across the spectrum, and are never interrupted like 

 those of the metals. 



The author observed that many of these gases, such as protoxide 

 of nitrogen, hydrochloric and sulphurous acid, presented a consider- 

 able obstacle to the passage of the sparks from the induction-coil. 



" On the Long Spectrum of Electric Light." By Professor George 

 G. Stokes, M.A., Sec. R.S. &c. 



The author's researches on fluorescence had led him to perceive 

 that glass was opaque for the more refrangible invisible rays of the 

 solar spectrum, and that electric light contained rays of still higher 

 refrangibility, which were quite intercepted by glass, but that quartz 

 transmitted these rays freely. Accordingly he was led to procure 

 prisms and a lens of quartz, which, when applied to the examination 

 of the voltaic arc, or of the discharge of a Leyden jar, by forming a 

 pure spectrum and receiving it on a highly fluorescent substance, 

 revealed the existence of rays forming a spectrum no less than six 

 or eight times as long as the visible spectrum. This long spectrum, 

 as formed by the voltaic arc with copper electrodes, was exhibited 

 at a lecture given at the Royal Institution in 1853; but the 

 author, for reasons he mentioned, did not then further pursue the 

 subject. Having subsequently found that the spark of an induction- 

 coil with a Leyden jar in connexion with the secondary terminals 

 yielded a spectrum quite bright enough to work by, he resumed 

 the investigation, and examined the spectra exhibited by a variety of 

 metals as electrodes, as well as the mode of absorption of the rays 

 of high refrangibility by various substances. The spectra of the 

 metals may be viewed at pleasure by means of fluorescence, and the 

 mode of absorption of the invisible rays by a given solution may be 

 at once observed ; but there are difficulties attending the preparation 

 in this way of sufficiently accurate maps of the metallic lines ; and 

 the great liability of the rays of high refrangibility to be absorbed 

 by impurities present in very minute quantity renders the certain 

 determination of the optical character, in this respect, of substances 

 which are only moderately opaque a matter of considerable difficulty. 

 Having found that Dr. Miller had been engaged independently at 

 the same subject, working by photography, the author deemed it 

 unnecessary to attempt a delineation of the metallic lines (for which, 

 however, he has recently devised a practical method that was found 

 to work satisfactorily), or to examine further the absorption of rays 

 of high refrangibility by solutions of metallic salts, &c. 



The present paper contains therefore mainly results obtained in 

 other directions in the same wide field of research. Among the 

 metals examined, the author had found aluminium the richest in 

 invisible rays of extreme refrangibility ; and accordingly aluminium 

 electrodes were employed when the deportment of such rays had to 

 be specially examined. As the bright aluminium lines of high re- 

 frangibility do not appear to have been taken by photography, a 



