LONDON, EDINBURGH and DUBLIN ■^''•ro,^*^ 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[THIRD SERIES.] 

 AUGUST 1845. 



XV. Experiments and Observations on some Cases of Lines in 

 the Prismatic Spectrum produced by the passage of Light 

 through Coloured Vapours and Gases, and from certain Co- 

 loured Flames. By W, A. Miller, M.D., F.R.S.t Profes- 

 sor of Chemistry in King's College, London *. 

 [With two coloured Plates.] 



THE inquiry into the cause of the dark lines in the solar 

 spectrum is one involved in so much difficulty and ob- 

 scurity, and the interest which attaches to its solution, in con- 

 nexion with some of the most refined questions relating to the 

 nature of lightj is so great, that I trust I shall be pardoned 

 for bringing forward some additional facts bearing upon the 

 subject, however little I may have to say in explanation of 

 them. These facts may, however, at a future period, assist us 

 in arriving at some general conclusion. 



In examining the prismatic spectrum of light that had been 

 transmitted through the deep red vapours of the nitrous acid 

 (NO4), Sir D. Brewster made the remarkable discovery, that 

 the absorption of the rays by this medium differs from that of 

 coloured liquids and solids in general, in the production of a 

 multitude of lines crossing the spectrum in the same direction 

 as those observed by Fraunhofer ; these lines being broadest, 

 darkest, and most abundant towards the more refrangible ex- 

 tremity of the spectrum. He found them to occur equally, 

 whether solar or artificial light were employed. Shortly after, 

 Prof. Miller of Cambridge, and the late Prof. Daniell, of 

 King's College, extended this inquiry to other coloured va- 

 pours, viz. to chlorine, iodine, bromine, euchlorine and indigo. 

 Between the spectra of iodine and bromine they discovered a 

 very exact parallelism, the coloured image in each case being 



* Read (June 21, 1845) at the Meeting of the British Association held 

 at Cambridge, and communicated by the Author. 



Phil. Mag. S. 3. Vol. 27. No. 178. Augtist 1845. G 



