1881; 



on the Tvarhlngs of Modern Spectrosco'pij. 



iOl 



clilorido tliey wero placed most towards tlic blue end of tlic spectrum, 

 that when the sulphate was substituted for the chloride, a slight 

 shift towards the less refrangible end took place, and that a greater 

 shift in tlie same direction 

 occurred on examining tlie 

 acetate. Professor Bunseu 

 remarks that the molecular 

 weight of the acetate is 

 larger than that of the sul- 

 phate, and that the molecule 

 of the sulphate again is 

 heavier than that of the 

 chloride. He adds : " These 

 dititereuces in the absorption 



spectra of ditfereut didy- ^ Zi'^< 



mium compounds cannot in 

 our present comjilete state 

 of ignorance of any general 

 theory for the absorption of 

 light in absorptive media, 

 be connected with other 

 phenomena. They remind 

 one of the slight gradual ^ 

 alterations in pitch which ^• 

 the notes from a vibrating ^ 

 elastic rod undergo when 

 the rod is weighted, or of 

 the change of tone which an 

 organ pipe exhibits when 

 the tube is lengthened." 

 The accompanying wood- 

 cut, copied from Professor 

 Bunsen's paper, may serve 



to illustrate the shift ob- ^ <5 



served in one of the absorp- k M 11 n || 



tion bands. L ^ ^m <5 M o 



Similar changes take 

 place when some substances 

 like cyanin and chlorophyll 

 are dissolved in different 

 liquids. Absorption bands 

 characteristic of these vari- 

 ous substances appear, but 

 they slightly vary in posi- 

 tion. Professor Kundt, who 

 has carefully examined this displacement of absorption bands, has 

 come to the conclusion that as a rule the liquids of high dispersive 

 powers were those which shifted the bauds most towards the red end 



M 



