230 



bands are generally not coincident with any part of the band, 

 sometimes being less and sometimes more refrangible. Thus 

 the broad band in the flame-spectrum of calcium named Ca [5, 

 is replaced in the spectrum of the intense calcium-spark by 

 five fine green lines, all of which are less refrangible than 

 any part of the band Ca /3 ; whilst in place of the red or 

 orange band Ca a, three more refrangible red or orange lines 

 are seen. The total disappearance in the spark of a well 

 defined yellow band seen in the calcium spectrum at the 

 low^er temperature, was strikingly evident. We have assured 

 ourselves by repeated observations that, in like manner, the 

 broad bands produced in the flame-spectra of strontium and 

 barium compounds, and especially Sr a, Sr /3, Sr y, Ba a, 

 Ba /B, Ba y, Ba S, Ba ^, Ba rj, disappear entirely in the spectra 

 of the intense spark, and that new bright non-coincident lines 

 appear. The blue Sr S line does not alter either in intensity 

 or in position with the alterations of temperature thus 

 effected, but, as has already been stated, four new violet 

 lines appear in the spectrum of strontium at the higher 

 ten^perature. 



If, in the present incomplete condition of this most 

 interesting branch of inquiry w^e may be allowed to express 

 an opinion as to the possible cause of the phenomenon of the 

 disappearance of the broad bands and the production of the 

 bright lines, we would suggest, that at the lower temperature 

 of the flame or weak spark, the spectrum observed is pro- 

 duced by the glowing vapour of some conipound, probably 

 the oxide, of the difficultly reducible metal ; whereas, at the 

 enormously high temperature of the intense electric spark 

 these compounds are split u}), and thus the true spectrum of 

 the metal is obtained. 



In conclusion, we may add that in none of the spectra of 

 the more easily reducible alkaline metals (potassium, sodium, 

 lithium) can any deviation or disappearance of the maxima of 

 light be noticed on change of temperature. 



