SECT. IT. ON VARIOUS SPECTRA. 143 



apparatus having several prisms like that of Kirchhoff, 

 they saw that the two blue lines differed by one division 

 of the measuring scale, the lithium line being the most 

 refrangible. A great change was produced on the stron- 

 tium spectrum by increased electric temperature : three 

 of the red bands vanished, and new bright lines appeared, 

 that were not coincident with those they replaced ; the 

 blue line was not affected, but four new violet lines were 

 added. With the intense heat of the electric spark, the 

 broad green band of the calcium spectrum is replaced by 

 five green lines of less refrangibility, the well-defined 

 yellow line vanishes, and instead of the red band three 

 red or orange lines appear, of greater refrangibility 

 than those that have vanished. Six of the bright green 

 bands in the spectrum of barium entirely vanish, and 

 bright new non-coincident lines appear. Thus, not 

 only new lines appear at very high temperature, but 

 the broad bands, characteristic of the metal or metallic 

 compound at a low temperature of the flame or a 

 weak spark, totally disappear at the higher temperature. - 

 The new bright lines, which supply the part of the broad 

 bands, are generally not coincident with any part of the 

 band, sometimes being less and sometimes being more 

 refrangible. The gentlemen who made these experiments 

 add, that possibly the cause of the disappearance of the 

 broad bands and the production of the bright lines may 

 be, that at the lower temperature of the flame or weak 

 spark, the spectrum observed is produced by the glowing 

 vapour of some compound, probably the oxide of the 

 difficultly reducible metal, whereas, at the enormously^ 

 high temperature of the intense electric spark, these j 

 compounds are split up, and the true spectrum is ob- < 

 tained, namely, the narrow bright lines. No such 

 changes take place in the easily reducible metals, 

 potassium, sodium, or lithium, which remain unaltered 

 by change of temperature. In these experiments, a 



