COMPLEX ORIGIN OF SHORT LINES. 



291 



CHAP. XXI.] 



given and accepted was that they were produced by a more 

 complex vibration imparted to the " atom " in the region of 

 greatest electrical excitement, and that these vibrations were 

 obliterated, or prevented from arising, by cooling or by admixture 

 with dissimilar " atoms." 



Subsequent work, however, has shown 1 that the different 

 behaviour of these lines seemed to suggest the probability that 

 not all of the short lines of spectra were } in reality, true products 

 of high temperature. 



Now if not all but only some of the short lines are products 

 of high temperature, we are bound to think that the others are 

 remnants of the spectra of those molecular groupings first to 

 disappear on the application of heat. 



FIG. 97. A. Highest temperature. C. Lowest temperature. 



At any particular heat-level, then, some of the short lines 

 may be due to the vibrations of molecular groupings 'produced 

 with difficulty by the temperature employed, while others may 

 represent the fading out of the vibrations of other molecular 

 groupings produced on the first, application of the heat. 



In the line of reasoning advanced in Chap. 18, 2 both these 

 results are anticipated, and are easily explained. Slightly vary- 

 ing Fig. 86, we may imagine furnace A to represent the tempe- 

 rature of the jar spark, B that of the Bunsen burner, and C a 

 temperature lower than that of the Bunsen burner (Fig. 97). 



Then in the light of the hypothesis the lines b and c if seen 



1 Proc. R. Soc. vol. xxviii. p. 159. 



2 Ibid. p. 162. 



u 2 



