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Mr. J. N. Lockyer. 



[Dec. 18, 



With regard to the second point, the passage from the heat-level 

 of the flame to that of the spark, after volatilisation is complete, pro- 

 duces no visible effect ; indicating that in all probability the effects 

 heretofore ascribed to quantity have been due to the presence of the 

 molecular groupings of greater complexity. The 'more there is to 

 dissociate, the more time is required to rim through the series, and the 

 better the first stages are seen. 



Let us now turn to lithium. 



Seeing that the red line is absent while the violet lithium line is 

 strong among the Fraunhofer lines, we may imagine that the flame 

 has not done the work of dissociation in the case of lithium so 

 completely as the sun does it, so that (1) the other lines of lithium 

 should not be visible, even with the new precautions, in the flame 

 spectrum, and (2) a passage from the heat-level of the flame to that of 

 the spark after volatilisation should produce the other lines which we 

 know to exist in the spectrum of the metal in the orange, blue, and 

 violet. 



Experiment and observation have also confirmed this result, so far 

 as the yellow and blue lines go ; that in the violet is difficult of 

 observation.* 



We next come to potassium. 



The potassium lines usually recorded as not seen in a flame, but 

 which are observed with a spark, are not very brilliant ; nor are they 

 strong among the Fraunhofer lines. Seeing therefore that a high 

 temperature dqes not greatly develop them, we may expect to find 

 them in the flame. They are almost all there when they are looked 

 for with proper precautions, but those in all probability present in the 

 sun are brightened on passing the spark,' showing apparently that the 

 flame volatilises with some difficulty the molecule which gives the line 

 in the red. 



The flame spectrum of magnesium perhaps presents us best with 

 the beautiful effects produced by the passage from the lower to the 



* The way in which the lines ordinarily seen in the flame are unaffected by the 

 spark strikingly reminds me of the following remarks of Angstrom and Thalen : — 

 " The Fraunhofer fines can in general be divided, according to their appearance, 

 into two classes : the one sharply defined and tolerably deep black, the other by no 

 means so decidedly marked either as to form or colour. These two different kinds 

 •of lines are, as regards their appearance, very happily characterised by the opinion 

 expressed on a former occasion, that the former, especially when the illumination 

 is feeble, look as if they were situated considerably in front of the faint ground on 

 which the latter seem to lie. The most prominent lines of the former class almost 

 all proceed from iron : and those which remain, after the iron-lines are abstracted, 

 belong to the other metals: calcium, manganese, chromium, &c." — ("Angstrom 

 .and Thalen on the Fraunhofer Lines, together with a Diagram of the Yiolet Part 

 of the Solar Spectrum." Upsala, 1866 ; p. 5.) 



