152 



Mr. J. Norman Lockyer. 



differently from others. Among these lines may be mentioned the 

 two lines of calcium producing the solar lines H and K and two 

 lines of iron at 4924*1 and 5018*6 (A\R). These lines were enhanced 

 in intensity on passing to the temperature of the spark, while a large 

 number of similar lines disappeared, and it was found that the lines 

 thus enhanced in intensity were of considerable importance in the 

 spectrum of the solar chromosphere. 



These facts seemed to show that short lines might be produced by 

 two causes : (1) the increased temperature of the core ; (2) the rapid 

 breaking up of the solid metal used as poles into various complex 

 molecular groupings as the vapours passed from the core to the outer- 

 edge of the arc* This last action was apparently responsible for by 

 far the greater portion of the short lines. 



Flame, Arc, and, Spark Lines. 



In 1879 I attempted to carry the matter farther by volatilising 

 those substances which give us spectra in a Bunsen flame and 

 passing a strong spark through the flame, first during the process of 

 volatilisation, the substance being put into the flame just below the 

 platinums, and then after the temperature of the flame has produced 

 all the simplification it is capable of producing,* the substance in 

 this case being introduced into the base of the flame. The passage 

 from flame to spark represented a stronger case than the passage 

 from arc to spark, and the view that the above-named two causes 

 were at work was greatly strengthened by the observation of mag- 

 nesium, lithium, and other metals recorded. In the first place, the 

 differences observed in dealing with different quantities were 

 attributed to the fact that " the more there is to dissociate, the more 

 time is required to run through the series, and the better the first 

 stages are seen." 



Further, lines invisible in the flame spectrum when the spark was 

 not passing were rendered visible by the passage of the spark. The 

 blue line of lithium about X 4602 and the line of magnesium about 

 X 4481 may be given as examples. Some of the flame lines were 

 dimmed or became invisible at the time of the production of the new 

 lines. The lines intensified by the spark in the flame were the same 

 as those enhanced on the passage from the arc to the spark. 



This strengthened the view that the result of a higher temperature 

 was to produce an important change in the spectrum, and it was con- 

 ceivable that in a space entirely heated up to the highest tem- 

 perature the spectrum would consist entirely of the enhanced lines. 



The employment of the flame in the experiment just referred to 

 suggested a series of observations at flame temperatures with a view 



* « Koy. Soc, Proc.,' 1879, vol. 30, p. 22. 



