CREW AND BAKER. — SPARK SPECTRUM OF CARBON. 405 



arc, while the later phases represent the spark. If this be true, the nine 

 members of this series constitute nine different steps between the arc and 

 the spark spectra. 



A similar diminution of E. M. F. between the hot poles is indicated 

 by the work of Schenck, * who finds that, with hot poles, the " Mg. 

 spark line at A 4481 shrinks down close to the electrodes, while the arc 

 triplet at A 5170 does not." And this view is rendered all the more 

 probable by a fact noted by Basquin, f viz. that an auxiliary cold spark 

 gap, in series with the hot spark gap, suffices to render the spark lines 

 immediately visible. 



The general effect of the hot spark upon metallic impurities may 

 perhaps be most clearly described in the following three statements : 



1. Some new impurities are introduced, e.g. Potassium AX 4047.34, 

 4044.29, 3447.49, 3446.49. This is analogous to the introduction of the 

 nitrogen fluting at A 3371 above mentioned. 



2. Among lines due to a single element some may be diminished while 

 others are enhanced in intensity. Thus the calcium pair at AA 3968.6 

 and 3933.8, and also the calcium pair at AA 3179.4 and 3159.0, are 

 immensely diminished, while the calcium line at A 4226.9 is so greatly 

 enhanced by the hot spark that, after the potassium pair, it becomes the 

 strongest in the entire region studied. It is perhaps worth noting that 

 all of the lines belonging to any one of Kayser and Runge's series 

 are similarly affected. It would be interesting to know just how this 

 behavior of potassium and calcium is explained in terms of the dissocia- 

 tion hypothesis. 



3. The lines of some elements are affected either not at all, or very 

 slightly, by the hot spark. This class is illustrated by the omnipresent 

 copper pair at AA 3274 and 3247; also by the aluminium pair between 

 Fraunhofer's H and K ; and by the great majority of the iron lines. 



In general, it may be noted that there is nothing in the nature of 

 a sudden change anywhere in the series. Indeed the growth of the air 

 lines and the diminution of certain impurity lines is so gradual and defi- 

 nite that one might use their relative 1 intensities to determine the phase 

 at which any particular photograph was taken. The triplet formed by 

 the potassium pair at AA 4047 and 4044, together with the strong iron 

 line between them, serve to illustrate this principle and also to point out 

 an exception to the rule that the iron lines are generally unaffected by 

 the hot spark. For curiously enough this iron line increases in intensity 

 as the spark-gap (the medium) cools down, while, as noted above, the 



* Schenk, Astroph. Jour., 14, 131 (1901). t Basquin, Ibid., 14, 15 (1901). 



