24 



JNORtiANIC EVOLUTION. 



[CHAP 



. 18. The longs and shorts of sodium taken under the same conditions, showing 

 that the orange line extends furthest from the poles. 



Next the spectra of different parts of the sun chromosphere and 

 prominences and spots were compared with different parts of the 

 light source, the core of , the arc, and the centre of the spark, and the 

 outer regions of both. 



It will be seen that the inquiry now had a very broad base, and it 

 could be immediately tested in many ways at every stage. 



Wonderful anomalies were at once detected ; lines known to belong 

 to the same chemical element behaved differently in several ways. 

 Some were limited to prominences, others to spots (Fig. 20), and in 

 solar storms different iron lines indicated different velocities (Fig. 21). 

 In the spectrum of the hottest part of the sun open to our inquiries, 

 the region namely immediately overlying the photosphere, which I 

 named the chromosphere, the anomalies became legion ; suffice to say 

 that in the hottest part of the sun we could get at, the spectrum of 

 iron then represented in Kirchhoff's map of the ordinary solar spec- 

 trum by 460 lines was reduced to three lines. 



It was no longer a question merely of settling the difficulties raised 

 by the observations of Pliicker and Hittorf. 



Many observations and cross references of this kind during the 

 next few years convinced me that the view that each chemical element 

 had only one line spectrum was erroneous, and that the results ob- 



