ix.] FIRST RESULTS. 109 



method of determining the chemical nature of this exterior 

 atmosphere as Kirchhoff employed in determining the compo- 

 sition 'of the general light of the sun. Only we have a great 

 advantage in this case, for whereas Kirchhoff had to suggest an 



x D. 2 L> 3 

 FIG. 42. Line D 3 (yellow), with radial slit. 



hypothesis to explain the possible locus of the region which pro- 

 duced the lines due to the different chemical substances, we 

 have the hard fact beneath our eyes, because if we encounter 



F 



FIG. 43. Line F (blue-green), with radial slit. 



a prominence, and if it be built up, let us say, of iron vapour, then 

 we shall see iron lines ; if it be built up of calcium vapour, then 

 we shall see calcium lines, and so on. Now what are the facts ? 

 The first observation that was recorded with absolute certainty 



