336 THE CHEMISTRY OF THE SUN. [CHAP. 



greater differences are seen between the spectra of the oxy- 

 hydrogen flame and the jar spark. 



The line 5433 is seen rather faint in the sun and very strong 

 in the oxyhydrogen flame. 5197'5 is very faint in the sun, but 

 its intensity is doubled and even trebled with certain conditions 

 of the coil. 



I have introduced these facts in this place to repeat a remark 

 about Kirchhoff's statement, which one is bound to insist upon 

 in connection with this modern work. When Kirchhoff made 

 his statement he was amply justified by the science of the 

 time. He was familiar naturally with the spectrum of iron, 

 which he had studied in his own laboratory, and other good 

 observations of the spectrum of iron had also been recorded. 

 But, with observations like these before one, which must be 

 taken into account, it is too coarse a statement I do not use the 

 word in any offensive sense to say that the iron lines in the 

 sun correspond with the iron lines seen on the earth. Which 

 iron lines which of these horizons is to be taken ? It will 

 be seen in a moment, if there are differences between these 

 horizons, that if we take any one, we throw all the others out 

 of court ; and we have no right to do that. The statement about 

 the coincidence in the intensity of solar and terrestrial spectra 

 could not be made with the facts at our disposal now. 



3. Some Details of the Inversions of Iron Lines in Spot 

 Spectra. 



The observations made of the various inversions of iron lines 

 in sun-spots have been laid down on specially prepared maps, 

 showing the results of the laboratory work, each strip of the 

 map called an " horizon " showing the spectrum produced at 

 each temperature. 



In different horizons we have recorded the results observed 

 when we use either the arc, or coil, or oxyhydrogen flame, and we 



