io6 New Theories of the Great Forces. 



a long* time dwelt in the north of Sweden : 

 " The matter of the aurora borealis some- 

 times descends so low that it touches the 

 ground. At the summit of high mountains 

 it produces upon the face of the traveller an 

 effect analogous to that of wind." 



We should pronounce this effect to be the 

 production of a true wind of a circumscribed 

 or local character. 



Solar Spectrum, its origin. 



14. (Page 80.) PROF. KIRCHHOFF was led 

 to the study of a coincidence between the 

 bright yellow line given in an incandescent 

 sodium vapor, and the solar line " D," which 

 coincidence had already been noticed by 

 FRAUENHOFER. Upon applying a greater dis- 

 persive power he noticed that the line " D " 

 was a double one ; but so also was the sodi- 

 um line under these conditions. ' Moreover, 

 each line of the one coincided with each line 

 of the other. The suspicion became strong 

 that it was the sodium in the sun which 

 caused the " D " line. He then extended the 

 comparisons to other elements. He carefully 

 measured sixty bright lines in the spectrum 

 of iron ; and found every one of these sixty 



