THE AURORA. 13 



longing to the metal calcium (the principal ingredient 

 of common chalk), we are by no means to infer that he 

 supposes the substance which causes the presence of 

 the bright line has any resemblance to that element. 

 Until we can find an element which has a bright line in 

 its spectrum absolutely coincident with the bright line 

 detected by Angstrom in the spectrum of the aurora, 1 

 all speculation as to the real nature of the vapour in 

 which the auroral electric discharge takes place, or of 

 the substances between which the spark travels, is 

 altogether precluded. 



It was supposed after the total solar eclipse of 1869 

 that the spectrum of the sun's corona exhibited the 

 same bright lines as the aurora. But recent observa- 

 tions show that the coincidence is not so close as had 

 been supposed, and, in fact, there is no evidence to 

 show that the lines are the same. 



1 Other green lines have since been discovered in the auroral 

 spectrum ; and occasionally a red line is seen. 



(From Prater's Magazme, February 1870.) 



