242 Mr. J. N. Lockyer. On the Classification [Jan. 10,. 



ought to again meet with some of the lines indicating higher 

 temperatures. 



Dr. Schuster made a series of observations on the spectrum of 

 lightning in Colorado in 1878. The region of the spectrum dealt 

 with extended from wave-length 500 to 580, and the following lines 

 were observed : 



559-2 

 533-4 



518-2 

 516-0 



There can be little doubt that the first line on the list is the 

 remnant of the manganese fluting at 558, the same as seen in auroras. 

 The second is in all probability the thallium line at wave-length 535, 

 the third is probably 6 (518'3), and the fourth the edge of the carbon 

 fluting at 516. 



The lines at 559-2 and 516 were only seen on one occasion. 



These observations are of very great importance, inasmuch as they 

 appear to indicate that the difference between the spectrum of 

 feeble or diffused lightning and the spectrum of aurora is due to a 

 difference of temperature only. 



Not only can we thus trace the difference in the spectrum as we 

 pass from aurora to lightning, but just as we can trace the effects 

 of gradually increasing temperatures on the spectrum of aurora, we 

 can trace the changes due to variations in the intensities of lightning 

 discharges, as I shall now proceed to indicate. 



The spectrum of lightning as observed by Schuster in Colorado 

 was obviously one produced by a comparatively feeble discharge. It 

 differs from what may be conveniently called a " high- temperature 

 aurora " only in having Mg 500 replaced by 6. It is important to 

 note, however, that the difference in the number of lines often seen 

 in auroras and in lightning is in all probability due to the fleeting 

 character of the latter. 



As we pass to the spectrum of such a discharge as Yogel observed 

 in September, 1871, the 500 line of nitrogen makes its appearance, 

 and Mn 558 disappears. Yogel's complete list of lines* is as follows : 



534-1 

 518-4 



500-2 

 486-0 



The band seen by Vogel was in all probability the carbon band 

 * Poggendorff's 'Annalen,' vol. 143, p. 654. 



