474 E.. S. Holden—Spectrum of L[nghtning. 
Arr. LVIiL—Speetrum of Lightning ; by Epwarp S. HoLpEN, 
Lieut. of Engineers, U. 8. Military Academy, West Point. 
I DESIRE to communicate to you a few observations on the 
spectrum of lightning, which I could wish to be more complete. 
The instrument was a pocket spectroscope of Hawkins & Wales. 
The first set was made in Philadelphia shortly after sunset, on 
the evenings of August 18, 14, and 15, 1872. There was a 
continuous play of sheet lightning and frequent vivid flashes. 
In the sheet lightning and in the fainter flashes the green 
and blue portions of the spectrum were visible, the violet and 
red cut off; in the brighter flashes a complete and continuous 
spectrum appeared and superposed on it bright lines. The red 
end of this spectrum (of vivid flashes) seemed to be shorter 
than that of the spectrum of a common gas-jet turned down 
low, with which it was constantly and almost instantaneously 
compared, without moving from the place of observation. 
From the sheet lightning I repeatedly obtained series of 
bright bands in the green, but the width and intensity of these 
bright bands continually changed. Of the bright and sharp 
lines I saw but three :—1, line in green; 2, line in blue; 3, line 
in violet (or extreme blue?). 
Green. Red. Notes—The red ends slightly 
Violet. rs =—__ ond 1. 
2=D line, : 
3 bounds yellow 
5 near boundary of green 
| green metimes blue. 
7 6 6 4 a ee rane erat 
The spectroscope was then turned to the lightning, and with 
the above dark lines as reference lines the following br) 28 
lines were mapped: (a) bright line Jess refrangible than red 
(border) of spectrum, i. e., extra red; (b) bright line sligh y 
ore refrangible than 4 (see fig.); (c) bright line near 9 OF 
_ (fig.) “ green or blue” ; (d) bright line in blue between 6 and 7, 
le. 
