82 G. F. Barker—Spectrum of the Aurora of Oct., 1872. 
the lines centrally were recorded, the slit being about a millt- 
meter wide. Measured in this way, the seven auroral lines and 
bands, beginning at the least refrangible, had the following 
positions on the scale: 89°5, 110, 120-125, 182-1385, 188-142, 
150-155, and 181. The bands extended over the divisions of 
the scale above given. These numbers are the mean of three 
closely accordant and complete measurements by myself, and 
of one by my friend, Mr. C. B. Dudley, of this city. Count- 
ing the lines in order from red to blue, the brightness of the — 
seven was as follows: 2, 1, 7, 8, 6, 4,5; the line marked 110 
being the brightest. The lines 895 and 110 were sharp on the 
edges, the line 181 nearly so, and the lines 8, 4, 5, and 6, from 
the red end, were more or less broad bands nebulous on the 
edges, but shading away equally apparently on each side. 
The measurements may be regarded as accurate to within half 
a division of the scale. 
he value of these scale-numbers in wave-lengths was deter- 
mined, as before, by a series of measurements of certain of the 
characteristic elemental lines and of the principal lines of Fraun- 
hofer in full sunlight. The elemental lines measured had the 
following readings upon the scale of the instrument: 
K a@ 66, Lia 81, Sr 6 81°5, Ha 83, Sry 84, Caa 92, Li 6 94, 
Sr a 95, Naa 100, Ca # 111°5, Tla 119, H 6 141°5, Sr 6 157, Hy 
181, Ca y 187, K £ 206. 
The scale-numbers for the Fraunhofer lines read as follows: 
A 66, a 72°5, B 77, C 83, D 100, E 122, 6 126, F 141°5, G 181. 
The wave-lengths of these lines being taken from Angstrém’s 
tables as given by Gibbs, the wave-lengths of the auroral lines 
were obtained by direct interpolation from these; it bein 
assumed that no error greater than those of the instrumen 
measurement would be thus introduced. The following table 
gives the auroral data as obtained thus far: 
Scale Auroral Other 
Lines. number. Wave-length. lines. measurements. 
6 
e 72-5 716 
B 77 687 
C 83 656 
: 630 N. R. 
1} Hae: 805 630 630 | ee i 
623 Barker. 
D 100 589 
Barker. 
(2) line 110 555 BBB 1 Bi Wuntosk 
trom. 
E 122 527 ae ee 
582 A. Clark, Jr- 
(8) band 120-125 583-520 —»- 88-520 jeer 
