ON THE MEASUREMENTS OF WAVE-LENGTHS. 
69 
Spectra to the left. 
Fiducial lines. 
Angular measurements. 
Corresponding -wave¬ 
lengths. 
I. 
O 
32 
43 
// 
41 
467L7 
11. 
33 
4 
21 
4515-27 
III. 
33 
25 
1 
4357-85 
IV. 
33 
45 
41 
4199-49 
V. 
34 
6 
21 
4040-2 
VI. 
34 
27 
1 
3880-0 
VII. 
34 
47 
41 
3718-93 
VIII. 
35 
8 
21 
3557-00 
IX. 
35 
29 
1 
3394-22 
X. 
35 
49 
41 
3230-63 
XI. 
36 
10 
21 
3066-27 
XII. 
36 
31 
1 
2901-14 
XIII. 
36 
51 
41 
2735-26 
XIV. 
37 
12 
21 
2568-68 
XV. 
37 
33 
1 
2401-41 
XVI. 
37 
53 
41 
2233-46 
XVII. 
38 
14 
21 
2064-87 
XVIII. 
Spectra to the right. 
Fiducial lines. 
Angular measurements. 
Corresponding wave¬ 
lengths. 
IX'. 
o / II 
37 33 1 
3426-02 
X'. 
37 12 2L 
3250-71 
XI'. 
36 51 41 
3075-71 
XII'. 
36 31 1 
2901-00 
XIII'. 
36 10 21 
2726-61 
XIV'. 
35 49 41 
2552-57 
The fiducial lines I. to X. inclusive, photographed on the spectra to the left of the 
regularly reflected image of the slit, were contained on Plates 6-12, IX. to XV. on 
Plates 11-18, and XII. to XVII. on Plates 17-26. 
Photographs of the portion 11-18 only were taken of the spectrum to the right. 
It will be seen from the table that the differences between consecutive readings to 
the left are the same as those to the right for the same part of the spectrum. 
The reading on the goniometer when the spectra to the right were being 
photographed was 30° 39' 38". 
Determinations of the wave-lengths of the spectral lines. —The linear positions, or as 
these will be hereafter termed the scale numbers of the fiducial lines, and spectral 
lines of each plate were carefully measured off by means of the dividing engine in 
hundredths of an inch and fractions thereof. Interpolation curves were constructed 
from the wave-lengths and the scale numbers of the fiducial lines. The wave-lengths 
of the metallic lines were determined from these curves. 
