—— 
G, Hinrichs on Spectral Lines, — 351 
Having now some direct determinations of wave-lengths, we 
resume our investigation. It will be seen that the results of our 
preliminary investigation are fully confirmed in their essential 
features, and that the number of elements to which they apply 
is greatly enlarged. 
number of the lines laid down in Kirchhoff’s map of the spec- 
trum, thereby enabling us by a simple geometrical interpolation 
to find the wave-length of any of Kirchhoff’s lines with great 
accuracy, the number of lines determined by Ditscheiner being 
sufficiently extensive to warrant the use of a large scale in this 
interpolation. The scale we used was 1 mm. of Kirchhoff’s scale 
and one ten-millionth millimeter wave-length, severally equal to 
two millimeters. On this scale the length of the spectrum from 
to G, or from 600 mm. to 2800 mm. Kirchhoff, taken as ab- 
Scissx, becomes 4400 mm., or nearly 15 feet. In some instances 
we used a five times longer scale, making the spectrum 75 feet. 
There is still another series of determinations by Angstrém,* 
but the original memoir is not accessible to us, and the extract 
in this Journal does not admit of direct comparison with Kireh- 
hoff’s scale. 
3. We will now first give the extension of our laws to the _ 
e ; and in 
make a few theoretical remarks suggested in the course of our 
Investigation. 
Tn the following, W will always denote the wavelength ex: 
pressed in ten-millionths of a millimeter, D the differences, 1 the 
assumed number of equal intervals, W’ the calculated wave- 
lengths, E the error, the difference between observation and cal- 
culation, E=W—W’ and d the interval, 
$4. Hydrogen spectrum. Ps 
Line, Ww D - ¢ 
Ww’ E 
5 6533 6533 0 
1690 10 
4 
: lies one . 4390 +3 
7 43 
where d=169, Range from red to indigo, or C to G. 
is Journal, 1865, vol, xxix, pp. 217-18. 2 ; 
* Bestimmung der Wellenlinge der Fraunhofer’schen Linien des ne gE e 
trum. Sitzungsberiechte der Akad. d. Wies. Wien, 1864, Bd. 50, pp. 206-341. a ee 
Journal, 1866, vol. xli, pp. 395-396. 
This Journal, 1865, xxxix, 215. ; 
fel ae 
