of the lines of the Solar Spectrum. ? 185 
lengths must be multiplied by 1:00016 to agree with Bell, 
while the correction for Angstrom’s error of scale would be 
1000110. 
It is impossible for me to give at present all the data on 
which my determinations rest, but I have given in Table I 
many of the coincidences as observed with several yvratings, 
the number of single readings being given in the parenthesis 
over each set. 
Table II gives the wave lengths as interpolated by the 
micrometer. It is scarcely possible that any error will be 
found (except accidental errors) of more than ‘02, and from the 
agreement of the observations, I scarcely expect to make any 
changes in the final table of more than ‘01, except in the ex- 
tremities of the spectrum, where it may amount to 03 in the 
region of the A and H lines. The wave lengths of weight 
greater than 1 will probably be found more exact than this. 
The lines can be identified on my new photograph of the spec- 
trum down to 5790. Below this there is little trouble in find- 
ing the right ones. All maps of the spectrum, especially above 
F, are so imperfect that it is almost impossible to identify my 
lines upon them. “The lines can only be properly identified 
by a power sufficient to clearly divide 6, and 6, Some of them 
are double and most of these have been marked, but asthe table 
has been. made,for my own use, I have not been very careful 
to examine each line. This will, however, be finally done. 
Micrometric measures have now been made of nearly all the 
lines below 6 with a view of making a map of this region. 
Table I gives the coincidences of the different orders of the 
spectra as observed with several concave gratings on both sides 
of the normal, the numbers in the brackets indicating the num- 
ber of observations. The observations have been reduced as 
nearly as possible to what I consider the true wave length, the 
small difference from the numbers given in table II, being the 
variation of the observations from the mean value. The true 
way of reducing these observations would be to form a linear 
equation for each series and reduce by the method of least 
squares. A simpler way was, however, used and the relative 
wave length of the standard lines, marked S in table II, was 
obtained; however, some other observations were also included. 
Table II gives the wave lengths reduced to Bell’s value for 
the absolute wave length of the D line. These were obtained 
by micrometric measurement from the standards as described 
before. The weights are given in the first column and some 
of the lines, which were measured double, have also been 
marked. But the series has not yet been carefully examined 
for doubles. 
The method is so much more accurate than by means of 
