566 
MR, J. NORMAN LOCKYER ON SPECTRUM-ANALYSIS 
In the first place, Cornu’s map, although by far the best ever published of this region 
of the spectrum, was found to be considerably wanting in detail when compared with 
the best negatives taken with the camera before described. For example, the follow¬ 
ing lines are represented as single in Cornu’s map :— 
Section 3900-4000. 
Approximate 
'wave-lene'th. 
O 
State in new 
map. 
3920-4 . 
.Double. 
3920-8 . 
. » 
3921-3 . 
.Triple. 
3935-2 . 
.Double. 
3937-8 . 
. 33 
3952-0 . 
.Triple. 
3965-0 . 
.Double. 
3965-9 . 
. 33 
3993-3 . 
. JJ 
3993-9 . 
3997-3 . 
. 3 ’ 
• * * * * * * * * 33 
In the next place, on the increased scale of the new map, the omission of lines by 
Cornu gives rise to blank spaces of too great an extent to enable one to interpolate 
new lines by eye with sufficient accuracy. 
Cornu admits that he has attempted to give groups of lines a natural appearance 
(when contrasted with photography), without special reference to the position of lines 
o 
within the groups. Slight errors thus introduced, although unimportant on Ang¬ 
strom’s scale, would be considerably exaggerated on the scale now adopted. 
The table of wave-lengths of the refraction map depends then (l) upon Cornu’s 
values as far as they are available, and (2) upon the interpolation curves for all the 
other lines. I have already stated the degree of accuracy which they may be expected 
to possess. 
III. DIFFRACTION MAP. 
A. Instruments, &c. 
The stand and collimator of the spectroscope of the Bunsen and Kirchhoff model 
already referred to were utilised, the train of prisms being removed and replaced by 
the grating. This grating, which as I have already said I owe to the great kindness 
of Mr. Rutherfurd, contains 13,321 lines 25 millims. long (17,280 to the inch). The 
ruled portion occupies the centre of a plate of glass 40 millims. square ; a deposit of 
silver is made on the ruled side, and then another plate is cemented with Canada 
balsam to the silvered side, to protect the surface. The grating is mounted with 
