486 
ME. J. NORMAN LOCKYER ON SPECTRUM-ANALYSIS 
By these means we not only obtain a photographic record of the long and short lines 
with the individuality of each, but we get the solar spectrum as a scale. 
The accompanying diagrams show the arrangements adopted in the cases mentioned. 
Eig. 1. — Arrangement for obtaining solar spectrum alone. 
Fig. 2.— Arrangement for obtaining long and short lines. 
Fig. 3. — Arrangement for obtaining and comparing lines with solar spectrum. 
A, collimating lens ; B, slit ; C, opera-glass ; Gr, heliostat ; D, lens ; E, poles ; F, lens throwing image of sun 
between poles. 
In that branch of the research which deals with the causes of the coincidences of the 
lines in the various spectra, it is not absolutely essential that we should refer the lines 
to the solar spectrum each time ; thus if we study the cases of aluminium and calcium 
impurities, it is better to photograph the suspected spectra side by side and confront 
them. 
To do this all that is necessary is to extend the application of the principle already 
referred to. In fact the only practical limit to the number of spectra we can get on to 
one plate is the time the plate takes to dry, and instead of uncovering half of the slit at 
one time we may uncover any smaller portion. (See Plate XXXIX.) 
This I have effected by means of a brass shutter with a square opening cut through 
it, which slides in grooves in front of and up and down the slit. On one side of the 
shutter holes are bored, the distance between each hole being the same as the height of 
the opening in the shutter. A short pin fixed to a spring falls into each hole in suc- 
cession as the shutter is moved up or down, and so ensures that there shall be neither 
superposition of spectra nor gaps between them. The accompanying diagram (fig. 4) 
will make the arrangement quite clear. 
I find that, by the use of the shutter, four or more spectra showing positions and 
thicknesses (but not lengths of the lines) can readily be obtained on one plate ; and by 
