The intensity of the three principal lines seemed to me to run in the following order:—
| Yellow. | Green. | Blue. | |
|---|---|---|---|
| Coal-gas | β | α | γ |
| Oxygen | γ | α | β |
Between the lines γ and α in the Geissler O tube I found a rather bright line, which I shall have occasion to refer to hereafter.
At 12 inches distance from the slit the O spectrum lost nearly all its light; the H line, and the three lines γ, α, and β, alone faintly remaining, α being decidedly the brightest. At 24 inches no spectrum at all was to be seen.
Comparison of spectra of coal-gas and O tubes.
I carefully compared together the three principal lines of the two spectra of coal-gas and O by means of:—
1st, the photographed micrometer before described;
2nd, a comparison-prism on the slit plate;
3rd, a piece of very fine brass foil cut as a pointer and fixed in the focus of a positive eyepiece.