There is clearly no theoretical limit to the resolving power of gratings, even in spectra of given order.
This is the ordinary formula for a reflecting plane grating, and it shows that the spectra are formed in the usual directions.
Attacked in detail, they vanish one after another into as many teasing spectra of uncertainty.
A series of equivalent solutions all containing the same coloured ion have absorption spectra which, when photographed, show identical absorption bands of equal intensity.
We have now reduced the law for the bands to a form which we have found applicable to a series of lines, but with this important difference that while a in the case of line spectra is a small corrective term, it now forms the constant on which an essential factor in the appearance of the band depends.