Spectra synonyms

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.

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.

The application of photography to exact astronomy has created the necessity for new forms of apparatus to measure the relative positions of stellar and planetary images on photographic plates, and the relative positions of lines in photographic spectra.

complex spectra of stars of the solar type this is by no means the case; for, as Dr Hartmann remarks, " in the first place the lines in these spectra are so numerous that their complete measurement and reduction would require many days, and in the second place a rigorous reduction of such material has hitherto not been at all possible because the wave-lengths of the lines are not known with sufficient accuracy.