, for all the lines in the visible region, has the value 2, while
takes for the successive lines the values 3, 4, 5, 6, etc. In the hydrogen series in the infra-red discovered by Paschen[152]
and
takes the successive values 4, 5, 6, etc. It is since the development of the Bohr theory that Lyman[153] discovered his hydrogen series in the ultra-violet in which
and
