, and, in view of the experimental work presented in the next chapter, Bohr placed it proportional to
, and wrote:
being the so-called Planck constant to be discussed later. It is to be emphasized that this assumption gives no physical picture of the way in which the radiation takes place. It merely states the energy relations which must be satisfied when it occurs. The red hydrogen line
is, according to Bohr, due to a jump from orbit 3 to orbit 2 ([Fig. 26]), the blue line
to a jump from 4 to 2,