and the velocity of light. (We have to divide by the velocity of light, because in this chapter we have been speaking of frequencies, while in [Chapter IV] we were speaking of wave-numbers.) Now
is easily calculated since we know the charge on a hydrogen nucleus and on an electron, the mass of an electron, and the radius of the minimum orbit; also
and the velocity of light are known. It is found that the calculated value of Rydberg’s constant, from these data, agrees closely with the observed value; this was, from the first, a powerful argument in favour of Bohr’s theory.
For different kinds of light, the frequency
is different; in the visible parts of the spectrum, it determines the colour, being smallest for red and greatest for violet. By measuring the frequencies of the different lines in the hydrogen spectrum, and multiplying each by