 In other words, although the “frequency correspondence” does not hold for these low quantum numbers (nor can the intensities of these lines be calculated directly from the classical amplitudes via the “intensity correspondence”), what Bohr is here calling the more general correspondence principle does hold; specifically, these \(\tau = 1\) and \(\tau = 2\) transitions are allowed because there is, in the Fourier decomposition of the electron’s classical orbit in the initial stationary state, a first and second harmonic component. Such passages are a challenge for those who want to interpret the correspondence principle as some sort of asymptotic relation holding in the classical limit.