Professor Kayser's well-known Tabelle der Schwingungszahlen may be used for wave-lengths beyond $\lambda 10,000$ by merely interchanging the labels of the two quantities tabulated. The vacuum wave-number thus derived, though not exactly correct, is sufficiently accurate for most of the data now available. For higher accuracy small corrections are tabulated.

• Received 15 June 1934

DOI:https://doi.org/10.1103/PhysRev.46.382