Abstract: IN previous communications1–3, the principle of a method for converting a single monochromator into a multiple monochromator and the application of this principle to the construction of double monochromators were described. An infrared spectrometer constructed on this principle showed a considerable improvement over a single monochromator. A quadruple monochromator has now been constructed on the same principle, and our experience indicates that the construction of higher-order monochromators will not be unduly difficult.