This paper describes an automatic ratio recorder as applied to infra‐red spectroscopy, incorporating special control devices developed and constructed for E. I. du Pont de Nemours and Company. This instrument is designed for recording the ratio of the energies in the two channels of an infra‐red spectrophotometer. It includes two preamplifiers and automatic control equipment for making readjustments periodically in the spectrometer and the preamplifiers. The instrument is provided with an electronic strip‐chart recorder and has an effective span of 0.5 microvolt.