A spectrometer of new design is described, which makes easier the investigation of the far infrared spectra of either solids, liquids or gases. With this instrument a very high degree of resolution has been obtained and several substances have been studied from 30&mgr; to 180&mgr;. From 30&mgr; to 85&mgr; the effective slit‐width was 1.04&mgr;; from 85&mgr; to 122&mgr;, 1.67&mgr;; and from 122&mgr; to 180&mgr;, 2.59&mgr;.