Far infrared spectra of crystals and solids in a large range of temperatures have been studied from 20 to 700 micrometers: pure single crystals mainly of high symmetry (potassium bromide, potassium iodide, thallium halides, cesium halides, silver halides; magnesium oxide, iron oxide, manganese oxide; zinc selenide, zinc telluride, cadmium selenide, copper chloride, quartz and potassium bichromate; silicium dioxide polymorphs, binary glasses); doped single crystals (KBr:Cl, KBr:Na, KI:Na, KI:Cl, KC1:Na, KCl:I, NaI:Cl); molecular crystals either inorganic or organic; hydrogen bonded crystals; rare earth and transition metals salts; clathrates of hydroquinone with HC; and H2S. (Author), See also AD-636 614.