Dr. C. H. DESCH delivered a Research and Development Lecture under the auspices of the Royal Institution and the British Science Guild on February 6, taking as his subject “The Microscope and the Metal Industry”. Although a careful drawing of a metallic object (the edge of a razor) was published by Robert Hooke in 1665, it was two hundred years before any further use was made of the microscope in the study of metals. H. C. Sorby, a Sheffield amateur, began in 1854 to apply the microscope to polished and etched surfaces of steel and succeeded in identifying correctly a number of separate constituents in the varieties of steel and cast iron available to him. It was twenty years before these results attracted any attention, but from that time onwards, the microscope has become an indispensable tool in the metallurgical industry. Specimens of metals are ground and polished, care being taken to avoid distortion, and are then etched by means of a suitable reagent which will distinguish between the various constituents. All metals and alloys are built up of crystals, and the relative sizes of the component crystals frequently determine the properties of the mass. With this object in view, systematic measurements of crystal size are made as metals are passing through the processes of manufacture. The reading of a micro-section may be compared with the reading of a map, which conveys the more information the greater the experience of the person using it. A further important application of the microscope is in the study of failures. The fracture of crankshafts and other moving parts by fatigue, the cracking of boiler plates and superheater tubes, the breakage of wire ropes, and the cracking of severely cold-worked sheets, are typical examples of occurrences on which the microscope is capable of throwing light by indicating the nature of the processes concerned in the failure, and thereby giving a clue as to their origin. The microscope has now become an essential part of the equipment of every works dealing with the production of metal, and also with the transformation of metals into useful products on a large scale.