A PAPER, read by G. W. Tomlinson and H. M. Wright before the Institution of Electrical Engineers in London on December 13, records the progress made in the application of powdered mineral insulation to metal-sheathed conductors, and describes manufacturing methods and the application of those products which have reached a commercial stage of development. The -paper reviews the raw materials used, their properties, and the various manufacturing methods employed. Those applications of the various types of mineral-insulated conductors which have found particular favour are described, and their limitations are indicated. The most recent development, namely, mineral-insulated copper-covered cable, and its variations, is dealt with at greatest length. While this type of cable should be regarded as being designed to meet ordinary requirements, it can be used under conditions which no other type of cable will withstand.