A PAPER read in London on November 14 before the Institution of Electrical Engineers, by W. J. Nicholls, reviews the progress that has taken place in the past fifteen years in the design of the steel-tower high-voltage transmission lines of the Central Electricity -Board in Britain. Lines operating at 132 kV. are dealt with separately from those operating at 66 kV. and 33 kV. Changes in conductors, joints, insulators and towers have been made in the light of experience, and a record of these is given as well as of other improvements of a minor character. The behaviour of steel-cored aluminium conductor and the methods employed for jointing it are described in detail, and alternative copper conductors are also mentioned. The development of new types of insulators to suit operating conditions in country districts is also described. The steps taken to reduce the effect of lightning, for example, more effective earthing, gap control, and the limited use of double earth-wires, are covered, and alterations in towers which have proved advisable are detailed.