iron wire barretters, which were designed to give enough current to operate an alarm relay on small faults but to limit the operating current considerably on the higher fault current values.

A far-reaching development was the application of the metadyne to industrial processes requiring accurate control of position and movement with high sensitivity and quick response. During the war the metadyne generator was used extensively in various forms and under different names ('amplidyne' is well known) in servomechanisms, where it was employed to amplify the output of electronic circuits, photoelectric cells and so on. These amplifying features have now been applied to many automatic and semi-automatic control schemes in industry. Examples are the control of main drives, reel motors and auxiliaries on rolling mills and of electrode motors on arc furnaces. It is actually twenty years since the Company first used metadyne control in a steelworks: a metadyne transformer equipment on a steelladle crane. The first use of metadynes for the control of strip tensioning reels was in a 100-hp equipment installed at Newport, Monmouth, in 1945. Metadynes are also used to control marine propulsion equipment on a constant current system.

While the metadyne was being developed as a power amplifier, other problems were being solved by the use of electronic control. Since 1945 a range of standardized electronic equipment has been developed for the speed control of industrial motors, and precise and rapid control of speed and position has been made available in many industries. In paper-making and linoleum mills and on machine tools, rubber calenders and cable-making machinery, electronic control is giving increased output and improved quality, and it is being provided for the screwdown gear on a rolling mill. Continuous strip mills have been equipped with mercury arc rectifiers.

An automatic contouring equipment introduced in 1947 for repetition machining is unique in British practice. It enables irregular shapes to be reproduced automatically by means of an electromagnetic tracer head, which hugs the profile of a template and controls the driving motors through an electronic amplifier; the motion of the cutting tool is thus controlled in two directions at right angles, causing it to follow the profile, even re-entrant portions, with great accuracy.

TRACTION
Traction motors have been improved since the war by using new varnishes and insulating materials, including glass, to permit operation at higher temperatures. Roller suspension bearings have been introduced for railway and tramway motors (with rubber-resilient suspension for trams), and new designs of trolleybus motors have been brought out. For trolleybuses the auxiliary motor generator sets also have been redesigned, and a new self-contained control unit for the driver's cab has been welcomed by the operators.

The decision of the L.N.E.R. to embark upon the first British 1500-V main line electrification—from Manchester to Sheffield—brought orders for seventy four-axle mixed