SUNVIC CONTROLS, LTD., 10 Essex Street, Strand, London, W.C.2, manufacturers of vacuum switches, temperature control and associated equipment, have recently issued a 16-page illustrated pamphlet describing their hot-wire vacuum switches. The Sunvic hot-wire vacuum switch is contained within an evacuated glass tube not much larger than an ordinary radio valve, and is a non-arcing electric relay, the operation of which depends on the fact that when an electric current is interrupted by the separation of two surfaces in a vacuum no arc is formed. The movement necessary to close or open the switch is quite small and is provided by the thermal expansion of a special steel wire through which a control current of some 25-60 m.amp. is passed. The switch contacts are tungsten and are normally held apart against a compressed spring, which is released by the expansion of the hot wire. The operating characteristics of many different forms of hot-wire vacuum switches with various time delays, closing currents and current-carrying capacities are listed, and twelve different standard circuit and wiring diagrams are shown. The hot-wire vacuum switch is capable, in various sizes, of handling up to 10 kW. at 440 volts, and is suitable for controlling alternating or direct currents up to 30 amp. and voltages from 10 to 600.