In recent years other methods have been developed for generating electrical power in relatively small quantities for special applications. Semiconductors, which combine heat insulation with good electrical conduction, are used for thermoelectric generators to power isolated weather stations, artificial satellites, undersea cables and marker buoys. Specially developed diode valves are used as thermionic generators with an efficiency, at present, of only 20% but the heat taken away from the anode is used to raise steam for conventional power generation. Sir Humphry Davy (1778-1829) one of Britain's leading chemists of the 18th century, is best remembered for his safety lamp for miners which cut down the risk of methane gas explosions in mines. It was Davy who first demonstrated that electricity could be used to produce light. He connected two carbon rods to a heavy duty storage battery. When he touched the tips of the rods together a very bright white light was produced. As he drew the rods apart, the arc light persisted until the tips had burnt away to the critical gap which extinguished the light. As a researcher and lecturer at the Royal Institution Davy worked closely with Michael Faraday who first joined the institution as his manservant and later became his secretary. Davy's crowning honour in the scientific world came in 1820, when he was elected President of the Royal Society. In the U.S.A. the prolific inventor Thomas Alva Edison (1847-1931) who had invented the incandescent carbon filament bulb, built a number of electricity generators in the vicinity of the Niagara Falls. These used the power of the falling water to drive hydraulic turbines which were coupled to the dynamos. These generators were fitted with a spinning switch or commutator (one of the neatest gadgets Edison ever invented) to make the current flow in unidirectional pulses (D.C.) In 1876 all electrical equipment was powered by direct current. Today mains electricity plays a vital part in our everyday lives and its applications are widespread and staggering in their immensity. But we must not forget that popular demand for this convenient form of power arose only about 100 years ago, mainly for illumination. Recent experiments in superconductivity, using ceramic instead metal conductors have given us an exciting glimpse into what might be achieved for improving efficiency in the distribution of electric power.