"The most powerful combination that exists, in which number of alternations is combined with extent of surface, is that constructed by the subscription of a few zealous cultivators and patrons of science in the laboratory of the Royal Institution. It consists of 200 instruments, connected together in regular order, each composed of ten double plates arranged in cells of porcelain, and containing in each plate thirty-two square inches; so that the whole number of double plates is 2,000, and the whole surface 128,000 square inches. This battery, when the cells were filled with sixty parts of water, mixed with one part of nitric acid, and one part of sulphuric acid, afforded a series of brilliant and impressive effects. When pieces of charcoal about an inch long and one-sixth of an inch in diameter were brought near each other (within the thirtieth or fortieth part of an inch), a bright spark was produced, and more than half the volume of the charcoal became ignited to whiteness, and by withdrawing the points from each other, a constant discharge took place through the heated air, in a space equal at least to four inches; producing a most brilliant ascending arch of light, broad, and conical in form in the middle. When any substance was introduced into this arch, it instantly became ignited. Platina melted as readily in it as wax in the flame of a common candle; quartz, the sapphire, magnesia, lime, all entered into fusion; fragments of diamond, and points of charcoal and plumbago, rapidly disappeared, and seemed to evaporate in it, even when the connection was made in a receiver exhausted by the air pump; but there was no evidence of their having previously undergone fusion." The philosopher also showed that, when the Voltaic or electric arc is produced in the exhausted receiver of an air pump, the phenomena are as brilliant in character, and the charcoal points can be more widely separated, thus proving that the electric light is quite independent of the oxygen of the air for its support. Owing to the crude nature of the Voltaic batteries of that day, and also to the great expense of maintaining a large battery of that nature, nothing practical resulted from Davy's discovery of the electric or Voltaic arc. Professor Faraday, the great physicist, by his discovery of the principle of magneto-electricity, has enabled the electric light to be brought into practical use. As early as 1833 Pixii applied the principle practically in the construction of a magneto-electric machine with revolving magnets; he was followed by Laxton, Clark, Nollet, Holmes, and others, who made machines with fixed magnets. In 1854 Dr. Werner Siemens, of Berlin, introduced the "Siemens' Armature," which, from its compact form, permitted a very high velocity of rotation in an intense magnetic field, giving powerful alternating currents, which, when required, were commutated into one direction.