The more important discoveries since those days relate rather to electricity produced by voltaic or magnetic action.
In the later history of electricity no name is greater than that of Michael Faraday, who was born in London in 1794, was appointed by Sir Humphry Davy assistant in the laboratory of the Royal Institution in March, 1813, and in 1831 commenced the publication of a series of splendid discoveries in elec tricity.
The past history of electricity centers round the frictional machine and the vol taic battery. The first-named is now only of experimental interest, and the second, if we except its use in signaling (telegraphy and telephony), is quickly being supplanted by the more economical and vastly more powerful dynamo machine. To this contrivance, in its various forms, as designed by different makers, and in less degree to the second ary battery (now quite in its infancy), electricians look for the advancement of their science. The fact that the Gramme and similar machines are reversible is considered to be one of the most im portant discoveries of the century. By reversible is meant its power to act as a motor when coupled up with a distant machine, under which circumstances its armature rapidly revolves in the reverse direction to what it would do if used directly—as in the production of the elec tric light. By such means the electrical transmission of power from place to place has become possible.
Important advances in the knowledge of the connection between electricity and matter have in recent years been made through the observation of the ionization of gases. The principal researches along
this line were made by Professor J. J. Thomson, at the Cavendish Laboratory, at Cambridge, England.
All gases can be made conductors of electricity when the molecules of the gas have been broken into parts, that is, ion ized. Among the methods for ionizing gas are (1) application of high temper ature; (2) the passage of a spark in the neighborhood; (3) exposure to Röntgen rays or to rays from a radioactive sub stance such as uranium; (4) exposure to "cathod" rays; (5) exposure to "ultra violet" light. It has been established that the negative ions of all gases, how ever they may be produced, are identical.
The practical application of electricity to industry and to domestic uses has been one of the great developments of the last generation. The development of the automobile has called for storage batteries of high power and electricity and has also been employed as a motor power for motor vehicles. See MOTOR VEHICLE. In transportation, the use of electricity has come to be common, espec ially in suburban lines of railroad where a long haul is not required. For domes tic use electricity is employed not only for lighting and heating but for devices in cluding vacuum cleaners, electric irons, washing machines, and countless other devices.
For a discussion of the different phases of electricity and its use, see STORAGE BATTERIES, ELECTRICAL MACHINE, TRANS MISSION OF ELECTRIC POWER, DYNAMO,