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FOR MERCHANTS AND MANUFACTURERS OF ELECTRICAL MACHINERY AND SUPPLIES [Sidenote: Construction and Operation] Electrical machinery and supplies include three main groups of appliances: The apparatus by which electricity is originally generated; the apparatus by which current is transmitted and, if necessary, modified before it is used; and the infinitely various appliances for its final employment. In connection with any one of the latter, information may be needed as to its structure and its mechanical or electrochemical method of operation, or as to its uses, and in the treatment of these two aspects of a vast number of subjects the advantages of the encyclopaedic plan of the Britannica are obvious. One article will explain the method by which the same principles are applied to a number of different machines. Another article will deal with a group of appliances all used for similar purposes; and a reference to the Index of 500,000 entries (Vol. 29) will at once guide the reader who turns to the name of any electrical appliance to either kind of information he desires at the moment, whether he wants to know how the machine is made and operated, or what kind of work it does and how efficiently it does it. The reader to whom this chapter is addressed is already familiar with the general subject of electricity, but he may at any moment desire to review or to supplement his general knowledge in connection with some new appliance which, for the first time, applies to commercial use one of the many and intricate laws of electrical vibration. The whole subject of the nature and action of electricity is outlined in the article ELECTRICITY (Vol. 9, p. 179), by Prof. J. A. Fleming, of the University of London, one of the world’s foremost authorities. In a space equivalent to hardly more than 30 pages of this Guide, the field covered in detail by many other articles is so concisely and clearly surveyed that you get a complete view of the theoretical and practical developments by which electrical science and industry have reached their present position. The same contributor then considers ELECTROSTATICS (Vol. 9, p. 240) and ELECTROKINETICS (Vol. 9, p. 210); and, in CONDUCTION, ELECTRIC (Vol. 6, p. 855), deals with metallic, non-metallic, dielectric and gaseous conductors. One section of this article is by Sir J. J. Thomson, winner, in 1906, of the Nobel Prize for Physics. The form in which metal is chiefly employed for the conduction of electricity is the subject of a separate article, WIRE (Vol. 28, p. 738); and the articles on the individual metals deal with their electrical properties. [Sidenote: Batteries and Dynamos] The whole subject of the chemical production of electricity is discussed in ELECTROLYSIS (Vol. 9, p. 217), by W. C. D. Whetham, of the technical staff of Cambridge University. BATTERY (Vol. 3, p. 531), fully illustrated, deals with all the forms of primary battery, and ACCUMULATOR (Vol. 1, p. 126), also illustrated, by Walter Hibbert, of the London Polytechnic, with all the secondary types. The alkaline accumulators, of which the Edison apparatus is a well known type, are the subject of a special section. Turning to mechanically produced electricity, the first article to read is ELECTROMAGNETISM (Vol. 9, p. 226). This brings you naturally to the article DYNAMO (Vol. 8, p. 764), by C. C. Hawkins, author of one of the best practical text-books on the subject. This copiously illustrated article, in length equivalent to 50 pages of this Guide, discusses _continuous current dynamos_, _lap-winding_, _commutators_, _field-magnets_, _forgings and castings for magnets_, _air-gaps_, _armature cores_, _carbon brushes_, _cooling surfaces_ and _alternators_. Having thus covered the subject of obtaining current, the group of articles next to be considered is that dealing with its measurement and the examination of resistances. The general article UNITS, PHYSICAL (Vol. 27, p. 740), contains a section on _electrical units_. Then come POTENTIOMETER (Vol. 22, p. 205); METER, ELECTRIC (Vol. 18, p. 291); VOLTMETER (Vol. 28, p. 206), illustrated; AMPEREMETER (Vol. 1, p. 879), illustrated; OHMMETER (Vol. 20, p. 34); WATTMETER (Vol. 28, p. 419); GALVANOMETER (Vol. 11, p. 428), illustrated; ELECTROMETER (Vol. 9, p. 234), illustrated; ELECTROSCOPE (Vol. 9, p. 239), illustrated; WHEATSTONE’S BRIDGE (Vol. 28, p. 584), illustrated; and OSCILLOGRAPH (Vol. 20, p. 347), illustrated. [Sidenote: Lighting Appliances] The commercial supply of current is covered by a series of articles of which the first to be read is ELECTRICITY SUPPLY (Vol. 9, p. 193), to which Emile Garcke, the famous electrical engineer, contributes a section. POWER TRANSMISSION, _Electrical_ (Vol. 22, p. 233), is by Louis Bell, chief engineer of the General Electric Co., Boston; and contains full details as to the use of both two-phase and three-phase generators in transmission. INDUCTION COIL (Vol. 14, p. 502) and TRANSFORMERS (Vol. 27, p. 173) are both fully illustrated. LIGHTING, _Electric_ (Vol. 16, p. 659) deals with arc, incandescent and vapour lamps, and with wiring. The section on household work gives excellent practical information about the best arrangements of lights. A special class of electric light supplies is discussed in LIGHTHOUSE (Vol. 16, p. 627), by W. T. Douglass, who erected the new Eddystone and the Bishop’s Rock lights, and by N. G. Gedye, another practical expert. The appliances used to convert current back again into the mechanical energy from which it had been derived are described in the article MOTORS, ELECTRIC (Vol. 18, p. 910). This article divides continuous current motors into five classes: _Separately excited_; _series-wound constant current_; _series-wound constant potential_; _series-wound interdependent current and potential_; and _shunt-wound constant potential_. Alternating current motors are similarly classified as _Synchronous constant potential_; _induction-polyphase constant potential_; _induction monophase constant potential_; _repulsion commutating_, and _series-commutating_. [Sidenote: Trolley Cars and Railroads] Machinery for applying electric power to transportation, both for trolley cars and heavy railroad traffic, is described in the article TRACTION (Vol. 27, p. 118), by Prof. Louis Duncan, who designed the first electric locomotives employed with large loads—those introduced in 1895 by the Baltimore & Ohio R.R. for its track in the tunnel under Baltimore. The article gives, with many mechanical diagrams, accounts of the appliances by which the current is taken from trolley wires, conduits and third rails, and of the types of motors and controllers employed. CRANE (Vol. 7, p. 368), by Walter Pitt, describes the peculiar type of “crane-rated” motor, by the aid of which steam and hydraulic cranes can be displaced. The electric furnaces used for the reduction of ores and for manufacturing processes in which exceptionally high temperatures are required, are treated in ELECTROMETALLURGY (Vol. 9, p. 232), by W. G. M’Millan, lecturer on metallurgy at Mason College, Birmingham. Electric machinery for the refining of metals is dealt with in the article ELECTROCHEMISTRY (Vol. 9, p. 208). Under SURGICAL INSTRUMENTS (Vol. 26, p. 133) there is a description of the apparatus used for cautery and for illuminating parts of the interior of the body. The appliances used in ELECTROTHERAPEUTICS are dealt with under that heading (Vol. 9, p. 249). Information as to other medical and surgical apparatus will be found under RÖNTGEN RAYS (Vol. 23, p. 694), X-RAY TREATMENT (Vol. 28, p. 887), by Dr. H. L. Jones, of St. Bartholomew’s Hospital, London; and FLUORESCENCE (Vol. 10, p. 575), by Prof. J. R. Cotter, of Trinity College, Dublin. [Sidenote: Telegraph and Telephone] TELEGRAPH (Vol. 26, p. 510), equivalent in length to 70 pages of this Guide, and fully illustrated, is by a number of contributors, and discusses both land lines and submarine cables. The section on instruments, by H. R. Kempe, electrician to the General Post Office, London, includes a full description of the transmitters and receivers employed in the various systems of wireless telegraphy. TELEPHONE (Vol. 26, p. 547) deals with the fixed and portable instruments, the batteries and switchboards, the new automatic exchange “selectors,” and with special applications of the microphone. A number of other electric appliances are discussed in separate articles, such as BELL (Vol. 3, p. 692), by H. M. Ross, in which burglar alarm devices are described; and VENTILATION, _Fan_ (Vol. 27, p. 1011), by James Bartlett; while sparking plugs and other ignition appliances are treated under OIL ENGINE (Vol. 20, p. 35). There are also a number of appliances used mostly in experimental and educational work. Such, for instance, are ELECTRICAL OR ELECTROSTATIC MACHINE (Vol. 9, p. 176), with many illustrations; ELECTROPHORUS (Vol. 9, p. 237), and LEYDEN JAR (Vol. 16, p. 528). The metals, chemicals and other materials sold by dealers in electrical supplies, and their properties and uses, are described in COPPER (Vol. 7, p. 102), ZINC (Vol. 28, p. 981), LEAD (Vol. 16, p. 314), SULPHURIC ACID (Vol. 26, p. 65), SODIUM, _Compounds_ (Vol. 25, p. 341); CHROMIUM (Vol. 6, p. 296); NITROGEN, _Compounds_ (Vol. 19, p. 715); SAL AMMONIAC (Vol. 24, p. 59), BICHROMATES AND CHROMATES (Vol. 3, p. 912), CARBON (Vol. 5, p. 305), RUBBER (Vol. 23, p. 795), and GUTTA PERCHA (Vol. 12, p. 743). The following is a partial list, in alphabetical order, of articles of peculiar interest to dealers in electrical supplies. Accumulator Amperemeter, or Ammeter Armature Battery Bell Bichromates and Chromates Carbon Chromium Condenser Conductor, Electric Copper Dielectric Dynamo Electricity Electrical, or Electrostatic, Machine Electricity Supply Electrokinetics Electrolysis Electromagnetism Electrometer Electrophorus Electroscope Electrotherapeutics Fluorescence Fuze, or Fuse Galvanometer Gutta Percha Induction Coil Lead Leyden Jar Lighting Meter, Electric Motors, Electric Nitrogen, _Compounds_ Ohmmeter Oil Engine Oscillograph Potentiometer Power Transmission Röntgen Rays, _Apparatus_ Rubber Sal Ammoniac Sodium, _Compounds_ Sulphuric Acid Surgical Instruments Telegraph Telephone Thermometry, _Electrical_ Traction, _Electric_ Tramway Transformers Units, Physical Vacuum Tube Ventilation Voltmeter Wattmeter Wheatstone’s Bridge Wire Zinc