ELECTKIC RAILWAYS. ELECTRO-CHEMISTRY. first ear motors wore entirely too light median- ically and of too small eapaeity. From a single lifteen-liorsei>i>«er motor (lri ing one ear-axle, the eapacity of the car equipments has been gradually increased up to the present practice of using two twenty-liorse- power motors, one geared to either axle. A marked improvement has also been made in the reduction of armature speeds, so that the use of a double reduction in
- |)eed by means of a countershaft and two pairs
of gears between the armature shaft and the car- a.xle is almost obsolete. Gcarless motors, in which the armature is built on the car-axle, have been introduced, but single reduction motors hav- ing the armature shaft geared directly to the car- axle are the most commonly used at present. Almost all modern car motors are of the multi- polar type instead of the bipolar, as formerly, and the reduction in armatvire speeds is due to this change of design. The severe service to which street-car motors are subject has led to making them very substantial in design, in order to avoid mechanical injury, and so-called iron- clad motors, in which the field-magnets form a closed iron bo.x, arc largely used to prevent short- circuiting by water, or by nails or scraps of iron picked up by the magnets, ilost of the single- Teduction four-pole motors are supported on one side on the car-axles by journals set in projecting lugs at each end of the motor frame, the armature shafts being parallel to the car-axles. The op- posite sides of the motors are connected to the frame of the car-truck by means of s])rings. and a pinion on each armature shaft meshes with a gear-wheel on either axle. The function of the springs is to avoid a shock on starting the car, by permitting the motors to turn through a small arc about the axles. In gearless motors the armature shaft is a hollow tube, through which the car-axle passes, and to which it is flexibly connected by means of springs. Another method in use with some geared motors is to place the motor on the truck with its shaft at right angles to the car-axles. The shaft carries a bevel pinion at each end which meshes with bevel gears on both of the car-axles. With this system a single motor of large capacity is used. A number of attempts have been made from time to time to connect the armature shaft and the axle by belts, sprocket chains, friction clutches, etc., none of which has been able to stand the service. See illustration of street-railway motor under Dv>amo-Ei,ectbic M.cniXEBY. The starling and regulation of speed of the car is efTccted by means of the controlling switches on the car platforms. The methods of regulation of the ditferent electric railway sys- tems are too numerous to be described in detail, but the same general plan is common to them all. S<'ries machines are always used in railway work, and the field-windings are wimnd in a number of separate sections, the ends of which are carried to contact pieces in the controlling switches. In addition to the resistance of the field-winding, a resistance box is also used. The contact pieces in the controller press against corresponding rows of metal plates, each row having its plate connected so as to vary the con- nections of the wires from the motor. In start- ing the car, the resistance box, sections of the field-coils and armature are all in series to prevent a too large passage of ctirrent through the armature. The next turn of the switch ctits out more or less of tlie resistance-box circuit, allowing more current to pass, and by successive movements of the switch, the field-coils pass through various combinations, from all in scries to all in multiple, the latter corresponding to the highest "car speed. To stop the car, the switch is reversed, making the same combina- tions in i-everse order. To change the direction of the car, a .separate switch is generally pro- vided, which changes the direction of the current through the armature with reference to its direc- tion tiirough the fields. In systems where there is no commutation of the field-coils, the changes in speed depend entirely upon the variable amounts of e.xtra resistance thrown into the circuit. The cars used on electric railways vary from 16 feet to 35 feet long, and weigh 6 to 11 tons. For illustration of controller, see Dy- .NAJIO-ElECTKIC ilAClll.NERY. Consult: Dawson, Electric Raihcays and Trainirays (London, 1897) : Bell, Power Dis- tribution for Electric Railroads (Xew York, 1900) ; Hanchett, Modern Electric Railiiay Mo- tors (Xew York, 1900) ; Herrick. Practical Elec- tric Railicaii Handbook (Xew York. 1901): Herring, Recent Proyress in Electric Railways (Xew York, 1897). For descriptions of the generators used in power-houses, see Dyxasio- Electric Maciiixery. ELECTRIC TELEGRAPH. See Telegraph. ELECTRIC WAVES. See Electricity. ELECTRIC WELDING. See Weldi.ng. ELEC'TRIDES (l.at., from Ok. 'HeicTp(5fj, Elekirides. irom ^XcKTpov, elektroti, amheT) . The Amber Islands of (ireek mythology, situated at the mouth of the Eridanus, a large river which was identified with the Po, because amber was found at the mouth of the latter. The name was applied also to islands on the northern coast of Europe. ELECTRO-BALLISTIC MACHINES. See Ballistics. ELECTRO-BALLISTICS. See Ballistics. ELECTRO-CHEMISTRY, General. The branch of general chemistry that deals with chem- ical changes producing, or caused by, electrical energy. The growing industrial applications of electro-chemistry are rendering the science itself more and more important every year. Another title of electro-chemistry to general interest con- sists in the fact that the phenomena it deals with have long formed a bond between two great branches of human knowledge — physics and chemistry — the science of the various forms of energj' and the science of the various kinds of matter. The bond may become even more in- timate if the comparatively recent hypothesis, according to which electricity itself is a subtle form of matter, turns out to be in agreement with facts. This hypothesis is briefly as follows: Electricity consists of two chemical elements whose atoms, termed 'electrons.' have exceedingly small (perhaps zero) relative weights; the atoms of positive electricity, or 'positive electrons,' may be denoted by the symbol © : the atoms of nega- tive electricity, or 'negative electrons,' may be denoted by the symbol @; like the atoms of hydrogen, electrons of either kind are univalent; so that, for instance, an atom of hydrogen when in the ionic state (i.e. when charged with elec- tricity) is combined with a single positive elec-
