first coil. The powdered charcoal filled the two coils of wire and bridged the gap between, and current passing through the bridge heated it to incandes

cence.

The first arc lamp was patented in 1845; eleven years later the 'differential' method of control of the arc was discovered, whose use was universally established about 1876, with the commercial establishment of the arc lamp. The year 1862 witnessed the first commercial installation of an electric light when an English lighthouse installed an arc light.

Arc light systems were commercially established in the United States in 1877-8, and the following year Thomas Edison invented an incandescent lamp, consisting of a high resistance carbon filament operating in a high vacuum maintained by an all-glass globe, the principle now used in all incandescent lamps, and also a new system of distributing electricity at constant pressure, now in universal use. Other important inventions which have proved commercially valuable are Stanley's constant pressure alternating current system of distribution (1886); Bremer's flame arc lamp (1898); Nernst's lamp (1900); Moore's vacuum tube light (1904); von Welsbach's osmium incandescent lamp (1905); Just and Hanaman's tungsten filament incandescent lamp (1907); Coolidge's drawn tungsten wire (1911); and Langmuir's gasfilled tungsten filament incandescent lamp (1913).

Some idea of the present enormous use of electric lighting may be gained from the fact that in the United States today there are more than 350,000,000 incandescent and 200,000,000 magnetite arc lamps in use and there is an annual increase of about 10 per cent. About 85 per cent. of all lamps are for 110-voltage and the most popular lamp is the 40watt size. The use of incandescent lamps in all other countries together about equals that in the United States.

Electric Lighting of Streets. The illumination of streets was one of the first applications of electric lights, and in many of the smaller communities it was the very first application of all. In the United States two 'systems' were first to offer practical street lighting. Each was the product of a pioneer inventor and each was promoted by a pioneer electrical manufacturing company.

The older of these two systems was that of Charles F. Brush, of Cleveland, introduced in 1877 and 1878 and manufactured first by the Telegraph Supply

Company of Cleveland, later by the Brush Electric Company, which succeeded the former concern. The other pioneer system was that of Elihu Thomson, of Philadelphia, introduced in 1879 and 1889, manufactured first in a very modest way at Philadelphia, then by the American Electric Company at New Britain, Conn., and finally by the Thomson-Houston Electric Company at Lynn, Mass.

Each of these inventors developed first of all a practical and fairly efficient dynamo electric machine, then an arc lamp to be used with the dynamo.

They increased the capacity of their dynamos until one machine could supply fifty or sixty arc lamps. The circuits required from six to ten amperes of direct current and the pressure at the terminals of the lamps ranged from forty to fifty volts.

Meanwhile Thomas A. Edison had introduced his incandescent lamp for lighting interiors, operating on multiple circuits at 110 volts. In 1885 he adapted this system for street lighting under the title of the Edison Municipal System, with incandescent lamps of 16 and 32 candle power, and circuits of 1,200 volts. The

first installation was at Lockport, N. Y. This was followed by a large installation at Portland, Me., and soon about fifty such installations had been made in different parts of the country, the largest being at Denver, Col.

The arc lamp, however, continued to dominate street lighting in the United States, the early lamps continuing more or less unchanged and being manufactured, after 1892, by the General Electric Company, which inherited all the early work of both Brush and Thomson, as well as Edison. These early lamps were for series circuits, but in the early nineties arc lamps for multiple circuits were developed. They had enclosing globes of more or less translucent glass, and the oxidation of the electrodes was considerable. About 1895 the socalled enclosed arc lamp appeared, having a special enclosing globe around the arc. through which air was fed in a carefully regulated stream. This lamp had less oxidation, consequently a longer life, but its efficiency was lower.

Ten years later there came a revolutionary development, in the magnetite, or luminous, arc lamp, perfected from an original idea of Dr. Charles P. Steinmetz (q.v.), who suggested replacing the carbon electrodes with one containing magnetite. After some years of effort and experiment this lamp was made prac

tical and soon had superseded all previous types of arc lamps. The first installation of a commercial sort was at Jackson, Michigan, soon after 1905. Between 1908 and 1910. Boston became interested in a more intensive type of luminous arc lamp developed by General Electric expressly for its use, and operating at 500 watts. Three thousand of these lamps were eventually installed, becoming very popular.

About 1916, New Haven installed the first General Electric system of ornamental luminous arc lamps, and attracted wide attention. This was known as the 'great white way' of New Haven, the term being derived from the application of that phrase to Broadway, New York City, on account of its numerous electric signs. The 'white way' movement, using ornamental high intensity luminous are lamps, spread to many communities far and wide.

The use of incandescent lamps for street lighting had languished until it again came to the front with the invention, about 1912, of the tungsten gas-filled incandescent lamp, permitting high candle power lamps to be manufactured. Up to 1911, tungsten vacuum lamps were being made as high as 350 candle power. Since then, and up to the present time, tungsten gas-filled lamps have been made in units of 1,000. 2,000 and 2,500 candle power, and some notable installations of street lights have employed incandescent lamps of these high candle powers. These lamps. with the luminous arc. now comprise some of the largest city street lighting systems in different parts of the world.

Electric Meters, a popular but loose expression, generally meaning integrating watt-meters, or watt-hour meters, which register total electrical energy furnished.

Integrating Current Meters, registering total quantity of electricity (coulombs) passed, were the forerunners of watthour meters, but are now obsolete as energy meters. They were used as such on constant voltage circuits, and hence could be used to show energy supplied. The most prominent type was the Edison electro-chemical meter. This consisted of one or more cells, with zinc plates in a solution of zinc sulphate, connected in parallel, and to the ends of a low-resistance shunt. through which the main current flowed. A definite percentage of the main current flowed through the meter, dissolving the anodes and building up the cathodes. The plates had to be weighed, and the current and

energy calculated from the change. The accuracy depended on care, attention, and continuous use. The cost of upkeep was too heavy, and the device proved too mysterious.

Ampere-hour Meters, acting on the electromagnetic principle of the D.C. watt-hour meter, are commonly used to integrate the product of amperes draft and hours use in electrolytic processes such as storage battery charging. In place of the voltage electromagnet of the watt-hour meter, the ampere-hour meter has a permanent magnet; since this field is constant, the torque and hence the speed, is directly proportional to current strength. Most of these meters are of the mercury type rather than the commutator type.

Watt-hour Meters are small, delicate motors, usually having jewel bearings, so designed and adjusted that their speed depends on the energy supplied to the circuit on which they are connected. A counting device registers total revolutions, which are calibrated to show corresponding value in energy units. There are three types of such meters: (1) The Thomson. (2) the induction, (3) the Faraday disc.

The Thomson or commutator meter (Fig. 1) is a complete little direct-current motor, made without iron parts. The armature shaft is vertical, and carries at its upper end a silver commutator and a revolution counter. Near the opposite end is a large copper disc, revolving between the poles of two or more C-shaped permanent magnets. The armature is connected across (parallel) the supply circuit, so that the armature current is proportional to the voltages. All the current supply passes through the field coils, so that the force causing the armature to revolve is proportional to the circuit voltage times the current supplied (see DYNAMOS AND MOTORS); i.e., to the watts, which is the power or the rate of supplying energy. The armature speed is made to increase directly as does the driving force or torque; therefore the speed, or rate of turning, is proportional to the rate at which work is done (or energy is furnished) in the circuit, and the total revolutions are proportional to the total energy, or watt-hours. copper disc mentioned revolves between the poles of the permanent magnets; eddy currents are generated in the disc proportional to the speed, and produce a magnetic reaction on the Cmagnets, which is also proportional to the speed. The effect is to keep the speed always proportional to the driving force.

The

This meter (like some series

motors) can be used on directcurrent or simple alternatingcurrent circuits. (See DYNAMOS AND MOTORS.) For alternating currents, however, simpler, cheaper, and equally accurate instruments are available.

The induction meter (Fig. 2) is in reality a small induction motor with revolving magnetic field polarity produced by two field coils one connected in series with the supply circuit, and the other in parallel; so that the one carries the current supplied and the other the voltage. The disc brake used on the commutator motor is used here, also, to keep the speed always proportional to torque. When the current and voltage are in phase-that is to say, have their maximum and minimum values occur simultaneously-the rotating element is threaded by two magnetic fluxes a quarter-cycle (90 degrees) apart electrically, and coming from coils 90 degrees

apart mechanically. This is a condition for producing a rotating magnetic polarity which depends on the product of the two fluxes, and is proportional to the product of current and voltage. If the current and voltage are not in phase, then the power supplied in the circuit is the product of three factors-voltage, current, and the cosine of an angle expressing the cycle degrees of 'lag' or 'lead' of maximum current over maximum voltage. The torque of the induction meter on such a circuit also is proportional to the product of current, voltage, and cosine of phase angle, so that it records actual power. Sometimes the disc-braking is done on the disc, which serves as the induction-motor armature, thus simplifying and cheapening construction.

Polyphase alternating-current circuits may be metered by a watt-meter in each leg, or by two watt-meters in a three-phase circuit, etc. Two rotors may be mounted on one shaft to add the effect of each; or for the same result, two sets of fields may act on a single rotor.

The Faraday-disc type (socalled from its similarity to Faraday's early dynamo) is repre

sented by the Sangamo watt-hour meter (Fig, 3), put out to overcome commutator and friction troubles and cost in the Thomson type. A copper disc armature floats in mercury, which serves as a bearing and to carry the current to the armature. Under the edge of the disc, diametrically opposite, are the field-magnet poles. The main current flows across the disc, and the shunt coil, carrying full-line voltage, excites the field. The meter acts like the Thomson type on direct current. The same sort of magnetic brake is necessary as with other meters.

Maximum-Demand Meters.— In the sale of electrical energy in the larger quantities, an effort is often made to charge in proportion to the cost of rendering the service. This necessitates the determination of the maximum power draft of the individual consumer. The sustained value of this 'demand' for a predetermined period, such as fifteen or thirty minutes, is of importance in basing the charges as well as is the consumption in kilowatthours. Instruments designed to indicate or record maximumdemand are called demand meters. There are several types: (1) the thermal, (2) the induction integrating (usually with time lag), (3) the graphic.

The thermal type is best represented by the Wright maximum ampere-demand indicator (Fig. 4). A colored liquid is hermetically sealed in a U-tube; the main current, or a definite fraction, passes around a bulb, expands the air, and raises one leg of the double liquid column until it spills over into the central branch. The amount of spill depends on the heat developed in the bulb, which in turn depends on the current (approximately as its square), This indicator is purposely lagged or, in other words, made slow in its indications. Thus, if the maximum current lasts four minutes, the meter shows only 90 per cent. of the maximum; in ten minutes, 97 per cent. is shown; in forty minutes, 100 per cent.

The induction principle is employed in the integrating demand meter, either as a separate device or in conjunction with an ordinary watt-hour meter. Inasmuch as a record of the instantaneous demand is not in general desired, it is necessary to provide a timelag in the indication so that only an integrated value for the predetermined time period will be recorded. This is accomplished in various ways; for example, the speed of rotation of the adjunct watt-hour meter is transmitted in impulses to the demand indicator, and the timing-period, during which the demand pointed is advanced by these impulses, is

regulated by an inductively driven disc running at constant speed. After a given number of revolutions (i.e., given time) the disc actuates the resetting of the demand mechanism. The pointer, however, retains its extreme deflection until reset by the meter reader.

The graphic demand meter not only indicates the maximum demand during a definite time interval but also shows the time of occurrence and duration of each demand.

Electric Motors. See DYNAMOS AND MOTORS.

Electric Ore Finder. Attempts have been frequently made to employ electricity and magnetism as aids in locating metalliferous deposits. The methods have consisted (1) of observing the actions of a magnetic needle; (2) of measuring and comparing the resistance of the earth between various points; (3) of observing differences of sound in a telephone receiver connected to small earth electrodes, variously placed in a larger area, across which high-tension currents have been caused to pass. Such methods are not accepted by mining and electrical engineers, and their promoters are generally considered to be self-deceived, if not worse.

Electric Peak. See YELLOWSTONE NATIONAL PARK.

Electric Power Transmission: DIRECT- AND ALTERNATING-CURRENT SYSTEMS. Among the more important advantages possessed by the electrical method of power transmission may be mentioned (1) the extraordinarily high efficiency of transmission, which need never fall below 50 per cent., and is in most cases about 90 per cent.; (2) the high efficiency of all forms of electric motor, even at small loads; (3) the great flexibility of the system, which allows of a change of position of the motor without involving great expense.

We have really to consider two distinct problems. In one case, only short distances are involved; in the other, the reverse is true. See ELECTRICITY, DISTRIBUTION

OF.

The two greatest applications of electric energy are in lighting and mechanical power, though electric heating in industry and in the household is of growing importance. Lighting service comes mostly at night, and that of power in the day. Usually, to make a power station pay it is essential to develop both uses together, so that the same equipment shall be in as near continuous service as possible. This reduces the cost of unit supply through the distribution of interest, repair, and depreciation

charges upon the greatest possible amount of service. With modern equipment for controlling and regulating the voltage delivered to the ultimate consumer, it has become possible to render all these different kinds of service from one universal system, the alternating current system, and street lighting, house lighting and appliance service, industrial power and heat processes, street railway power, are all served from the same generating units through appropriate transformation and conversion apparatus. When

certain mechanical requirements, such as variable-speed machine drive, demand direct-current motors, it may be necessary to put in rotary converters to transform the alternating current to

In Fig. 1 three single-phase lighting circuits are led off from a three-phase line supplying a threephase motor. In Fig. 3 the motor circuit is drawn from a separate set of main step-down transformers. In Fig. 2 a three-wire single-phase lighting circuit is drawn from one phase of the three-phase power line.

Long-distance Transmission.— For long-distance transmissionas is often necessary in using electricity from a waterfallsome permissible loss (say 10 per cent.) is decided on. This is chiefly heat, I2R, where I = amperes and R = ohms (see ELECTRICITY, CURRENT). If the I'R is to remain at the same percentage as the distance of transmission increases, either the current or the resistance per mile, or

Step-Down Lighting Ckts. Transformers,

Alternating-Current, Power, and Lighting-Circuit Diagrams

I direct. Such a conversion is also common for electric railways. Direct-current distribution systems are still found in a few thickly settled areas; but the alternating-current system is employed for all other situations. (See ELECTRICAL SUPPLY.)

A complication is encountered with alternating current. The lamps have but one pair of terminals, and lighting service is best served by a simple, singlephase line, while mechanical power is best obtained from polyphase motors requiring at least three feed wires. The problem is to combine single-phase lighting with poly-phase power circuits. Three of the most common arrangements are shown in Figs. 1, 2, and 3. Fig. 1 shows a system of generation, transmission, and distribution, while Figs. 2 and 3 show only the distribution lines.

both, must be cut down. As the loss depends on I2, if the current is cut in two, R may be increased four times for the same IR loss. Taking a tenth of the current, R may be increased a hundred times. For instance, it is proposed to transmit 100 kilowatts (100,000 watts) over half a mile distance, at 500 volts and 200 amperes. This means 0.25 ohm total resistance, which would be secured with a mile of about No. 0000 Brown & Sharp gauge copper wire (-mile metallic circuit 1 mile of wire), weighing 0.64 lb. per foot. To transmit 100 kw. 25 miles at 500 volts and 10 kw. loss requires the resistance (0.25 ohm.) to be for 50 miles of conductor, instead of one. That means a wire 50 times as big, which is out of the question on the score of cost alone. By jumping, say, to 33,000 volts-as

long distances is the alternatingcurrent, on account of the simplicity and efficiency of raising and lowering voltages with the 'static' transformer (see TRANSFORMER). A typical alternatingcurrent system (see Fig. 1) has (1) 11,000 volt, three-phase generators; (2) step-up transformers, to raise the voltage up to 66,000 for transmission; (3) a three-wire transmission line 50 miles long; (4) step-down transformers, reducing the voltage to 4,600 or 2,300 for the distributing lines; (5) motors connected directly to the 2,300 line, or through transformers that reduce the voltage to 220; (6) local single-phase lighting-lines run

structed in 1892 between San Bernardino and Pomona, California. The line was 2834 miles long, and transmitted 800 H.P. at 10,000 volts single-phase. This plant owed its origin directly to a successful, experimental, temporary plant erected just previously between Lauffen and Frankfort, Germany. To-day the distances have increased to over 200 miles and the voltages to as high as 220,000, with 500,000 in contemplation. The large electrical manufacturing companies have installed testing and experimental outfits of as The high as 2,000,000 volts. Pacific Gas and Electric Company has a system (installed in

tinuous currents are not generally used. The difficulty of generating high pressure in a single machine has, however, been overcome by Réné Thury, in France, who uses several continuous-current generators connected in series with each other, so that each machine contributes only a fraction of the total pressure used in transmission. At the far end of the line, similarly constructed machines, also joined in series, receive the current and act as motors; they may be employed for driving any other kind of generator more suitable for distribution. A few powertransmission schemes on the Thury system are at work in Europe.

The system par excellence for

1921) for transmitting 254,000 kw. 282 miles-from Cottonwood to Vaca Dixon-at 220,000 volts over two three-phase circuits. Conductors are 518,000 cir. mil. copper spaced 15 feet apart vertically. The standard span

is 800 feet and the steel supporting towers are 56 feet high to the lowest conductor. The wire is suspended from insulators each of which is a series of porcelain discs.

From 11,000 to 22,000 is the common voltage, to-day, up to 20 miles. Above this the lowest common voltage is 33,000-as there is neither advantage nor economy in building for lower voltage, if step-up transformers have to be used. The next step is 44,000 for still longer lines.