LIGHTING . Artificial See also:

• LIGHT

Hence 3 million foot-pounds changed to heat in the electric arc may be said roughly to affect our eyes six times as much as 6o million foot-pounds changed to heat in an ordinary gas burner. Owing to the high temperature at which it remains solid, and to its See also:

• GREAT

A typical example of the Argand burlier and chimney is represented in fig. 1, in which the burner is composed of three tubes, d, f, g. The tube g is soldered to the bottom of the tube d, just above o, and the See also:

• INTERVAL

When the air in the chimney is rarefied by the heat of the flame, the surrounding heavier air, entering the See also:

• LOWER

In what are termed See also:

• FOUNTAIN (Late Lat. fontana, from ions, a spring)

The under reservoir bb fills from it to the burner level ee, on a See also:

• LINE

3.-Section of Moderator Lamp. along with new supply oil it descends into the lower side by means of See also:

• LEATHER (a word which appears in all Teutonic languages; cf. Ger. Leder, Dutch leer or leder, Swed. leder, and in such Celtic forms as Welsh llader)
• LEATHER, ARTIFICIAL

See also:

• DRAKE, NATHAN (1766-1836)
• DRAKE, SIR FRANCIS (c. 1545-1595)

When the lamp is lighted the oil See also:

• BURNS, JOHN (1858– )
• BURNS, ROBERT (1759-1796)
• BURNS, SIR GEORGE

Sperm candle 0.41 0.41 Oil lamp 0.24 0.18 Gas-See also:

• FLAT (a modification of O. Eng. flet, an obsolete word of Teutonic origin, meaning the ground beneath the feet)

. 63.9 97.2 9 9 Wizard, 15-line . . 56.9 51.3 t8 19 Wanzer, no glass 42.6 48.3 17 17 Flat wick, single Solid slip, See also:

• GAUZE

By these means the See also:

• RISK

This jet of gas was then led into what was practically an atmospheric burner, and See also:

• DREW
• DREW, SAMUEL (1765-1833)

In the earlier forms of incandescent oil lamps the general idea was to suck the oil up by the capillarity of a circular wick to a point a short distance below the opening of the burner at which the flame was formed, and here the oil was vaporized or gasified by the heat of the head of the burner. An air supply was then drawn up through a tube passing through the centre of the wick-tube, while a second air current was so arranged as to See also:

• DISCHARGE (adapted from the O. Fr. discharge, modern decharge, from a med. Lat. discargare, to unload, dis- and earn care, to load, cf. " charge ")

One of the best illustrations of this system was the Aerogene gas introduced by A. I. See also:

• VAN

B. See also:

• NEILSON, ADELAIDE (1846—188o)

R. See also:

• BOWDITCH, NATHANIEL (1773-1838)

Union jet flat flame, No. o 0.59 I 0.85 2 I.22 3 1.63 4 1.74 5 1.87 6 2.15 7 • 2.44 Ordinary Argand • 2.90, Standard Argand 3.20 Regenerative 7 to 10 The luminosity of a coal-gas flame depends upon the number of carbon particles liberated within it, and the temperature to which they can be heated. Hence the light given by a flame of coal-gas can be augmented by (I) increasing the number of the carbon particles, and (2) raising the temperature to which they are exposed. The first See also:

• PROCESS

In 1835 W. H. See also:

• FOX
• FOX, C
• FOX, CHARLES JAMES (1749-1806)
• FOX, EDWARD (c. 1496-1538)
• FOX, GEORGE (1624-1691)
• FOX, RICHARD (c. 1448-1528)
• FOX, ROBERT WERE (1789—1877)
• FOX, SIR STEPHEN (1627–1716)
• FOX, SIR WILLIAM (1812-1893)

After the introduction of the atmospheric burner the idea of the incandescent mantle was revived early in the eighties by the Clamond See also:

• BASKET

Atmospheric influences must not have any action upon them, and they must be sufficiently refractory not to melt or even soften to any extent at the temperature of the flame; they must also be non-volatile, whilst the shrinkage during the process of " burning off " must not be excessive. The following table gives the light-emissivity from pure and commercial samples of the oxides which most nearly conform to the above requirements; the effect of impurity upon the lighting power will be seen to be most marked. Pure. Commercial. Metals 1.5 3'1 Zirconia . Thoria . . 0.5 6•o Earth metals 0.4 0.9 Cerite earths—Ceria . . Lanthania 6•o Yttrite earths—Yttria 3'2 Erbia . o•6 1.7 See also:

• COMMON

It is also possible to employ zirconia and alumina. Zirconia has the drawback that in the hottest part of the flame it is liable not only to shrinkage and semi-See also:

• FUSION

The cotton is then wrung out to free it from the excess of liquid, and one end is sewn together with an See also:

• ASBESTOS

One of the earliest attempts in this direction was the " Sunlight " mantle, in which cotton was saturated with the oxides of See also:

• ALUMINIUM (symbol Al; atomic weight 27.0)

In general the process consisted in forcing a thick solution of the nitrated cellulose through capillary glass tubes, the See also:

• BORE

The structure of the cotton mantle differed widely from that obtained by the various collodion processes, and this alteration in structure was mainly responsible for the increase in life. Whereas the average of a large number of Welsbach mantles tested only showed a useful life of 70o to See also:

• I000

The manufacturers of the Plaissetty mantle have also made a modification in the process by which the saturated fabric can be so prepared as to be easily burnt off by the consumer on the burner on which it is to be used, in this way doing away with the initial cost of burning off, shaping, hardening and collodionizing. Since 1897 inventions have been patented for methods of intensifying the light produced by burning gas under a mantle and increasing the light generated per unit volume Intensify- of gas. The systems have either been self-intensifying See also:

• ING

The light obtained by this system when the gas pressure is 91 in. is 300 candle power with an hourly consumption of to cub. ft. of gas, equivalent to 30 candles per cubic foot, and with a gas pressure equal to 14 in. of water 400 candles are obtained with an hourly consumption of 121 cub. ft., which represents a duty of 32 candles per cubic foot of gas consumed. High pressure incandescent lighting makes it possible to burn a far larger volume of gas in a given time under a mantle than is the case with low pressure lighting, so as to create centres of high total illuminating value to compete with arc lighting in the illumination of large spaces, and the Lucas, See also:

• KEITH
• KEITH, FRANCIS EDWARD JAMES (1696-1758)
• KEITH, GEORGE (c. 1639-1716)
• KEITH, GEORGE KEITH ELPHINSTONE, VISCOUNT (1746-1823)

When later on it was desired to make incandescent mantle burners that should not need the aid of a chimney to increase the air supply, the long Bunsen tube was reverted to, and the See also:

• KERN, JAN HENDRIK (1833– )

Bernt and E. Cervenka set themselves to solve the problem of making a Bunsen burner which should consume gas under ordinary gas pressure in an inverted mantle. They took the short Bunsen burner, as found in the most commonly used upright incandescent burners, and fitted to it a long tube, preferably of non-conducting material, which they called an isolator, and which is designed to keep the flame at a distance from the Bunsen. They found that it burnt fairly well, and that the tendency of the flame to burn or See also:

• LAP

Candle power. Low pressure upright incandescent burners 15 to 20 candles Inverted burners . 14 to 21 Kern burners . 20 to 24 High pressure burners 22 to 36 (V. B. L.) 3. ELECTRIC LIGHTING. Electric lamps are of two varieties: (I) Arc Lamps and (2) Incandescent or Glow Lamps. Under these headings we may briefly consider the history, See also:

• PHYSICAL

The statement that Sir See also:

• HUMPHRY, OZIAS (1742-1810)

If carbons impregnated with various salts are used to colour or increase the light, the arc is called a chemical or flame arc. The carbons or electrodes may be arranged in line one above the other, or they may be inclined so as to project the light downwards or more in one direction. In a carbon arc if the current is continuous the See also:

• POSITIVE (or PORTABLE) ORGAN

L. See also:

• FOUCAULT, JEAN BERNARD LEON (1819—1868)

In some cases they are cored, that is to say, have a See also:

• LONGITUDINAL

See also:

• BREMER, FREDRIKA (r8or–1865)

If the carbons are See also:

• VERTICAL (from Lat. vertex, highest point)

Niaudet (La Lumiere electrique, 1881, 3, p. 287). It has been shown by Mrs See also:

• AYRTON, WILLIAM EDWARD (1847-1908)

Let V stand for the potential difference of the carbons in volts, A for the current through the arc in amperes, L for the length of the arc in millimetres, R for the resistance of the arc; and let a, b, c d, &c., be constants. Erik Edlund in 1867, and other workers after him, considered that their experiments showed that the relation between V and L could be expressed by a simple linear See also:

• EQUATION (from Lat. aequatio, aequare, to equalize)

See also:

• ANN

Subsequently W. Duddell (Prot. See also:

• ROY, WILLIAM (1726-1790)

In the above experiments the potential difference between the carbons and the arc was measured by using a third exploring carbon as an electrode immersed in the arc. This method, adopted by Lecher, F. Uppenborn, S. P. See also:

• THOMPSON
• THOMPSON, FRANCIS (1860-1907)
• THOMPSON, LAUNT (1833-1894)
• THOMPSON, SIR HENRY, BART
• THOMPSON, SIR JOHN SPARROW (1844-1894)
• THOMPSON, THOMAS PERONNET (1783-1869)
• THOMPSON, WILLIAM HEPWORTH (18ro–1886)

Simply considered as an electrical conductor, the arc resembles an intensely heated rod of magnesia or other refractory oxide, the true resistance of which is decreased by rise of temperature. Hence an increase of current through such a rod of refractory oxide is accompanied by a decrease in the potential difference of the ends. This, however, does not imply a negative resistance, but merely the presence of a resistance with a negative temperature coefficient. If we See also:

• PLOT
• PLOT, ROBERT (164o-1696)

Abney's values See also:

• LIE, JONAS LAURITZ EDEMIL (1833—1908)
• LIE, MARIUS SOPHUS (1842–1899)

See also:

• WILSON, ALEXANDER (1766-1813)
• WILSON, HENRY (1812–1875)
• WILSON, HORACE HAYMAN (1786–1860)
• WILSON, JAMES (1742—1798)
• WILSON, JAMES (1835— )
• WILSON, JAMES HARRISON (1837– )
• WILSON, JOHN (1627-1696)
• WILSON, JOHN (178 1854)
• WILSON, ROBERT (d. 1600)
• WILSON, SIR DANIEL (1816–1892)
• WILSON, SIR ROBERT THOMAS (1777—1849)
• WILSON, SIR WILLIAM JAMES ERASMUS
• WILSON, THOMAS (1663-1755)
• WILSON, THOMAS (c. 1525-1581)
• WILSON, WOODROW (1856— )

3. The nature of the variation of the current and arc P.D. can be examined by one of two methods, or their modifications, originally due to Jules See also:

• JOUBERT, BARTHELEMY CATHERINE (1769–1799)
• JOUBERT, JOSEPH (1754–1824)
• JOUBERT, PETRUS JACOBUS (1834–1900)

The second method, due to Blondel, depends on the use of the See also:

• OSCILLOGRAPH

161) gave a number of potential and current curves for alternating-current arcs, obtained by the Joubert contact method, using two movable coil galvanometers of high resistance to measure respectively potential difference and current. Blondel's deductions were that the shape of the current and volt curves is greatly affected by the nature of the carbons, and also by the amount of inductance and resistance in the circuit of the alternator. Blondel, W. E. Ayrton, W. E. Sumpner and Steinmetz have all observed that the alternating-current arc, when hissing or when formed with uncored carbons. See also:

• ATE

Tobey and Walbridge in 1890 gave the results of a number of observations taken with commercial forms of alternating-current arc lamps, in which the same deformation was apparent. Blondel in 1896 came to the conclusion that with the same alternator we can produce carbon P.D. curves of very varied character, according to the material of the core, the length of the arc, and the inductance of the circuit. Hard carbons gave a P.D. curve with a flat top even when worked on a low inductance alternator. The periodic variation of light in the alternating-current arc has also been the subject of inquiry. H. Gorges in 1895 at Berlin applied a stroboscopic method to steady the variations of illuminating power. Fleming and Petavel employed a similar arrangement, See also:

• DRIVING (from " to drive," i.e. generally to propel, force along or in, a word common in various forms to the Teutonic languages)

The same observers made experiments which seemed to show that for a given See also:

• EXPENDITURE

Its shape depends on the total resistance in the circuit, but is almost independent of the type of alternator, whereas the current wave form is largely dependent on the machine used, and on the nature and amount of the impedance in the circuit; hence the importance of selecting a suitable alternator for operating alternating-current arcs. The same observers drew attention to the remark-able fact that if the arc is formed between a carbon and metal rod, say a See also:

• ZINC

The authors of this paper give numerous instructive curves taken with the oscillograph, showing the form of the arc P.D. and current curves for a great variety of alternating-current arcs. If a continuous-current electric arc is formed in the open air with a positive carbon having a diameter of about 15 millimetres, and a negative carbon having a diameter of about 9 millimetres, and if a current of ro amperes is employed, Bncbsed at'c (amps. the potential difference between the carbons is gener- ally from 40 to 5o volts. Such a lamp is therefore called a Soo-watt arc. Under these conditions the carbons each burn away at the rate of about r in. per hour, actual combustion taking place in the air which gains access to the highly-heated crater and negative tip; hence the most obvious means of preventing this disappearance is to enclose the arc in an air-tight glass vessel. Such a device was tried very early in the history of arc lighting. The result of using a completely air-tight globe, how-ever, is that the contained oxygen is removed by combustion with the carbon, and carbon vapour or hydrocarbon compounds diffuse through the enclosed space and See also:

• DEPOSIT (Lat. depositurn, from deponere, to lay down, to put in the care of)

An arc lamp operated in this way is called an enclosed arc lamp (fig. 8). The top of the enclosing bulb is closed by a gas check plug which admits through a small hole a limited supply of air. The peculiarity of an enclosed arc lamp operated with a continuous current is that the carbons do not burn to a crater on the positive, and a See also:

• SHARP, GRANVILLE (1735-1813)
• SHARP, JAMES (1618-1679)
• SHARP, JOHN (1645-1714)
• SHARP, RICHARD (1759-1835)
• SHARP, WILLIAM (1749-1824)
• SHARP, WILLIAM (1856-1905)

If a third carbon is dipped into the arc so as to constitute a third See also:

• POLE (FAMILY)
• POLE, REGINALD (1500-1558)
• POLE, RICHARD DE LA (d. 1525)
• POLE, WILLIAM (1814—1900)

415). Let BMC (fig. 9) be a semicircle which by revolution round the diameter BC sweeps out a sphere. Let an arc be situated at A, and let the See also:

• ELEMENT (Lat. elementum)

Owing to the inequality in the distribution of light from an electric arc, it is impossible to define the illuminating power by a single number in any other way than by stating the mean spherical candle-power. All such commonly used expressions as ` an arc lamp of 2000 candle-power " are, therefore, perfectly meaningless. The See also:

• PHOTOMETRY (from Gr. (Pews, xarrbs, light, µerpov, a measure)

Let A (fig. to) be an arc lamp placed at a height h(=AB) above a horizontal plane. Let ACD be the illuminating power curve of the arc, and hence AC the candle-power in a direction AP. The illumination (I) or brightness on the horizontal plane at P is equal to AC cos APM/(AP)2=FC/(h2+x2), where x=BP. Hence if the candle-power curve of the arc and its height above the surface are known, we can describe a curve BMN, whose See also:

• ORDINATE

Inst. Elec. Eng., 1903, 19, p. 1465), or the lumen-See also:

• METER, ELECTRIC

Trotter, it is easy to measure the illumination in candle-feet at any point in a street surface, and to plot out a number of See also:

• CONTOUR

Hence the total illumination at any point may be obtained by adding together the illuminations due to each arc separately. Given the photometric polar curves or illuminating-power curves of each arc taken outside the shade or globe, we can therefore draw a curve representing the resultant illumination on the horizontal surface. It is obvious that the higher the lamps are placed, the more uniform is the street surface il- lumination, but the less its aver- See also:

• AGE (Fr. age, through late Lat. aetaticum, from aetas)

846) gives the following rule for the height (h) of the arc to afford the maximum illumination at a distance (d) from the foot of the lamp-See also:

• POST

Globe. Mean spherical c.p. . . 319 235 16o 144 Mean hemispherical c.p. . 450 326 215 138 Percentage value of trans- Too 53 23 19 mitted light . . 0 47 77 81 Percentage absorption By using Trotter's, Fredureau's or the holophane globe, the light may be so diffused that the whole globe appears uniformly luminous, and yet not more than 20% of the light is absorbed. Taking the absorption of an ordinary opal globe into account, a 5oo-watt arc does not usually give more than 500 c.p. as a maximum candle-power. Even with a naked 5oo-watt arc the mean spherical candle-power is not generally more than 500 c.p., or at the rate oft c'p. per watt. The maxi-mum candle-power for a given electrical power is, however, greatly dependent on the current density in the carbon, and to obtain the highest current density the carbons must be as thin as possible. (See T. Hesketh, " Notes on the Electric Arc,” Electrician, 39, p. 707.) For the efficiency of arcs of various kinds, expressed by the mean hemispherical candle power per ampere and per watt expended in the arc, the following figures were given by L.

See also:

• ANDREWS, JAMES PETTIT (c. 1737–1797)
• ANDREWS, THOMAS (1813–1885)

As soon as the current passes, they must be moved slightly apart, and gripped in position immediately the current reaches its right value, being inside the way down %See also:

• ILL

L. M. Serrin (1857), J. Duboscq (1858), and a See also:

• HOST

The moment the carbons separate, there will be a difference of potential between them, and the shunt coil will then come into action, and will act on the core so as to draw the carbons together. Hence the two solenoids act in opposition to each other, one in-creasing and the other diminishing the length of the arc, and maintaining the carbons in the proper position. In the lamp of this type the upper carbon is in reality attached to a rod having a side-rack gearing, with a See also:

• TRAIN (M. Eng. trayn or trayne, derived through Fr. from Late Lat. trahinare, to drag, draw, Lat. trahere, cf. trail, trace, ultimately from the same source)

In the clutch-lamp mechanism the lower carbon is fixed, and the upper carbon rests upon it by its own weight and that of its holder. The latter consists of a long rod passing through guides, and is embraced somewhere by a ring capable of being tilted or lifted by a See also:

• FINGER

These were not really true arc lamps, the light being produced by the incandescence of the extremity of a thin carbon rod pressed against a larger rod or See also:

• BLOCK
• BLOCK (from the Fr. bloc, and possibly connected with an Old Ger. Block, obstruction, cf. " baulk ")
• BLOCK, MAURICE (1816–19or)

It is impossible to give here detailed descriptions of a fraction of the arc-lamp mechanisms devised, and it must suffice to indicate the broad distinctions between various types. (I) Arc lamps may be either continu®us-current or alternating-current lamps. For outdoor public illumination the former are greatly preferable, as owing to the form of tha illuminating power-curve they send the light down on the road surface, provided the upper carbon is the positive one. For indoor, public room or factory lighting, inverted arc lamps are sometimes employed. In this case the positive carbon is the lower one, and the lamp is carried in an inverted metallic reflector See also:

• SHIELD (0. Eng. scild, cf. Du. and Ger. Schild, Dan. Skjold; the origin is doubtful, but may be referred to the root seen in " shell " or " scale "; another suggestion connects it with Icel. skjalla, to clash, rattle; it is not connected with the Indo-Ger
• SHIELD, WILLIAM (1748—1829)

(4) Another subdivision is into hand-regulated and self-regulating lamps. In the hand-regulated arcs the carbons are moved by a screw attachment as required, as in some forms of search-light lamp and lamps for optical lanterns. The carbons in large search-light lamps are usually placed horizon-See also:

• TALLY

In this mechanism a shunt and series coil are placed side by side, and have iron cores suspended to the ends of a rocking arm held partly within them. Hence, according as the magnetic action of the shunt or series coil prevails, the rocking arm is tilled back-wards or forwards. When the series coil is not in action the motion is free, and the upper carbon-holder slides down, or the lower one slides up, and starts the arc. The series coil comes into action to withdraw the carbons, and at the same time locks the mechanism. The shunt coil then operates against the series coil, and between them the carbon is fed forwards as required. The See also:

• CONTROL (Fr. contrdle, older form contre rolle, from Med. Lat. contra-rotulus, a counter roll or copy of a document used to check the original; there is no instance in English of the use of " control " in this, its literal, meaning)

It is found, however, that the arc is unsteady unless a suitable magnetic field is employed to keep the arc in position at the carbon tips. This method has been adopted in the Carbone arc, which, by the employment of inclined carbons, and a suitable electromagnet to keep the true arc steady at the ends of the carbons, has achieved considerable success. One feature of the Carbone arc is the use of a relatively high voltage between the carbons, their potential difference being as much as 85 volts. Arc lamps may be arranged either (i.) in series, (ii.) in parallel or (iii.) in series parallel. In the first case a number, say 20, may be traversed by the same current, in that case a magnetic cut-out, so that if the carbons stick together or remain apart the current to the other lamps is not interrupted, the function of such a cut-out being to close the main circuit immediately any one lamp ceases to pass current. Arc lamps worked in series are generally supplied with a current from a constant current dynamo, which maintains an invariable current of, say ro amperes, independently of the number of lamps on the external circuit. If the lamps, however, are worked in series off a constant potential circuit, such as one supplying at the same time incandescent lamps, See also:

• PROVISION (Lat. provisio)

Alternating-current lamps take a larger effective current, and work with a less effective or virtual carbon P.D., than continuous current arcs of the same wattage. The cost of working public arc lamps is made up of several items. There is first the cost of supplying the necessary electric cost. energy, then the cost of carbons and the labour of recarboning, and, lastly, an See also:

• ITEM (a Latin adverb meaning " also," " likewise ")

The high-pressure flame arc lamp with inclined chemically treated carbons has, however, put a different complexion on matters. Although the treated carbons cost more than the plain carbons, yet there is a great increase of emitted light, and a 9-ampere flame arc lamp supplied with electric energy at 1-d. per unit can be used for r000 hours at an inclusive cost of about £5 to £6, the mean emitted illumination being at the rate of 4 c.p. per watt absorbed. In the Carbone arc lamp, the carbons are worked at an angle of 15° or 200 to each other and the arc is formed at the lower ends. If the potential difference of the carbons is low, say only 50-6o volts, the crater forms between the tips of the carbons and is therefore more or less hidden. If, however, the voltage is increased to 9o-roo then the true flame of the arc is longer and is curved, and the crater forms at the exteme tip of the carbons and throws all its light downwards. Hence results a far greater mean hemispherical candle power (M.H.S.C.P.), so that whereas a so-ampere 6o volt open arc gives at most r200 M.H.S.C.P., a Carbone 10-ampere 85 volt arc will give 2700 M.H.S.C.P. Better results still can be obtained with impregnated carbons. But the flame arcs with impregnated carbons cannot be enclosed, so the consumption of carbon is greater, and the carbons themselves are more costly, and leave a greater ash on burning; hence more trimming is required. They give a more pleasing effect for street lighting, and their golden yellow globe of light is more useful than an equally costly plain arc of the open type. This improvement in efficiency is, however, accompanied by some disadvantages. The flame arc is very sensitive to currents of air and therefore has to be shielded from draughts by putting it under an " economizer " or chamber of highly refractory material which surrounds the upper carbon, or both carbon tips, if the arc is formed with inclined carbons. (For additional information on flame arc lamps see a paper by L.

B. Marks and H. E. See also:

• CLIFFORD
• CLIFFORD, JOHN (1836- )
• CLIFFORD, WILLIAM KINGDON (1845-1879)

See also:

• KING
• KING (O. Eng. cyning, abbreviated into cyng, cing; cf. O. H. G. chun- kuning, chun- kunig, M.H.G. kiinic, kiinec, kiinc, Mod. Ger. Konig, O. Norse konungr, kongr, Swed. konung, kung)
• KING [OF OCKHAM], PETER KING, 1ST BARON (1669-1734)
• KING, CHARLES WILLIAM (1818-1888)
• KING, CLARENCE (1842–1901)
• KING, EDWARD (1612–1637)
• KING, EDWARD (1829–1910)
• KING, HENRY (1591-1669)
• KING, RUFUS (1755–1827)
• KING, THOMAS (1730–1805)
• KING, WILLIAM (1650-1729)
• KING, WILLIAM (1663–1712)

Abandoning this, he next directed his attention to the construction of an " electric candle," consisting of a thin cylinder or rod formed of finely-divided metals, platinum, iridium, &c., mixed with refractory oxides, such as magnesia, or zirconia, lime, &c. This refractory body was placed in a closed vessel and heated by being traversed by an electric current. In a further improvement he proposed to use a block of refractory oxide, round which a bobbin of fine platinum or platinum-iridium wire was coiled. Every other inventor who worked at the problem of incandescent lighting seems to have followed nearly the same path of invention. Long before this date, however, the notion of employing carbon as a substance to be heated by the current had entered the minds of inventors; even in 1845 King had employed a small rod of See also:

• PLUMBAGO (from Lat. plum-bum, lead)

W. See also:

• SWAN (A. S. swan and swan, Icel. svanr, Du. zwaart, Ger. Schwan)
• SWAN, J
• SWAN, JOHN MACALLAN (1847-1910)
• SWAN, SIR JOSEPH WILSON (1828– )

At one time Edison employed a filament of See also:

• BAMBOO

In the course of manufacture a process is generally applied to the carbon which is technically termed " treating." The carbon filament is placed in a vessel surrounded by an atmosphere of hydro-carbon, such as coal gas or vapour of benzol. If current is then passed through the filament the hydrocarbon vapour is decomposed, and carbon is thrown down upon the filament in the form of a lustrous and dense deposit having an appearance like See also:

• STEEL, FLORA ANNIE (1847– )

Dornfeld (fig. 16, a and a') two spring pistons, in contact with the two sides of the circuit, are fitted into the bottom of a short metallic tube having See also:

• BAYONET

A simple method is to See also:

• SAND
• SAND, GEORGE (1804-1876)

This is an important figure, because it is deter-See also:

• MINED

The possibility of employing high-efficiency lamps dependsgreatly on the uniformity of the electric pressure of the supply. If the voltage is exceedingly uniform, then high-efficiency lamps can be satisfactorily employed; but they are not adapted for See also:

• STANDING

In an ordinary oil lam ,p m the luminous m enats.. teslta-+ rays do not form much more than 3% of the total radiation. In the carbon-filament incandescent lamp, when worked at about 3 watts per candle, the luminous efficiency is about 5%; and in the arc lamp the radiation from the crater contains about 10 to 15% of eye-affecting radiation. The temperature of a carbon filament working at about 3 watts per candle is not far from the melting-point of platinum, that is to say, is nearly 1775° C. If it is worked at a higher efficiency, say 2.5 watts per candle-power, the temperature rises rapidly, and at the same time the volatilization and molecular scattering of the carbon is rapidly increased, so that the average duration of the lamp is very much shortened. An improvement, therefore, in the efficiency of the incandescent lamp can only be obtained by finding some substance which will endure heating to a higher temperature than the carbon filament. Inventors turned their attention many years ago, with this aim, to the refractory oxides and similar substances. See also:

• PAUL
• PAUL (PAULUS)

temperature it becomes conductive, and can then be maintained in an intensely luminous condition by passing a current through it after the flame is withdrawn. Nernst found that by mixing together, in suitable proportions, oxides of the rare earths, he was able to prepare a material which can be formed into slender rods and threads, and which is rendered sufficiently conductive to pass a current with an electromotive force as low as loo volts, merely by being heated for a few moments with a spirit lamp, or even by the radiation from a neighbouring platinum spiral brought to a state of incandescence. The Nernst lamp, therefore (fig. 17), consists of a slender rod of the mixed oxides attached to platinum wires by an oxide paste. Oxide filaments of this description are not enclosed in an exhausted glass vessel, and they can be brought, without risk of destruction, to a temperature consider- ably higher than a carbon filament; hence the lamp has a higher luminous efficiency. The material now used for the oxide rod or " glower " of Nernst lamps isa mixture of zirconia and yttria, made into a paste and squirted or pressed into slender rods. This material is non-conductive when cold, but when slightly heated it becomes con- ductive and then falls considerably in resistance. The glower, which is straight in some types of the lamp but curved in others, is generally about 3 or 4 cm. long and I or 2 mm. in diameter. It is held in suitable terminals, and close to it, or round it, but not touching it, is a loose ' coil of platinum wire, also covered with oxide and called the " heater " (fig. 18). In series with it is a spiral of iron wire, enclosed in a bulb full of hydrogen, A Type. The socket also contains a switch con- trolled by an electromagnet.

When the current is first switched on it passes through the heater coil which, becoming incandescent, by radiation heats the glower until it becomes conductive. The glower then takes current, becoming itself brilliantly incandescent, and the electromagnet becoming energized switches the heater coil out of circuit. The iron See also:

• BALLAST (O. Swed. barlast, perhaps from bar, bare or mere, and last, load)

When used on modern supply circuits of 220 volts a number of lamps may be run in series, or a step-down transformer employed. The next great improvement came when W. von See also:

• BOLTON (BOLTON-LE-MOORS)
• BOLTON (or BOULTON), EDMUND (1S75?-1633?)
• BOLTON, DUKES OF

The tantalum lamp so made (fig. 19), working on a See also:

• ITO, HIROBUMI, PRINCE (1841-1909)

28154 of 1904) described methods of making metallic filaments from any metal. He employs the metals in a colloidal condition, either as hydrosol, organosol, gel, or colloidal suspension. The metals are thus obtained in a gelatinous form, and can be squirted into filaments which are dried and reduced to the metallic form by passing an electric current through them (Electrician, 57, 894). This process has a wide field of application, and enables the most refractory and infusible metals to be obtained in a metallic wire form. The zirconium and tungsten wire lamps are equal to or surpass the tantalum lamp in efficiency has attended all attempts to use a carbon filament covered with such substances as thoria, zirconia or other of the rare oxides. H. W. Nernst in 1897, however, patented an incandescent lamp. in which the incandescent body consists entirely of a slender rod or filament of magnesia. If such a rod Metallic filament lamps. and are capable of giving light, with a useful commercial life, at an efficiency of about one watt per candle. Lamps called osram lamps, with filaments composed of an alloy of osmium and tungsten (wolfram), can be used with a life of r000 hours when run at an efficiency of about 1.5 watts per candle. Tungsten lamps are made by the processes of Just and Hanaman (German patent No.

154262 of 1903) and of Kuzel, and at a useful life of r000 hours, with a falling off in light-giving power of only 10-15%, they have been found to work at an efficiency of one to 1.25 watts per c.p. Further collected information on modern metallic wire lamps and the patent literature thereof will be found in an See also:

• ARTICLE (from Lat. articulus, a joint)

A 3-ampere Cooper-Hewitt mercury lamp has an efficiency of 0'15 to 0.33 watts per candle, or practically the same as an arc lamp, and will burn for several thousand hours. A similar lamp with mercury vapour included in a tube of uviol glass specially transparent to ultra-violet light (prepared by Schott & Co. of See also:

• JENA

The holder which carries the lamp should allow the lamp to be held with its See also:

• AXIS (Lat. for " axle ")

In the case of the tantalum lamp the exponent x has a value near to 6, but the exponent y is a number near to 4, and the same for the osmium filament. Hence for these metallic glowers a certain percentage variation of voltage does not create so great a variation in candle-power as in the case of the carbon lamp. Curves delineating the relation of these variables for any incandescent lamp are called its characteristic-curves. The life or average duration is a function of W/c.p., or of the watts per candle-power, and therefore of the voltage at which the lamp is worked. It follows from the above relation that the watts per candle-power vary inversely as the fourth power of the voltage. From limited observations it seems that the average life of a carbon-filament lamp varies as the fifth or See also:

• SIXTH

In the case of carbon filaments this is due to two causes. As already explained, carbon is scattered from the filament and deposited amepas of upon the glass, and changes also take place in the filament which cause it to become reduced in temperature, even when subjected to the same terminal voltage. In many lamps it is found that the first effect of See also:

• RUNNING

The following Mercury vapour lamps. figures show the results of some tests on typical 3•1 watt lamps run at voltages above the normal, taking the average life when worked at the marked volts (namely, roo) as r000 hours: At rot volts the life was 818 hours. „ 102 „ 681 „ „ 103 " 662 104 „ 452 105 374 ro6 „ 310 ,, Self-acting regulators have been devised by which the voltage at the points of consumption is kept constant, even although it varies at the point of generation. If, however, such a device is to be effective, it must operate very quickly, as even the momentary effect of increased pressure is See also:

• FELT (cognate with Ger. Filz, Du. vilt, Swed. and Dan. fill; the root is unknown; the word has given Med. Lat. filtrum, " filter ")

A. Edison, W. H. Preece and J. A. Fleming. effect. If into an ordinary carbon-filament glow lamp a platinum plate is sealed, not connected to the filament but attached to a third terminal, then it is found that when the lamp is worked with continuous current a galvanometer connected in between the middle plate and the positive terminal of the lamp indicates a current, but not when connected in between the negative terminal of the lamp and the middle plate. If the middle plate is placed between the legs of a horse-shoeshaped filament, it becomes blackened most quickly on the side facing the negative See also:

• LEG
• LEG (a word of Scandinavian origin, from the Old Norwegian leggr, cf. Swed. lagg, Dan. laeg; the O. Eng. word was sceanca, shank)

At the present time Domestic hardly any other method of distribution is adopted than that of an arrangement in parallel; that is to the other pole. The lamp filaments are thus arranged between the conductors like the rungs of a ladder. In series with each lamp is placed a switch and a fuse or cut-out. The lamps them-selves are attached to some variety of ornamental fitting, or in many cases suspended by a simple See also:

• PENDANT (through Fr. from Lat. pendere, to hang)

On a See also:

• THEATRE (BEarpov, " a place for seeing," from OeacOae)

For details as to the various modes of placing conducting wires in houses, and the various precautions for safe usage, the reader is referred to the article See also:

• ELECTRICITY

(1895); T. Heskett, " Notes on the Electric Arc," Electrician, vol. xxxix. (1897); G. S. See also:

• RAM
• RAM, PIERRE FRANCOIS XAVIER DE (18o4-1865)

(1903), 32, p. I (in this paper a copious bibliography of the subject of photometry is given) ; J. Dredge, Electric Illumination (2 vols., London, 1882, 1885) ; A. P. Trotter, " The Distribution and Measurement of Illumination," Proc. Inst. C.E. vol. cx. (1892) ; E. L. See also:

• NICHOLS, JOHN (1745–1826)

Eng. vol. vi. (1889); Sir W. de W. Abney, Photometry, Cantor Lectures, Society of Arts (1894) ; A. Blondel, " Photometric Magnitudes and Units," Electrician (1894) ; J. E. Petavel, "An Experimental See also:

• RESEARCH (O. Fr. recerche, from recercher, re- and cercer, mod. chercher, to search; Late Lat. circare, to go round in a circle, to explore)

to say, each lamp on the circuit has one terminal connected to a wire which finally terminates at one pole of the generator, and its other terminal connected to a wire leading Candle Power of Incandescent and Arc Lamps," Phil. Mag. (1905) ; the ."reliminary See also:

• REPORT (O.Fr. report or raport, modern rapport, from O.Fr. reporter, mod. rap porter, Lat. reportare, to bring back, in poetical use only, of bringing back an account, news, &c.)

(1907); L. Andrews, " Long Flame Arc Lamps," Jour. Inst. Elec. Eng. (1906) ; W. von Bolton and O. Feuerlein, " The Tantalum Lamp," The Electrician (See also:

• JAN

Consumers vary largely both in respect to the quantity and to the period of their demands, but the cost of supplying any one of them with a given amount of electricity is chiefly governed by the amount of his maximum demand at any one time. The reason for this is that it is not generally found expedient to See also:

• STORE (from O. Fr. estor or estoire, Late Lat. staurum or instaurum, stock, provisions, supply, from the late use of instaurare, to provide, properly to construct, renew, restore)

If the indicator shows that say twenty lamps is the greatest number which the consumer has turned on simultaneously, then he gets a large discount on all the current which his ordinary meter shows that he has taken beyond the equivalent of one hour's daily use of those twenty lamps. Generally the rate charged under this system is 7d. per unit for the equivalent of one hour's daily use of the maximum demand and rd. p r unit for all surplus. It is on this principle that it pays to supply current for See also:

• TRAMWAY

The cost of wiring may be taken at 15s. to £2 per lamp installed including all necessary wire, switches, fuses, lamps, holders, casing, but not electroliers or shades. Many undertakers carry out wiring on the easy See also:

• PAYMENT (Fr. paiement, from payer, to pay; Lat. pacare, to appease, pax, peace)

In the United States a co-operative electrical development association canvasses both the general public and the electricity supply undertakers. Funds are provided by the manufacturing companies acting in See also:

• CONCERT (through the French from Lat. con-, with, and certare, to strive)

11.1d. Single burner high-pressure gas 9.0 Double burner high-pressure gas 1I.7 Arc lamp Old type of See also:

• LANTERN (an adaptation of the Fr. lanterne from Lat. lanterna or laterna, supposed to be from Gr. Aa urritp, a torch or lamp, Aaµaew, to shine, cf. " lamp "; the 16th- and 17th-century form " lanthorn " is due to a mistaken derivation from " horn," as a m

As regards the other source of economy, the Nernst, the tantalum, the osram, and the metallized carbon filament lamp, although costing more in the first instance than carbon lamps, have become popular owing to their economy in current consumption. Where adopted largely they have had a distinct effect in reducing the rate of increase of output from supply undertakings, but their use has been generally encouraged as tending towards the greater popularity of electric light and an ultimately wider demand. Mercury vapour lamps for indoor and outdoor lighting have also proved their high efficiency, and the use of flame arc lamps has greatly increased the cheapness of outdoor electric lighting. The existence of a " daylight load " tends to reduce the all-round cost of generating and distributing electricity. This daylight load is partly supplied by power for See also:

• INDUSTRIAL

The Board of Trade are now prepared to receive electric measuring instruments for examination or testing at their electrical standardizing laboratory, where they have a battery power admitting of a maximum current of 7000 amperes to be dealt with. The London See also:

• COUNTY (through Norm. Fr. comae, cf. O. Fr. cunte, conk', Mod. Fr. comae, from Lat. comitatus, cf. Ital. comitato, Prov. comtat; see COUNT)