Page:EB1922 - Volume 31.djvu/805

Rh he was made major-general and commander of the Western Department but in Sept. went to France as commander of the 41st division of the A.E.F. The following year he commanded the 1st army corps and later the I. Army. He was at the second battle of the Marne, at St. Mihiel, and in the Argonne. In 1919 he was made commander of the Western Division and in 1920 commander of the IX. Corps, retiring March 21 1921. LIGHTING, ELECTRIC (see 16.659). Notable progress in illuminants was made during the period 1911-21. Advances in the art of applying artificial light to the best advantage have been even more remarkable, and as these apply to all illumi- nants they are dealt with in a separate article (see ILLUMINATING ENGINEERING).

Progress in Lamps. Some idea of (he position in regard to electric lamps at the end of 1910 may be gathered from two papers read by E. W. Marchant (Ri cent Progress in Electric Lighting, Ilium. Eng. Soc., London De :. 9 1910) and Haydn T. Harrison (Street Lighting by Modern Electric Lamps, Inst. of Elec. Engrs. Nov. 24 1910).

Metal filament lamps were in general rte, and their advantages, in comparison with arc lamps, were already the subject of discussion; tabular data of cost are given in Maurice Solomon's work on Electric Lamps. The use of arc lamps with flame carbons was extending, but ordinary carbons were still widely used. Efforts were made to extend the period of burning of flame arcs before recarboning became necessary. In the magazine flame arcs carbons are automatically replaced from a stock in the lamp as they burn away. In this way a period of burning of 80-100 hours has been secured. In the Jandus Regenerative arc lamp the flame carbons were enclosed in an air- tight chamber, with a special circulatory system to prevent deposi- tion of fumes on the globe. Approximately five c.p. (mean hemi- spherical) per watt and 70 hours burning with one pair of carbons were stated to be obtained. The enclosed Carbone arc was designed with a similar object, a special shape of globe being used to prevent inconvenient deposition of fumes. Quite recently a form of enclosed flame arc has been developed in Germany, the burning period being 80-120 hours, and the efficiency, on direct current 4-6 c.p. per watt (Lichttechnik, by L. Bloch). Inclined carbons are commonly used in flame arc lamps, but in the Crompton-Blondel arc vertical car- bons, one above the other, were adopted. Marchant (toe. cit.) gives values ranging from 3-72 to 6-85 c.p. per watt for various flame arcs efficiencies well above those yet attained with incandescent lamps.

Various circumstances have tended to limit the field for arc lamps. During the World War carbons were almost unobtain- able, and their cost has risen considerably. Moreover, gas-filled incandescent lamps tend to displace arc lamps for many purposes. At the present time (1921) lamps using ordinary carbons are becoming obsolete, but flame arcs still hold their own for light- ing large areas. Most flame arcs furnish light of a pronounced yellow colour, owing to the influence of calcium salts in their electrodes. Flame carbons yielding white light have, however, been used for photographic and cinema work. The arc lamp using a magnetite negative electrode, with a life of 150-175 hours, is still used in America but little known in England.

A step of great scientific interest has been the introduction, during the war, of searchlights using carbons cooled either by a spray of alcohol (Beck-Goerz system) or a blast of air (Sperry searchlight). (See Harrison, Ilium. Eng. March 1918; also Ilium. Eng. Feb. 1915; also McDowell, Trans. Ilium. Eng. Soc., U.S.A., Sept. 1916; also Electrician Feb. 2 1917). This leads to a smaller crater of increased intrinsic brightness, estimated at 200,000-300,000 candles per sq. in. as compared with 85,000 for the ordinary arc-crater. Thus, a much more powerful beam, which is stated to approach 500 million candles (max.) may be attained, and a diminished angle of dispersion. Intrinsic brilliancies of 600,000 c.p. per sq. in. are said to have been obtained in Germany (Lichttechnik by L. Bloch), while Lummer, with an arc operating in a pressure of 22 atmospheres and at a tem- perature of 7,600 Abs., attained 1,500,000 candles per sq. in.

No very striking advances in illuminants using the lumines- cence of metallic vapours are recorded. The tubular mercury vapour lamp has been improved by the use of devices enabling the lamp to start automatically without tilting by hand. At- tempts have been made to supply the missing red rays by mount- ing over the tube a fluorescing rhodamine reflector, but the effect is comparatively slight.

Wolfke, in Germany, obtained an approximately white light by using an amalgam of cadmium and mercury (Elektrot. Zeitschr. 1912, p. 917), but the lamp does not appear to have reached a commercial stage. In the other familiar form of mercury vapour lamp with a

quartz or silica glass tube, operated at a high temperature, the red and orange rays are not entirely missing. The chief feature of this lamp, apart from the higher luminous efficiency (estimated at about five c.p. per watt) is the high proportion of ultra-violet rays emitted. For ordinary lighting purposes these rays are masked by an outer globe of dense glass. Forms of lamps enabling the ultra-violet light to be applied in a concentrated form for therapeutic purposes are also available.

The Moore tube lamp, utilizing the luminescence arising from a high tension (5,000-17,000 V.) discharge through rarified nitrogen gas, is little known in England. The length of tube is usually con- siderable, but a small and compact form using carbon dioxide gas, the light of which is stated to resemble daylight closely in colour is used in industries involving accurate colour-matching.

The use of the rare gas neon in such luminescent tubes, announced by Claudes in 1911 (Comptes Rendus, May 22 1911) and since de- veloped to a commercial stage, has had interesting results. Owing to the higher brightness and greater efficiency of luminescent neon (approx. two candles per watt) tubes of moderate dimensions and varied shape can be constructed. Such lamps can now be operated direct on 220 volts, but a special starting device, applying an induc- tive discharge, is necessary. The vivid orange colour of the light is favourable to its use for spectacular lighting. Quite recently small neon lamps, resembling an ordinary glow lamp in appearance and capable of being inserted in an ordinary lamp holder, were exhibited before the Illuminating Engineering Society (see Ilium. Engineer Jan. 1921; ibid Aug. 1920). The cathode is extended and brought close to the anode, light appearing as a diffused orange glow. Although the efficiency is as yet low (apparently of the order of 0-06 c.p. per watt) such lamps consume only five watts or less on 220 volts. They may therefore prove useful in cases where only a weak light is necessary but a small consumption of electricity desirable. Further improvements may be anticipated.

Incandescent lamps using tungsten filaments in vacuo have now displaced the Nernst, tantalum and other forms, and the proportion of carbon filament lamps in use is constantly decreasing. The in- troduction in 1911 of filaments drawn out as wire from ductile tungsten has had important consequences. Filaments made by other processes (e.g. squirted or pasted) are now little used. The ductile tungsten wire now prepared can be more easily mounted in the bulb, can be readily wound in any desired shape, and is better able to resist shock and vibration. Ten-watt lamps are now available on 100-105 volts and 20- watt lamps on 200-210 volts, thus rendering such special devices as running lamps in series and the reduction of supply voltage by transformers largely unnecessary. Useful life and efficiency have also improved. Candle-power should not diminish by more than 20% in 1,000 hours' burning, the luminous efficiency being at>out o- 75-0^9 candles per watt, according to type. Filaments can be arranged in a bunched compact form suitable for automobile lamps, pocket torches, etc., and special " traction " forms, designed to withstand vibration, have been developed.

Another step of importance has been the development of the gas- filled or so-called " half-watt " lamp, announced in 1913 (see Lang- muir and Orange, Trans. Am. Inst. of Elec. Engrs. 1913; Gen. Elec. Rev., U.S.A. Oct., Dec. 1913; Pirani and Meyer, Elektrot. Zeitschr. 1915). The filament consists of a compact tungsten spiral brought to incandescence in an atmosphere of inert gas (usually nitrogen but in the smaller forms argon). The tendency of the tungsten to vola- tilize is checked by the pressure exerted by this envelope of gas. Fila- ments can accordingly be run at a higher temperature, with corre- spondingly improved efficiency. Recent specifications indicate that lamps should operate at I-I-6 candles per watt with a useful life of 1,000 hours. Still higher efficiencies may be expected from high candle-power low voltage units. A feature of the lamp is the forma- tion of convection currents within the bulb which has a long neck in which particles of tungsten tend to deposit, thus largely obviating blackening of the bulb proper. In England the smallest units avail- able on ordinary lighting pressures are 40 watts on 100-130 volts, and 60 watts on 200-260 volts. The largest lamps ordinarily listed consume 1,500 watts. Thus we have for the first time incandescent lamps of a candle-power comparable with that of arc lamps. For special purposes even larger units have been developed. Special lighthouse lamps consuming 2,400 watts have been used in Holland, and 4,ooo-watt types are stated to be in course of preparation. Filaments of gas-filled lamps may assume a wide variety of shapes. In the United States special forms have been developed for use in cinema lanterns.

The " arc-incandescent," (" Pointolite ") lamp, developed in the Ediswan laboratory during the war, has interesting features (Ilium. Eng. Jan. 1916; Jan. 1920). The source of light is a globule of tungsten brought to incandescence as the anode of an arc within a sealed glass bulb. The cathode is a rod composed of tungsten and certain rare earths, which is heated by the passage of a current, ionizes the space between the electrodes and starts the arc. As an approximate " point-source," with a brightness near 13,000 candles per sq. in., the lamp is adapted for use with optical lanterns, etc. Lamps giving up to 1 ,000 c.p. have been developed, and it is hoped that a 4,ooo-c.p. type now being prepared will prove valuable for cinema lanterns in view of the steady light and the fact that no manipulation is needed once the lamp is switched on.