seventeen-hour lamp burning carbons 600 mm. long. There is a twenty-hour lamp on the market burning carbons 650 mm. long. The color of the light of the flame arc depends on the chemicals with which the carbons are impregnated. The yellow light is usually the most efficient and for that reason is most widely used. The red is next, giving an efficiency of 10 to 20 per cent. lower than that of the yellow, while the white is still lower-25 to 40 per cent. lower than the yellow. STRIKING POINT. To obtain a long life from flame arc carbons the arc should always burn within the bowl of the economizer. To obtain this the carbons must have the correct striking point. For adjusting this, the lamp manufacturers furnish steel rods with squared ends of the exact size of the V line Striking Paint For should be in Fig. 14 10MM Striking Point For Fig. 15 For the motor feed lamps the striking point should be % inches below the lower edge of the economizer, as in Fig. 15. If the rods are not available, carbons whose ends have been squared with a file may be used. When the lamps operate poorly and whenever new lamp parts are supplied, the striking point should be adjusted. BURNED-OUT ECONOMIZERS. If the arc is allowed to burn too near the top of the economizer, or with too high an arc voltage, the economizer is liable to be burned out. This trouble may also occur if both carbons stick and the arc travels up the carbons. SLIPPING. Trouble is sometimes experienced due to carbons slipping. This may be caused by some part of the lamp mechanism sticking or by projections on the carbon. Care should be taken to see that the carbons are smooth before inserting them in the lamp. When one carbon hangs, the other will be fed downward to the end of its travel and if it is long enough to strike the ash pan, it will connect one side of the line to the frame of the lamp. This may develop a short circuit at some weak spot in the lamp. This trouble could only occur in lamps using independent carbon holders. CLEANING. At each retrimming, the globe equipment and all lamp parts on which the products of combustion have condensed should be cleaned thoroughly with a brush or with a dry cloth. The condensing tubes of the regenerative lamp should be cleaned with a brush. The manufacturers give the following rules for cleaning: Insert the brush into the lower opening of the regenerative chamber; the brush can then be passed up into both tubes and also through the globe, taking special care to clean deposit from the portion over the globe, and leave the tubes unobstructed. Obstruction in the tubes will prevent the lamp burning. Before inserting the lower cone holder, care should be taken to clean off all traces of white powder from the cone surface, both on the lamp frame and holder. An occasional application of graphite will entirely prevent sticking of the cone in its seating. Deposit in the outer globe is caused by the inner globe cap not seating tightly upon the inner globe. With the regenerative lamp, care should be taken in seating the globes properly as it is necessary to secure air-tight joints in order to obtain a maximum life from the carbons. Heavy globe deposit will cause a decided decrease in the light. Flickering may be caused by wet or greasy carbons, or by a wet globe. Jumping is caused by high arc voltage and by damp or greasy carbons. Intermittent jumping may be caused by a loose connection in the circuit. One of the large manufacturers of flame arc lamps gives the following rules for operation. If lamp fails to operate satisfactorily, open case and carefully inspect the following parts: Dashpot-Must be quite clean and plunger slide easily in same; if it does not, wipe carefully with clean cloth. On no account use ordinary emery paper or oil in the dashpot. Examine the screws holding the dashpot to its seat and see if they are tight and hold the dashpot firmly. Armature-See if this works smoothly and freely within the solenoid tube throughout its range of motion. If necessary, clean the inside of solenoid tube with a clean cloth. Upper Holder-See that the slotted end of the holder grips the carbon firmly. Be sure that the carbon requires a perceptible pull to come out of holder, or it may drop out accidentally and short-circuit the lamp. Use a full length carbon, pushing it upwards to its full movement, and allowing it to fall by its own weight, with fingers supporting it. This will show that it is free from friction and all danger of binding or sticking when lamp is burning. Clutch-See that this rises smoothly on its guide rod. Note that it grips carbon promptly and firmly, and that the carbon when gripped by clutch cannot slip through, even when pulled downwards by hand. Try if the clutch is easily released by the weight of the mechanism; the mechanism when moving as slowly as possible (guide this with a finger) should be able to press the clutch flat on its seat. Chips off upper carbon will sometimes collect under clutch and should be removed. TABLE 1 Light Reflected by Various Colors White blotting paper Per Cent. 82 Plain boards, clean 80 70 .50 to 70 62 50 45 20 40 36 25 40 20 18 13 12 12 12 0.5 0.4 3.5 1.2 0.4 Black cloth Black velvet Table shows how important it is to have light colored walls and ceilings. TABLE 2 Interior Illumination The desirable intensity of illumination for various classes of interior service has been given as follows: Station Equipment Multiple arc lamps require no special equipment, but are connected directly across incandescent lighting or power circuits. The series lamps, however, require special apparatus to hold the line current at a constant value at all times, no matter how many lamps are cut out of the circuit. Series lamps may be operated on either D. C. or A. C., but at the present time very few D. C. series carbon lamps are being installed. Constant cur A.C SUPPLY لسة CONSTANT CURRENT TRANSFORMER CONSTANT CURRENT APPARATUS. rent D. C. may be supplied by a special arc dynamo, or from a mercury arc rectifier. These dynamos are series wound and, in most cases, use a solenoid regulator connected in series with the line for controlling the current. In one type of machine the brushes are shifted on the commutator, increasing or decreasing the line voltage as may be necessary. In another, a resistance is shunted across the field 1ERCURY winding. By varying this resistance the strength of the field and consequently the voltage of the machine is varied. The armatures are sometimes made with several independent windings for supplying separate lamp circuits. The voltage that can be obtained from each of these circuits is 3000 to 5000 and usually about 50 enclosed lamps are connected in series on a single circuit. RECTIFIER FIG./6. DC CONSTANT CIRCUITCURRENT LAMPS A mercury arc rectifier is sometimes used to obtain constant current. It is connected on the secondary winding |