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Bausch & Lomb Optical Company Figure 3—Model C Balopticon with Large Lamp House and Water Cell. Where electricity is available and an outlet is provided with a carrying capac- ity of 15 or more amperes, we recommend the arc lamp and a rheostat of 15 amperes or more capacity. Should no other outlet than the ordinary lighting socket be available, the carbon holders of the arc lamp can be fitted with bushings and the small pencil carbons used in connection with one of our 4/4-ampere rheostats. This feature makes it possible to use the lantern under different wiring conditions by having a combination 5, 10 and 15-ampere rheostat. The arc lamp supplied is a 90° hand-feed arc lamp with horizontal and vertical carbons and with feeding gears controlling the carbons independently or together. A very desirable form of illuminant, and one that is rapidly taking the place of the arc lamp for general class room use, is the new 400-watt, gas-filled Mazda lamp with its reflector. It is entirely automatic and noiseless in operation, can be attached to any convenient lamp socket and gives illumination considerably exceeding that of a 5-ampere arc lamp. For large lecture rooms, or auditoriums where the lantern is placed 50 feet or more from the screen and a fairly large picture is to be projected, we recommend the 1000-watt, gas-filled Mazda lamp, which draws about 9 amperes but gives illumination fully equal to the 15 or 20-ampere arc lamp. The size of this lamp necessitates the use of the large, light-tight lamp-house, as shown in Figure 3. In cases where electricity is not available, either the acetylene or oxyhydro- gen burner is a very satisfactory substitute. The acetylene burner which we supply consists of two jets with a special, spherical glass reflector. The consumption of gas per hour is 1J4 cubic feet. The illumination from this burner equals that from a four-jet burner and is entirely free from flare streaks or flicker. The most convenient and satisfactory source of gas supply is the acetylene tank, as used on motorcycles and automobiles. The oxyhydrogen burner gives illumination exceeding in brilliancy that of the acetylene burner, but is not so convenient and costs somewhat more to operate. An oxyhydrogen generator is recommended as a source of supply. 28