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Bausch & Lomb Optical Company As an automatic lamp, this can only be used on direct current, but by disen- gaging the automatic mechanism it is readily transformed into the hand-feed type for use on either current. A rheostat must always be used with this lamp to regulate the current. Note—This lamp may be substituted for the hand-feed arc on any of our Balopticons when ordering, at an additional cost of $65.00. Gas-filled Mazda Lamps ___ Figure 1—400-Watt Gas-Filled Mazda Lamp. The new gas-iilled Mazda lamps with concentrated filament, which have been especially developed for projection purposes, furnish an automatic, steady-burning and very efficient and economical light source for the simpler types of Balopticons. The efficiency varies from 0.8 watt per candle power in the lower wattages to 0.55 watt per candle power in the higher wattages. They are rated by the manufacturer to have a life of approximately 200 hours and we stand ready to replace any that may prove defective or burn for an unduly short period. If the Mazda burned only one-half its rated life, the cost of operating this type, including renewals, would be much less than the cost of an arc lamp giving equal illumination, when the saving in current and carbon consumption is considered. In addition, the Mazda is entirely automatic, noiseless and steady in operation and its efficiency per number of amperes used is higher than that of the A. C. arc. These lamps are not recommended for microscopical projection as they are not sufficiently concentrated or homogeneous. With the exception of the 1000-watt lamp, they may be attached to any regular lamp socket. They are used without resistance on circuits of 110-115 volts. For 220-volt circuits a resistance (listed on page 107) must be used in series with the lamp. 104