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THE PROJECTOR 211
the open air. It should be thoroughly insulated from all inflammable material and provided with an adjustable damper — since constant adjustment of the draught is essential to good operation of the light source.
(10) Lamphouse ventilation helps to reduce projection room temperature in summer and in all seasons in warm climates. High temperature inside the lamphouse is hard on the mechanism, causing it to deteriorate much more rapidly than would be the case at moderate temperature.
(11) It is not at all necessary that the lamphouse vent pipe be covered with a screen. Such sparks as pass into it are extremely light and harmless. The objection to a screen — it must be of fine mesh to be effective against sparks — is that it would quickly become clogged with carbon ash, and interfere with or entirely stop all ventilation. If you have a vent-pipe screen, we advise its removal unless local authorities object.
(12) Where Mazda serves as the projector light source there is no need for a vent pipe, since it generates no gases and relatively little heat. It is enough to leave the vent in the top of the lamphouse open.
(13) Every lamphouse should have convenient means for the removal of carbon chips and other refuse from the lamphouse floor. The workmanlike projectionist keeps his lamphouse scrupulously clean.
The Dowser
(14) With all straight high intensity light sources a dowser blade should be located between the light source and the condenser collector lens. When the arc is struck, all high intensity light sources throw off incandescent particles of carbon which will quickly destroy the polished surface of the collector lens if it is not protected.
Regardless of the type of arc light source, if a condenser is used in front of the arc there should be a dowser blade of substantial thickness (15) located as close to the collector lens as is practicable. Not only does this blade protect the lens from flying particles of