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210 RICHARDSON'S BLUEBOOK OF PROJECTION
them, forming an ideal anchorage for the projectors.
(4) It is possible to embed anchor bolts in a cement floor that is already laid. Drill holes four inches deep and of sufficient diameter to just admit the heads of the anchor bolts, which need only be one-eighth inch larger than the bolts themselves. Then, with a small, roundnose or diamond point cold chisel, cut small holes around the sides of the bolt holes or roughen their sides by gouging out pieces of concrete. This helps the metal filling to be well anchored.
Next set the anchor bolts in place, heads to the bottom, and fill the space around them with molten lead or babbitt.
(5) The supporting base must have an up-and-down adjustment with a proper locking device, for raising or lowering the projector mechanism. (6) Means must also be provided by which the table supporting the lamphouse and mechanism may be tilted and locked rigidly in position to provide an upward projection angle of not less than 10 degrees and a downward angle of not less than 25 degrees. Greater projection angles are used, but it is poor practice.
In the supporting base of the pedestal type, provision should be made for carrying the various circuit wires upward through the supporting column. It is not essential, but makes a neater job.
(7) The projector must be set perfectly level sidewise, else the screen image will itself be out of level.
The Lamphouse
(8) Except in case of the mazda light source, the lamphouse should have maximum ventilation without disturbing the light source. It is a good general rule to follow because it reduces the room temperature as well as the temperature of the lenses, mirrors, wires and mechanisms inside the lamphouse.
(9) Lamphouse ventilation should be through a metal pipe having riveted or otherwise well secured joints. The pipe should connect either with the main theatre ventilation system or, preferably, directly with