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314 RICHARDSON'S BLUEBOOK OF PROJECTION
should sit immediately on either rubber, cork or springs, which will absorb any slight vibration the machine may create.
(128) Located thus the motor-generator set will be under the constant observation and care of the projectionist which it cannot have when removed far from the projection room. Moreover, basements are often damp and sometimes flooded — both of which damage the equipment.
Spacing
(129) Be sure to leave clear space on every side of the set. Men must have room to work around a set if it is to be well taken care of. Install a drop light (preferably a reel light) on a long cord so that the projectionist may be able to illuminate any part of the machine without difficulty.
A thick layer of cork or rubber absorbs vibration for a time, but with the passage of time these substances lose a part if not all of their resiliency. (130) Were we considering the installation of a motor-generator set in a theatre of our own, we would set it on coil springs not less than six inches long, and of such capacity that four of them, one under each corner, would carry the weight with no more than one inch depression. Coil spring supports are not expensive. Any responsible spring manufacturer will supply them. Order four springs that will carry the weight of the set and he will guarantee sufficient resiliency to absorb all vibration.
It is necessary to make a strong concrete frame of proper depth and size and sufficiently massive, with a half-inch bolt embedded head down near each corner and protruding about one and one-half inches above the surface. The springs themselves should consist of a spiral of from four to five inches diameter at one end, tapering to about two and one-half inches at the other, the extreme large diameter of the steel being turned in to the axis of the spring and curled to take a half-inch bolt readily.
The smaller end of the spring is then bolted to the bot