Richardson's handbook of projection (1930)

1016 HANDBOOK OF PROJECTION FOR dealing with the action of light and electricity, both of which are enormously rapid — more rapid than can be understood or conceived by the untrained mind. When you have the foregoing clearly fixed in your mind, consider that (a) this light-sensitive material will ionize the gas in exact proportion to the amount of light reaching it at any split fraction of the millionth of a second, and (5) that the amount of light reaching it depends at any split fraction of the millionth of a second upon the density of one one-thousandth of an inch (up and down) of the sound band then passing under the light incident upon it from the slit. Don't overlook the fact that the current flow between the anode and cathode of the cell will be dependent (voltage constant, remember) upon the ionization, and you have the complete action of the photo-electric cell, which sends forward to the first amplifier in the form of electric current exactly what the microphone sent forward to the actuating impulse governing the variations in intensity or brilliance of the light beam which made the original record upon the film sound track at the camera. Another interesting thing, and one which it is well that the projectionist understand, is that the impulses sent out by the photo-electric cell are almost inconceivably weak. Indeed, so weak are they that before they can be made to operate the horns or loud speakers, acceptably, they must be built up by the amplifiers approximately one hundred million (100,000,000) times. The projectionist will understand from this that he is handling very delicate forces and apparatus which must function with high efficiency if maximum results are to be attained. Naturally a force so enormously weak that it