Richardson's handbook of projection (1930)

MANAGERS AND PROJECTIONISTS 1021 insulating" material will break down in the form of what we term a "puncture." The simple form of condenser described is seldom met with in actual practice, just as rubber bands are seldom found applied to mechanical practices, except for holding papers together. However, it was from such a simple beginning that the devices now in use were developed. In the electrical condensers now in use we find the metal plates and the insulating material, but because it is often desirable to secure considerable capacity without using the large amount of space the use of flat plates would entail, we find in their stead their equivalent in sheets of tin foil only about two one-thousandths of an inch thick, with insulation, in the form of paper, of only slightly greater thickness. Both these are cut into long strips and wound into rolls for the sake of compactness. A condenser of considerable capacity may therefore occupy small space, yet it operates just the same as does the flat plate condenser described, and is just as efficient. THE RUBBER BAND AGAIN.— Returning to our rubber band as the most convenient illustration, let us see just how our condenser works. If we attach a weight to one end of a rubber string, formed by cutting a rubber band in two, of just sufficient weight to stretch it moderately, we shall find that if we give the end we hold a sharp twitch upward and then hold it stationary, the weight will bob up and down and continue to do so at exactly the same rate of movement per minute for some time. We shall also find that, provided we keep time with that movement, it will require only a very slight movement of our hand up and down to maintain that bobbing at the same value. However, if we alter the