"But the stream of electrons will be diverged if it falls through a field of increasing positive potential. In order to bring the stream to a focus, we must follow the first anode with another anode of a potential less than the first anode but still higher than the cathode. That bollixes up the works. It focuses the stream and slows it at the same time. So we follow this anode with another high positive electrode and speed them up again, and then focus them and so on until we get the required velocity. These anodes are shaped like rings so that their electrostatic effect will exist in the center of them; the beam passes through this center." "In other words the ring-shaped electrodes are electrostatic lenses?" "Nope. It is the space between them. The lens is either convex or concave depending upon whether the voltage gradient is from positive to less positive or if it is positive to more positive, respectively. In an electrostatic lens for electrons, the thing is not like a glass lens for light. Whether your lens is diverging or converging depends upon which way your electron stream is running through it. With light, a convex lens will converge the light no matter which direction the light is coming from." "Uh-huh. I see in a sort of vague manner. Now, fellows, go on from there. What's necessary to make this dingbat tick?" "I want to think out loud," said Channing. "That's nothing unusual," said Arden. "Can't we get into Joe's? You can't think without a tablecloth, either." * * * * * "What I'm thinking is this, Walt. You've been trying to squirt electrons like a fireman runs a hose. Walt, how long do you suppose a sixteen-inch rifle would last if the explosives were constantly replaced and the fire burned constantly?" "Not long," admitted Walt. "A gun is an overloaded machine," said Don. "Even a little one. The life of a gun barrel is measured in seconds; totaling up the time of transit of all the rounds from new barrel to worn gun gives a figure expressed in seconds. Your electron gun, Walt, whether it be fish, flesh, or fowl, must be overloaded for an instant." "Is overload a necessary requirement?" asked Arden. "It seems to me that you might be able to bore a sixteen-inch gun for a twenty-two. What now, little man?" "By the time we get something big enough to do more than knock paint off, we'll have something bigger than a twenty-two," grinned Channing. "I was speaking in terms of available strength versus required punch. In the way that a girder will hold tremendous overloads for brief instants, a gun is extremely overloaded for milliseconds. We'll have a problem--" "O.K., aside from that, have you figured out why I haven't been able to do more than warm anything larger than a house brick?" "Sure," laughed Channing. "What happens in a multigrid radio tube when the suppressor grid is hanging free?" "Charges up and blocks the electron stream ... hey! That's it!" "What?" asked Arden.