"But in the betatron, the thing is run differently. The magnet is built for A. C. and the electron gun runs off the same. As your current starts up from zero, the electron gun squirts a bouquet of electrons into a chamber built like a pair of pie plates set rim to rim. The magnet's field begins to build up at the same time, and the resulting increase in field strength accelerates the electrons and at the same time, its increasing field keeps the little devils running in the same orbit. Shoot it with two-hundred-cycle current, and in the half cycle your electrons are made to run around the center a few million times. That builds up a terrific velocity--measured in six figures, believe it or not. Then the current begins to level off at the top of the sine wave, and the magnet loses its increasing phase. The electrons, still in acceleration, begin to whirl outward. The current levels off for sure and begins to slide down--and the electrons roll off at a tangent to their course. This stream can be collected and used. In fact, we have a two-hundred-cycle beam of electrons at a couple of billion volts. That, brother, ain't hay!" "Is that enough?" "Nope." "Then how do you hope to increase this velocity? If it is easier to run this up than it would be the cyclotron, how do we go about it?" Channing smiled and began to draw diagrams on the tablecloth. Joe looked over with a worried frown, and then shrugged his shoulders. Diagrams or not, this was an emergency--and besides, he thought, I need another lesson in high-powered gadgetry. * * * * * "The nice thing about this betatron," said Channing, "is the fact that it can and does run both ends on the same supply. The current and voltage phases are correct so that we do not require two supplies which operate in a carefully balanced condition. The cyclotron is one of the other kinds; though the one supply is strictly D.C., the strength of the field must be controlled separately from the supply to the oscillator that runs the D plates. You're sitting on a fence, juggling knobs and stuff all the time you are bombarding with a cyc. "Now let us inspect the supply of the betatron. It is sinusoidal. There is the catch. There is the thing that makes it possible. That single fact makes it easy to step the power up to terrific quantities. Since the thing is fixed by nature so that the input is proportional--electron gun initial velocity versus magnetic field strength, if we increase the input voltage, the output voltage goes up without having to resort to manipulistic gymnastics on the part of the operator." "Go on, Professor Maxwell." "Don't make fun of a great man's name," said Arden. "If it wasn't for Clerk Maxwell, we'd still be yelling out of the window at one another instead of squirting radio beams all over the Solar System." "Then make him quit calling me Tom Swift." "Go on, Don, Walt and I will finish this argument after we finish Hellion Murdoch."