"If the figures we collected on the magnetic field strength of Jupiter forced us to retire the equations, then none of the rest of the information we've gotten from the Bridge would have been worth the money we spent to get it. On the other hand, Jupiter was the only body in the solar system available, to us which was big enough in all relevant respects to make it possible for us to test those equations at all. They involve quantities of infinitesimal orders of magnitudes.

"And the figures showed that Dirac was right. They also show that Blackett was right. Both magnetism and gravity are phenomena of rotation.

"I won't bother to trace the succeeding steps, because I think you can work them out for yourself. It's enough to say that there's a drive generator on board this ship which is the complete and final justification of all the hell you people on the Bridge have been put through. The gadget has a long technical name, The Dillon-Wagoner gravitron polarity generator, a name which I loathe for obvious reasons but the technies who tend it have already nicknamed it the spindizzy, because of what it does to the magnetic moment of any atom, any atom within its field.

"While it's in operation, it absolutely refuses to notice any atom outside its own influence. Furthermore, it will notice no other strain 'or influence which holds good beyond the borders of that field. It's so snooty that it has to be stopped down to almost nothing when it's brought close to a planet, or it won't let you land. But in deep space well, it's impervious to meteors and such trash, of course; it's impervious to gravity; and it hasn't the faintest interest in any legislation about top speed limits. It moves in its own continuum, not in the general frame."

"You're kidding." Helmuth said.

"Am I, now? This ship came to Ganymede directly from Earth. It did it in a little under two hours, counting maneuvering time. That means that most of the way we made about 55,000 miles per second with the spindizzy drawing less than five watts of power out of three ordinary No. 6 dry cells."

Helmuth took a defiant pull at his drink. "This thing really has no top speed at all?" he said. "How can you be sure of that?"

"Well, we can't," Wagoner admitted. After all, one of the unfortunate things about general mathematical formulae is that they don't contain cutoff points to warn you of areas where they don't apply. Even quantum mechanics is somewhat subject to that criticism. However, we expect to know pretty soon just how fast the spindizzy can drive an object. We expect you to tell us."

"I?"