always in a field, even landing in atmosphere, and
the ship has practically no mass even when it's letting down to landing.
It has weight, but next to no mass. Didn't you notice the difference?"

"Stupid as it may seem, I didn't," admitted Cochrane. "I haven't the
least idea what you're talking about."

Jones looked at him patiently.

"Now we can shoot our exhaust out of the field! The ship-field, not the
main one!"

"I'm still numb," said Cochrane. "Multiple sclerosis of the brain-cells,
I suppose. Let me just take your word for it."

Jones tried once more.

"Try to see it! Listen! When we landed the first time we had to use a
lot of fuel because the tail of the ship wasn't in the Dabney field. It
had mass. So we had to use a lot of rocket-power to slow down that mass.
In the field, the ship hasn't much mass--the amount depends on the
strength of the field--but rockets depend for their thrust on the mass
that's thrown away astern. Looked at that way, rockets shouldn't push
hard in a Dabney field. There oughtn't to be any gain to be had by the
field at all. You see?"

Cochrane fumbled in his head.

"Oh, yes. I thought of that. But there is an advantage. The ship does
work."

"Because," said Jones, triumphant again, "the field-effect depends
partly on temperature! The gases in the rocket-blast are hot, away up in
the thousands of degrees. They don't have normal inertia, but they do
have what you might call heat-inertia. They acquire a sort of fictitious
mass when they get hot enough. So we carry along fuel that hasn't any
inertia to speak of when it's cold, but acquires a lunatic sort of
substitute for inertia when it's genuinely hot. So a ship can travel in
a Dabney field!"

"I'm relieved," acknowledged Cochrane. "I thought you were about to tell
me that we couldn't lift off the moon, and I was going to ask how we got
here."

Jones smiled patiently.

"What I'm telling you now is that we can shoot rocket-blasts out of the
Dabney field we make with the stern of the ship! Landing, we keep our
fuel and the ship with next to no mass, and we shoot it out to where it
does have mass, and the effect is practically the same as if we were
pushing against something solid! And so we started off with fuel for
maybe five or six landings and take-offs against Earth gravity. But with
this new trick, we've got fuel for a couple of hundred!"

"Ah!" said Cochrane mildly. "This is the first thing you've said that
meant an