id Russ slowly, "what planets have exchanges?"

"All of them except Mercury. The Jovian exchange is at Ranthoor. There's
even one out at Pluto. Just mining and chemical shares listed, though."

Russ did not reply. Smoke curled up from his pipe. He was staring into
the fire.

"Why do you ask?" Greg wanted to know.

"Just something stirring around in my mind. I was wondering where
Chambers does most of his trading."

"Ranthoor now," said Greg. "Used to do it on Venus. The listing is
larger there. But since he took over the Jovian confederacy, he switched
his business to it. The transaction tax is lower. He saw to that."

"And the same shares are listed on the Callisto market as on the New
York boards?"

"Naturally," said Greg, "only not as many."

Russ watched the smoke from his pipe. "How long does it take light to
travel from Callisto to Earth?"

"Why, about 45 minutes, I guess. Somewhere around there." Greg sat
upright. "Say, what's light got to do with this?"

"A lot," said Russ. "All commerce is based on the assumption that light
is instantaneous, but it isn't. All business, anywhere throughout the
Solar System, is based on Greenwich time. When a noon signal sent out
from Earth reaches Mars, it's noon there, but as a matter of fact, it is
actually 15 minutes or so past noon. When the same signal reaches
Callisto, the correct time for the chronometer used in commerce would be
noon when it is really a quarter to one. That system simplifies things.
Does away with varying times. And it has worked all right so far because
there has been, up to now, nothing that could go faster than light. No
news can travel through space, no message, no signal can be sent at any
speed greater than that. So everything has been fine."

Greg had come out of the chair, was standing on his feet, the glow of
the blaze throwing his athletic figure into bold relief. That calm
exterior had been stripped from him now. He was excited.

"I see what you are getting at! We have something that is almost
instantaneous!"

"Almost," said Russ. "Not quite. There's a time lag somewhere. But it
isn't noticeable except over vast distances."

"But it would beat ordinary light signals to Callisto. It would beat
them there by almost 45 minutes."

"Almost," Russ agreed. "Maybe a split second less."

Greg strode up and down in front of the fireplace like a caged lion. "By
heaven," he said, "we've got Chambers where we want him. We can beat the
s