ot a word--get that?
Let me have a written report: full details, but concise as possible."

He went back to the radio room, and the operator there received the
same instructions.

"What are you going to do?" the lieutenant questioned.

Captain Blake was reaching for a head-set. "Listen in," he said
briefly; "try to link up that impossible ship with those messages,
then report at once to the colonel and whoever he calls in. I'll want
you along, Mac, to swear I am sober."

* * * * *

He had a head-set adjusted, and McGuire took up the other. Again the
room was still, and again from the far reaches of space the dark night
sent to them its quavering call.

The weird shrillness cried less loudly now, and the men listened in
strained silence to the go and come of that variable shriek. Musical
at times as it leaped from one clear note to another, again it would
merge into discordant blendings of half-tones that sent shivers of
nervous reaction up the listeners' spines.

"Listen," said McGuire abruptly. "Check me on this. There are two of
them, one loud and one faint--right?"

"Right," said Captain Blake.

"Now notice the time intervals--there! The faint one stops, and the
big boy cuts in immediately. No waiting; he answers quickly. He does
it every time."

"Well?" the captain asked.

"Listen when he stops and see how long before the faint one answers.
Call the loud one the ship and the faint one the station.... There!
The ship is through!"

There was pause; some seconds elapsed before the answer that whispered
so faintly in their ears came out of the night.

"You are right, sir," the operator said in corroboration of McGuire's
remark. "There is that wait every time."

"The ship answers at once," said McGuire; "the station only after a
wait."

"Meaning--?" inquired the captain.

"Meaning, as I take it, that there is time required for the message to
go from the ship to the station and for them to reply."

"An appreciable time like that," Captain Blake exclaimed, "--with
radio! Why, a few seconds, even, would carry it around the world a
score of times!"

Lieutenant McGuire hesitated a moment. "It happens every time," he
reminded the captain: "it is no coincidence. And if that other station
is out in space--another ship perhaps, relaying the messages to yet
others between here and--Venus, let us say...."

* * * * *

He left the thought unfini