operator needed only to set the co-ordinates for the part
of the sky to be examined, then clock mechanisms of remarkable precision
would keep the telescope on target until the target sank below the
horizon.

The boys examined banks of amplifiers that would turn faint signals into
usable ones. The latest techniques had been used to ensure maximum
performance.

Outside, Farid showed them the self-contained diesel-electric power
plant. They stood directly under the massive concrete mount for the
great dish and marveled at its size. The main bearings on which it moved
were bigger around than Scotty was tall, yet the whole affair was so
delicately balanced that a tiny electric motor could control it with
fantastic precision.

Still under construction were offices and barracks. The latter would
allow the scientists to stay there for days at a time when working on
particular projects. The offices were nearly done, and plasterers were
at work, but the forms for the barracks floor were just being completed.
The pouring of concrete would start on the following day.

Rick looked at the pyramids on the horizon and contrasted this scene of
construction with the one that had produced the great tombs. Then, it
was only men--thousands of them. Today, it was a handful of skilled
workers plus machinery.

"Now," Farid said, "let's get back to the control room. Kerama is going
to review the situation for the staff. Some of them are new on the job."

As Farid and the boys rejoined the others, Dr. Kerama was pointing to a
series of peaks on the Sanborn tracings. "You will note that these peaks
occur at intervals, with the spacing apparently random. The main
sequence of noise out of which the peaks rise is the 21-centimeter
hydrogen line. Notice also that the peaks have nearly identical
amplitudes. Obviously, the source is neutral hydrogen, which is to say
hydrogen in its normal form, not ionized as we find it in plasma in a
star's atmosphere. Our problem is simply to locate the source of the
peaks. Somewhere in the circuit there seems to be an effect that serves
to modulate the incoming signal. Our antenna will be useless unless we
eliminate this interference so that the signal can be pure once again."

Rick had seen Sanborn tracings before. The system was a standard method
of recording. His first experience with it had been in making permanent
records of telemetered signals from rockets.

A technician asked, "Sir, do these peaks o