Then, the computer has to look at each frequency separately and try to decide if it is carrying an intelligent signal as opposed to noise.

Even if no intelligent signals are detected, they point out, such a comprehensive survey of the heavens is likely to produce other important discoveries.

"You said there were over two hundred separate frequencies upon which you were finding apparently intelligent signals."

They were all imitating supposedly intelligent signals from outer space, which had been received by radio telescopes only the week before.

Dr. Drake was proud of this historic test even though, he wrote later, "we could discern no trace of an intelligent signal."

Its computerized job is to compare readings with a telescope in Georgia and confirm that detected intelligent signals are in fact genuine.

So why were they heading there when no intelligent signals originated from it?

However, there had been no reaction, or any hint of an intelligent signal, from below the steadily thickening clouds.

Seven months later, radio astronomer Frank Drake became the first person to start a systematic search for intelligent signals from the cosmos.

Some countries have "intelligent" pedestrian signals, where the pedestrian must push a button in order to assert his intention to cross.