The two men went back to the shadow of the cliff and got down from their robots.
What did you say to Speedy when you s him for the selenium? Powell asked. "Did you tell him that it was urgent? Important?'
"No," Donovan replied. "It was just a routine order. I just told him that we needed some selenium and that he should and get it.
Right,' said Powell. "Well, let's start with the Three Laws of Robotics that are built into a robot's positronic brain. First, a robot must not injure a human being, or allow a human being to come to harm.
Second, a robot must obey the orders given by human beings unless they conflict with the First Law.
Third, a robot must protect itself, unless this conflicts with the First or Second Laws.
"And how does that help us?'
"Speedy is one of the most expensive robots available. To protect the SPDs, their brains were made a little differently: the Third Law was built in more strongly than is usually done. Perhaps there's a danger at the selenium pool which Speedy is avoiding.
"What danger?'
"Well, where does the selenium come from?
It's produced after a volcano has been active, Donovan said quickly.
"That's it! Maybe there's some gas above the selenium pool, escaped from underground, which is a risk to Speedy. Perhaps carbon monoxide. At this temperature, it could combine with the iron parts of Speedy's machinery and cause him to explode.