"Harla understands."
"Now," said Lou Graham triumphantly, "we make our battery by immersing the carbon and the zinc in the electrolyte. The carbon is the positive electrode and should be connected to the start of our electromagnet, whereas the end of the winding must go to the zinc. This will place the north pole to the left hand."
"Harla understands," said Teresa. "So far, Harla can perform this experiment in his mind. But now we must identify which end of the steel bar is north-pole magnetic."
"If we make the bar magnetic and then immerse it in acid, the north magnetic pole will be selectively etched."
"Harla says that this he does not know about. He has never heard of it, although he is quite familiar with electromagnets, batteries, and the like."
I looked at Lou Graham. "Did you cook this out of your head, or did you use a handbook?"
He looked downcast. "I did use a handbook," he admitted. "But—"
"Lou," I said unhappily, "I've never said that we couldn't establish a common frame of reference. What we lack is one that can be established in minutes. Something physical—" I stopped short as a shadowy thought began to form.
Paul Wallach looked at me as though he'd like to speak but didn't want to interrupt my train of thoughts. When he could contain himself no longer, he said, "Out with it, Tom."