It was the next afternoon that the four were escorted by a trim-uniformed guard of honor across the flat spaceport to the Discovery. "The Jovians wanted to reduce Earth to colonial status, to be exploited for its natural resources," John explained to his companions as they walked. "All atomic installations were destroyed, all technicians and scientists exterminated systematically and all scientific books burned. They were very thorough about it.
"The successful revolt was accomplished with a concealed stock-pile of atomic weapons. Since that time, they've been garrisoned against the return of the Jovians. But atomic power was gone and so were the scientists who could bring it back and the books from which new scientists could learn.
"It's because they can't replace even so small a thing as an electric light bulb that destruction or unnecessary use of any sort of equipment is the rankest sort of treason. They've been saving all their technological capital for a last-ditch stand against the expected invasion.
"And it was ............