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The Second Trip is a 1972 science fiction novel by Robert Silverberg. Prior to its publication by Doubleday, it was published in serialized form in Amazing Stories from July to September 1971.

The Time Hoppers is a science fiction novel by American writer Robert Silverberg, first published by Doubleday in 1967. The plot concerns Joe Quellen, a 25th-century bureaucrat charged with investigating "hoppers", travelers from the future whose presence in the past has been documented for hundreds of years, and his …