Cronos — Robert Silverberg

Letters to Atlantis: Time travel has allowed Roy¹s consciousness to enter the mind of the heir to Atlantis¹s throne, and what he found disturbed him. How could such an advanced city exist at this time? The rest of the world was, as Roy¹s partner, Lora, discovered in her travels, a dark, barbaric land still thawing from the ice age. Roy knew the island¹s fate‹according to legend, it would vanish into the sea. But if Roy was in an Atlantis unlike anything the researchers had predicted, then what were its secrets? And when would it be destroyed? PROJECT PENDULUM: The nature of time mechanics requires that the two travelers¹ masses be precisely matched; for that reason, the first time travelers must be a pair of identical twins. For paleontologist Sean Gabrielson, the chance to journey back to the age of dinosaurs was worth any risk. For his physicist brother, Eric, the chance to see ninety-five million years in the future was equally irresistible. What neither planned on, however, was how the inhabitants of those times would react to their presence. . . . THE TIME HOPPERS: In the 25th century, the only escape from suffocation in a totally controlled environment is to hop backward through time. However, since time-hopping rearranges the past on which the structure of current existence is based, it must be stopped‹but not too quickly. For the history of the 1970s includes the arrival of hoppers who have not yet left the 2490s‹and whose departure must be stopped!