The Coils of Time — A. Bertram Chandler

Dr. Henshaw had created what he thought was a time travel machine and he had sent guinea pigs through it. But now he needed a human guinea pig to test it with.

Christopher Wilkinson thought the whole idea was absurd, until a book that had been sent through the machine came back with a thumb print on it, the fingerprint of Vanessa, his long lost sweetheart!

So Wilkinson agreed to the experiment. He stood in the white circle facing the machine as it began to gleam and spin, pulling him down through the tortuous coils of time...