"The Man Who Mastered Time" by Ray Cummings

Ray Cummings's The Man Who Mastered Time was unusual in that it was not an original work but a reprint of a 1920s story which reads like a riff on H.G. Wells's famous work The Time Machine. In it, a father-and-son duo of scientists stumble across a process that allows them to peer into the indeterminate future. 

Witnessing a beautiful girl imperiled by a thuggish brute, the two turn a hoverable aeroplane into a time machine, which the hormonally-driven son uses to travel thousands of years into the future to rescue the maiden. He soon finds himself in the midst of a political struggle between the people of an ice-age north and the remaining civilization, which has retreated to the Caribbean and reflects a class divide that ol' Herbert George would have found familiar (seriously, it wouldn't surprise me in the least to find that he sued for copyright infringement). The young man soon summons his father for aid, and with the help of a friend, aid the civilized underdogs against the barbarian hordes. There are some aspects of the novel – such as the employment of "girls" in combat – that but for the most part it's a prime piece of pulp science fiction, and while it had it's share of problematic elements (the scientist's friend zeroing in on the beautiful girl's teenage sister seemed a little predatory even for the time) I enjoyed it for the action adventure it was. (Mark, GoodReads)