By the 1860s, there was strong demand for adventure, detective, sensational, and science-fiction novels. Indeed, the late nineteenth century saw a tremendous amount of technological progress, which inspired authors to write in the genre of science fiction. Herbert George Wells' "The Time Machine" (1895) was a commercial success; in it, he introduced the notion of time travel. In some instances, science fiction inspired new technology and scientific research. Explorer Ernest Shackleton acknowledged that the novel "Twenty Thousand Leagues Under the Sea" by Jules Vernes was an inspiration.