Wikipedia
"Life-Line" is a short story by American author Robert A. Heinlein. Published in the August 1939 edition of Astounding , it was Heinlein's first published short story.
The protagonist, Professor Pinero, builds a machine that will predict how long a person will live. It does this by sending a signal along the world line of a person and detecting the echo from the far end. Professor Pinero's invention has a powerful impact on the life insurance industry, as well as on his own life.
Pinero is mentioned in passing in the novels Time Enough for Love and Methuselah's Children when the practically immortal Lazarus Long mentions having been examined and being sent away because the machine is "broken".
Heinlein was motivated to write the story by an editorial in Thrilling Wonder Stories magazine, in which Hugo Gernsback wrote that he wanted to foster new talent in the field, and that "We shall endeavor to present one amateur writer's story in each forthcoming issue [...] until further notice." TWS's rate at the time was 0.5 cents per word. After Heinlein had written the 7000-word story, he submitted it first to a rival magazine, Astounding, which paid 1 cent per word. Astounding bought the story, and at their higher rate, Heinlein was paid $70. This was a significant sum in 1938 (approximately $1100 in 2015 dollars). In Grumbles from the Grave, on receiving the check for the story Heinlein is reported to have said, "How long has this racket been going on?" Later, Heinlein's fictionalized professional bio came to include an inaccurate version of the story, in which TWS had advertised a $50 contest. (At TWS's word rate, a story that was the maximum length of 10,000 words would have been bought for $50.)
The story made a later appearance in The Worlds of Robert A. Heinlein, a collection of short stories published in 1966, in Expanded Universe in 1980, and in a Baen edition of "The Man Who Sold The Moon", ISBN 0-671-65623-6, 1987.
Usage examples of "life-line".
Then the messboy came hurrying along the after-deck, clinging like a monkey to the life-line that had been rigged.
Although the gale was very heavy indeed, filled with blinding rain and sleet, and although at first it blew against the swell and cut up a wicked sea, it was not foul, and the frigate, under close-reefed topsails, raced south at a tremendous pace, half smothered in flying water, shipping green seas every other minute, so that her decks were aswim and men could never move without clinging to the life-lines stretching fore and aft.