eight o'clock
The log-line was one hundred and fifty fathoms in length , and was wound on a reel , which turned very easily , so that the resistance of the chip to the water would unwind it . The log-line is divided into certain spaces called knots , the length of each of which is the same fractional part of a mile that a half minute is of an hour . If there be sixty-one hundred and twenty feet in a nautical mile , or the sixtieth part of a degree of a great circle , which is not far from accurate , and the ship be going ten knots an hour , she will run sixty-one thousand two hundred feet in an hour . If the chip were thrown overboard at eight o'clock , and the line were long enough , the ship would have run out sixty-one thousand two hundred feet , or ten miles , at nine o'clock , or in one hour . In one minute she would run one sixtieth of sixty-one thousand two hundred feet , which is ten hundred and twenty feet ; in half a minute , five hundred and ten feet . The half-minute glass is the measure of time generally used in heaving the log . While the sand is dropping through , the line runs out five hundred and ten feet , the ship going ten knots an hour being the basis of the calculation .