to a peg, which
is inserted in a hole, just hard enough to keep it in place, while there
is no extra strain on the board, but which can be drawn out with a smart
pull. When the log-line has run out as far as desired, there would be
some difficulty in hauling in the chip while it was upright in the
water; but a sudden jerk draws the peg at the angle, and permits the
board to lie flat, in which position the water offers the least
resistance to its passage.

The half-minute glass used on board the Young America, held by the
quartermaster, was like an hour glass, and contained just sand enough to
pass through the hole in the neck in thirty seconds. 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. One knot, therefore, will be fifty-one feet. If the
line pays out five hundred and ten feet in thirty seconds, by the glass,
the ship is going ten knots an hour. If it pays out four hundred and
eight feet in half a minute, or eight hundred and sixteen feet in a
minute, she will pay out a mile in as many minutes as eight hundred and
sixteen feet is contained in sixty-one hundred and twenty feet, which is
seven and a half minutes. Then the ship goes a mile in seven and a half
minutes, or eight miles an hour.

A knot on the log-line is therefore invariably fifty-one feet; and the
number of knots of the line run out in half a mi