may be ascertained. Allowance must of course be made for the state of the tide; the soundings on the charts, as I have already explained, being calculated for low water, ordinary spring tides.
The log-ship, log-line, and log-glass enable one to calculate a vessel's speed through the water. The log-ship is a triangular piece of wood, about five inches broad, weighted with lead on one side so as to sink it and keep it perpendicular. The end of the log-line is attached to the corners of the log-ship by three small lines, forming a bridle. One of these lines terminates in a peg which fits into a hole in the log-ship, in such a way that it is released when a strain is put on the log-ship; the log-ship then being turned on edge, offers small resistance to the water, and can be more easily hauled on board.
The Log-Glass is a common sand-glass constructed so as to run out in a certain number of seconds—generally fifteen or thirty seconds.
The Log-line, which is 120 fathoms long, is knotted at regular intervals, the distances between knot and knot bearing the same proportion to a nautical mile as the number of seconds in which the glass runs out bears to one hour. The last few fathoms of line next to the log-ship are not knotted, and this portion, known as the stray-line, is marked by a bit of bunting. The log-line is wound round a reel.
