The speed of a vessel was first obtained by throwing overboard a floating subject at the bow and noting the time elapsed when it passed an observer at the stern. From this the log line with "knots" was derived, with the fourteen and twenty-eight seconds sand glasses to record speed. A "knot" indicates a geographical or sea mile which has been standardized at 6080 feet; the land or statute mile is 5280 feet, therefore, if a vessel is said to be sailing at the rate of thirteen knots, a railroad train going at the same speed would be running at the rate of fifteen miles an hour. The term "knot" is used solely to indicate rate of speed; the distance covered is always stated in nautical or sea miles. "Heaving the log" meant throwing out from the stern of a vessel a small float attached to a line running from a reel held clear of the rail, the float remaining stationary in the water. At the instant the log is "heaved" a sand glass is turned. On the line are knots (hence the term), pieces of marline or rags tied through the strands and spaced the same fraction of a mile apart,--above forty-six feet and six inches,--which twenty-eight seconds is the fraction of an hour,--about one one-hundred and twenty-eighth. Therefore, using a twenty-eight seconds glass and checking the line the instant the sand runs out, the number of knots and fractions paid out on the line will at once indicate the number of sea miles per hour which the vessel is going. This, of course, is doubled if the fourteen-seconds glass is used, which is done when the vessel is going very fast. The old log lines have been superseded by many forms of the "patent log" and the museum is indeed fortunate which possesses an original log line, reel and float in perfect condition. There is an excellent example in the museum collections of the Marblehead Historical Society. Once discarded, the lines were soon used to tie up packages and the reels and floats were thrown away. The patent log with its revolving blades, now universal, was devised by Humfray Cole in 1578; it was improved by various persons from time to time but, strange to say, did not come into general use for nearly three centuries. The rotating blades in the water record the rate on an indicator on the vessel which may be read at any time. So far, the earliest reference to the use of a device of this sort among our New England navigators is the "Gould's patent log" used by Captain George Crowninshield on his famous yacht _Cleopatra's Barge_ during the voyage to the Mediterranean in 1817.