The old-fashioned ship’s “log” is a piece of wood in the form of a quadrant, loaded with lead at the circumference, to which is attached a line of 120 fathoms or more. Allowance being made for “stray line,” the balance is divided into equal distances by knots and small bits of coloured cloth. The distance between each knot is the same part of a mile that 30 seconds is of an hour (the 120th); the length between knots should thus be a trifle over 50 feet. The number of knots run out in half a minute (as measured by the sand-glass) indicate the number of nautical miles the ship is running per hour. Even express steamships do not always sail between given points exactly as the crow flies. Various reasons lead to the selection of different routes, and even when following the same route, the actual distance run varies a little on each voyage. The Cunard Line, as a precautionary measure, has four sharply defined “tracks” across the Atlantic—two for the westward and two for the eastward voyages—one pair being used in summer and the other in winter, or the ice season.[31] The northern route, used from July 15th to January 14th, is considerably shorter than the southern route, which is followed from January 15th to July 14th. The distances by these routes are given by the company as follows: Queenstown to Sandy Hook, by northern track 2,782 knots. " " " " southern " 2,861 " Sandy Hook to Queenstown, " northern " 2,809 " " " " " southern " 2,896 " Daunt’s Rock, Queenstown, being about 244 knots from Liverpool, and Sandy Hook lightship 26 knots from New York, the distance from Liverpool landing-stage to the dock in New York by the Cunard’s northern track is about 3,052 knots, and by the southern track, 3,131 knots; from New York to Liverpool, 3,079 and 3,166 knots, respectively. Captain W. H. Smith says that the shortest distance that can be made between Liverpool and New York is 3,034 knots. TABLE OF DISTANCES.[32]