NAVIGATION. 457 



effected, in square sails, by bracing the yards obliquely in one or 

 the other direction. When a ship turns, with her head from the 

 wind, so as to receive it on the other quarter, she is said to veer. The 

 danger arising from strong winds, is diminished by shortening sail ; 

 either taking in a part of the sails ; or reefing, that is, contracting 

 them, by tieing them in folds. In a sudden gust of wind, fore-and- 

 aft rigged vessels should bear up, or head towards the wind ; but 

 square rigged ones should receive it abeam. In a storm, vessels 

 sometimes lie to, or head towards the wind ; and sometimes they 

 scud, or drive, heading from the wind, when there is no danger from 

 a lee shore. 



2. Dead Reckoning, is the mode of estimating the course and 

 distance which a ship has sailed, by means of the compass and log, 

 without the aid of celestial observations. The course, or direction 

 sailed, as well as the bearing, or direction, of distant objects, is 

 reckoned from the north or south point of the horizon, towards the 

 east or west; on land, usually in degrees, but at sea, in points, each 

 of which is equal to Hi degrees. The point called N. N. E. (north- 

 north east), for example, is half way between N. E. and North ; and 

 E. N. E. is half way between N. E. and East. The log, consists 

 of a flat, quadrantal piece of wood, loaded on the curved side, so as 

 to make it float edgewise in the water, and attached by its three 

 corners to a line, which, unwinding from a reel, when the log is 

 thrown overboard, measures the distance which the ship sails, away 

 from the log, in a half minute. The number of knots, run out by 

 the log line, indicates the number of miles, per hour, that the ship 

 is sailing. The log is cast at frequent intervals ; the course being 

 continually noted ; and from these data, the actual course an.d dis- 

 tance gained, or made good, each day, are calculated by what is 

 called Traverse Sailing ; an application of plane trigonometry. 



Distance gained by a ship, northward or southward, is called dif- 

 ference of latitude ; and that gained eastward or westward, is called 

 departure. The former, compared with the previous latitude, gives 

 the latitude attained ; but the departure, being expressed in nautical 

 miles, differs, numerically, from the difference of longitude ; except 

 at the equator; owing to the convergency of the meridians. When, 

 near the equator, this difference is neglected, in finding the longitude, 

 the calculation of the ship's place is then called Plane Sailing. At 

 a distance from the equator, the reduction is usually made by means 

 of the proportion, cosine of the latitude : radius :: departure : dif- 

 ference of longitude ; which last is thus found, by the method called 

 Middle Latitude Sailing. In high latitudes, the surface sailed over 

 may be considered as a portion of a cone, having its vertex beyond, the 

 pole ; and the method of finding the ship's progress, on this prin- 

 ciple, is called Parallel Sailing. The most accurate solution of this 

 problem, is by the principle of Mercator's Chart ; in which the 

 parts of the earth towards the poles are represented as enlarged, to 

 make the meridians parallel ; the degrees of latitude being enlarged 

 in the same proportion ; by which the true bearings of places are 

 accurately preserved. The application of this principle to problems 

 in Navigation, is hence called Mercator's Sailing. 

 58 2Q 



