460 PASSAGES OVER THE ATLANTIC. 



well known as the rhumb course, and is that in universal use from its sim- 

 plicity. But it is not the sliortest course, except it be due East or West on 

 the Equator, or North or South on a meridian, which are Great Circles. 

 This course, developed on a sphere, is found to be a spiral, and is con- 

 siderably removed from a Great Circle, or shortest distance, if a great ex- 

 tent of longitude is traversed by it. We need not pursue this subject, but 

 an example will explain its application. 



From a position off the Land's End, in lat. 50° N., long. 5° 30' W., to 

 Cape St. John, in the Bay of Notre Dame, in Newfoundland, also in lat. 

 50° N., and long. 55° 30' W., the course, true, is of course West, and the 

 distance on this parallel is 1,928| miles. But if a ship were to quit the 

 Lizard on a N. 70° 20' 30" W. (true) course, and then, gradually bearing 

 more Westward, attain the latitude of 50° 45' N., in long. 30° 30' W., thence 

 bearing more Southward, and approaching Cape St. John on a similar 

 angle to the parallel that she had left the Land's End, she will have sailed 

 1,893 miles, or 35|^ miles less than on the parallel ; but, in her greatest 

 separation, she will have been 165 miles distant from the rhumb course. 

 Therefore, if she were to take any course between this Great Circle course 

 and the parallel of 50°, she would have a less distance to traverse ; and 

 this is the great advantage which the Great Circle Sailing offers — that of 

 a wide range of choice (in a higher latitude) without increasing the 

 distance. 



Further, if she were to assume a course as much higher in latitude as 

 the Great Circle course is above the rhumb, she will find that it will be of 

 the same length as the latter. Thus, in the example cited, if on leaving 

 the Land's End she bear away for a point in lat. 55° 30' N., longitude 

 30° 30' W., and then approach Cape St. John, such a curve will be found 

 to be exactly 1,928|^ miles in length, and yet be, in its maximum separation, 

 330 miles apart from the parallel. The advantage of such a range of choice 

 will appear subsequently in the remarks upon the Transatlantic Passages. 



(473.) The great difficulties in the application of the principle of Great 

 Circle Sailing to practice were, the laborious nature of the calculations, 

 now, however, much reduced, and the inference as to how a course so much 

 at variance with that which the chart will apparently dictate as the most 

 direct, will place a ship in respect to favourable Winds or Currents. Still, 

 the scope it allows to the navigator must be considered as no mean advan- 

 tage, even if its shorter distance may not be an inducement to rigorously 

 follow out its principles. 



(474.) In the following general sailing directions, the application of the 

 facts in physical geography which have been described in the preceding 

 sections of this work, must be left to the discretion of the commander in 

 most cases. In fine weather, and with fair winds, the estimation of the 

 various influences which affect the ship's course is not difficult to make. 

 But it is the adverse circumstances of a voyage that call for the seaman's 

 skill and intelligence, and what has been said will help him to form a judg- 

 ment of what is going on and how best to proceed. 



There is an infinite variety of circumstances which render it impossible 

 to lay down any fixed rule which may be implicitly followed to advantage 

 at all times. Therefore, in cases where a definite com'se is pointed out as 



