274 



Mr GODFRAY, ON A CHART AND DIAGRAM 



These advantages are clearly explained in an able article on Great-circle Sailing in the 

 Nautical Magazine for 1847, p. 228, from which the substance of some of the following 

 remarks has been extracted. 



1. Suppose two vessels together in the southern hemisphere bound to a place situated to 

 the east on the same parallel, the wind also being due east. A who guides himself by Mer- 

 cator's sailing will consider the wind as being right ahead, and will be as likely to put his ship 

 on the one tack as on the other ; while B who sails on a great-circle will see that the wind is 

 not exactly a head-wind, for his course may differ ], 2, or even in extreme cases 5 or 6 points 

 towards the south ; — let it be only 1 point, that is E. b. S., and suppose his ship to sail within 

 6^ points of the wind. He will then choose the port-tack, that being only 5^ points from his 

 course, whereas the starboard-tack is 7^ points away ; so that on the port-tack he will by 

 running 100 miles be 47 miles nearer to his destination, while on the other tack, a run of 

 100 miles will diminish his distance by 9| miles only. 



Cmir-fe by Mercator 



Wind 



We have supposed the wind due east, so that the seaman A is as likely to select one tack 

 as the other, but if the wind blow from any point between the course by Mercator and the 

 great-circle course, he will be sure to select the wrong one. 



