92 POPULAR LECTURES AND ADDRESSES. 



and drawn on the ordinary working chart. Then 

 the navigator knows that the ship is somewhere on 

 that line, even though he may not know his 

 latitude within twenty or thirty miles. 



I have known a case of a ship bound from South 

 America to England, intending to call at Fayal, 

 Azores, for provisions, and being saved from passing 

 out of sight of the island before noon by the 

 Sumner line, calculated from observation at seven 

 in the morning. This observation proved the ship 

 to be about eleven miles further west than estimated 

 from the afternoon observation of the previous day ; 

 and a timely change of the course, three points 

 to the eastward at eight o'clock, brought the heights 

 of Fayal in view ahead about half-past ten. If 

 the ordinary course had been held on till noon, 

 the ship would then have been eleven miles 

 to the west of the west end of Fayal, and the 

 island still unseen as the weather was somewhat 

 cloudy ; and the ship must have been turned 

 round at right angles to her course to look for 

 the island. 



53. Having been much impressed with the value 



