no POPULAR LECTURES AND ADDRESSES. 



uncertainty when he runs over the same course 

 month after month and year after year in the 

 same ship ; but it is not overcome by any skill 

 hitherto applied to the compass at sea when a 

 first voyage to a fresh destination, whether in a 

 new ship or in an old one, is attempted. 



All things considered, a thoroughly skilled and 

 careful navigator may reckon that, in the most 

 favourable circumstances, he has a fair chance 

 of being within five miles of his estimated place, 

 after a two hundred miles' run on dead reckon- 

 ing ; but with all his skill and with all his care, 

 he may be twenty miles off it ; and he will no 

 more think of imperilling his ship and the lives 

 committed to his charge on such an estimate, 

 than a skilled rifle-shot would think of staking 

 a human life on his hitting the bull's-eye at five 

 hundred yards. What, then, do practical navi- 

 gators do in approaching land after a few days' 

 run on dead reckoning ? Too many, through 

 bad logic and imperfect scientific intelligence, 

 rather than through conscious negligence, run 

 on, trusting to their dead reckoning. In the 



