NAVIGATION. 107 



its "Atlas of Wind and Current Charts." These 

 charts show, in scarcely any part of the ocean, 

 less than ten miles of surface current per twenty- 

 four hours, and they show as much as forty or 

 fifty miles in many places. Unless these currents 

 are taken into account then, the place of a ship, 

 by dead reckoning, may be wrong by from ten 

 to fifty miles per twenty-four hours ; and the 

 most accurate information which we yet have 

 regarding them is, at the best, only approximate. 

 There are, in fact, uncertain currents, of ten miles 

 and upwards per day, due to wind (it may 

 be wind in a distant part of the ocean) which 

 the navigator cannot possibly know at the time 

 he is affected by them. I believe it would be 

 unsafe to say that, even if the steerage and the 

 speed through the water were reckoned with 

 absolute accuracy in the "account," the ship's 

 place could in general be reasonably trusted to 

 within fifteen or twenty miles per twenty-four 

 hours of dead reckoning. And, besides, neither 

 the speed through the water, nor the steerage, 

 can be safely reckoned without allowing a con- 



