io6 POPULAR LECTURES AND ADDRESSES. 



the water is too deep for soundings, if the sky 

 is cloudy so that neither sun nor stars can be 

 seen, the navigator, however clear the horizon 

 may be, has no other way of knowing where he 

 is than the dead reckoning, and no other guide 

 for steering than the compass. 



We often hear stories of the marvellous exact- 

 ness with which the dead reckoning has been 

 verified by the result. A man has steamed or 

 sailed across the Atlantic without having got a 

 glimpse of sun or stars the whole way, and has 

 made land within five miles of the place aimed 

 at. This may be done once, and may be done 

 again, but must not be trusted to on any one 

 occasion as probably to be done again this time. 

 Undue trust in the dead reckoning has produced 

 more disastrous shipwrecks of seaworthy ships, I 

 believe, than all other causes put together. All 

 over the surface of the sea there are currents of 

 unknown strength and direction. Regarding these 

 currents, much most valuable information has 

 been collected by our Board of Trade and 

 Admiralty, and published by the Admiralty in 



