Magnetism. 27 



quarters of the horizon, that is, east, west, north, 

 and south, with their intermediate points, are 

 marked on a card. As the magnetic needle al- 

 ways points nearly towards the north, by observ- 

 ing the course or direction of the ship, that is, 

 which way her head is turned, it is easy to know 

 to what point she steers ; and by keeping a regular 

 account of the distance she traverses, the sea- 

 man can go with considerable exactness from one 

 place to another. Before this great and import- 

 ant invention, seamen usually steered by ob- 

 serving the fixed stars, and particularly the polar 

 or north star. But as this could only be done in 

 fine weather, and when the stars were visible, 

 they frequently lost their way and suffered ship- 

 wreck. Indeed few of them dared to sail out of 

 sight of land. But when they had a tolerably cer j 

 tain means of knowing one point of the heavens, 

 it was easy to know the others ; and it became, 

 after this invention, neither necessary to observe 

 the stars, nor to be afraid of the open sea, out of 

 sight of the shore. It was by means of the mariner's 

 compass that Columbus was enabled to make the 

 great discovery of the American continent, and 

 by means of it subsequent voyagers have sailed 

 quite round the globe. 



Though the position of the magnetic needle, 

 when it comes to rest on a vertical pivot, is, as 

 we have remarked, nearly north and south, or 

 coincident with the meridian, yet it is not exactly 

 so, nor is it the same at different places, or in the 



