SCIENCE OF COMMON THINGS. 297 



The magnetic compass. ^Discovery and first use of the compass. 



needle balanced upon & pivot placed beneath its centre 

 of gravity in such a way that it can turn horizontally 

 without obstruction. This needle is usually inclosed in 

 a box, upon the bottom of which is a card, with the 

 various points- north, south, east, west, etc., etc., 

 marked upon it. 



Fig- 92. 



Such a needle, if the box containing it be- placed on a level surface, will 

 generally be observed to vibrate more or less, till it settles in such a 

 direction that one of its extremities or poles will point towards the north, 

 and the other consequently towards the south. If the position of the box 

 be altered or reversed, the needle will always turn and vibrate again, till 

 its poles have attained the same direction as before. 



1933 Does the compass needle always point exactly north and south ? 



It does not / its natural direction is towards the north 

 and south poles, but it seldom points due north or 



south. 



1934 Who first discovered the fact that a magnet would invariably 

 point to the north -and the south, and made use of this knowledge in construct- 

 ing a ompass? 



It is claimed to have been discovered by the Chinese: 

 it was known in Europe, and used in the Mediterranean, 

 in the thirteenth century. 



1935 How were the compasses of that time constructed? 



They were merely pieces of loadstone fixed to a cork, 

 which floated on the surface of water. 



1936 Is the earth itself supposed to be a magnet? 



It is undoubtedly a great magnet. 



