170 ON MAGNETISM. 



placing the iron in that position in which the earth's 

 power acts most strongly on it, suggest the trial of a 

 steel magnet for the same purpose. Lay a steel mag- 

 net E and W on a table, and bring a nail near it in 

 the same direction, not touching the magnet. In this 

 state, the earth's magnetism has no effect: and the 

 nail receives from the magnet no permanent mag- 

 netism (as is easily verified by applying it end-on to 

 a compass). Now place the nail in its former position, 

 and strike it with a hammer; upon withdrawing it, it 

 will be found that it has become a magnet in all re- 

 spects like a steel magnet, the pole which was nearest 

 to the large magnet having magnetism opposite to that 

 of the pole which it approached. 



If a bar of iron be dropped endwise upon a stone 

 pavement, it immediately acquires polar magnetism 

 of permanent character, like that of a steel magnet. 

 But if it be dropped on a carpeted floor, it scarcely 

 receives any sensible magnetism. This experiment 

 shews that a state of sharp tremor or violent jar among 

 the particles of the iron is necessary to enable it to 

 receive this magnetism. 



As matter of familiar observation it may be men- 

 tioned that a common fire-place poker, of which the 

 same end is usually downwards and is frequently 

 struck upon the hard floor, is almost always well 

 charged with magnetism, its red end being the 

 lower. 



