DUALITY OF MAGNETIC POWERS. 9 



several times without lifting the horse-shoe magnet. 

 The red- and blue ends of the resulting magnets are 

 respectively opposed in position to those of the horse- 

 shoe magnet. (On the mode of distinguishing the ends 

 of a horse-shoe magnet, we shall speak shortly.) 



In either process, after a time, a limit to the inten- 

 sity of the communicated magnetism is reached. This 

 is usually expressed by the phrase "magnetized to 

 saturation." 



The steel which is the most valuable for retention 

 of magnetism is also the most favourable for reception 

 of a strong dose of magnetism. 



For preserving the magnets with full magnetic 

 intensity, it is found prudent to place them side by side 

 with their red and blue ends in opposite positions, and 

 to connect the opposite ends (the red end of each with 

 the blue end of the other) by pieces of iron in contact 

 with both. 



Valuable information connected with this subject 

 will be found in the Encyclopaedia Metropolitana, article 

 Magnetism. 



9. The terrestrial force upon a magnet is a Couple : 

 the red end is drawn towards the north, the blue end to- 

 wards the south, with equal forces. First Law of Mag- 

 netism, the Duality of Powers. 



If a magnet, on which the Earth's directive power is 

 strong, be suspended by a very long suspension-thread, 

 and the position of the thread be noted ; if then the 

 magnet be removed and a lump of lead of equal weight 



