MAGNETIZATION OF STEEL BARS. 7 



magnetism in iron, have been known from a very dis- 

 tant age. But, magnets having been once formed, there 

 is little difficulty in forming other magnets from them. 

 The most convenient process for magnetizing a steel bar 

 or compass-needle, &c. is that known by the name 

 "double touch." It requires the use of two magnets. 

 The bar which is to be magnetized being laid horizon- 

 tally, with some slight band to prevent it from moving, 

 the operator takes one magnet in his right hand with 

 (say) the red end downwards, and one in his left hand 

 with the blue end downwards (or both in the opposite 

 positions, according to the nature of the magnetism 

 which he wishes to impart), and, touching the bar with 

 the ends of the magnets near the middle of its length 



Fig. 1. 



(see Figure 1), he draws the two magnets simultaneously 

 to the two ends of the bar (constantly maintaining the 

 contact) till they slip off. He raises the magnets, again 

 places them in contact with the middle of the bar, and 

 again slides them to the ends : and repeats this opera- 

 tion : the motion, while in contact, being always from 

 the middle to the ends. The bar is thus converted into 

 a magnet : the end of the bar which was touched by 

 the red end of the magnet employed becomes a blue 

 end; and vice versa. The magnetizing magnets, in 



