172 



MAGNETISM 



small magnets of very great power. One, for example, weighing 

 1 oz. troy, when armed with iron at the two ends so that the weight 

 was still under 2 oz., lifted forty-four times its own weight. The 

 method is especially applicahle to compass needles or short hars. 

 Two magnets are used and are placed with their unlike poles 

 initially as close together as possible, and the needle or bar is laid 



IN. 



N' 



FIG. 115. 



under them as in Fig. 116, and fixed by a button. The two ma-ix -Is 

 are then gradually drawn apart till their ends slide off the bar, 

 leaving the bar magnetised as indicated in the figure. The t\\o 

 magnetising poles are again brought together or mar each other, 

 and then brought down on the middle of the in ague I. and the 

 process is repeated three or four times. Tin- bar is then turned 

 over and the same number of operations rep-ated on the other 

 face. The explanation of the magnetisation is obvious. The 



N / 



S 



FIG. 116. 



me 



...cthod of divided touch requires in general moiv poueri'ul in 

 than the following method, known as that of 



Double touch. In this method the magnet i.sing s\.| ( ,,, 

 consists of two unlike poles. NS, \\hich are kept a constant distance 

 apart. A horseshoe magnet may he u-cd.or its equivalent, t\\o bar 

 magnets with a piece of wood between their lower poles, their 



upper poles bfin united bv M>ft 

 iron, Fig. H7. If one bar is' to be 

 magnetised, the magnetising poles 

 are brought down on to the middle 

 of it and moved to and fro several 

 times, each half being traversed the 

 same number of times. They are 

 then withdrawn from the centre. 

 If several bars are to be magnetised 

 they may be laid end to end and 

 treated as one bar. After several 



journeys of the magnetising poles the end bars are brought into 

 the middle and the process is continued until all the bars have 

 thus been in the middle. 



FIG. 117. 



