GENERAL ACCOUNT OF MAGNETIC ACTIONS 171 



They are all modifications of three, called respectively the methods 

 of single, double, and divided touch. In our description we shall 

 assume that the object is to make flat bar magnets, and it appears 

 that good dimensions for such magnets are on the scale length 

 10 to 15, breadth 1, depth \. 



Single touch. The bar to be magnetised is rubbed several 

 times in the same direction by one pole of the magnetising magnet, 

 which is moved parallel to itself either at right angles to the bar 

 or inclined as shown in Fig. 114, the course of the magnet being 



\ 



FIG. 11 1. 



indicated by the solid line, the dotted line indicating the return 

 journey at such a distance from the bar that the magnet has no 

 appreciable influence on it. 



The probable action of the process is that when the N pole of 

 the magnetising magnet is put on the end of the bar to be mag- 

 netised it induces a SSP at a immediately under it and North- 

 seeking polarity chiefly on the other side, b, but also at the more 

 distant parts of the bar and at the other end, c. But as N moves 

 along the bar it carries along with it the SSP originally at a, while the 

 NSPati moves round to occupy the whole of the end N', and the SSP 

 carried to the other end neutralises the weak North-seeking polarity 

 already there. Repetition with the same magnet somewhat in- 

 creases the effect, but if a magnet weaker than that employed at 

 first be substituted in the repetition it partially demagnetises the 

 bar. The process is unsatisfactory, inasmuch as it does not lead 

 to strong magnetisation or to symmetrical distribution. It may 

 be somewhat improved by beginning with, say, the N magnetising 

 pole in the middle of the bar and drawing it along to the end. 

 The magnetising magnet is then turned over and the S magnetising 

 pole is drawn from the middle to the other end. It is best in this 

 last process to slide the one over the other as indicated in Fig. 115. 

 But practically the same process may be carried out much more 

 effectually by the method of 



Divided touch. This method was devised by Dr. Knight 

 about the middle of the eighteenth century, and he made by it 



