26 Experimental Philosophy. [Lecture 3. 



pole of the other, they will mutually repel or 

 drive away each other: if, on the contrary, the 

 south pole of the one is presented to the north 

 pole of the other, they will be mutually attracted. 

 It is on this account that it is necessary, in mak- 

 ing artificial magnets, to draw the magnet, with 

 which they are rubbed or touched, always one 

 way. It is most effectually done also by applying 

 one of the poles of the magnet to the bar or piece 

 of iron which is to be rendered magnetic, and 

 drawing it slowly along several times. It is ex- 

 traordinary that the end of the bar which is first 

 touched with the magnet will have the contrary 

 property to the end of the magnet with which it 

 is touched or rubbed. If, for instance, the end 

 with which the bar is touched is the north pole 

 of the magnet, the end of the bar to which it is 

 first applied will be a south pole, and the con- 

 trary. 



It is obvious that the directive power of the 

 magnet, or that which causes it, when placed so 

 as that it can freely turn of itself, to take always 

 a position nearly north and south, is the most 

 useful property of the magnet. This is practi- 

 cally applied by means of the mariner's compass, 

 in which a fine needle, index, or piece of steel- 

 wire, formed like the index or hand of a clock or 

 watch, is so balanced as to turn horizontally with 

 great ease on the prop which supports it. The 

 needle or index is fixed in a box ; and under- 

 neath it the points of the compass, or the different 



