ELECTRO-MAGNETS. 705 



iron, be observed, it will be found that, as in the last 

 experiment of the preceding article, the current ascends 

 on the side of the coil turned towards the west, and 

 descends on the east. If the observer stands south of 



UNIVERSITY 



U. s'l 



FIG. 356 (Can.proj.\ 



the spiral, and looks upon the south pole of the electro- 

 magnet, the direction of the current is that of the arrow 

 in fig. 356 A\ if he stands north of the spiral, and looks 

 at the north pole, the direction is that at B ; and finally, 

 when seen from the side, the currents in a magnetic 

 body flow in the direction of the arrows in C, where 

 n and s indicate the north pole and the south pole 

 respectively. 



We may then establish the following rule: The south 

 pole of a magnet is that end at which the direction of the 

 Amperian currents is the same as that of the motion of the 

 hands of a watch. 



In the preceding figure and in some that follow, the 

 currents are represented as traversing only the outside 

 of the electro-magnet. This is strictly correct only 

 as far as the current in the spiral is concerned ; but in 

 a magnetic piece of iron we have an infinite number of 

 small currents each flowing round an individual mole- 



z z 



