Vlll CONTENTS. 



ART. PAOB 



8. Method of magnetizing steel bars, and of preserving their 



magnetic power 6 



9. The terrestrial force upon a magnet is a Couple: the red 



end is drawn towards the north, the blue end towards the 

 south, with equal forces. First Law of Magnetism: the 

 Duality of Powers 9 



10. Action of one magnet upon another. Second Law of 



Magnetism. There is attraction between dissimilar ends, 

 repulsion between similar ends. This is exhibited in 

 various ways. Idea of poles. When one magnet dis- 

 turbs a compass, another magnet may be so placed as to 

 neutralize the disturbance. Poles of a horse-shoe magnet. 10 



11. The 'action of the Earth is exactly the same as that of a 



large magnet whose red end is on the south side and 

 whose blue end is on the north side. For experimental 

 purposes, the Earth's action may be neutralized over a 

 large space. Or its action on a special magnet may be 

 rendered insensible by use of the astatic needle . . .13 



12. Experimental examination of the action of a large magnet on 



a small needle. Third Law of Magnetism: magnetism 

 collected in or near each pole of a magnet acts (as to 

 sense) equally in all directions 16 



13. Experimental proof of the Fourth Law of Magnetism, that 



the attraction or repulsion (as the case may be) between 

 two masses of magnetism, estimated as a statical force, is 

 proportional to the product of their inagnetical energies. 

 Definition of the units of the elements used in succeeding 

 investigations ; novel unit of statical pressure . . .19 



SECTION III. 



ALGEBRAICAL INVESTIGATIONS OF THE ACTION OF ONE MAGNET UPON 

 ANOTHER, THE MAGNETS BEING IN THE SAME PLANE, AND THE 

 FORCE OF ATTRACTION OR REPULSION VARYING AS A POWER OF 

 THE DISTANCE. 



Articles 1421. Pages 2441 . 



14. The disturbing magnet presents the center of one side at 



right angles to the disturbed magnet (a position which we 

 shall hereafter term "broadside-on"), and the disturbed 

 magnet presents one end to the center of the disturbing 



