48 The Realm of Nature CHAP, in 



80. Electro-magnetism. The properties of magnets 

 would be inexplicable had not an accidental discovery shown 

 the close relation of magnetism and electricity. It was 

 found that when electric energy is passing through a wire 

 placed above a balanced magnetic needle, the needle 

 swings round and sets itself at right angles to the wire. 

 It was found later that when a coil of copper wire traversed 

 by electricity surrounds a bar of iron, the iron becomes a 

 powerful magnet and retains its properties of polarity and 

 attraction as long as the electricity passes, losing them the 

 instant the current ceases. A coil of copper wire without 

 any iron in the centre was subsequently found to possess 

 polarity, and to exert attraction and repulsion as long as an 

 electric current flowed through it. Hence magnetism can 

 be produced by electricity, and the reverse also holds good. 

 A magnet placed inside a coil of common wire generates a 

 momentary current of electricity. By merely making a coil 

 of wire move in the field of a powerful magnet electricity 

 can be produced in the wire, and thus work can be changed 

 directly into electric currents. 



In Nature nothing is so simple as has been represented 

 in this and the last chapter. We do not know how particles 

 vibrate and oscillate, and only guess at the real nature of 

 the forms of matter and energy. Authorities differ in their 

 interpretation of many of the facts, and we have only pre- 

 sented a few of the simpler conclusions in order to assist 

 the student who does not know much of physics and 

 chemistry to follow the chapters which come after. 



BOOKS OF REFERENCE 



Balfour Stewart, Elementary Physics. Macmillan and Co. 

 P. G. Tait, Recent Advances in Physical Science. Macmillan 

 and Co. 



