A TREATISE 

 C.L.CORY. 



ELECTRICITY AND MAGNETISM 



PART I. STATICAL ELECTRICITY. 



CHAPTER I. 

 INTRODUCTORY. 



1 . MOST bodies, when rubbed, acquire, at any rate temporarily, 

 the property of attracting light bodies. They are then said to be 

 electrified. If the attracted body comes in contact with the electrified 

 body, it is sooner or later repelled, and it is then itself found to be 

 electrified. Electrical properties can accordingly be transmitted 

 from one body to another by mere contact. 



On the other hand, bodies which show no electrical properties 

 are said to be in the natural state, or in the neutral state. 



2. CONDUCTORS. INSULATORS. On certain bodies, such as 

 glass, resin, silk, caoutchouc, etc., electricity remains localised for 

 a shorter or longer time, at the place where it has been produced 

 by friction, or by contact. Such bodies are said to be bad conductors 

 of electricity. 



On other bodies, on the contrary, such as the metals, electrical 

 properties imparted to any one part, are almost instantaneously 

 transmitted to all parts; these are said to be conductors. Most 

 substances composing the earth belong to this latter class ; air, and 

 vapours, and generally all gases, belong to the former. Electricity 

 can only be retained on a conductor by insulating it from the 

 ground that is, supporting it by a bad conductor, such as a rod 

 of glass, or sealing-wax, or ebonite, or by silk threads. Hence we 

 have the term insulators^ applied to bad conductors. 



B 



