CHAPTER I. 



PHYSICAL PRINCIPLES. 

 THE FUNDAMENTAL CONCEPTIONS OF ELECTROSTATICS. 



I. State of Electrification of a Body. 



5. WE proceed to a discussion of the fundamental conceptions which 

 form the basis of Electrostatics. The first of these is that of a state of 

 electrification of a body. When a piece of amber has been rubbed so that it 

 attracts small bodies to itself, we say that it is in a state of electrification 

 or, more shortly, that it is electrified. 



Other bodies besides amber possess the power of attracting small bodies 

 after being rubbed, and are therefore susceptible of electrification. Indeed 

 it is found that all bodies possess this property, although it is less easily 

 recognised in the case of most bodies, than in the case of amber. For 

 instance a brass rod with a glass handle, if rubbed on a piece of silk or cloth, 

 will show the power to a marked degree. The electrification here resides in 

 the brass ; as will be explained immediately, the interposition of glass or 

 some similar substance between the brass and the hand is necessary in order 

 that the brass may retain its power for a sufficient time to enable us to 

 observe it. If we hold the instrument by the brass rod and rub the glass 

 handle we find that the same power is acquired by the glass. 



II. Conductors and Insulators. 



6. Let us now suppose that we hold the electrified brass rod in one hand 

 by its glass handle, and that we touch it with the other hand. We find that 

 after touching it its power of attracting small bodies will have completely 

 disappeared. If we immerse it in a stream of water or pass it through a 

 flame we find the same result. If on the other hand we touch it with 

 a piece of silk or a rod of glass, or stand it in a current of air, we find 

 that its power of attracting small bodies remains unimpaired, at any rate 

 for a time. It appears therefore that the human body, a flame or water 



