viii CONTENTS 



or if it ends it ends on an equal and opposite charge The product intensity 

 X cross-section is constant along a tube of force which contains no charge 

 If a tube of force passes through a charge and q is the charge within the 

 tube, the product intensity x cross-section changes by 4^ The intensity 

 outside a conductor is 47r<r Representation of intensity by the number of 

 lines of force through unit area perpendicular to the lines Number of lines 

 starting from unit quantity The normal component of the intensity at any 

 surface is equal to the number of lines of force passing through unit area of 

 the surface Fluid displacement tubes used to prove the properties of tubes 

 of force Spherical shell uniformly charged Intensity outside the shell 

 Intensity inside the hell Intensity at any point in the axis of a uniformly 

 charged circular disc Intensity due to a very long uniformly charged 

 cylinder near the middle Potential The resolute of the intensity in any 

 direction in terms of potential variation Equipotential surfaces The energy 

 of a system in terms of the charges and potentials The potential due to a 

 uniformly charged sphere at pointa without and within its surface 



Pp. ::i l>: 



CHAFrER IV 



THE FIELD CONSIDERED WITH REGARD TO 



THE INDUCTION OR ELECTRIC STRAIN 



PRODUCED IN IT 



The two kinds of charge always present and facing each other Electric action 

 in the medium Electric strain No strain in conductors win n the charges 

 are at rest Diiection of electric strain The electric strain ju>t outside a 

 conductor is normal to the surface of the conductor Magnitude of electric 

 strain Variation of electric strain with distance from the charged bodies : 

 The inverse square law Lines and tubes of strain Unit tube Results 

 deduced from the inverse square law The transference of tubes of strain 

 from one charge to another when the charged bodies move Molecular hypo- 

 thesis of electric strain l'j>. 47-60 



CHAPTER V 



THE FORCE ON A SMALL CHARGED BODY 

 IN THE FIELD, AND THE PULL OUT- 

 WARDS PER UNIT AREA ON A CHARGED 

 CONDUCTING SURFACE 



The inverse square law for the force deduced from that for electric strain 

 Coulumb's direct measurements General statement of the inverse square law 

 Electric intensity Unit quantity Relation between electric intensity and 



