

CHAPTER 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 when 

 the charges are at rest Direction of electric strain The electric strain 

 just 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 tabes of strain from one charge to another when the 

 charged bodies move Molecular hypothesis of electric strain. 



The two kinds of charge always present and facing 

 each Other. l'.\p riments of tin- kind desc-rilx-d in Chapter II 

 show that tin- two kinds ot electrification an- always produced 

 together in e<pial (juautit i< -, that they accompany each other 

 while they continue in :.d that on ceasing to cxi>t 



tip v ili^ipp. .11 in i-.jn d quantities. Sometime i, in experimenting, we 



te all our attention to a charge of one kind alone and speak as 

 if it :-nllv ; hut it isoftl. - 1 .importance to 



mlier that tin- opposite or complementary charge is really in 

 U*nce, perhaps on the neighbouring surface of a non-conductor 

 usecl lop tin- ell 'ion \\hich we an- studying, or 



perhaps on the 'in^ table, Hoor, or walls of the room, 



so that not only is it in existence, hut is in the presence of the 

 inducing c har^ . If we have a charge in one room we cannot 

 have the iry charge in another. If we attempt thus to 



separate the two kii i will at once induce its own opposite 



surface of the surrounding conducting walls. Again, 

 when we put a charged conductor " to earth " we sometimes speak 

 of the disappearance of the charge as if it merely spread away to 



infinite conducting earth. lint in fact we are making a con- 

 due* ILJI- hv means of which the charge and its opposite 



may md neutralise each other. The two kinds of 



///<; in the electric field, each, 

 a it were, inducing the other. A I lay* put it, "Uodics 



Erp. to*, vol. I. 1178. 



