applied to Statical Electricity. 13 



I conceived the rotating matter to be the substance of certain 

 cells, divided from each other by cell-walls composed of particles 

 which are very small compared with the cells, and that it is by 

 the motions of these particles, and their tangential action on the 

 substance in the cells, that the rotation is communicated from 

 one cell to another. 



I have not attempted to explain this tangential action, but it 

 is necessary to suppose, in order to account for the transmission 

 of rotation from the exterior to the interior parts of each cell, 

 that the substance in the cells possesses elasticity of figure, 

 similar in kind, though different in degree, to that observed in 

 solid bodies. The undulatory theory of light requires us to 

 admit this kind of elasticity in the luminiferous medium, in 

 order to account for transverse vibrations. We need not then 

 be surprised if the magneto-electric medium possesses the same 

 property. 



According to our theory, the particles which form the partitions 

 between the cells constitute the matter of electricity. The 

 motion of these particles constitutes an electric current; the 

 tangential force with which the particles are pressed by the 

 matter of the cells is electromotive force, and the pressure oi 

 the particles on each other corresponds to the tension or poten- 

 tial of the electricity. 



If we can now explain the condition of a body with respect to 

 the surrounding medium when it is said to be " charged " with 

 electricity, and account for the forces acting between electrified 

 bodies, we shall have established a connexion between all the 

 principal phenomena of electrical science. 



We know by experiment that electric tension is the same 

 thing, whether observed in statical or in current electricity ; so 

 that an electromotive force produced by magnetism may be 

 made to charge a Leyden jar, as is done by the coil machine. 



When a difference of tension exists in different parts of any 

 body, the electricity passes, or tends to pass, from places of 

 greater to places of smaller tension. If the body is a conductor, 

 an actual passage of electricity takes place ; and if the difference 

 of tensions is kept up, the current continues to flow with a 

 velocity proportional inversely to the resistance, or directly to the 

 conductivity of the body. 



The electric resistance has a very wide range of values, that 

 of the metals being the smallest, and that of glass being so 

 great that a charge of electricity has been preserved* in a glass 

 vessel for years without penetrating the thickness of the glass. 



Bodies which do not permit a current of electricity to flow 

 through them are called insulators. But though electricity does 

 * By Professor W. Thomson. 



