Properties of the Electric Field. 155 



least trace of conductivity, such as water or alcohol, have 

 specific inductive capacities ranging from 70 to 100, it is 

 probable that for good conductors K is exceedingly large. 

 If, however, its value for metals were no greater than that for 

 distilled water, the time required for the disappearance of a 

 tube of force would be comparable with the time of vibration 

 of a light-wave ; so that the conductivity would be much 

 smaller for these waves than for steady currents. 



We may picture to ourselves the tubes of electrostatic 

 induction shortening in a conductor in some such way as the 

 following : — Let us take the case of a condenser discharging 

 through the gas separating its plates. Then, before discharge, 

 we have a tube stretching from an atom on the positive 

 plate to another atom P on the negative one. The molecules 

 AB, CD, ... of the intervening gas will be polarized by the 

 induction, the tubes of force connecting the atoms in these 

 molecules pointing in the negative direction ; as the strength 

 of the field increases the tube in the molecule AB will 

 lengthen and bend towards the tube OP, until when the field 

 is sufficiently strong the molecular tube runs up into the 

 tube OP. The tubes then break up into two tubes OA and 

 PB, and the tube OA shortens to molecular dimensions. 

 The result of this operation is that the tube PO has shortened 

 to PB, and the atoms and A have formed a molecule. This 

 process is then continued from molecule to molecule until the 

 tube PO has contracted to molecular dimensions. Instead of 

 the tube PO jumping from molecule to molecule, several 

 molecules may form a chain and be affected at once ; in this 

 case the tube would shorten by the length of the chain in the 

 same time as on the previous hypothesis it shortened by the 

 distance between two molecules. 



The remarkable agreement between the values of the 

 velocity of the ions as calculated by Hittorf and Kohlrausch 

 and those found by Prof. Lodge in the experiments described 

 in the British Association Report, 1887, makes it essential 

 that any theory of conduction through electrolytes should lead 

 to the same expressions for the ionic velocities. According to 

 the preceding theory of conduction, if the molecules of the 

 electrolyte form chains between the electrodes, the sum of the 

 distances traversed by the anion and cation each time the tube 

 of electrostatic induction breaks down is d, where d is the dis- 

 tance between two molecules of the electrolyte measured along 

 a tube of induction. If the tube breaks down n times a second, 

 the sum of the distances traversed by the ion and cation in one 

 second is nd ; so that, if a and v are the velocities of the anion 

 and cation respectively, u , v _ W£ ^ 



