244 



On the Viscosity of Dielectrics. 



[Mar. 21, 



goes on continually yielding under the action of a constant stress, we 

 must assume, since we cannot imagine a breach of continuity in the 

 phenomenon, that glass even when cold is also a " truly viscous fluid," 

 although the gain of strain per day may be almost infinitely small 

 after the first few days. Similarly, as the true conductivity is very 

 considerable in hot glass, we may conclude that there does exist true 

 conductivity in cold glass, although the amount will probably be so 

 small as to make its separation from surface conduction or other 

 extraneous loss extremely difficult. 



From the curves we have obtained of the charging of condensers, 

 and assuming that there is no discontinuity, we must assume that even 

 the first charging is itself a very rapid absorption, and since there is 

 viscosity, even the very first charging must be accompanied with a 

 generation of heat, that is, true conduction. Also since it is known 

 that gases, like all other substances, are to a certain extent viscous, we 

 cannot believe that air and other gaseous condensers show absolutely 

 no absorptive phenomena, in fact, sufficiently accurate experiments 

 have not yet been made on the subject. 



We conclude, therefore, that the less the specific resistance of a sub- 

 stance the greater is its molecular plasticity, and the more plastic the 

 substance is the greater will be the first charge ; therefore from the 

 stress and strain analogy it follows that the less the specific resistance 

 of a substance the greater will generally be the specific inductive 

 capacity, the result obtained experimentally at the commencement of 

 this paper : according to what law, however, the one increases as the 

 other diminishes, we are not at present in a position to state. 



From all that precedes it follows that when the potential of a body 

 surrounded by a dielectric is altered by induction, a portion of the 

 electric energy is converted into heat, the amount being greater as the 

 dielectric is more viscous. Consequently a charged body A, perfectly 

 surrounded by a dielectric, may be discharged without contact with 

 any conductor, by alternately bringing near and withdrawing a distant 

 conductor B ; for the capacity of the arrangement is alternately getting 

 greater and less, therefore the potentials must be alternately growing 

 less and greater, and since all alteration of potential is accompanied 

 by an alteration of strain in the viscous substance composing the 

 dielectric, the potential energy of the system must be gradually con- 

 verted into heat, whereas from the almost infinite resistance of the 

 dielectric, if the bodies were motionless, this result could never have 

 been attained. Consequently since the particles of any body are in 

 rapid motion, they must all tend to acquire the same potential, even if 

 we imagine them separated by a dielectric of very great resistance, 

 provided the relative motions are motions of translation. But if the 

 movements are motions of rotation only, then this equalization of 

 potential will only take place after a very great time, if it takes place 



