II. On the viscosity of dielectrics. No. I

Abstract

It is well known that india-rubber has a greater specific resistance and a less specific inductive capacity than gutta-percha. Now a popular explanation of this might be given as follows:—Imagine a portion of the india-rubber in an india-rubber condenser replaced by a metallic or other conducting substance either in a single piece or in the form of grains scattered throughout the mass of the dielectric, then the resistance of the condenser will be diminished while its capacity will be increased. As more and more metal is introduced into the dielectric the capacity will become greater and greater, so that at last, if all the india-rubber be replaced by metal, we ought to consider such a condenser as having an extremely great capacity, although on account of the conduction it would be impossible to experimentally measure the charge. If the above consideration, which of course really applies to a dielectric of heterogeneous constitution, be also applicable to different homogeneous dielectrics, then we might expect to find that for all dielectrics the specific inductive capacity diminishes as the specific resistance increases. Now the experiments we have lately been engaged on concerning specific resistances enable us to prove that in the case of several well-known dielectrics this is really so, as will be seen from the following table:— It will be observed that the conventional specific inductive capacity of shell-lac does not follow our law that small specific inductive capacity accompanies high specific resistance. We are inclined, however, to think that the real capacity may be far greater than this conventional one, since M. Boltzmann proved in 1874 that the true specific inductive capacities of sulphur and resin were respectively twice and one and a half times as great as the capacities for these substances given in books. Up to the present time we have not ourselves had an opportunity of finding the true specific inductive capacity of shell-lac.