[A] Annales de Chimie, xxi. pp. 127, 178, or Quarterly Journal of
  Science, xv. 145.

1337.  I might go on now to consider induction and its concomitant, conduction, through mixed dielectrics, as, for instance, when a charged body, instead of acting across air to a distant uninsulated conductor, acts jointly through it and an interposed insulated conductor.  In such a case, the air and the conducting body are the mixed dielectrics; and the latter assumes a polarized condition as a mass, like that which my theory assumes each particle of the air to possess at the same time (1679).  But I fear to be tedious in the present condition of the subject, and hasten to the consideration of other matter.

1338.  To sum up, in some degree, what has been said, I look upon the first effect of an excited body upon neighbouring matters to be the production of a polarized state of their particles, which constitutes induction; and this arises from its action upon the particles in immediate contact with it, which again act upon those contiguous to them, and thus the forces are transferred to a distance.  If the induction remain undiminished, then perfect insulation is the consequence; and the higher the polarized condition which the particles can acquire or maintain, the higher is the intensity which may be given to the acting forces.  If, on the contrary, the contiguous particles, upon acquiring the polarized state, have the power to communicate their forces, then conduction occurs, and the tension is lowered, conduction being a distinct act of discharge between neighbouring particles.  The lower the state of tension at which this discharge between the particles of a body takes place, the better conductor is that body.  In this view, insulators may be said to be bodies whose particles can retain the polarized state; whilst conductors are those whose particles cannot be permanently polarized.  If I be right in my view of induction, then I consider the reduction of these two effects (which have been so long held distinct) to an action of contiguous particles obedient to one common law, as a very important result; and, on the other hand, the identity of character which the two acquire when viewed by the theory (1326.), is additional presumptive proof in favour of the correctness of the latter.

* * * * *

1339.  That heat has great influence over simple conduction is well known (445.), its effect being, in some cases, almost an entire change of the characters of the body (432. 1340.).  Harris has, however, shown that it in no respect affects gaseous bodies, or at least air[A]; and Davy has taught us that, as a class, metals have their conducting power diminished by it[B].

  [A] Philosophical Transactions, 1834, p. 230

  [B] Ibid. 1821, p. 431.