RELATION OF CONDUCTION AND IfJSULATION. 89 



either of the air or of dust, in it. It is equally certain, however, that with higher 

 degrees of tension or charge they discharge to one another, and that is conduction. 

 If they possess the power of insulating a certain low degree of tension continuously 

 and perfectly, such a result may he due to their peculiar physical state, and the con- 

 dition of separation under which their particles are placed. But in that, or in any 

 case, we must not forget the fine experiments of Cagniard de la Tour*, in which 

 he has shown that liquids and their vapours can be made to pass gradually into each 

 other, to the entire removal of any marked distinction of the two states. Thus, hot 

 dry steam and cold water pass by insensible gradations into each other; yet the one 

 is amongst the gases as an insulator, and the other a comparatively good con- 

 ductor. As to conducting power, therefore, the transition from metals even up to 

 gases is gradual ; substances make but one series in this respect, and the various 

 cases must come under one condition and law (444.). The specific differences of 

 bodies as to conducting power only serves to strengthen the general argument, that 

 conduction, like insulation, is a result of induction, and is an action of contiguous 

 particles. 



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 inter- 

 posed 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. But 

 I fear to be tedious in the present condition of the subject, and hasten to the con- 

 sideration 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 conti- 

 guous 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 in- 

 tensity 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 per- 

 manently polarized. If I be right in my view of induction, then I consider the re- 

 duction of these two effects (which have been so long held distinct) to an action of 



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

 MDCCCXXXVIII. N 



