1631.  The same point, i.e. uniformity in every part, may be illustrated by what may be considered as the inexhaustible nature of the current when producing particular effects; for these effects depend upon transfer only, and do not consume the power.  Thus a current which will heat one inch of platina wire will heat a hundred inches (853. note).  If a current be sustained in a constant state, it will decompose the fluid in one voltameter only, or in twenty others if they be placed in the circuit, in each to an amount equal to that in the single one.

1632.  Again, in cases of disruptive discharge, as in the spark, there is frequently a dark part (1422.) which, by Professor Johnson, has been called the neutral point[A]; and this has given rise to the use of expressions implying that there are two electricities existing separately, which, passing to that spot, there combine and neutralize each other[B].  But if such expressions are understood as correctly indicating that positive electricity alone is moving between the positive ball and that spot, and negative electricity only between the negative ball and that spot, then what strange conditions these parts must be in; conditions, which to my mind are every way unlike those which really occur!  In such a case, one part of a current would consist of positive electricity only, and that moving in one direction; another part would consist of negative electricity only, and that moving in the other direction; and a third part would consist of an accumulation of the two electricities, not moving in either direction, but mixing up together! and being in a relation to each other utterly unlike any relation which could be supposed to exist in the two former portions of the discharge.  This does not seem to me to be natural.  In a current, whatever form the discharge may take, or whatever part of the circuit or current is referred to, as much positive force as is there exerted in one direction, so much negative force is there exerted in the other.  If it were not so we should have bodies electrified not merely positive and negative, but on occasions in a most extraordinary manner, one being charged with five, ten, or twenty times as much of both positive and negative electricity in equal quantities as another.  At present, however, there is no known fact indicating such states.

  [A] Silliman’s Journal, 1834, xxv. p. 57.

  [B] Thomson on Heat and Electricity, p. 171.

1633.  Even in cases of convection, or carrying discharge, the statement that the current is everywhere the same must in effect be true (1627.); for how, otherwise, could the results formerly described occur?  When currents of air constituted the mode of discharge between the portions of paper moistened with iodide of potassium or sulphate of soda (465. 469.), decomposition occurred; and I have since ascertained that, whether a current of positive air issued from a spot, or one of negative air passed towards it, the effect of the