1362.  All the effects prior to the discharge are inductive; and the degree of tension which it is necessary to attain before the spark passes is therefore, in the examination I am now making of the new view of induction, a very important point.  It is the limit of the influence which the dielectric exerts in resisting discharge; it is a measure, consequently, of the conservative power of the dielectric, which in its turn may be considered as becoming a measure, and therefore a representative of the intensity of the electric forces in activity.

1363.  Many philosophers have examined the circumstances of this limiting action in air, but, as far as I know, none have come near Mr. Harris as to the accuracy with, and the extent to, which he has carried on his investigations[A].  Some of his results I must very briefly notice, premising that they are all obtained with the use of air as the dielectric between the conducting surfaces.

  [A] Philosophical Transactions, 1834, p. 225.

1364.  First as to the distance between the two balls used, or in other words, the thickness of the dielectric across which the induction was sustained.  The quantity of electricity, measured by a unit jar, or otherwise on the same principle with the unit jar, in the charged or inductive ball, necessary to produce spark discharge, was found to vary exactly with the distance between the balls, or between the discharging points, and that under very varied and exact forms of experiment[A].

  [A] Philosophical Transactions, 1834, p. 225.

1365.  Then with respect to variation in the pressure or density of the air.  The quantities of electricity required to produce discharge across a constant interval varied exactly with variations of the density; the quantity of electricity and density of the air being in the same simple ratio.  Or, if the quantity was retained the same, whilst the interval and density of the air were varied, then these were found in the inverse simple ratio of each other, the same quantity passing across twice the distance with air rarefied to one-half[A].

  [A] Philosophical Transactions, 1834, p.229.

1366.  It must be remembered that these effects take place without any variation of the inductive force by condensation or rarefaction of the air.  That force remains the same in air[A], and in all gases (1284. 1292.), whatever their rarefaction may be.

  [A] Philosophical Transactions, 1834, p. 237, 244.

1367.  Variation of the temperature of the air produced no variation of the quantity of electricity required to cause discharge across a given interval[A].

  [A] Philosophical Transactions, 1834, p. 230

Such are the general results, which I have occasion for at present, obtained by Mr. Harris, and they appear to me to be unexceptionable.