those which assume the opposite state, in consequence of the induction, inducteous bodies.  This distinction is not needful because there is any difference between the sums of the inductric and the inducteous forces; but principally because, when a ball A is inductric, it not merely brings a ball B, which is opposite to it, into an inducteous state, but also many other surrounding conductors, though some of them may be a considerable distance off, and the consequence is, that the balls do not bear the same precise relation to each other when, first one, and then the other, is made the inductric ball; though, in each case, the same ball be made to assume the same state.

1484, Another liberty which I may also occasionally take in language I will explain and limit.  It is that of calling a particular spark or brush, positive or negative, according as it may be considered as originating at a positive or a negative surface.  We speak of the brush as positive or negative when it shoots out from surfaces previously in those states; and the experiments of Mr. Wheatstone go to prove that it really begins at the charged surface, and from thence extends into the air (1437. 1438.) or other dielectric.  According to my view, sparks also originate or are determined at one particular spot (1370.), namely, that where the tension first rises up to the maximum degree; and when this can be determined, as in the simultaneous use of large and small balls, in which case the discharge begins or is determined by the latter, I would call that discharge which passes at once, a positive spark, if it was at the positive surface that the maximum intensity was first obtained; or a negative spark, if that necessary intensity was first obtained at the negative surface.

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1485.  An apparatus was arranged, as in fig. 129. (Plate VIII.):  A and B were brass balls of very different diameters attached to metal rods, moving through sockets on insulating pillars, so that the distance between the balls could be varied at pleasure.  The large ball A, 2 inches in diameter, was connected with an insulated brass conductor, which could be rendered positive or negative directly from a cylinder machine:  the small ball B, 0.25 of an inch in diameter, was connected with a discharging train (292.) and perfectly uninsulated.  The brass rods sustaining the balls were 0.2 of an inch in thickness.

1486.  When the large ball was positive and inductric (1483.), negative sparks occurred until the interval was 0.49 of an inch; then mixed brush and spark between that and 0.51; and from 0.52 and upwards, negative brush alone.  When the large ball was made negative and inductric, then positive spark alone occurred until the interval was as great as 1.15 inches; spark and brush from that up to 1.55; and to have the positive brush alone, it required an interval of at least 1.65 inches.