126 DR. FARADAY'S EXPERIMENTAL RESEARCHES IN ELECTRICITY. (SERIES XIII.) 



opposite electrical condition. I propose to call those bodies which are originally 

 charged, inductric bodies ; and 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 the one, and 

 then the other, is made the inductric ball ; though, in each case, the same hall be 

 made to assume the same state. 



1484. Another liberty which I may also occasionally take in language I will ex- 

 plain 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 previ- 

 ously 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 maxi- 

 mum 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. 



1485. An apparatus was arranged, as in fig. 15. (Plate III.) : 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 con- 

 ductor, which could be rendered positive or negative directly from a cylinder ma- 

 chine : the small ball B, 0"25 of an inch in diameter, was connected with a dischar- 

 ging 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 be- 

 tween that and 0*5 1 ; 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. 



1487. The balls A and B were now changed for each other. Then making the 

 small ball B inductric positively, the positive sparks alone continued only up to 0*67; 

 spark and brush occurred from 0-68 up to 0*72 ; and positive brush alone from 074 

 and upwards. Rendering the small ball B inductric and negative, negative sparks 



