. Popular science monthly. by which the proper contacts were also auto-matically made. This doubler Nicholson presented to Bennett, and itwas used by him in his investigation of the adhesive effects of elec-tricity. Bennetts original figure of this doubler is here reproduced. Inthis figure A is the fixed plate which remains permanently insulated andupon which it was desired to build up the charge. B is the movableplate which is carried on an arm from an axis which may be turned bya crank, and C is a fixed plate which may be either insulated, joined toA or joined to earth. I is a ball which ser
. Popular science monthly. by which the proper contacts were also auto-matically made. This doubler Nicholson presented to Bennett, and itwas used by him in his investigation of the adhesive effects of elec-tricity. Bennetts original figure of this doubler is here reproduced. Inthis figure A is the fixed plate which remains permanently insulated andupon which it was desired to build up the charge. B is the movableplate which is carried on an arm from an axis which may be turned bya crank, and C is a fixed plate which may be either insulated, joined toA or joined to earth. I is a ball which serves to counterpoise the crank DISCOVERY OF CONTACT ELECTRIFICATION 443 and the plate B so that B may be stopped in any position. When thecrank is turned B passes alternately in front of and parallel to A and contacts are so arranged that when B is parallel to A it is joined toearth and so charged oppositely to A. It is then revolved in front of C,at which instant C is joined to earth and is charged by induction oppo-. sitely to B and like A. As B again conies in front of A, A and C arejoined and B is earthed. B now receives by induction a greatercharge than before, since A has now received the greater part of Cscharge. By successive revolutions of B the charge may thus be built upto any desired intensity upon A. Bennett performed many experiments with this doubler, and afterlearning how to discharge it completely he tested the electrificationinduced upon metal plates by being placed in contact with various sub-stances, both solid and liquid. He concludes that different substances: have a greater or less affinity with the electrical fluid, and he then 444 THE POPULAR SCIENCE MONTHLY undertakes his experiments on this adhesive affinity in the case of differ-ent metals. At the beginning of Section VII., page 91, he says: Having fully proved by a frequent repetition of experiments, that thepositive or negative spontaneous charge of the doubler depended upon theabsorption or r
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