The nature of tribo-electricity or electricity of friction and other kindred matters

Abstract

BEFORE the days of the discovery of the voltaic battery or the generation of electricity by contact of two different metals, the only source of electricity and the only knowledge which we had or which the world possessed depended on the development of electrical charges on the surfaces of non-conductors by friction. At least, the charges were the accompaniment of friction, the earliest manifestation of which was the ancient observation of Thales that amber (electron) when rubbed would attract light bodies. In the early part of the eighteenth century, experimentation in this field of the generation of electricity by friction really led to the discovery of some of the most fundamental principles of the science, such as the division of substances into conductors and non-conductors, electrics and dielectrics, positive and negative charges, and discharges uniting the two. Von Guericke constructed an electrical generator and frictional machine consisting of a revolving globe of sulphur, rubbed generally by the hand, while Franklin carried on many of his original experiments by the rubbing of glass rods or tubes, using fibrous material or fur as a rubber, and Franklin's famous machine for the generation of electricity was the well-known form consisting of a revolving glass sphere provided with a rubber on the one end of the diameter, and a collector at the other end communicating a charge from the rubbing surface of the globe to what was known as the “prime conductor.” This machine was soon succeeded by the revolving glass cylinder of the cylinder machine, which, in the hands of Ramsden, Von Marum, and others, became modified into the plate machine, where a circular glass plate instead of a cylinder was mounted so as to be rubbed on both sides, while the collector was a set of points on both sides connected with a prime conductor. The glass plate was found to be superior to the cylinder. I have not, however, noticed any reason having been given for this in the literature with which I am acquainted, other than that the plate gave the possibility of a greater velocity of travel, and with it gave greater length of rubbing surfaces in moderate space, since both sides were rubbed. It had been noticed that if the revolving plate was too thick it was not as effective as when it was of moderate thickness. We can now readily ascribe the true cause for the superiority of the plate machine in that when both sides were subjected to the action of the rubber, and if the sides were not too far apart, as would be the case in too thick a plate, the electrification would inductively act through the plate, or more properly, the capacity of the plate after it left the rubber would be less than in the case of the cylinder where only one side of the glass was charged by the friction, which charge would tend to bind to itself through the glass an opposite charge on the other side. There could not, therefore, be, when the glass left the rubber, anything like the elevation of potential, which must occur in the case of the plate, for be it understood that when the rubber and the glass surfaces are in contact, the electricity developed is “bound,” and does not manifest itself until the separation of the charges by the movement of rotation, attended by an enormous change of capacity leading by the diminution of capacity to the electrification taking on a high tension or voltage.