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ONE:In electricity great strides were made. Between the years 1705 and 1711 Francis Hawksbee published in the Transactions of the Royal Society several experiments, in which he had, for the first time, discovered the production of the electric spark by friction, and electrical attraction and repulsion. In 1720 Stephen Gray, a pensioner of the Charterhouse, published the result of his experiments on this subject, with a list of the substances which showed electricity under friction; and in 1732 he discovered the conducting property of non-electrical bodies. Before 1739, Dufray, keeper of the King's Garden at Paris, discovered the repellent power of two similarly-electrified bodies, and the attraction of these positively and negatively electrified��or, as he termed it, possessing the vitreous and the resinous electricity. Cuneus and Lallemand discovered the mode of accumulating the electric fluid in what was called the Leyden jar in 1745. This discovery gave a new impetus to inquiry, and Nollet, in France, and Watson, in England, conceived the hypothesis of the jar being overcharged on one side and undercharged on the other. This growing perception of the positive and negative conditions of the electric fluid received confirmation from the experiments of Benjamin Franklin, in America. Franklin soon improved the Leyden jar into an electrical battery; and, in 1752, he proved the identity of electricity and lightning by his grand experiment of the kite. On this he recommended lightning conductors, which, however, were not used in England till ten years afterwards.It is, at any rate, certain that the successors of Aenesid��mus adhered to the standpoint of Pyrrho. One of them, Agrippa, both simplified and strengthened the arguments of the school by reducing the ten Tropes to five. The earlier objections to human certainty were summed up under two heads: the irreconcilable conflict of opinions on all subjects; and the essential relativity of consciousness, in which the percipient and the perceived are so intimately united that what things in themselves are cannot possibly be discovered. The other three Tropes relate to the baselessness of reasoning. They were evidently suggested by Aristotle��s remarks on the subject. The process of proof cannot be carried backwards ad infinitum, nor can it legitimately revolve in a circle. Thus much had already been admitted, or rather insisted on by the great founder of logic. But the Sceptics could not agree to Aristotle��s contention, that demonstration may be based on first principles of self-evident certainty. They here fell back on their main argument; that the absence of general agreement on every point is fatal to the existence of such pretended axioms. A still further simplification was effected by the reduction of the five Tropes to two��that all reasoning rests on intuition, and that men��s intuitions are irreconcilably at variance with one another.300 As against true science, the sceptical Tropes are powerless, for the validity of its principles has nothing to do189 with their general acceptance. They are laid before the learner for his instruction, and if he chooses to regard them as either false or doubtful, the misfortune will be his and not theirs. But as against all attempts to constrain belief by an appeal to authority, the Tropes still remain invincible. Whether the testimony invoked be that of ancient traditions or of a supposed inward witness, there is always the same fatal objection that other traditions and other inward witnesses tell quite a different story. The task of deciding between them must, after all, be handed over to an impersonal reason. In other words, each individual must judge for himself and at his own risk, just as he does in questions of physical science.