This doctrine of two different electricities, produced by exciting different substances, was dropped after Mr. Du Fay; and even this philosopher himself adopted at last the opinion of Dr. Franklin that the two electricities differ only in degree, and that the stronger attracts the weaker. Although many of the experiments of Mr. Grey led directly to it, yet to the French philosopher just mentioned, belongs the merit of first drawing the electrical spark from the human body.—And we cannot forbear remarking, in this place on the regular and progressive advances which the human mind makes in the investigation of science. Electrical attraction was, for a long period, the single phenomenon known to philosophers.—Repulsion was then observed to be also a property of electrics.—In the investigation of these we read of the accidental discovery of the electric light.—To this naturally succeeded, Mr. Grey’s distinction between conductors and non-conductors; and then the difference between vitreous and resinous electricities by Mr. Du Fay. We shall have to remark in the sequel of this history, how each succeeding fact and invention grew out of that which immediately preceded it. The knowledge of electricity did not stop in France. The Germans began to labour in the same field; and with laudable success. Their success arose chiefly from the improvements they made in the electrical apparatus. The simple experiments of Gilbert, and the early electricians, were made by exciting a piece of amber or sulphur. Mr. Boyle found the electric power increased by smoothing the surface of bodies. Otto Guericke made his experiment with a _globe of sulphur_, formed by melting that substance in a hollow globe of glass, and afterwards breaking the glass from off it, little supposing that the glass itself would better have answered his intention. In 1709 Mr. Hawksbee first observed the great electric power of glass. He used a _glass globe_, which he mounted upon an axis, whirling it round, and at the same time applying his hand to it. He also, to increase the power, inclosed an exhausted cylinder within another, exciting the outermost. After Mr. Hawksbee’s death, the glass globe was laid aside, and his successors confined themselves to the use of _tubes_. Mr. Boze, professor of philosophy at Wittemburgh, in 1742 returned to the use of the _globe_. He also added a _prime-conductor_ of tin or iron, supported, at first, by a man standing on cakes of rosin, but afterwards by silken lines extended horizontally, under the conductor. Mr. Winckler, of Leipsic, to excite the globe, substituted a _cushion_, instead of the hand. The electrical _star_ and the electrical _bells_ were also the invention of the German philosophers. Dr. Desagulier, likewise, assisted electricians by some electrical terms. He first gave to bodies conveying electricity the name of _conductors_; and those in which electricity may be excited by heating and rubbing he calls _electrics per se_.