chapter 1._

ELECTRICITY: A. D. 1745-1747. Franklin's identification of Electricity with Lightning.

"In 1745 Mr. Peter Collinson of the Royal Society sent a [Leyden] jar to the Library Society of Philadelphia, with instructions how to use it. This fell into the hands of Benjamin Franklin, who at once began a series of electrical experiments. On March 28, 1747, Franklin began his famous letters to Collinson. ... In these letters he propounded the single-fluid theory of electricity, and referred all electric phenomena to its accumulation in bodies in quantities more than their natural share, or to its being withdrawn from them so as to leave them minus their proper portion." Meantime, numerous experiments with the Leyden jar had convinced Franklin of the identity of lightning and electricity, and he set about the demonstration of the fact. "The account given by Dr. Stuber of Philadelphia, an intimate personal friend of Franklin, and published in one of the earliest editions of the works of the great philosopher, is as follows:--'The plan which he had originally proposed was to erect on some high tower, or other elevated place, a sentry-box, from which should rise a pointed iron rod, insulated by being fixed in a cake of resin. Electrified clouds passing over this would, he conceived, impart to it a portion of their electricity, which would be rendered evident to the senses by sparks being emitted when a key, a knuckle, or other conductor was presented to it. Philadelphia at this time offered no opportunity of trying an experiment of this kind. Whilst Franklin was waiting for the erection of a spire, it occurred to him that he might have more ready access to the region of clouds by means of a common kite. He prepared one by attaching two cross-sticks to a silk handkerchief, which would not suffer so much from the rain as paper. To his upright stick was fixed an iron point. The string was, as usual, of hemp, except the lower end, which was silk. Where the hempen string terminated, a key was fastened. With this apparatus, on the appearance of a thunder-gust approaching, he went into the common, accompanied by his son, to whom alone he communicated his intentions, well knowing the ridicule which, too generally for the interest of science, awaits unsuccessful experiments in philosophy. He placed himself under a shed to avoid the rain. His kite was raised. A thunder-cloud passed over it. No signs of electricity appeared. He almost despaired of success, when suddenly he observed the loose fibres of his string move toward an erect position. He now pressed his knuckle to the key, and received a strong spark. How exquisite must his sensations have been at this moment! On his experiment depended the fate of his theory. Doubt and despair had begun to prevail, when the fact was ascertained in so clear a manner, that even the most incredulous could no longer withhold their assent. Repeated sparks were drawn from the key, a phial was charged, a shock given, and all the experiments made which are usually performed with electricity.' And thus the identity of lightning and electricity was proved. ... Franklin's proposition to erect lightning rods which would convey the lightning to the ground, and so protect the buildings to which they were attached, found abundant opponents. ... Nevertheless, public opinion became settled ... that they did protect buildings. ... Then the philosophers raised a new controversy as to whether the conductors should be blunt or pointed; Franklin, Cavendish, and Watson advocating points, and Wilson blunt ends. ... The logic of experiment, however, showed the advantage of pointed conductors; and people persisted then in preferring them, as they have done ever since."

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_P. Benjamin, The Age of Electricity,