In lieu of an abstract, here is a brief excerpt of the content:

The Key to Electricity MICHAEL WEISBERG The name "Benjamin Franklin" often evokes the image of an a\uncular man flying a kite on a stormy night. It is indeed a striking picture: one of the founders of our countr!-, a successfi~l businessman, a diplomat, and the public face of the Anlerican Revolution spending his time contributing to the advancement of science-and putting his life at risk in the process. Copious mythology surro~~nds Franklin and his kite experiment. St11dents are often told that Franklin discovered electricity, or, even Inore ridiculously, that he invented it. Even a cursol? look at the histoi? of science 1vo11ldsho~v that these claims are false, !-et Franklin's experiment isjustly famous. He did not discover electricity, but he did conclusively sho~v that lightning is an electrical phenomenon. The kite experiment also paved the way for the lightning rod, perhaps his nlost important invention. In 1746,Franklin rnet "a Dr. Spence [r],~vho was lately arrived [in Boston ] from Scotland, and sho~v'd me some electric experiments." Some of Dr. Spencer's experiments ~vould be familiar to students in modern physics courses. Upon rubbing a glass tube ~vithfelt, he caused small flakes of brass or gold tojump around or be attracted to the tube. More dramaticall!-, an associate of Franklin describes a boy ~vho"was s ~ s pended horizontally and the Dr. rubbed a glass tube, a little distance from his feet, ~vhich made sparks of the fire fly fi-ornhis face and hands." Although Dr. Spencer was not an expert on electricity and his experiments were "ver!- imperfectly perforrn'd," Franklin's interest was piq~~ed. 1111chlvas known about the behavior of electricity before Franklin encountered Dr. Spencer, so the often-heard claim that Franklin discol: ered electricity is clearly false. Franklin did perform many electrical experiments and contributed to the growing stock of experimentall!derived knowledge about electricity. However, his nlost important contributions to electrical research la!- else~vhere. The first of these contributions was theoretical: the electrical fluid theory. 160 Michael LVeisberg Franklin posited that an electrical fluid is present in all bodies. This electrical fluid is subtle, meaning that it can permeate even the densest of objects. All bodies have a natural quantity of the electrical fluid, but this quantity can be increased or decreased by contact wit11 other electrified bodies or by friction. Franklin used this theon to account for nlost electrical phenomena, including the most basic electrical properties: attraction and repulsion. Two charged bodies solnetirnes exhibit repulsion, moving aliay fi-om one another when brought together. In Franklin's theory, this is attributed to both bodies possessing excess electrical fluid, or being positive@ charged. Mien a body possesses excess fluid, the fluid flows around the body's surface and forms ~ i h a t Franklin called an eZ(~ctriccrlnttnosphere. The atmospheres of two positivel!- charged bodies repel one another because the!- cannot occup!- the same space. Franklin's theon also accounted for electrical attraction. In an essay describing his electrical theory, he described matter as "a kind of sponge to the electrical fluid." Mllen a body lacks electrical fluid relative to its norrnal state, its sponge-like character dra~is fluid fi-orn a positive bod!-. Although Franklin was justly proud of these and other theoretical explanations of well-known phenomena, he was also interested in more practical matters. Eighteenth-century Philadelphia suffered from frequent fires caused b ! - lightning strikes. The density of buildings increased the prohahilit!- that lightning ~iould start a fire, and the proximity of the buildings meant that a fire could ravage a whole block. About ten years before Franklin's kite experiment, he had devised a volunteer fire company which ensured that Philadelphia "never lost more than one or tlio houses at a time" fl-orn fire. Lightning-induced fire could be contained, but it could not be prevented. Franklin sought a way to keep lightning from starting fires in the first place. The first step involved determining ~ i h a t kind of phenomenon lightning actuallywas. In a notebook e n t n dated Sovember 7, 1749,Franklin made the follo~iing observations: Electrical fluid agree7 ~\.ith lightning in theye particular^: 1. Giving light. 2. Colour of the light. 3. Crooked direction. 4. Slrift rnotion. 5. Being conducted by metals. 6. Crack or n o i ~ e in exploding. 7. Subsisting in \rater or ice. 8. Rending bodie~ it payses through. 9. Destroying animals. 10. Slelting metals. 11. Firing inflarnrnable sub...

Share