#28a.     The Direction Assigned to Electric Currents

The choice of which type of electricity is called "positive" and which "negative" was made around 1750 by Ben Franklin, early American scientist and man of many talents. Franklin studied static electricity, produced by rubbing glass, amber, sulfur etc. with fur or dry cloth. Among his many discoveries was proof that lightning was a discharge of electricity, by the foolhardy experiment of flying a kite in a thunderstorm. The kite string produced large sparks but luckily no lightning, which could have killed Franklin.

Franklin knew of two types of electric charge, depending on the material one rubbed. It is not known whether he tossed a coin before deciding to call the kind produced by rubing glass "positive" and the other "resinous" type "negative" (rather than the other way around), but he might just as well have. Later, when electric batteries were discovered, scientists naturally assigned the direction of the flow of current to be from (+) to (-). A century after that electrons were discovered and it was suddenly realized that often the electrons were the ones that carried the current, moving in exactly the opposite direction. However, it was much too late to change Franklin's naming convention

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Last updated March 13, 1999