ABSTRACT
Any of us can sometimes observe a ow of electricity by accumulating static electricity on our bodies (shufing your feet on a carpeted oor often works) and seeing a spark jump between a ngertip and an object we’re reaching for. In dim light, we can see a momentary ash of electricity as the “electric uid” ows from us to the object we’re about to touch. But note that the spark happens only once, and it appears to be nearly instantaneous. Similarly, lightning, which is a ow of electricity driven by enormous potential differences, literally occurs in a “ash.” Until the end of the eighteenth century, only these momentary ows of electricity could be produced. To put electricity to work for us, we need a continuous ow of electricity, to provide for the continuous operation of the many electrical devices that form part of everyday life.
