Stumbled across this nice little story whilst researching the electrical telegraph:
Jean-Antoine Nollet, the Abbot of the Grand Convent of the Carthusians in Paris decided to test his theory that electricity traveled far and fast. He did the natural thing on a fine spring day in 1746, sending 200 of his monks out in a line 1 mile long. Between each pair of monks was a 25-foot iron wire.
Once the reverend fathers were properly aligned, Nollet hooked up a battery to the end of the line and noted with satisfaction that all the monks started swearing, contorting, or otherwise reacting simultaneously to the shock.
A successful experiment: an electrical signal can travel a mile and it does so quickly. Of course, this is the kind of experiment you can only run once as your monks may prove less-than-cooperative the second time around. So, in another demonstration he discharged a Leyden jar in front of King Louis XV at Versailles by sending current through a chain of 180 Royal Guards. The King was both impressed and amused as the soldiers all jumped simultaneously when the circuit was completed.