When Benjamin Franklin was studying the Leyden Jar, he wondered if there were equal and opposite charges on the inner and outer foils. So he arranged electrodes near one another, one connected to the inside and one to the outside of a charged Jar. Then he hung a pith ball from a silk (insulating) thread, and placed the ball between the electrodes. It was attracted to one electrode, touched it, picked up a charge of its own, and then was repelled. (Like charges repel.)

But opposite charges attract; so the pith ball was attracted to the other electrode, where it gave up its charge. It went back-and-forth, back-and-forth, each time carrying a little bit of charge. And the charge it took from one electrode, it delivered to the other.

At last the pith-ball had carried all the charge there was. Franklin tested the Leyden Jar. No charge on the outside foil; no charge on the inside foil. No shock. Therefore, the initial charges must have been equal (though opposite).

Franklin realized that if he had two bells for electrodes, and a little piece of metal for the charge-carrier, the bells would ring merrily as the charge shuttled back and forth. He tried it, and it worked.

And so, he created the first electrical alarm-bell. He took one bell and grounded it; he took the other, and hooked it to his lightning-rod. He hung a clapper between them. And when the bells started ringing, he knew there was an electrically-charged cloud overhead for him to study.

Museum Hours: Tuesday - Saturday 10 to 5
Thursdays 10 am to  8pm 
Closed Major Holidays
Library Hours: Monday - Friday 9 to 4:30

Admission: $7 Adults; $5 Students & Seniors; Children 3 and under are FREE!

© The Bakken Updated: April 6, 2007