Leyden jars come in all sizes and shapes, but the basic definition is this: a jar or bottle of an insulating material, with a conductive lining and a conductive outer coat. There is usually a metal rod with a ball atop it placed in the mouth of the bottle, so it is simple to connect electrically with the conductive lining. Today, we call such devices capacitors, and they are smaller and far more efficient.

Benjamin Franklin studied the Leyden Jar, and decided he could increase their ability to store electricity most efficiently by hooking several Jars together, instead of making one big jar. He called the result a battery of Leyden Jars. A four-Jar battery is shown above, held in a wooden box. The outer coat is tin foil; the inner conductive lining is gold leaf (a common substance in early Jars.

But a battery? We all know what batteries are, and this isn't it. And that is an interesting tale of the English language. Our word comes from the root word batter, to smash down by force. We may have heard of the battering ram, for instance; and in the middle ages, armies used heavy rock-throwing catapults to batter down the enemy castle.

When cannons came along, armies could do their battering from a safe distance, away from the boiling oil, rocks, and other unpleasantnesses the defenders of the castle were ready to throw down upon their heads. But early cannons were slow to reload - the defenders would have time to shore up the damage the previous shot had done. So the besieging armies brought along as many cannons as they could, to keep up a constant rain of projectiles. This bunch of cannons was called a battery. (If you live in New York, part of your city is called "The Battery". That's where the early settlers kept their cannons, to fight off pirates and invaders.)

One Leyden Jar can give a bad shock. Four Jars hooked together can give a shock four times as terrible.  Franklin called that a battery, by analogy with a battery of cannons.

(When Volta discovered bi-metallic electricity, he piled quite a few metal couples on top of one another, and called it a pile. But other inventors put the metals side-by-side. "Pile," with its connotation of vertical, wasn't a good generic name. It didn't take them long to settle on a "battery of cells", by analogy with the battery of Leyden Jars; and slowly "battery" began to take on the meaning we use today.)

Museum Hours: Tuesday - Saturday 10 to 5
Thursdays 10 am to  8pm 
Closed Major Holidays
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Admission: $7 Adults; $5 Students & Seniors; Children 3 and under are FREE!

© The Bakken Updated: April 6, 2007