During the eighteenth century electricity interested almost everyone but no one really thought that it could do anything useful. People attended lectures about electricity and there were constant attempts to produce larger and larger sparks and crackling noises for the assembled crowd.
Activities:
The activities that are offered are ones which will show the kind of spectacular affects that made people go to see the demonstrations and hear the lectures on these new affects.
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1. What does electricity sound like? To do this you need a metal tray or the top of a cookie tin, and a lump of clay large enough to act as a handle, and a plastic garbage bag. Then stick the clay to the metal tray so you can pick it up without touching the metal. Then place the tray on the plastic and spin it on the plastic bag for two minutes. Don't touch the tray with your hands but lift it off the plastic with the clay handle. With your free hand pick up the metal fork and touch the edge of the tray with it. You should hear the sparks crackle.
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2. Can we store up a charge and make a large flash? This demonstration results in the building of a Leydon jar which can store a number of charges and then be released for a grander affect.
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3. If you have access to a static electricity generator you can do a lot of nice demonstrations about the power of static electricity. Students can join hands and actually make a charge go from one person to the other. The machine is harmless but the results are invaluable.
Around 1750, Pieter Van Musschenbroek (1692-1761) is credited with having made the first electrical storage jar. It was called the Leyden jar after the University of Leyden in Holland where he taught. The Leydon jar is a forerunner of what is now called a capacitor. It is used to store electricity and can generate a great burst of light when it is fully charged. It is similar to the device, which produces the flash in a flash camera. Televisions and radios and computers all depend on a capacitor to hold electricity for hours even days. The Leydon jar showed that you could store electricity, which would prove important later. It also showed that you could store a number of consecutive charges and fill the jar almost like filling a jar spoonful by spoonful until it was filled. It definitely held more electricity than a friction machine.17
Students will readily see the power of electricity and the importance of experiments like the Leydon Jar. It showed how storage of electrical charge could generate power.
Benjamin Franklin (1706-1790) was one of those people who were fascinated by this electricity idea. When a Professor Spencer of Edinburgh gave a lecture in Philadelphia on electricity Franklin was curious. He even ordered a static generator and a Leydon jar and did his own experimentation. Franklin repeated many of DuFay's experiments and reached the same conclusion (which he did not know of) that there were two kinds of electricity. Dufay called them vitreous and resinous. Franklin called them positive (+) and negative (-).18
Franklin also stated that electricity was not created by rubbing a cloth on a glass tube of the generator. The electricity was merely being transferred. He also stated that when an unelectrified object was rubbed it did one of two things: it either gained electricity and reached a positive state, or it lost some of the "electric fluid" and was left in a negative state. These principles are still used today.19
Luigi Galvani (1737-1798) was a professor of anatomy at the University of Bologna in Italy. While teaching class in 1780 Galvani was dissecting a frog in class when he put the frog down near an electrical machine which had been used in a previous experiment. A spark passed between the machine and when the frog's nerve center was touched with a scalpel the frog's leg twitched. Galvani could never really explain what happen but he kept experimenting. He always believed, incorrectly, that the electricity was somehow stored in the frog's leg.20