Nairne and Blunt Electrostatic Generator
London, 1774-1793

Edward Nairne and Thomas Blunt were partners during the years 1774-1793. Somewhere during this time, they made a traveling electrical kit, in a box about the size of a footlocker. This picture displays most of the contents of one such kit, less an insulating platform and a Leyden jar capacitor. Over 200 years old, it still works quite well.

At right we see the glass globe, which is spun rapidly when the handle is turned on the gearbox beneath it. A leather-covered friction cushion can be pressed against the glass, with pressure adjustable by a thumbscrew. The gearbox fastens to the edge of the table with a clamp.

The main terminal to the left holds the static charge, which is harvested from the glass globe by a pointed metal rod. This point works much like Franklin's lightning-rod. The main terminal is held up by an insulating glass rod, held in a wooden base weighted with lead. One of the variants of this machine sold by Nairne and Blunt had the main terminal suspended from above by silken cords.

The amount of electricity in the main terminal can be read from the Henley electrometer plugged into the left sphere of the main terminal. It has a protractor, and a pith ball suspended by a thin piece of wood. As the terminal charges up, the pith ball and the wooden upright rod begin to repel electrostatically. The angle of repulsion can be measured with the protractor on the rod. The concept of "voltage" had not yet been defined, but electricians of the day knew that by charging the equipment until the electrometer reached the same angle, they could repeat an earlier experiment.

The hanging bells chime merrily when electrically charged. The center bell is grounded, the two outer bells are connected to the high voltage, and light metal balls on silk threads are attracted back and forth. This trick was invented by Benjamin Franklin, who attached such a bell to his lightning rod. When the bell started ringing, Franklin knew there was an electrically-charged cloud overhead for him to study.

Other accessories to this generator include the "dance of the puppets", the electrostatic pinwheel, and discharging rods to connect the high voltage to the object being studied.

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Thursdays 10 am to  8pm 
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© The Bakken Updated: April 6, 2007