| Kinnersley's Thermometer is a demonstration of the heating
power of the electric spark and so is the ancestor of the apparatus
to demonstrating the expansion
of air by electrical heating. Inside the larger glass tube is a pair
of discharge knobs, and water fills the tube up to the level of the bottom
of the lower knob. Applying a spark to the system heats and expands the
air in the larger tube, driving the water into the smaller tube.
Ebeneezer Kinnersley of Philadelphia was a contemporary
of Benjamin Franklin, and one of a small group who investigated the properties
of static electricity with him. He observed that two types of electricity
existed -- positive and negative or resinous and vitreous -- shortly after
Charles duFay made the same observation in France. In the years before
the American Revolution he started a lecture tour to demonstrate various
The apparatus is in the collection of Transylvania University.