Plate electrical machine, 1770.
© Science Museum / Science & Society Picture Library
This is a relatively early plate electrical machine with a Lane micrometer electrometer. The Lane micrometer is attached to the mahogany base and can be raised or lowered as required. Lane invented this type of electrometer in 1767. It is esentially a micrometer screw which is used to adjust the distance a spark must jump. The conductor has reached a certain potential when the spark jumps a certain distance.