People from ancient times knew that rubbing certain materials and then touching something caused a spark. Studying what is called electrostatics laid the groundwork for understanding electricity and magnetism. Natural philosophers, scientists, and instrument makers created many ingenious devices to generate electrostatic charges starting in the 1600s. These machines varied in size and technique but all involved rotary motion to generate a charge, and a means of transferring the charge to a storage device for use.
In the latter 1700s electrical researchers adopted improved electrostatic machines that replaced earlier glass cylinders with a flat glass plate. This increased the machines’ efficiency by passing the glass plate between leather rubbing pads that increased the contact area. Experience with plate machines brought many design variations with sizes ranging from small table-top units for laboratory use to large cabinets that powered early x-ray machines.
This plate machine was made by Dutch physician and scientist Martinus van Marum (1750-1837) in 1791. Two glass plates are mounted parallel on a single crank-shaft although the handle is missing from this unit. Each plate has its own pair of leather pads set at top and at bottom that feed two shared prime conductors. The two primes are connected via a distinctive brass frame arching over the top of the unit and supported by three glass insulating rods.
The origin of this machine is uncertain but a paper tag marked “12 E” associates the machine with other electrical devices used in laboratory experiments. All of these devices have similar tags with a number and “E” written in ink in the same hand.
