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.
Many early electrostatic machines generated a charge by friction. In the later 19th century several designs were introduced based on induction. Electrostatic induction occurs when one charged body (such as a glass disc) causes another body (another disc) that is close but not touching to become charged. The first glass disc is said to influence the second disc so these generators came to be called influence machines.
This small revolving doubler, developed by William Nicholson (1753-1815) in England, shows the basic principle of an influence machine. The user turns a crank that rotates a charged disc in front of the stationary discs. The rotating disc induces a charge on each stationary disc as it passes. The two stationary discs on this piece are connected briefly so both become charged. The charge is almost doubled each time the rotating disc passes a stationary disc and the effect repeats, building up a high voltage on the brass ball. This doubler was made in London by instrument makers William and Samuel Jones in the early 1800s. Since the charge is not quite doubled the term multiplier was later used for these types of devices.
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