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 influence machine from the firm E. S. Ritchie & Sons, shows the design of German instrument maker Robert Voss and has two glass plates. The fixed plate has two paper sectors with foil contacts and locations for edge-mounted brushes. The rotating plate has six foil points for contacts and there is black paint leading from each contact point to the axle, although the paint may be simply for show. There are small brass brushes set amid the brass combs on the neutralizer bar, a feature of Voss machines. This unit would appear to have seen extensive use at the university given that the brushes are missing from the fixed plate and the brass contact buttons are missing from the rotating plate. Also, the paper sectors appear to have been made from the page of a text book and are probably not original to the machine. Unlike other Voss machines in the collection there is no switch on or under the base. Edward S. Ritchie (1814-1895) changed the name of his company to E. S. Ritchie & Sons in 1867 and the firm moved from Boston in 1886, so this unit probably dates from the 1870s.
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