From the mid-eighteenth century onward, one of the most common types of electrostatic machine was the plate model, which remained in use until the early twentieth century, at least for demonstration and teaching purposes.
Despite differences in shape and construction details, these machines displayed a set of common features: a disk, typically of glass, revolving on an axis fitted with a handle; one or more pairs of small leather cushions stuffed with horsehair or felt to rub the disk; and a pair of combs. These served to transfer the electric charges from the disk to the prime conductor, consisting of one or more hollow brass cylinders on which the charges accumulated.
When the disk is rotated, it is rubbed by the cushions, which charges the glass with positive electricity. Through electrostatic induction, the comb tips accumulate the negative charges, which tend to neutralize the positive charges on the glass. In this manner, the metal conductors to which the combs are connected become positively charged. By placing a grounded electrode near the combs, one can trigger a powerful spark, which instantly discharges the machine.
Globe and cylinder electrostatic generators, despite their different shapes, function in exactly the same manner.
Inv. 2739
Edward Nairne, London, ca. 1778
Inv. 392
George Adams junior, London, late 18th cent.
Inv. 3408
Maker unknown, ca. 1776
Inv. 1341, 1342, 2737
Museo di fisica workshops, ca. 1775
Inv. 507
Maker unknown, ca. 1870
Dep. LV, Torino
Maker unknown, Turin, ca. 1890
Inv. 2736
Edward Nairne, London, 1773
Dep. LV, Torino
Maker unknown, early 19th cent.
Inv. 3766
Maker unknown, second half 18th cent.
Inv. 3909
Maker unknown, second quarter 19th cent.
Inv. 2705
Maker unknown, English?, second half 18th cent.
Inv. 444
Edward Nairne, London, ca. 1770
Inv. 516
Maker unknown, late 18th cent.
Inv. 2686
Maker unknown, ca. 1775
Inv. 2688
Maker unknown, English?, ca. 1775
Inv. 374
Maker unknown, second half 18th cent.
Inv. 2689
Maker unknown, English?, ca. 1775
Inv. 2687
Maker unknown, English?, ca. 1775
Inv. 1526
Museo di fisica workshops, second half 19th cent.