pith ball electrometer
Date1870-1930
Inventory Number1997-1-0645
ClassificationElectrometer
Subject
Maker
American
?
Cultural Region
Dimensions29.3 x 29.3 x 33.5 cm (11 9/16 x 11 9/16 x 13 3/16 in.)
Material
DescriptionA curvy, lamp-shaped glass jar with a bell-shaped glass base stoppered by a perforated glass cap through which goes a brass rod with a large brass ball outside. From this brass rod inside the jar hang two pith balls from thin metal threads at the level of the widest section of the jar. At the same height, on opposite ends of the jar, are openings on the glass covered with brass caps, and which allow the insertion of identical thin rods with small brass balls at their ends. The brass caps have binding posts outside and long screws that alter the distance of the small brass ball from the edge of the glass.
One of the two pith balls has fallen to the bottom of the jar. The instrument as a blue triangle and the letter "E" written in (the letter next to the e has been crossed out).
One of the two pith balls has fallen to the bottom of the jar. The instrument as a blue triangle and the letter "E" written in (the letter next to the e has been crossed out).
Signedunsigned
FunctionThis device measures the amount of electric charge on an object. One would touch the object with the brass ball on top, which would communicate part of the charge to the pith balls inside. The pith balls would then repel each other in proportion to this charge. The smaller brass rods coming in horizontally are for discharging the pith balls and would be grounded.
Central Scientific Company
Date: circa 1940
Accessories: 2 Leyden condensers made of Pyrex
One rubber **gutta percha?** pulley, rotted.
Object number: 1997-1-0634
E. Ducretet & Cie
Date: 1870-1890
Accessories: the upper part of the capacitor is DW0045b.
Object number: DW0045a
