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The pith-ball electroscope, invented by British schoolmaster and physicist John Canton in 1754, consists of one or two small balls of a lightweight nonconductive substance, originally a spongy plant material called pith, [4] suspended by silk or linen thread from the hook of an insulated stand. [5]
Two massive 12-inch (300 mm), 348-pound (158 kg) lead balls, suspended separately, could be positioned away from or to either side of the smaller balls, 8.85 inches (225 mm) away. [9] The experiment measured the faint gravitational attraction between the small and large balls, which deflected the torsion balance rod by about 0.16" (or only 0.03 ...
Canton is now mainly remembered for his work in electrostatics, [2] particularly the invention of the pith ball electroscope, and his studies in atmospheric electricity. [8] He is honoured with a blue plaque at the site of his old school in his hometown of Stroud. [9]
It consists of a glass cylinder with a glass tube on top. In the axes of the tube is a glass thread, the lower end of this holds a bar of gum lac, with a gilt pith ball at each extremity. Through another aperture on the cylinder, another gum lac rod with gilt balls may be introduced. This is called the carrier rod.
English: Diagram showing how a pith-ball electroscope works. The molecules (yellow ovals) that make up the pith ball (A) consist of positive charges (atomic nuclei) and negative charges (electrons) close together. Bringing a charged object (B) near the pith ball causes these charges to separate
Cavendish experiment: Henry Cavendish: Measurement Gravitational constant: 1799 Voltaic pile: Alessandro Volta: Demonstration First electric battery: 1803 Young's interference experiment: Thomas Young: Confirmation Wave theory of light: 1819 Arago spot experiment François Arago: Confirmation Fresnel diffraction due to circular object 1838 ...
The early ideas for an electric telegraph included in 1753 using electrostatic deflections of pith balls, [17] proposals for electrochemical bubbles in acid by Campillo in 1804 and von Sömmering in 1809. [18] [19] The first experimental system over a substantial distance was by Ronalds in 1816 using an electrostatic generator.
The pit of despair was a name used by American comparative psychologist Harry Harlow for a device he designed, technically called a vertical chamber apparatus, that he used in experiments on rhesus macaque monkeys at the University of Wisconsin–Madison in the 1970s. [2] The aim of the research was to produce an animal model of depression.