Static gravity
Stories from Physics
for 11-14
14-16
Otto von Guericke proposed that the attractive force of the Earth was not gravitational in origin, but electrical. In the 1600s, he argued that the electrostatic attraction was caused by friction between the air and the surface of the Earth. He developed a demonstration to make his case: he formed a sulphur ball, the size of a child’s head, and mounted it on a rod through its diameter. He then placed it in a frame. Rotating the sulphur ball, which represented the Earth, against his hand, he showed it would attract small leaves and pieces of paper and gold.
Guericke was elected as mayor of Magdeburg (now in Germany) and, in order to impress the visiting Holy Roman Emperor, carried out the experiment now known as the Magdeburg hemispheres. Two copper hemispheres were joined to form a sphere which was evacuated and each hemisphere was harnessed to a team of eight horses. The horses were only sometimes able to separate the hemispheres but Guericke could release them simply by opening a stopcock.
References
W. D. Hackmann, Scientific Instruments: Models Of Brass And Aids To Discovery, In D. Gooding, T. Pinch, S. Schaffer, The Uses of Experiment: Studies in the Natural Sciences, Cambridge, Cambridge University Press, 1989, pp. 31-66, p. 51
M. B. Schiffler, Draw the Lightning Down: Benjamin Franklin and Electrical Technology in the Age of Enlightenment, Berkley, CA, University of California Press, 2002, p.18
